Nisr United States Department of Commerce

Technology Adm nistration

National Institute of Standards and Technology

NIST Special Publication 896

Conference Proceedings:

International Workshop on

Instrumented Indentation

San Diego, CA

April 22-23, 1995

Douglas T. Smith, Editor

QC

100

J57

iO.896

996
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'At Boulder, CO 80303. ^Some elements at Boulder, CO 80303.
NIST Special Publication 896

Conference Proceedings:

International Workshop on

Instrumented Indentation

San Diego, CA

April 22-23, 1995

Douglas T. Smith, Editor and Workshop Chairman

Ceramics Division

National Institute of Standards and Technology

Gaithersburg, MD 20899-0001

Sponsored by:

Institute for Mechanics and Materials

University of California

Standard Reference Materials Program

National Institute of Standards and Technology

Issued February 1996

U.S. Department of Commerce

Ronald H. Brown, Secretary

Technology Administration

Mary L. Good, Under Secretary for Technology

National Institute of Standards and Technology

Arati Prabhakar, Director
National Institute of Standards

and Technology

Special Publication 896

Natl. Inst. Stand. Technol.

Spec. Publ. 896

79 pages (Feb. 1996)

CODEN: NSPUE2

U.S. Government Printing Office

Washington: 1996

For sale by the Superintendent

of Documents

U.S. Government Printing Office

Washington, DC 20402-9325
Table of Contents

Acknowledgments vii

Executive Summary 1

Final Agenda 8

Extended Abstracts for Oral Presentations ^ 10

Richard L. White, IBM, San Jose, CA

"Nanoindentation of Magnetic Storage Materials" 11

Kevin M. O'Connor, Eastman Kodak Company, Rochester, NY

"The Use of Instrumented Indentation in the Design of Multilayer Coating

Structures for Imaging Applications" 12

Harry H. Fujimoto, Intel Corporation, Santa Clara, CA

"Micromechanics of Thin Films in Electronic Devices" 13

Clark V. Cooper, United Technologies Research Center, East Hartford, CT

"The Use of a Nanoindenter I: Case Histories and Lessons Learned" 15

Warren C. Oliver, Nano Instruments, Inc., Oak Ridge, TN

"Indentation Techniques for the Measurement of Several Mechanical

Properties" 16

Michael V. Swain, CSIRO, Lindfield, NSW, Australia

"Simple Procedures for Obtaining and Analysing Force Displacement

Data With Small, Spherically Tipped Indenters" 19

David J. Rowcliffe, Royal Institute of Technology, Stockholm, Sweden

"Controlled Indentation: A General Approach to Determine Mechanical

Properties of Materials" 20

Trevor F. Page, Univ. of Newcastle, Newcastle upon Tyne, U.K.

"Procedures for the Nanoindentation Testing of Coated Systems" 21

Neville R. Moody, Sandia National Laboratories, Livermore, CA

"Determination of Thin Film Properties Using Nanoindentation and

Microscratch Techniques" 25

William W. Gerberich, Univ. of Minnesota, Minneapolis, MN

"Multiple Yield Phenomena Under Light Contacts" 27

Jean-Luc Loubet, Centre National de la Recherche Scientifique, Cedex, France

"Some Measurements of Viscoelastic Properties With the Help of

Nanoindentation" 31

W. Howard Poisl, Univ. of Arizona, Tucson, AZ

"Indentation Creep in Amorphous Selenium" 35

^ Extended abstracts for the presentations by John Pethica and Hans-Hermann Behncke were not

available at the time of publication.

This abstract covers material presented in both of Dr. Oliver's presentations.

iii
George M. Pharr, Rice Univ., Houston, TX

"Effects of Residual Stress on the Measurement of Mechanical

Properties Using Instrumented Indentation" 39

Joost J. Vlassak, Stanford Univ., Stanford, CA

"Measuring the Indentation Modulus of Elastically Anisotropic Solids" 40

Antonios E. Giannakopoulos, Royal Institute of Technology, Stockholm, Sweden

"Three-Dimensional Finite Element Modeling of Sharp Indentations" 41

Subbiah Ramalingam, Univ. of Minnesota, Minneapolis, MN

"Modeling Stresses at the Film-Substrate Interface —

Significance to Indentation Testing" 42

Steven M. Hues, Naval Research Laboratory, Washington, D.C.

"Nanoindentation Using the AFM: Considerations for the Quantitative

Measurement of Mechanical Properties" 44

Jack E. Houston, Sandia National Laboratories, Albuquerque, NM

"Interfacial Force Microscopy Measurements of the Nanomechanical

Properties of Materials" 45

Stuart R.J. Saunders, National Physical Laboratory, Teddington, Middlesex, U.K.

"Development of Traceable Calibration Guidelines for Load Displacement

Instruments, and Their Validation by an Intercomparison Test" 46

Abstracts for Poster Presentations 48

W.R. Newson and S. Saimoto, Queen's University, Kingston, Ontario, Canada

"Determination of Thermodynamic Response of Polymers by

Micro-Indentation Rate Changes" 49

L. Riester and M.K. Ferber, Oak Ridge National Laboratory, Oak Ridge, TN

"Artifacts in Nanoindentation Procedures" 49

Th. Dietz, A. Schultz, H. Vetters and P. Mayr, Institut fiir Werkstofftechnik,

Bremen, Germany

"Development of Standards for the Validation of Hard, Thin Coatings" 50

W.J. Meng and G.L. Eesley, General Motors, Warren, MI

"Growth and Mechanical Anisotropy of TiN Thin Films" 50

M.P. de Boer and W.W. Gerberich, University of Minnesota,

Minneapolis, MN

"Adhesion of Metal Interconnects by Microwedge Indentation" 51

K.B. Yoder, M.F. Tambwe and D.S. Stone, University of Wisconsin,

Madison, WI

"Assortment of Techniques in Instrumented Indentation" 51

E.T. Lilleodden, W. Bonin, J. Nelson, J.T. Wyrobek and W.W. Gerberich,

Univ. of Minnesota, and Hysitron, Inc., Minneapolis, MN

"In Situ Imaging of Ultra-Light-Load Indents into GaAs and

Fe-3wt% Si" 52

iv
D. Zirkin, B. Farber and A. Heuer, Case Western Reserve University,

Cleveland, OH

"Modification of the Nikon QM High Temperature Microhardness

Tester to Obtain Load-Deflection Curves" 52

B. Taljat, F.M. Haggag and T. Zacharia, Askerceva, Slovenia; Advanced

Technology Corp., Oak Ridge, TN; and Oak Ridge National Laboratory,

Oak Ridge, TN

"New Analytical Procedure to Determine Stress-Strain Curve and

Elastic Modulus From Instrumented Ball Indentation" 53

S. Joshi and K.A. Richardson, Univ. of Central Florida, Orlando, FL - "Dynamic Hardness Testing of Infrared Materials" 53

Kangjie Li and J.C.M. Li, University of Rochester, Rochester, NY

"Effect of Indenter Shape, Yield Stress and Modulus on the

Indentation Process" 54

F. Yang and J.C.M. Li, University of Rochester, Rochester, NY

"Viscosity Measurement by Impression Test" 54

L. Zheng and S. RamaHngam, University of Minnesota, Minneapolis, MN

"Contact Stress Analysis of a Layered Solid Under a Rigid Indenter" 55

R. Upadhyaya, S. Saimoto and R.S. Timsit, AMP of Canada, Ltd., Markham,

Ontario, Canada; Queen's University, Kingston, Ontario, Canada

"Measurement of Strain-Rate Sensitivity by Nanoindentation Techniques" 55

S.V. Hainsworth, H. Sjostrom, J.-E. Sundgren, H.W. Chandler and T.F. Page,

Univ. of Newcastle, Newcastle upon Tyne, U.K.; Linkoping University,

Linkoping, Sweden

"Analysis of Nanoindentation Load-Displacement Loading Curves" 56

J. Marschall and F. Milstein, Univ. of California, Santa Barbara, CA

"Measurement and Theory of the Orientation Dependence of Knoop

Microhardness in a Layered Single Crystal" 58

K.E. Parmenter and F. Milstein, Univ. of California, Santa Barbara, CA

"Indentation and Strength of Fiber-Reinforced Aerogels" 58

Y. Abd Al-Jalil and P. Nelson, Univ. of Texas, Austin, TX

"Study of Rock Indentation Fracture in Mechanical Excavation" 59

A.S. Chekanov, T.S. Low, S. AUi and B. Liu, National Univ. of Singapore,

Singapore

"Indentation Testing of the Magnetic Thin-Film Head Alumina Substrate" 60

A. Kant, R.O. Ritchie, M.D. Drory, R.H. Dauskardt and LG. Brown,

Lawrence Berkeley Laboratory and Univ. of California, Berkeley, CA;

Crystallume, Santa Clara, CA; and Stanford Univ., Stanford, CA

"Bulk and Interfacial Crack-Propagation Behavior in CVD Diamond" 60

K. Zeng, D.J. Rowcliffe and P. Meier, Royal Institute of Technology,

Stockholm, Sweden

"Residual Stress Fields at Indentations" 61

V
O.L. Warren, P.R. Norton, W.K. Wan, J.E. Houston, C.A. DiRubio and

T.A. Michalske, University of Western Ontario, London, Ontario,

Canada; and Sandia National Laboratories, Albuquerque, NM

"Interfacial Force Microscopy of the Nanomechanical Properties of

Thin Films Formed on Carbon Steel from Zinc Dialkyl Dithiophosphate

Antiwear/Extreme Pressure Oil Additives" 62

List of Attendees 63

vi
Acknowledgments

The workshop would not have been possible without the financial support of both the Institute

for Mechanics and Materials (IMM) at the University of California, San Diego, and the Standard

Reference Materials Program (SRMP) at NIST. Thanks go to Dr. Richard Skalak, Julie Bennett

and Amy Graves at IMM for funding and administrative support, and to Nancy Trahey at the

NIST Standard Reference Materials Program for financial support. Additional funds from Warren

Oliver at Nano Instruments, Inc., and Steven Webb at Instron Corporation for student travel were

greatly appreciated. Thanks go also to Bob Tucker, Mary Gray and Phyllis Greene of

ICMCTF 95, for letting the workshop be part of their program on such short notice. Vanessa L.

Williams, of the NIST Ceramics Division, was responsible for the recording and transcribing of

the discussions.

Finally, the workshop would not have succeeded without the efforts of an informal planning

committee, which met at NIST in August 1994, largely at the members' individual expense, to

begin the organizational process. Those committee members included: Richard Colton (NRL),

William Gerberich (U. Minnesota), Chris Johnson (NIST), Jean-Luc Loubet (CNRS), Larry

Mosiman (MTS Systems), Warren Oliver (Nano Instruments, Inc.), William Ruff (NIST), Michael

Swain (CSIRO) and Steve Webb (Instron Corp.).

Certain commercial equipment, instruments, or materials are identified in this proceedings. Such

identification is not intended to imply recommendation or endorsement by the National Institute of Standards

and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best

available for a given purpose.

vii

Executive Summary

1. Introduction

An international workshop was held on April 22-23, 1995, at the Town and Country Hotel in

San Diego, to discuss the scientific and standardization issues associated with instrumented

indentation, also known as dynamic hardness testing or depth-sensing, ultra-low-load, or nano

indentation. The workshop was sponsored jointly by the NIST Standard Reference Materials

Program and the Institute for Mechanics and Materials in San Diego, with additional support for

student travel from Nano Instruments, Inc., Oak Ridge, TN, and Instron Corporation, Canton,

MA, and was part of the program of the 1995 International Conference on Metallurgical Coatings

and Thin Films (ICMCTF95). The 96 attendees represented 14 U.S. and 6 foreign companies,

18 U.S. and 7 foreign universities, and 15 national laboratories, including NIST, the National

Physical Laboratory (NPL) in England and the Commonwealth Scientific and Industrial Research

Organization (CSIRO) in Australia. The two-day program consisted of 22 oral presentations, 22

poster presentations, and several open discussion sessions.

2. Background

Indentation has been used for many years to measure the hardness of materials. The technique

involves pushing an indenter tip, typically a sphere, cone or diamond pyramid, into a material

under controlled load, then measuring the size of the residual impression. This testing is

economical, both in terms of equipment and time, and produces a reliable hardness measurement

in macroscopic specimens.

Recently, however, a more sophisticated form of indentation testing, known as "instrumented"

or "depth sensing" indentation, has been developed that offers significant advantages over

traditional indentation. In an instrumented indentation system, an indenter tip is loaded onto a

specimen under computer control of either the load or the displacement or both, and load,

displacement and time are recorded continuously throughout the loading-unloading cycle. These

data form what is known as a "load-displacement curve," and they contain a wealth of

information about the elastic, plastic and time-dependent deformation behavior of the material

being tested. Imaging of the residual impression is not necessary, although scanning and

transmission electron microscopy and atomic force microscopy can yield useful information about

deformation mechanisms. The technique is routinely used to determine mechanical properties

from indentations that are sub-micrometer in size, and is considered to be of particular value in

1
evaluating mechanical properties at high spacial resolutions (e.g., in functionally graded or

structurally modulated materials) or for assessing the mechanical properties of materials of limited

dimensions (thin films on substrates, nanostructures). When used to make sub-micrometer-scale

indentations, the technique is often referred to as ultra-low-load indentation or nanoindentation.

Several national standards laboratories, including NIST, NPL and CSIRO, have built their own

instrumented indenters, and at least four companies now market commercial machines with

varying levels of performance and sophistication. Instrumented indenters are currently used in

a number of industrial research laboratories, including 3M, Intel, Kodak, Rockwell, United

Technologies and several IBM sites.

Despite the ability of instrumented indentation to make micrometer- and nanometer-scale

mechanical properties measurements, use and acceptance of the technique is hampered by a lack

of standardization in the field. Not only are there no standard reference materials for use with

instrumented indenters, but there also are differences of opinion about exactly how best to analyze

load-displacement curves to yield quantities such as hardness and elastic moduli. The purpose

of the workshop was to bring together researchers from universities and from standards and other

government laboratories with industrial users of the technique to outline areas of agreement and

disagreement, and to begin the process of establishing standard, or at least recommended test

methods and data analysis techniques, and, ultimately, standard reference materials. The specific

goals of the workshop were:

• to assess the current industry use of instrumented indentation, and to hear from industry users

about their needs for standardization in the field;

• to provide attendees, particularly those from industry, with detailed, up-to-date information

on what material properties are currently being measured with the technique, and how those

properties can be extracted from load-displacement curves;

• to discuss the "state of the art" in analytical and finite-element modeling of the indentation

process; and

• to discuss standardization issues in instrumented indentation, including a) current

standardization efforts within international standards committees, b) machine and tip shape

calibration techniques, c) the effects of test parameters (loading rates, dwell times, etc.) on

results, and d) possible candidates for standard reference materials.

2
3. Workshop Program

The workshop ran for two full days and included four sessions of oral presentations and

discussion plus an evening poster session. Abstracts from the oral and poster presentations begin

on pages 10 and 48, respectively. A brief summary of each session follows.

3.1 Industrial Applications. Discussion Leader: Trevor Page, University of Newcastle.

The workshop began Saturday morning with a set of four talks from industrial users of

instrumented indentation. These presentations described how instrumented indentation techniques

are currently being used to characterize materials in industrial research and development, quality

assurance and process environments, together with problems encountered (both experimentally

and in terms of interpretive methods) in producing useful data. Richard White, from IBM's

Storage Systems Division, San Jose, began by describing how he is using instrumented

indentation to characterize the mechanical properties of the various hard materials used in layered

magnetic hard disk drive systems, and how those properties correlate with wear performance.

Kevin O'Connor, from Eastman Kodak, Rochester, then described the problems of studying much

softer coatings, such as the polymers and gelatins used in photographic materials. These materials

often exhibit strong creep and stress relaxation effects. Dr. O'Connor suggested that additional

work in the analysis of highly dissipative, viscoelastic systems, particularly layered systems,

would be a great help to him in interpreting his indentation data. Harry Fujimoto presented work

being done at Intel Corporation on the use of indentation to induce delamination in layered

systems as a means of measuring interfacial adhesion. Results on several systems, including a

tungsten coating on a softer metal substrate, were discussed. Finally, Clark Cooper, from United

Technologies Research Center (UTRC), summarized his experience with instrumented indentation.

His comments were of particular interest because UTRC purchased one of the first commercial

indenters from Nano Instruments, Inc., and has logged 10 years of use with it.

3.2 Determining Material Properties. Discussion Leader: William Nix, Stanford

University.

The purpose of the second session, "Determining Material Properties," was to present a series

of talks from an experimental perspective that described which material properties can, in

principle, be determined using instrumented indentation, and how they should be determined.

The session actually began before lunch, with two overview talks to set the tone for the

afternoon. First Warren Oliver, from Nano Instruments, Inc., gave a brief overview of the use

3
of sharp diamond indenters. He described in general terms the elastic and plastic response of

materials to sharp indenters, methods of calculating hardness and Young's modulus, and problems

inherent in determining the tip shape and contact area between tip and sample. His talk was

followed by one from Michael Swain, CSIRO. Dr. Swain focused primarily on the use of

spherical indenters and their advantages over sharp indenters for determining the full stress-strain

response of materials. He also described errors that can result if the indenter tip shape is not

perfectly spherical and suggested a procedure to correct for this in the analysis.

Six talks were presented in the afternoon, each presenting a detailed discussion of an

experimental method for determining a specific material property or set of properties. David

Rowcliffe, from the Royal Institute of Technology (KTH) in Stockholm, outlined a method of

analyzing Vickers load-displacement curves, supported by three-dimensional finite element

analysis, to determine hardness, yield stress, strain hardening and plastic zone size.

Two talks then followed that dealt specifically with coated systems. First, Trevor Page, from

the University of Newcastle, gave a detailed account of the problems associated with the use of

instrumented indentation to characterize coating/substrate systems and stressed the great care that

must be taken to interpret results sensibly. Various strategies for both performing experiments

and interpreting data were put forward. Neville Moody, of Sandia National Laboratories,

described how his group had combined nanoindentation, continuous scratch testing, and high

resolution transmission electron microscopy to study tantalum nitride films and their interface to

sapphire.

After a short break, William Gerberich presented work by his group at the University of

Minnesota on the yield of materials at very low loads. He showed evidence for initial yield in

Fe with mass fraction of Si, w(Si), of 0.03 at a load of 150 |a,N under a Berkovich diamond

indenter.

The final two talks in the session dealt with the determination of time-dependent properties.

Jean-Luc Loubet, of the Centre National de la Recherche Scientifique (CNRS) in France,

described his current work using a load oscillation technique to study viscoelastic behavior.

Howard Poisl, from the University of Arizona, showed, using experiments on amorphous

selenium, how indentation creep and indentation strain rate measurements could be related to

more conventional creep measurements.

4
3.3 Poster Session.

A poster session, containing 22 entries, was held Saturday evening. The posters covered a

broad range of experimental and theoretical topics, from standardization, calibration and

instrumentation issues to analytical analyses of contact stresses in layered systems. The session

was well-attended and generated a great deal of animated discussion.

3.4 Modeling of the Indentation Process. Discussion Leader: John Pethica, Univ. of

Oxford

The Sunday morning session consisted of four talks on theoretical and modeling aspects of

instrumented indentation. It began with a talk by George Pharr, of Rice University, comparing

experimental and finite element simulation results on the effect of residual stress in a material on

its measured hardness and modulus. Although the experimental results indicated a dependence

of both properties on residual stress, the finite element simulation indicated that the effect was

not real, but was instead a result of the residual stress changing the amount of pile-up around the

contact site, thus causing the actual contact area to differ significantly from the calculated area.

Joost Vlassak then described his work at Stanford University on the effects of elastic

anisotropy on the measured "indentation modulus," which is not, in general, the Young's modulus

in the direction of indentation for anisotropic materials. In the next talk, Antonios

Giannakopoulos presented results of three-dimensional finite element modeling of the sharp

indentation process, with and without friction at the contact, and with different degrees of strain

hardening.

Finally, Subbiah Ramalingam, from the University of Minnesota, presented an analytical

approach to the calculation of elastic stresses that develop in film/substrate systems. The approach

permitted an analysis of the stress fields within each material and at the interface between film

and substrate.

3.5 Methodology and Standardization. Discussion Leader: Douglas Smith, NIST

The final session combined several aspects of instrumentation and standardization. John

Pethica, from the University of Oxford, opened the session with some cautionary remarks about

problems that are encountered when performing indentation experiments on length scales

approaching atomic dimensions. He cited meniscus and surface adhesion forces as having

significant effects on measurements in that regime.

5
The next two talks dealt with the use of atomic force microscopy (AFM) technology for

mechanical property measurement. Steve Hues presented work from NRL on the use of AFM's

to make quantitative modulus measurements, by replacing piezoelectric actuators with

electrostrictive materials, in an effort to eliminate hysteresis and creep, and by using small glass

spheres as indenters, for their more easily characterized tip geometry. Jack Houston, from

Sandia, then described a novel force-balanced AFM tip support, developed at Sandia, that is

capable of accurately recording attractive tip-substrate interactions through a feedback system that

gives the tip support a near-infinite effective stiffness. Warren Oliver returned to finish the

instrumentation part of the session with a discussion of techniques for calibrating the shape of

sharp indenter tips.

The session then concluded with two talks directly addressing standardization efforts in the

instrumented indentation community. First, Stuart Saunders, from NPL, presented the results of

research, partly funded by the European Commission, on the "Measurement of Hardness

(Mechanical Properties) of Surfaces." The work involved developing machine and tip calibration

procedures, as well as conducting round-robin testing with three commercial machines at 14 sites.

Hans-Hermarm Behncke, from Helmut Fischer Company, described work being done in Germany

towards a draft ISO standard (TC 164, WG 3) for a quantity referred to as "Universal Hardness,"

based on Vickers indentation at depths greater than 3 micrometers. Dr. Behncke also presented

results from round robin testing of samples consisting of titanium nitride coatings on steel.

4. Summary

The workshop concluded with an open discussion period at the end of the Sunday afternoon

session. Although many topics were addressed, the theme throughout the discussion was to

determine to what extent "standardization" of instrumented indentation, in any sense of the word,

was desirable, or even possible in the near future. Just the array of names for the technique itself

highlights the lack of consensus in the field; it is referred to as instrumented indentation, dynamic

hardness testing, depth-sensing indentation, continuously recording indentation technique, and

more. At very low loads, the terms nanoindentation, ultra-micro-indentation and ultra-low-load

indentation are all used. The views of the participants on issues like standard test procedures and

standard reference materials ranged from considering them to be essential and long overdue to

considering such efforts premature and essentially impossible to implement until the indentation

process is better understood. One of the more memorable comments in the discussion came from

Bill Nix when he stated that the many different approaches to the problems presented in the

6
workshop represented a healthy level of scientific activity, and that people should not be overly

concerned about the lack of consensus. He felt that we should be pleased not only with the

progress that has been made so quickly in this new field, but also with the wide range of

applications involved and the amount of sensible scientific criticism that underpins the discussions

of how data should be interpreted. His remarks were greeted with applause.

There was however one area where many participants agreed. It was noted that very often

when values for hardness, modulus or other quantities obtained by instrumented indentation are

reported in the literature, little information is given on the test parameters that were used in the

measurements. It would be easier for people to compare their results to those by others in the

literature if authors gave, and editors required, a minimum amount of information on technique

from those publishing indentation results. That information should include details of specimen

preparation (sample mounting, surface roughness), experimental parameters like the loads used,

the depths of the indents at those loads, loading rates, and calibration corrections applied {e.g.,

tip shape, machine compliance and drift), as well as the precise definition of the reported result

{e.g., hardness, modulus) and how it was obtained from the load-displacement curves. Trevor

Page felt strongly that a representative load-displacement curve should always be published, to

allow the reader to assess the overall quality of the data and to help identify any obvious

problems arising from conditions such as soft or rough surfaces, thermal drift or crack "pop-in"

behavior. If this information is available, people will at least be able to determine whether they

can directly compare their results to those from another group.

There was also discussion at several points during the workshop about what materials might

make good standard reference materials. An ideal material should be easy to polish reproducibly,

as surface finish becomes critical at low loads, and should be as elastically isotropic as possible,

so that the precise orientation between sample and indenter geometry is not critical. Single

crystal tungsten and several glasses, including pure fused silica and BK-7 glass, have been used

in round-robin testing and are possible candidates.

By all comments received by the Chairman during and following the workshop, the

participants felt that the workshop had been a very valuable meeting, despite the failure of the

group to adopt any firm recommendations for test or analysis procedures. It brought together

many of the most experienced people in the field to exchange ideas, and many participants

expressed a desire to meet on a more regular basis. Several sessions at 1996 ICMCTF meeting

will include talks on instrumented indentation.

7
Final Agenda

SATURDAY, APRIL 22, 1995

8:00-8:30 Registration, outside California Room.

Session 1:

8:30-8:45

8:45-9:15

9:15-9:45

9:45-10:00

10:00-10:30

10:30-11:00

11:00-11:30

11:30-12:00

12:00-1:00

Session 2:

1:00-1:30

1:30-2:15

2:15-2:45

2:45-3:00

3:00-3:30

3:30-4:00

4:00-4:30

4:30-5:00

Session 3:

Industrial Applications: California Room

Session Chairman/Discussion Leader: Trevor Page, U. Newcastle

Douglas Smith, NISI

Richard White, IBM

Kevin O'Connor, Kodak

Break

Harry Fujimoto, Intel

Clark Cooper, UTRC

Warren Oliver, Nano Instruments

Mike Swain, CSIRO

Lunch Break

Introduction

"Nanoindentation of Magnetic Storage Materials"

"The Use of Instrumented Indentation in the Design

of Multilayer Coating Structures for Imaging

Applications"

"Microindentation for Electronic Thin Films"

"The Use of a Nanoindenter I: Case Histories and

Lessons Learned"

"Measuring Hardness, Modulus, Creep and Fracture

Toughness Using Instrumented Indentation Tests"

"Simple Procedures for Obtaining and Analysing

Force Displacement Data With Small, SphericalTipped Indenters"

Determining Material Properties: California Room

Session Chairman/Discussion Leader: William Nix, Stanford

David Rowcliffe, KTH

Trevor Page, U. Newcastle

Neville Moody, Sandia

Break

Bill Gerberich, U. Minn

Jean-Luc Loubet, CNRS

Howard PoisI, U. Arizona

"Controlled Indentation: A General Approach to Determine Mechanical Properties of Materials"

"Procedures for the Nanoindentation Testing of

Coated Systems"

"Thin Film Property Measurements Using

Nanoindentation and Microscratch Techniques"

"Multiple Yield Phenomena Under Light Contacts"

"Some Measurements of Creep and Viscoelastic

Behavior With the Help of Indentation Tests"

"Determination of the Relationship Between

Indentation and Uniaxial Creep Strain Rates in Amorphous Selenium"

Open Discussion

Poster Session, 5:00-7:00: Council/Chamber/Cabinet Rooms. Refreshments.

8
SUNDAY, APRIL 23, 1995

Session 4:

8:30-9:15

10:00-10:15

Modeling of the Indentation Process: California Room

Session Chairman/Discussion Leader: John Pethica, Oxford

George Pharr, Rice

9:15-10:00 Joost Vlassak, Stanford

Break

10:15-11:00 A.E. Giannakopoulos, KTH

11:00-11:45 S. Ramalingam, U. Minn

11:45-12:00 Open Discussion

"Effects of Residual Stress on the Measurement of

Mechanical Properties Using Instrumented

Indentation"

"Measuring the Indentation Modulus of Elastically

Anisotropic Solids"

"3-D Finite Element Modeling of Sharp Indentations"

"Analytical Modeling of Stresses in the Film/Substrate

System, and Their Significance for Indentation

Testing"

12:00-1:00 Lunch Break

Session 5:

1:00-1:15

1:15-1:45

1:45-2:15

2:15-2:45

2:45-3:00

3:00-3:30

3:30-4:00

Methodology and Standardization: California Room

Session Chair/Discussion Leader: Douglas Smith, NIST

John Pethica, U. Oxford

Steve Hues, NRL

Jack Houston, Sandia

Warren Oliver, Nano Instruments

Break

Stuart Saunders, NPL

"Detecting the First Contact - The Role of Adsorbed

Molecules" (abstract not available)

"Nanoindentation Using the AFM: Considerations for

the Quantitative Measurement of Mechanical

Properties"

"Interfacial Force Microscopy Measurements of the

Nanomechanical Properties of Materials"

"Tip Geometry Calibration: Is Fused Silica an

Effective Standard for Ultra-Low Load Indentation?"

"Calibration and Validation of Depth-Sensing

Indentation: The European Dimension"

Hans-Hermann Behncke, Fischer Tech. "European Efforts Under ISO TCI 64 for a Dynamic

Loading Hardness Test Specification" (abstract not

available)

4:00-5:00 Open Discussion and Wrap Up

9
Extended Abstracts for Oral Presentations

10
NANOINDENTATION OF MAGNETIC STORAGE MATERIALS

Richard L. White

IBM Storage Systems Division, San Jose, CA 95193

Nanoindentation data are presented for three different but interrelated components of

the thin film dislc magnetic recording system - the air bearing slider/recording head,

the dislc substrate, and the sputter deposited thin film disk recording media. Hardness

traces across the slider trailing edge (figure 1) demonstrate the hardness of the NiFe,

sputtered A1203, and the ceramic A1203/TiC are 8, 10 and 24-40 GPa, respectively.

Lapping under non-optimum, aggressive conditions can lead to significant recession in

these components which is directly related to their hardness.

Uiz

NIFs

! > AI203/nc

.•A

•-•••v.

ol I I I 1 I 1 0 20 40 60

POSITION ALONG SUDER (MICRONS)

Figure 1. Hardness trace along slider air bearing surface and head.

The hardness and modulus have been measured for a number of alternate substrate

materials ranging from AlMg/NiP to glass and glass ceramic. The ability of these

substrates to resist damage from slider shock forces generally increases with substrate

hardness, although other criteria (fracture toughness and plasticity initiation) can be

important. Finally, hardness and modulus data for carbon overcoat films are presented

which have been sputtered under various conditions. The process variations lead to

variations in hardness, the hardness/modulus (H/E) parameter, and tribological performance in slider/disk testing. The applicability of these mechanical property parameters to the wear degradation is discussed.

11
THE USE OF INSTRUMENTED INDENTATION IN THE DESIGN OF MULTILAYER

COATING STRUCTURES FOR IMAGING APPLICATIONS

Kevin M. O'Connor

Imaging Research and Advanced Development

Eastman Kodak Company

Rochester, NY 14650-2116

Media used for the capture, storage and display of images are generally multiple-layer structures

coated on flexible substrates. Examples include conventional photographic film and paper,

photoconductor belts for electrophotography, optical storage disks, and thermal dye-transfer

media. The layers are often polymer-based and highly filled with funtional components. In both

manufacturing and use, surface contact stresses and resulting physical damage can result in

image defects and degraded information content.

Instrumented indentation is a useful technique for determining fundamental material properties

such as hardness, modulus, yield, creep and stress relaxation. The sensitivity and depth

resolution of modem indentation instruments allows the characterization of thin coatings, and

advances in the field hold the promise that meaningful properties may be obtained from multiplelayer coatings as well.

In our work, we take advantage of additional capabilities including a variety of indenter tip

geometries and sizes, use of the AC method for continuous measurement of contact stiffness, and

tangential force measurement during micro-scratching. Our objective in using indentation

techniques is to gain mechanistic understanding of practical multilayer performance features

such as adhesion and resistance to scratching and abrasion. In addition to functional layers

related to imaging, special-purpose layers such as protective overcoats and adhesion-promoting

layers are commonly used. Their effectiveness can be limited by the properties of underlying or adjacent layers. It is critical to treat the design of a multilayer coating as a layered composite

structure rather than a collection of individual layers. Strategies such as matching adjacent layer

modulus and Poisson's ratio, or creating intentional gradients in properties, are part of the overall

design of new imaging media with excellent mechanical performance.

12
MICROMECHANICS OF THIN FILMS IN ELECTRONIC DEVICES

H. Fujimoto, T. Marieb, and B. Sun

Intel Corporation

3065 Bowers Ave SCI -03

Santa Clara, California 95054

Silicon process technology's rapid advance has enabled the design and manufacture of ever

increasing more powerful microprocessors and computers. This trend is driven by geometries of

features getting smaller. Current manufacturing uses 0.35um technology, but major advances in

speed must take place and interconnects are not scaling with feature size. As linewidths decrease

aspect ratios of lines increase, surface to volume increases, new methods to pattern, clean and fill are developed, and more interconnect levels are needed. All these affect the stresses in these

semiconductor structures and lead to potential cracking and voiding problems.

Comprehensive modelling is necessary. The model should include intrinsic material stresses,

interfacial adhesion, time dependent plasticity, crack propagation and fatigue. Integration of the

model into process and electrical models will be required to allow interactive modeling

capabilities. In order for this model to be useful, it is critical to measure the effects to verify the

model and materials parameters for input into the model. Stresses, interface adhesion energy,

fracture toughness, and elastic moduli are a few of the parameters required.

Stresses in the materials can be measured by conventional techniques, but there is an appalling

lack of tools and techniques to measure the adhesion of thin films. Several techniques are being

explored. This paper focuses on microindentation as a technique for differentiating adhesion in

certain thin film stacks.

Microindentation was developed to measure the materials properties of thin films. Using the

force displacement curve we show results determining adhesion between films in a thin film

stack.

Our results show that the force displacement curve can be used not only to determine materials

properties but to determine adhesion of the W to metal interface and the oxide to salicide

interface. Using a 20 |a,m spherical indenter tip, the samples were indented to a maximum load

of 500mN. When the interface is strong, the force displacement curve is smooth without any

discontinuities. In samples with weak W to metal interfaces, a jump in the displacement is

observed in the force displacement curve indicating debonding has occurred at the interface.

Optical microscopy shows that the good interface shows an indentation in the W the size of the

indenter tip. For the poor interface, a large area around the indentation appears to be debonded.

SEM cross-sections confirm that W has debonded from the metal. The Al has been pushed away

from the indentation location under the W. This pileup then levers the tungsten until debonding

occurs. SEM cross-sections of the good interface samples do not show any debonding and also

show the Al pileup under the tungsten.

13
The force at which there is a jump in the displacement curve, can be correlated to the relative

adhesion strength of different interfaces and can be used to develop processes which result in

good interfacial strength between the thin film stacks.

Two limitations for microindentation are described. One of the critical issues in indentation is

tip wear and tip calibration. Data indicate that the diamond tip in our experiments shows a

decrease in the standard deviation and the magnitude of the force required for decohesion as a

function of the number of indents. Results also show that different tips with nominally the same

radius give different forces for decohesion of the same samples. This is explained by the

different shapes of the nominally 20um spherical tips. SEM observations show that one tip was

more faceted due to tip wear from many indents that the second tip. This explains the increase

in scatter in the data using the same tip and decreasing load for debonding.

Tip wear is also an issue for scratch testing. Results show wear for sequential scratches of the

same material, making data analysis very difficult. As we scratched the thin film being tested

the force at which the film debonds under the diamond tip increases as a function of the number

of scratches. Five scratches were done sequentially and the last two scratches were done the next

day showing the same trend of increasing load to debond. Different tips also show very different

scratch characteristics as well.

We have shown that indentation can be used to determine the difference in adhesion between thin

films. Tip calibration and tip wear have been shown to be issues. This problem of tip calibration

needs to be addressed if indentation is to be used as a repeatable technique for both materials

properties and adhesion testing. Other limitations are that no quantitative interface energies are determined, the geometry of the test is not submicron, system to system calibration is needed, and

the technique doesn't work for all materials systems. We are investigating chip structures and

potential micromachining techniques to determine the interface adhesion of semiconductor thin

films. This values will be critical for comprehensive finite element method modeling of thermal

mechanical stresses and issues in thin film structures.

14
THE USE OF A NANOINDENTER I: CASE fflSTORIES AND LESSONS LEARNED

C. V. Cooper, D. M. Sanford, and L. F. Conopask

United Technologies Research Center

M. M. Abouelleil

University of Connecticut

This presentation will focus on several salient applications of a Nanoindenter I, the original

instrument as made commercially available through Nano Instruments, Inc., at United Technologies Research Center. This instrument was among the first of its kind delivered to a comn^rcial

customer almost a decade ago, and it has been a workhorse since its delivery. The representative

application examples, described below, have their own requirements and difficulties for the

instrumented indentation system, and a discussion of these and the maintenance requirements

which accompany a highly utilized instrument is the focus of the presentation. As motivation for

the application examples presented, an overview of United Technologies Corporation is given, in

which the various operating divisions and the major products manufactured by each are identified.

A clear transition over the past ten years from a corporation highly dependent on and supported by

defense initiatives to one which realizes far more sales and profit from its commercial/industrid

sector is noted.

An overview of the use of a Nanoindenter I for the determination of indentation hardness and

modulus is presented, including the experimental procedure required for a determination of the

indenter area function, the geometric similitude between Berkovich and Vickers indenters is noted,

and the positioning, force, and depth sensing transducers are presented and discussed. Equations

are provided to account for machine compliance, allowing the user to determine the reduced elastic

modulus, E,, from the force-displacement data [1]. Briefly presented and discussed are hard,

inorganic films, such as TiN deposited by various PVD processes, which appear to exhibit an

indentation size effect, and explanations and theories devised to account for this phenomenon are offered [2, 3].

Other application examples are given in which the Nanoindenter is used to characterize the

properties of a wide variety of materials. For example, nanoindentation has been applied to

thermal-barrier coatings composed of stabilized ZrOj to detect the presence of undesirable phases

or porosity. The complex, multiaxial stress state caused by the indentation process is shown to

lead to the accommodation of significant plastic deformation in quite brittle amorphous and

crystalline oxide and fluoride CCTamic materials [4]. The use of nanoindentation to determine the

properties of a SiC^-reinforced, lithium aluminosilicate glass composite material, including the

interfacial sliding resistance of the SiC fibers and the influence of processing on this measurement.

A final application example is provided, in which the Nanoindenter I is used to determine

differences in hardness and elastic modulus of diamond films synthesized by hot-filament CVD as a function of methane concentration [5, 6]. A clear, inverse relationship between indentation

hardness and methane concentration emerges, as does an imperative for the presence of smooth

surfaces for the acquisition of repeatable and low-scatter indentation data.

[1] W. C. Oliver and G. M. Pharr, /. Mater. Res., 7 (1992) 1564.

[2] P. J. Burnett and D. S. Rickerby, Thin Solid Films, 148 (1987) 41.

[3] B. R. Lawn, A. G. Evans, and D. B. Marshall, J. Am. Ceram. Soc, 63 (1980) 574.

[4] M. Abouelleil, L. Conopask, W. Nighan, W. Roman, and D. Price, Ceram. Trans., 15

(1990) 457.

[5] C. P. Beetz, Jr., C. V. Cooper, and T. A. Perry, /. Mater. Res., 5 (1990) 2555.

[6] C. V. Cooper and C. P. Beetz, Jr., Surf. Coat. Technol., 47 (1991) 375.

15
INDENTATION TECHNIQUES FOR THE MEASUREMENT OF SEVERAL

MECHANICAL PROPERTIES

W. C. Oliver

Nano Instruments, Inc.

1001 Larsen Dr.

Oak Ridge, TN 37830

Great strides have been made over the past few years in the development of techniques for

probing the mechanical properties of materials on the sub-micron scale [1-3]. The advances have

been made possible by the development of instruments which continuously measure force and

displacement as an indentation is made [4-7]. The indentation load-displacement data thus derived

can be used to determine mechanical properties even when the indentations are too small to be

imaged conveniently. Since the indentation positioning capability of some of the instruments is also

in the sub-micron regime, a means is available by which the mechanical properties of a surface can

be mapped with sub-micron resolution. An instrument with such capabilities can be described as a

mechanical properties microprobe [8-10].

In this document we will describe some analysis techniques for obtaining the hardness,

modulus, indentation strain rate sensitivity and the fracture toughness of brittle materials from the

experimental data obtained from mechanical properties microprobes. The first step towards

calculating all of these material properties from force-displacement information is some way of

determining the area of the contact at any point during the indentation process. One approach,

using a Berchovich indenter, that has been documented to be reasonably accurate for a fairly wide

variety of materials is the solution of the following set of equations [11].

P

j_j _ max

E =

S = -p^E,VA

VP

h=h,-£-

A = 24.5hJ + XQhr

i=0

Where: H = hardness

Pmax = the maximum load that has been applied to the contact

A = the area of contact under load

Er = the reduced modulus

S = the elastic stiffness of the contact

Es = Young's modulus of the sample

Vs= Poison's ratio of the sample

Ei = Young's modulus of the indenter

Vi = Poison's ratio of the indenter

ht = The displacement of the indenter beyond the point of contact

16
he = the vertical distance between the indenter tip and the perimeter of the

indentation under load

e = a constant equal to approximately 0.72

Ci-Cg = experimentally determined constants used to describe the geometry

of the indenter

A typical experiment involves slowly loading the indenter to some specified load or depth

and then unloading it. The experimentally determined parameters are Pmax > S, and h. The value of

S is available only at the point from which the loading is reversed. The stiffness of the contact at

Pmax is obtained from the slope of the unloading curve at peak load. The values of the constants in

the area function (Ci-Cg) must have already been determined in separate experiments. This will

be discussed bellow. The indenter properties must also be known quantities. Finally, Poison's

ratio for the sample and £ must be known or assumed. With these conditions H, E, A, and he can

be calculated. If the area function is accurately determined, and the effects of the testing system are properly removed from the data, reasonably accurate results can be obtained [11]. There are

several limitations of this technique. At high loads, the contact stiffness can approach that of the

load frame. When this occurs it becomes difficult to determine the modulus of the sample with

accuracy. This problem has only a small effect on the hardness measured as long as the stiffness

can be determined within an order of magnitude. The second limitation occurs at very low loads

where surface effects (roughness and physical effects of the surface) can make it very difficult to

determine the geometry of the tip of the indenter with accuracy. This problem degrades the

accuracy both the hardness and the modulus result. This technique should work well for other

indenter geometries for which pile up of material around the indenter is not a large effect; however,

its accuracy for other indenters has not been documented. Finally, this analysis is only valid for

samples that are effectively semi-infinite.

The constants in the area function can be determined using the same set of equations and

making the additional assumption that the modulus measured from a semi-infinite homogeneous

sample should be constant. The most up to date, detailed procedures for this technique are

available elsewhere [12].

Clearly, the stiffness of the contact must be known at the point of loading at which the

model described above is to be applied. As suggested above this can be accomplished with an

unloading procedure; however, this means that the contact must be unloaded from each point at

which the hardness and the modulus are to be calculated. An alternative technique using very small

oscillatory excitation of the contact during the loading process together with alternating signal

handling techniques can yield the stiffness of the contact continuously as the mean load on the

indenter is continuously increased. This leads to the data required to calculate stiffness, hardness

and modulus continuously during loading[13].

The indentation strain rate sensitivity can be obtained by performing a different experiment

and analysis. One experiment that can be used is to load the indenter at a constant loading rate to a

specified load or depth and then reverse the loading. The indentation strain rate is obtained by

using the displacement data to determine the rate of change of the displacement divided by the

displacement itself at each point in time. The hardness, at the same point in time, can be

considered to be proportional to the stress. The slope of a plot that is logarithmic in both the X

and Y axis of the hardness verses the indentation strain rate is the indentation strain rate sensitivity.

Under certain conditions this quantity has been shown to equal the strain rate sensitivity determined

by uniaxial tests[14-15]; however, this is certainly not always the case and the conditions under

which the equality exists are not at present understood.

Finally, indentation tests can be used to make a measure of the fracture toughness of brittle

materials. The indenter geometry that yields the most accurate results for which the best

documentation of those results exists is the comer of a cube [16]. To make these measurements an

indentation is made and fracture must occur around the indentation. These fractures should be

radial in nature and extend from the comers of the indentation to at least a distance equal to the

distance from the center of the indentation to its comer into the surrounding material. If these

17
conditions are met, microscopy must be used to measure the length of the cracks and the following

equation can be applied.

This technique will be effected by crystalline anisotropy of the sample, residual stresses, defects in

the material and possibly the environment.

The techniques discussed above are useful; however, they all suffer loss of accuracy under certain

conditions. Although some of these conditions are mentioned above this document is not intended

to be a critique of the techniques. The techniques should all be considered "under development".

1) J.B. Pethica, R. Hutchings, and W.C. Oliver, Philos. Mag. A 48, 593 (1983).

2) W.C. Oliver, R. Hutchings, and J.B. Pethica, in ASTM STP 889, edited by P.J. Blau and

B.R. Lawn (American Society for Testing and Materials, Philadelphia, PA, 1986), pp. 90-

108.

3) M.F. Doemer and W.D. Nix, J. Mater. Res. 1, 601 (1986).

4) J.B. Pethica, in Ion Implantation into Metals, edited by V.Ashworth, W. Grant, and R. Procter

(Pergamon Press, Exford, 1982), pp. 147-156.

5) J.L. Loubet, J.M. Georges, O. Marchesini, and G. Meille, J. Tribology 106, 43 (1984).

:6) D. Newey, M.A. Wilkens, and H.M. Pollock, J. Phys. E: Sci. Instrum. 15, 119 (1982).

7) D. Stone, W.R. LaFontaine, P. Alexopolous, T.-W. Wu, and Che-Yu Li, J. Mater. Res. 3,

141 (1988).

;8) J.J. Oilman, in The Science of Hardness Testing and Its Research Applications, edited by J.H,

Westbrook and H. Conrad (American Society for Metals, Metals Park, Ohio, 1973), pp.5 1-74.

'9) W.C. Oliver, MRS Bulletin 11, 15 (1986).

10) W.C. Oliver, C.J. McHargue, and S.J. Zinkle, Thin Solid Films 153, 185 (1987).

:il) W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)

12) Nano Instruments, Inc., 1001 Larsen Dr., Oak Ridge TN, 37830

13) W.C. Oliver and J.B. Pethica, U.S. Patent No. 4848141, July, 1989.

14) B. N. Lucas and W. C. Oliver, in Thin Films: Stresses and Mechanical Properties ID. edited

by W.D. Nix, J. C. Bravman, E. Arzt, and L. B. Freund (Mater. Res. Soc. Symp. Proc.

239, Pittsburg, PA, 1992), p. 337

:i5) W. H. Poisl, W. C. Oliver, and B. D. Fabes, J. Mater. Res. 10, 2024 (1995)

'16) D.S. Harding, W.C. Oliver, G.M. Pharr, in Thin Films: Stresses and Mechanical Properties

V, edited by P.H. Townsend, C.A. Ross,S. P. Baker, C.A. Volkert, and P. Borgsen

(Mater. Res. Soc. Symp. Proc. 356, Pittsburg, PA, 1995), p. 663

Where: Kc = the fracture toughness

C= the crack length

18
SIMPLE PROCEDURES FOR OBTAINING AND ANALYSING

FORCE DISPLACEMENT DATA WITH

SMALL SPHERICALLY TIPPED INDENTERS

M.V. Swain and J.S. Field

CSIRO, Division of Applied Physics

Lindfield NSW 2070 Australia, and

Department of Mechanical Engineering

University of Sydney, NSW 2006 Australia.

Force-displacement data of high precision are now readily obtainable with a number of

micro-mechanical probe systems. The emphasis to date has been on nominally pointed indenters,

although spherically tipped indenters have distinct advantages. These advantages include a more

well defined and analytical response during the initial elastic loading of the material. The

approach also enables the entire unloading response for an elastic-plastic contact to be predicted,

rather than the usual asymptotic response as favored for pointed indenters. A material's response

to spherical indentation has many similarities with traditional mechanical testing of materials in

that the initial elastic response precedes the material's non-linear behaviour. Often, however, the

transition from one regime to the other is asymptotic and difficult to distinguish. Another

inherent problem with the interpretation of all monotonic loading and unloading

force-displacement data is that of partitioning the elastic and inelastic contributions to the

displacement at a specific force. Such partitioning usually relies on the assumption of constant

elastic modulus throughout the test, with the modulus determined during the final unloading. A

simple procedure to overcome this limitation with spherical tipped indenters is via partial unload

steps throughout the penetration to maximum load. This procedure enables the contact pressure

and modulus to be determined independently throughout the excursion to maximum load. Using

the simple relationships proposed by Tabor (1953), and more recently rigorously confirmed by

Hill et al (1989), the materials stress-strain response may be determined. It is also possible to

further extend the analysis to determine work hardening response and also to incorporate

"pile-up" and "sinking-in" about the impression. As with all analysis of indentation

force-displacement data, interpretation of spherical contact requires a detailed knowledge of the

indenter tip shape. Examples of procedures used for such characterization and even their

extension to nominally sharp Berkovich indenters are discussed. Application of spherically tipped

indenters to the investigation of the stress-strain response of polymers, metals and ceramics will

also be shown and, in the case of polymers and metals, compared with conventional stress-strain curves. Issues involved with the extension of the spherical indentation approach to materials that

fracture and to very thin films will also be discussed.

19
CONTROLLED INDENTATION: A GENERAL APPROACH TO DETERMINE

MECHANICAL PROPERTIES OF MATERIALS

David Rowcliffe

Materials Science and Engineering

Royal Institute of Technology

S - 100 44 Stockholm SWEDEN

In recent years, depth sensing indentation techniques have been developed and widely used,

with both Vickers and Berkovich geometries (nano-indenter). Regardless of the shape of the

indenter the most important result from such a test is the indentation load-depth (P-h) curve. Various mechanical properties, not only hardness, but also modulus, yielding stress, and strain

hardening must affect the form of the penetration curve. Thus it should be possible to derive

these properties for any material provided an appropriate analysis of the penetration curve is

available. This paper presents a general methodology to analyse the loading cycle of

experimentally-obtained indentation P-h curves for Vickers indentation. The approach uses

results from a recent 3-D FEM analysis to derive various mechanical properties, including

hardness, yielding stress, strain hardening and plastic zone size. The validity of the approach

can be tested by reconstructing the P-h curves from these data.

The method is based on two assumptions which were confirmed by the 3D-FEM analysis: (1)

there is no elastic recovery from the diagonal of the plastic imprint after unloading, therefore

the generally-defmed hardness value is equal to the average pressure during loading; (2) the

average pressure during loading, in this case, the hardness, is a constant during indentation

loading, hence the true projected contact area can be found from the load and hardness values.

An important aspect is that surface displacement occurs during indentation and must be

accounted for in the analysis. This is done with a surface displacement factor which relates the

geometrical contact area to the true contact area under load. So far, various ceramics have been

investigated and it is found that, during loading, indentation is accompanied by different

amounts of sinking-in just outside the contact boundary. The study of the surface displacement

suggests, as a first approximation, that the Mises elastoplastic solution needs to be re-scaled by

the surface displacement factor in order to explain the results of indentation behaviour on

ceramic materials.

Values for compressive plastic properties derived in this way agree well with the limited data

available in the literature. Recent work suggests that this approach can be extended to include

other effects such as cracking or material densification during indentation. Ultimately it should

be possible to obtain a complete characterisation of all of the important compressive plastic and

elastic properties of materials from an analysis of a single indentation cycle.

References

K. Zeng, A.E. Giannakopoulos and D.J. Rowcliffe,"Vickers Indentations in Glass - II Comparison of Finite Element Analysis and Experiments," to appear in Acta metall. mater.

1995.

K. Zeng, E. Soderlund, A.E. Giannakopoulos and D.J. Rowcliffe,"Controlled Indentation: A

General Approach to Determine Mechanical Properties of Brittle Materials", to appear in Acta

metall. mater. 1995.

20
PROCEDURES FOR THE NANOINDENTATION TESTING OF COATED SYSTEMS

Trevor Page & Sarah Hainsworth

Materials Division

Department of Mechanical, Materials & Manufacturing Engineering

Herschel Building

The University of Newcastle

Newcastle upon Tyne

NEl 7RU; UK

Indentation testing methods where load, depth and time are continuously recorded (eg.

nanoindentation) have demonstrated considerable ability for studying the near-surface mechanical

properties of materials^^^'^. Such continuously recording indentation techniques (GRIT) have

a unique ability to probe mechanical properties at shallow penetration depths and, consequently,

appear particularly well-suited to the study of surface-engineered and coated systems

Indeed, for thin film coated systems, they offer one of the few possible means of making

mechanical property measurements at depths sufficiently shallow to allow the mechanical

response of the films alone to be studied with minimal contribution from the substrate. In

addition, at increasing displacements, the effects of film and substrate can be measured together,

and thus the behaviour of the coated system investigated over ranges of contact-affected volumes

and stresses. Further, the technique offers the possibility of experimentally determining

properties which may be very difficult to ascertain in other ways - eg. the elastic moduli of

coatings in the microstructural and residual stress states in which they are used in various coated

systems^^-''^'^^. Furthermore, since software control allows many indentations to readily be

made on quite extensive sample areas, GRIT are also ideally suited to assessing the point-to-point

reproducibility of coated systems though, as yet, this seems an under-exploited application.

At the outset, we have to face a central underlying problem which is that there are currently few

soundly-based mechanistic models for predicting 'how coated systems work'. Indeed, the pace

of technological demand for surface engineering has led to the development of many coated

systems where expectations of properties and behaviour are based upon experience and

empiricism. Thus, in the absence of well-founded models, it can be difficult both to plan how

best to utilise GRIT to probe the properties of coated systems - and to interpret the resultant data

- especially since many intuitive models simply fail to work. For example, the enhanced

hardness of coated systems can be strongly influenced by elastic bending and flexure of the

coating rather than its own hardness or indentation plasticity; thus typical 'law of mixtures'

hardness models are inappropriate. Similar comments can also apply to understanding the

effective elastic modulus of coated systems^^^ in various loading modes and even the effect of

substrate properties on system behaviour^^-'*^^. Thus, before we can properly either predict or

interpret the nanoindentation response of coated materials, we need to develop good models of

systems behaviour based on understanding not only the differing deformation mechanisms

controlling behaviour in various systems, but also the changing balance between dominant

deformation mechanisms over a range of contact scales and stresses. Arguably, this is the single

21
largest factor limiting current progress with applying CRIT techniques to the study of coated

systems.

On the positive side, there is certainly a wealth of information which, currently, we can access using nanoindentation. This presentation will highlight these areas which prescribe our present

approaches to, and procedures for, the CRIT testing of coated systems as follows.

(a) The general use of the 'fingerprinting' approach-^ whereby the responses of the coated

system can be compared to those of the substrate alone (as a function of indentation scale

etc). This underlines the importance of 'knowing your substrate' and recognising its

profound influence on coating structure and properties

(b) The examination of load-displacement curves for signs of behaviour peculiar to the coated

system (eg. the 'pop-in' (displacement discontinuity) behaviour often associated with

fracture and delami nation of the coating (or even nucleation of plasticity in the underlying

substrate))-^

(c) By making quantitative comparisons between the load displacement data for both the

coated system and the substrate alone, quantifying the enhancement provided by the

coating to the system (eg, comparing 5,„^ b^^^, stiffnesses, plastic work expended etc)^.

(d) Performing (a)-(c) over a range of indenter displacements (5). Since experience suggests

that many coatings flex elastically up to displacements approximately equal to the coating

thickness (t), it is suggested that at least three series of tests are performed (namely with

5<<t (the regime where the coating is mainly flexing to generate membrane stress^^),

with 5 = t (where the onset of coating fracture may occur and the substrate is playing a

significant role'^) and with 6> >t (where the sections of broken coating may simply act as blunt extensions to the indenter-profile)).

(e) The essential use of microscopy techniques to study both the initial states of test surfaces

and post facto evidence for deformation mechanisms. The preliminary assessment is

necessary to ensure that the surfaces are both flat enough for examination (eg. only

exhibit topography small in scale compared to the indentation sizes) and to identify

features (eg. metal globules in some coated systems) which could lead to artifacts in the

data. The post facto observations are critical in determining the occurrence and extent

of, for example, any coating fracture or delamination, evidence of substrate pile-up

beneath the coating etc-^.

(f) Considering the use of both cross section and taper section techniques as well as testing

coatings as stand-alone membranes with the substrate removed^'^'^'*.

(g) Assessing both the possible role of the substrate in supporting the contact load^^ and

using quantitative modelling techniques - especially those based on a proper understanding

of deformation and mechanisms - to predict and interpret the load-displacement

data^2.i3.i6_

22
(h) Using indenters of different geometry to investigate differing aspects of contact response -

eg. using hemispherical indenters to quantitatively explore elastic properties®^^^.

There are also areas for future development and assessment and these include

• The development of better models for predicting load-displacement response®^^-^'^^.

In particular the shapes of unloading curves for many coated systems are not always

amenable to the analytical approaches often used for calculating the stiffnesses and elastic

moduli of simpler systems^^'^^. In these cases, the generally more curved appearance

of the unloading curves is presumed due to the inhomogeneous nature of elastic recovery

in these systems and, in these cases, conventional analysis must either be approached with

caution or alternatives sought^^'^.

• Addressing the problem of deconvoluting properties as a 'function of depth', especially

in those cases where the coating is simply bent and flexed into the substrate under the

indenter contact. Even for isotropic specimens simply penetrated by the indenter,

different portions of the indenter surface are sampling properties of the specimen at

various depths. Thus, at best the load-displacement data can only supply some complex

summation of all properties experienced at all the depths sampled by the indenter profile.

This problem is even more complex with either inhomogenous samples or with coatings

which flex and bend to follow the contact profile-^.

• Furthering an understanding of the work of indentation approach®^^^ (conveniently

provided by the area under the load-displacement curve) to quantitatively describe the

enhancements provided by the coating to the system^^^^ Much of the problem here is

concerned not with measuring the reversible and irreversible components of the work

done, but on establishing the sample volume in which the work has been dissipated by

deformation. It should be noted that, since some of the earliest attempts to analyse

indentation behaviour*^^^^, the equivalence of indentation hardness as both a contact

pressure and work done per unit volume has been appreciated but under-used.

• Assessing how best to characterise multi-layer systems where the full system performance

may only be experienced when deformation spans scales larger compared to the

microstructural scale or characteristic length.

• Undertaking contact fatigue and creep experiments, especially in controlled

environments^^'^.

In order to obtain useful property data, many of these concepts need approaching with caution

but, given the right experimental approaches, continuously recording load-displacement

instruments can provide a wealth of unique information regarding coated systems. However,

more informed and imaginative use of nanoindentation techniques is required if we are to learn

more about coated systems and escape from the self-imposed shackles of simply trying to assess

their hardnesses.

23
Finally, it must be emphasised that CRIT do not exist in isolation but form part of the spectrum

of techniques (eg. bend tests, adhesion tests etc) available for studying different aspects of

coating performance^^^^'^'^.

Selected References - see also wider references cited therein.

1 Page T.F., Oliver W.C. & McHargue C.J., Journal of Materials Research, 7, 1992, 450-473.

2 Hainsworth S.V. & Page T.F., Journal of Materials Science, 29, 1994, 5529-5540.

3 Page T.F. & Hainsworth S.V., Surface & Coatings Technology, 61, 1993, 201-208.

4 Hainsworth S.V. & Page T.F., Surface & Coatings Technology, 68/69, 1994, 571-575.

5 Hainsworth S.V., Bartlett T. & Page T.F., Thin Solid films, 236, 1993, 214-218.

6 Wright T. & Page T.F., Surface & Coatings Technology, 54/55, 1992, 557-562.

7 Pharr G. & Oliver W.C, Materials Research Society Bulletin, 17, 1992, 28-33.

8 Weihs T.P., Hong S, Bravman J.C. & Nix J.C., Journal of Materials Research, 3, 1988, 931-

942.

9 Vlassak J.J. & Nix W.D., Philosophical Magazine A, A67, 1993, 1045-1056.

10 Page T.F. & Knight J.C, Surface & Coatings Technology, 39/40, 1989, 339-354.

11 Knight J.C, Page T.F. & Hutchings I.M., Thin Solid Films, 177, 1989, 117-132.

12 McGurk M.R., Chandler H.W., Twigg P.C & Page T.F., Surface & Coatings Technology,

68/69, 1994, 576-581.

13 Ramsey P.M., Chandler H.W. & Page T.F., Surface & Coatings Technology, 49, 1991, 504-

509.

14 Twigg P.C, Ph.D Thesis, 1995, University of Newcastle (in preparation).

15 Yu H.Y., Sanday S.C & Rath B.B., Journal of Mechanical Physical Solids, 38, 1990, 745-764.

16 Hainsworth S.V., Sjostrom H., Sundgren J-E., Chandler H.W. & Page T.F., 'Analysis of

Nanoindentation Load-displacement Loading Curves', this workshop, 1995.

17 Field J.S. & Swain M., Journal of Materials Research, 8, 1993, 297-306.

18 Doerner M.F. & Nix W.D., Journal of Materials Research, 1, 1986, 601-609.

19 Oliver W.C. & Pharr G.M., Journal of Materials Research, 7, 1992, 1564-1583.

20 Nowak R. & Sakai M., Journal of Materials Research, 8, 1993, 1068-1078.

21 Twigg P.C, McGurk M.R., Hainsworth S.V. & Page T.F., in ' Plastic Deformation of Ceramics

IIP (Eds. J. Routbort, R.C Bradt & C Brookes), Plenum Publ. Corp., New York, (1995 - in

press).

22 Stillwell N.A. & Tabor D., Proceedings of the Physical Society, London, 78, 1961, 169-179.

23 Knight J.C, Page T.F., Chandler H.W. & Ramsey P.M., in 'Designing Ceramic Interfaces IP

(Ed. S.D. Peteves). Official Publication of the European Communities (Luxembourg), Physical

Sciences EUR 15306. 1993, 453-467.

24 Ramsey P.M., Page T.F. & Chandler H.W., Thin Solid Films, 201, 1991, 81-89.

24
DETERMINATION OF THIN FILM PROPERTIES USING

NANOINDENTATION AND MICROSCRATCH TECHNIQUES

N.R. Moody, S. Venkataraman^ J.E. Angelo, J.C. Nelson^ and W.W. Gerberich^

Sandia National Laboratories

Livermore, CA 94551-0969

^University of Minnesota

Minneapolis, MN 55455

The reliability of many microelectronic thin film components is governed by the composition and

structure of the film and the film-substrate interface. Thin tantalum nitride films for resistor

applications are of particular interest, for miniaturization and high heat generation increase the

probability that changes in composition and structure over long service lives will degrade

properties. However, the lack of small volume test techniques have precluded quantifying the

effects of these changes on properties. We have therefore combined nanoindentation, continuous

microscratch testing, and high resolution transmission electron microscopy to determine how film

and film-substrate interface structure affects properties in thin tantalum nitride films.

The thin tantalum nitride films employed in this study were sputter deposited on (1 120) single

crystal sapphire substrates to nominal thicknesses of 100 and 600 nm. The elastic modulus of

each film was determined as a function of depth with a Nano IndenterTM II using a Berkovich

indenter. Each test included a 60 s hold at maximum load to minimize time-dependent effects

on property measurements, and a 60 s hold during the unloading segment to determine thermal

drift. The plastic contact area for each indentation in the 600-nm-thick as-sputtered film was

measured directly in a JEOL 840 SEM. The plastic contact areas in the 100-nm-thick films were

calculated using an indenter tip shape function determined from fused silica and verified with

values measured in the thick tantalum nitride film. Stiffness and elastic modulus were determined

from the slopes of each unloading curve as described by Oliver and Pharr.[l] Fracture toughness

was then determined on a Nano IndenterTM II and a microindentation test system by IBM,

configured to control normal and lateral displacements. These tests employed a conical diamond

indenter with a 1 jam tip radius and a 90° included angle that was simultaneously driven into the

films at a rate of 15 nm/s and across the films at a rate of 0.5 )im/s until a portion of the film

spalled from the substrate. The work of adhesion and interfacial fracture toughness values of the

thin TajN films were determined from the data using the elasticity based approach of

Venkataraman et al.[2].

The elastic modulus of the as-sputtered thin tantalum nitride films varied from area to area on

each wafer and between wafers from different deposition runs. For the 600-nm-thick films, the

elastic modulus ranged from 350 to 450 GPa. The elastic modulus of the 100-nm-thick film was

slightly higher at almost 500 GPa, with a smaller variation in values. With Poisson's ratio set

equal to the value for tantalum at 0.35, the work of adhesion and fracture toughness of both the

100 and 600-nm-thick films were near 0.6 J/m^ and 0.5 MPa-m'^^ respectively, with one sigma

approaching 50 percent. [3] The variation in elastic modulus of the 600-nm-thick films is

consistent with a highly variable columnar structure that forms near the film surface, while the

less variable values observed in the 1 00-nm-thick films are consistent with the somewhat uniform

25
amorphous structure observed. The variability in adhesion values can be directly attributed to

the variability in the several-monolayer-thick zone of damage that characterizes the film-substrate

interface.

'W.C. Oliver and G.M. Pharr, J. Mater. Res. 7, 1564 (1992).

^S. Venkataraman, D. Kohlstedt, and W.W. Gerberich, Thin Solid Films 223, 269 (1993).

^N.R. Moody, S.K. Venkataraman, J. Nelson, W. Worobey, and W.W. Gerberich, in Covalent

Ceramics II: Non-Oxides, (MRS Proc. 327, Pittsburgh, PA, 1994) pp. 337-342.

This work supported by U.S. DOE Contract DE-AC04-94AL85000.

26
MULTIPLE YIELD PHENOMENA UNDER LIGHT CONTACTS

W.W. Gerberich, J. Nelson, E. Lilleodden and S. Venkataraman

Yielding in small volumes imder sharp contacts has been observed for about 25 years

with the first direct observations in gold by Gane^ using direct transmission electron microscopy of tip deformation. Later Pethica and Tabor'^ used resistivity techniques. More

recently, such small volume yielding has been observed by others using depth sensing

instruments. Notably, Pharr and Oliver^ showed indirect evidence in silver. Page, et al.'^

directly imaged dislocation loops in AI2O3 after nanometer level indentations and Tangyunyong, et al.^ used an interfacial force microscope to monitor plastic deformation in gold as

produced by /^N level forces.

Probably the most convincing evidence of a yield point due to dislocation nucleation

is Page, et al. 's since they show a 10 nm "pop-in" displacement onto {1012} sapphire and

the approximate 10 dislocation loops associated with it. While we had previously shown

dislocation loops in Fe-3wt%Si^ and yield "pop-ins" at similar loads to the AI2O3 in both

Fe-3wt%Si^ and GaAs,^ in all of these experiments there was additional evidence that

deformation had occurred prior to the yield point. The present result sought to find if

there was even a lower load level yield point, particularly in Fe-3wt%Si, that might be

associated with the initial yield. In fact very clear evidence of two yield points was foimd,

these being shown in Figures 1 and 2. The first yield point occurred near 150 //N in over 10

contacts and the second yield point occurred near 1500 ^N for many more than 10 repeat

experiments.^

Using sharp diamond tips with radii in the range of 60 to 200 nm, we saw no evidence

of either phase transformation (densification) or microcracking which could be associated

with these yield phenomena. Clearly, the cavities produced carmot be associated with

surface diffusion considering the rapidity with which the displacement excursions occurred

at room temperature. Furthermore, as explained in more detail elsewhere^ time dependent

indentation and relaxation in GaAs can best be explained by a dislocation nucleation

mechanism.

Based upon previous information^ we propose that oxide breakdown is the most likely

process for the second yield point. We do recognize that with sharp indenters and the

27
0.00025

0.0002

2: 0.00015

V

rs 2 0.0001 h

5 10

r

-5 r

• •••

L V / • Ji

0 ^^^

0.01 0.02 0.03

Depth, )im

0.04 0.05

Figure 1: Initial yield point near 150 /i/N in Fe-3wt%Si (100) loaded at 1.5 nm/s. Hertzian

behavior is followed for the initial loading portion to 0.023 fim depth.

-O 0.002

o^ 0.0015

0 0.2 0.4 0.6

Depth, |im

0.8

Figure 2: Second yield point near 1500 /iN in Fe-3vvt%Si (100) loaded at 1.5 nm/s. Curve

irregularities are paxtially due to the slow rate of loading.

28
changes in the stress distribution associated with the elastic bending of an elastic film

on a ductile substrate, that the second yield may be associated with a shear stress shift

nucleating yield at either different locations or on different slip systems under the contact.

Irrespective of the reason for the second yield, we propose the oxide film to have major

effects on the initiation of yield in metallic systems. That is, the first dislocations are

proposed to nucleate at a load under a cylindrical plane strain contact, as given to first

order by

where E is the reduced modulus, R is the tip radius, hfo is the oxide layer thickness

and fia is the shear modulus of the plane that is involved in tip nucleation of the first

dislocation. While there are a number of simplifying assumptions here that relegate image

force contributions in Fe-3wt%Si to secondary effects, the major variables of moduli film

thickness and tip radius all should have major effects on the nucleation condition. Data

demonstrate yield points in the range of 70 to 300 fxN, the scatter being attributed to

small variations in the oxide film.

Upon nucleating the first dislocation, others follow imtil an arrest occurs associated

with an equilibrium of forces between the indenter tip and the dislocation back force. To

first order, this gives a good agreement with observed forces at arrest when utilizing the

number of dislocations estimated from residual displacement excursions at yield. This is

given by

_ ZfisbNa

PlYP ^ .r( s

where Hs is the shear modulus on the slip plane, N s the number of dislocations, h is

the burgers vector, a is the contact radius at the lower yield point and f{oi) is obtained

form the shear stress distribution. While this fit the Fe-3wt%Si data, one can also show

that it comes close to reproducing Page, et al. 's'^ average force of 1500 //N for nucleating

dislocations in (1012) AI2O3. Note here in this load controlled instrument that the force

for nucleating dislocations is also the force at arrest. There is a caveat here in that f{a) is

smaller in the AI2O3 case compared to Fe-3wt%Si, consistent with the fact that dislocation

loops less than 200 nm in diameter were observed for AI2O3.

29
FUTURE DIRECTIONS

We believe that a number of complementary instruments currently exist. These provide microindentations which scale from the mN to the kN regime, nanoindentation types

which scale from fiN to N levels and interfaciaJ force or atomic force types which can scale

from the nN to mN regime. Note that each of these may have a 10^ range of force capability with approximately a three order of magnitude overlap. While not all instnmients

have the ranges given above, there is sufficient overlap in each case with other instruments that scale effects can be appropriately examined. It is clear to us that there are

scale effects with near surface contacts at the atomic scale, as measured by STM, IFM or

AFM, being best modeled by molecular dynamics; small contacts at the mezoscopic scale

as measured by modified AFM, IFM or nanoindenters being best modeled by discretized

dislocations (in crystals); and large contacts at the continuum scale as measiured by depthsensing microindenters being modeled by FEM. We do not mean the above pairings to be

exclusive a^ much can be learned by using microindenters at the Newton level using large

spherical tips. For example, dislocation modeling may be best at some mezoscopic scales

by using a combination of many spherical tip indenters. Only by appropriate pairing of

experimental instruments, theoretical modeling and understanding of scale will the power

of instrumented indentation bring broad understanding and therefore usage by both the

academic and industrial commimities.

REFERENCES

1. N. Cane and F.P. Bowden, J. Appl. Phys. 39, 1432 (1968).

2. J.B. Pethica and D. Tabor, Surf. Sci. 89, 182 (1979).

3. G.M. Pharr and W.C. Oliver, J. Mater. Res. 4, 94 (1989).

4. T.F. Page, W.C. Oliver and C.J. McHargue, /. Mater. Res. 7, 450 (1992).

5. P. Tangyunyong, R.C. Thomas, J.E. Houston, T.A. Michalske, R.M. Crooks and A.J.

Howard, Phys. Rev. Lett. 71, 3319 (1993).

6. W.W. Gerberich, S.K. Venkataraman, H. Huang, S.E. Harvey and D.L. Kohlstedt,

Acta Metall. Mater. 43, 1569 (1995).

7. W. ZieUnski, H. Huang and W.W. Gerberich, /. Mater. Res. 8, 1300 (1993).

8. E. Lilleodden, W. Bonin, J. Nelson and W.W. Gerberich, "/ra situ imaging of ultralight load indents into GaAs," accepted /. Mater. Res. (1995).

9. E. Lilleodden, W. Bonin, J. Nelson, J.T. Wyrobek and W.W. Gerberich, "/n situ

imaging of ultra-Hght load indents into GaAs and Fe-3wt%Si," this workshop (1995).

30
SOME MEASUREMENTS OF VKCOELASTIC PROPERTIES

Wrra TBE HELP OF NANOINDENTATION

J-L LOUBET*. B N LUCAS**, W C OLIVER***

* Ecole Centrale de Lyon, LTDS, URA CNRS 855, BP 163. F-69131 Ecully Cedex, France

*

ORNL, Metals and Ceramics Division, MS 61 16, PC Box 2008, TN 37831

**

Nano Instruments, Inc., Box 14211, Knoxville, TN 37914

The viscoelastic behavior of surfaces is fundamental in fields dealing with interfaces, such as

adhesion, polymer blending, composite materials and tribology As a result, there has been

considerable recent effort devoted to investigating the viscoelastic properties of thin films using

surface force apparati (SFA) [1,2] and atomic force microscopy (AFM) [3,4]. Using a

nanoindentation instrument, the Nano Indenter® 11, we present results of the first measurements

of the linear viscoelastic properties of a polymer obtained with of a trigonal diamond tip

(Berkovich indenter). Small, oscillatory motions of the indenter yield a shear field in the material

from which the complex elastic modulus (G*) of the polymer can be deduced. The main objective

of this presentation is to report how this was accomplished. The polymer tested was a

unvulcanized natural rubber, an amorphous polyisoprene of molecular weight 800,000. It has the

chemical structure poly-cis 1,4-isoprene.

If a small, constant harmonic load oscillation is imposed on the specimen during the indentation

process and displacement response is measured at the same frequency (f), it is possible to

determine the experimental dynamic response of the system. The amplitude and phase relationship

between the excitation and the response are a composite of the response of the apparatus and the

material being indented. To separate the two, an accurate dynamic model for the apparatus must

be determined. Such a model has been established for tfie Nano Indenter® IT [5] but some

improvements in the method and the mechanical modeling are still needed. Having removed the

response of the apparatus, the remaining dynamic response can be divided into two parts [6]. The

portion of the displacement signal which is "in phase" with the excitation is the elastic response

of the contact. It is related to the stiffness (S) of the contact and to the elastic modulus, or storage

modulus (G'), of the material. The "out of phase" portion characterizes the energy being absorbed

by the material, i.e. the damping (Ceo) of the contact, and thus the loss modulus (G") of the

material where o is the angular frequency or pulsation of the harmonic oscillation of frequency

31
f (©=27rf) We show that both the "in phase" and the "out of phase" portions of the response scale

according to the square root of the contact area. Using the Principe de correspondance of linear

viscoelastic theory we propose that the storage modulus G' and the loss modulus G" can be

written as:

6 ^

6 ^

where A is the contact area. Two different experiments were conducted at room temperature (T=23.9®C) to test the proposed

method. The first one was performed at constant area of contact and different frequencies. Small

harmonic oscillations of the load were imposed while the area of contact was held constant. The

ratio of the amplitude of each force excitation and the amplitude of the resulting harmonic

displacement were measured. The phase angle between the force and the displacement were

measured simultanously. The range of tiie frequencies tested was 50 mHz to 50 Hz. This gives

the viscoelastic properties as a function of frequency, as they are determined from Ae complex

mechanical modulus G*=G'+iG" (see figure 1).

0.1

G' During Loading • Q' , L«450

* Q' . U300

A 0- , L>1S0

8

n G'DurIng Loading o G" , La450

o G" , Lb300

A G" , LalSO

I

o

LI

a

Q.

b

0.1

0.1 1 10

Pulsation, to (rad/s)

100

Figure 1: Changes of the storage modulus (G') and the loss modulus (G") as a function of

frequency at room temperature (T=23.9*'C) for unvulcanized natural rubber, poly-c/5 1,4-isoprene

(Mw=800,000) as measured in a microscopic contact between the material and a diamond tip,

Berkovich indenter.

32
The second set of experiments was performed at a constant frequency of about 1 Hz and different

indentation depths. A fixed frequency for the harmonic oscillations of the load was imposed and

the ratio and the phase angle between the harmonic force and the resulting harmonic displacement

were measured as a function of increasing indentation depth (with a corresponding increase of

the contact area). The indentation velocity was 10 nm/s. This gives the stiffness (S) and the

damping coefficient (C) of the contact as a function of the indentation depth (see figure 2). It was

found that both (S) and (C) vary linearly with the indentation depth. The slopes of these straight

lines are respectively proportional to the storage and loss modulus of the indented material, as

can be easily deduced from equations (1) and (2).

250

200

150

" I " " I " " I " I

•

3 6 % 24.56 _ G = 031MPa

100 -

S= 1.1097 + 6.2101h;

R= 0.99957

10 15 20 25 30

Indentation Depth (^im)

40

6

5

4

?

Z 3

O

1 .......

; r ^

Slope . 3 6 n24.56

v = 0.5

G" = 0.054MPa

,

.

. 1

.

.

.

. 1

•. . . . 1 . . . . 1 . . , . 1 , . .

-C = 0.35401 + 0.14398 h; " R= 0.99777

.1 1 .... 1 .... 1 ... . 10 15 20 25 30 35 40

Indentation Depth (^im)

Figure 2: Changes of the stiffness (S) and the damping coefficient (C) of the contact between a Berkovich diamond and an amorphous polyisoprene with indentation depth. The slopes of the

curves are proportional to the storage (G') and loss modulus (G") of the material as shown in the

insert formulas. The measured values of the storage and loss modulus (G-0.37 MPa and

G"=0.054 MPa) at 1 Hz are in good agreement with data in the literature [7].

In conclusion, it is shown for the first time that it is possible to measure the viscoelastic behavior

of materials such as solid polymers with the help of nanoindentation techniques. Accurate

measurements of the storage modulus and the loss modulus can be obtained using this method.

[1] J.M. Israelachvili, Colloid Polym. Sci. 264, 1060 (1986); S. Granick, Science 253, 1374

(1991).

[2] A. Tonck, J.M. Georges, J.L. Loubet. J. Coll. Int. Sci. 126, 150 (1988); J.P. Montfort, A.

Tonck, J.L. Lx)ubet, J.M. Georges, J. Polym. Sci., Part B 29, 677 (1991); E. Pelletier, J.P.

33
Montfort, J.L. Loubet, A. Tonck, J.M. Georges, Macromolecules 28, 1990 (1995).

[3] S. A. Joyce, R.C. Thomas, J.E. Houston, T.A. Michalske, R.M. Crooks, Phys. Rev. Lett 68,

2790 (1992).

[4] M. Radmacher, R W. Tillmann, H.E. Gaub, Biophys. J. 64, 735 (1993).

[5] J.B. Pethica, W.C. Oliver, in Thin Films: Stresses and Mechanical Properties, J.C. Bravman,

W.D. Nix, D M. Bamett, D A. Smith Eds., Mater. Res. Soc. Symp. Proc. 130, 13 (1989);

W.C. Oliver, G.M. Pharr, J. Mater. Res. 7, 1564 (1992).

[6] J.L. Loubet, M. Bauer, A. Tonck, S. Bee, B. Gauthier-Manuel, in Mechanical Properties and

Deformation Behavior of Materials Having Ultra-Fine Microstructure, M. Nastasi, D M.

Parker, H. Gleiter Eds., NATO ASI series. Series E: Applied sciences 233, KJuwer Academic

Publishers (1993), p 429.

[7] J. Brandrup, E H. Immergut, Polymer Handbook, third edition, J Wiley & Sons (1989).

34
INDENTATION CREEP IN AMORPHOUS SELENIUM

W. Howard Poisl

Department of Materials Science and Engineering

University of Arizona, Tucson, AZ, 85721

Indentation techniques can be used to obtain time-dependent, or indentation creep, properties of

materials. Since the development of instrumented indentation techniques, it is now easier to obtain

indentation creep data as the indentation size is directly obtainable from the displacement of the

indenter, obviating the need to stop the experiment in order to measure the indentation size. Using

instrumented indentation it has been found that many materials, even ceramics, creep at

temperatures well below half of their melting temperature.

While previous studies'-^ have indicated that the activation energy and stress exponents for

indentation creep are similar to conventional creep, there is no accepted, validated method for

analyzing indentation creep data. The power-law creep equation

£ = k&' (1)

where £ is strain rate, a is stress, n is the stress exponent and A: is a constant for a given

material/temperature, has been used by many researchers to describe the time-dependent properties

of materials during indentation creep. Values for the stress on the material under the indenter

during indentation creep can be obtained from the well known relationship between stress and

hardness, H = ciG, where C\ is a constant of about 3 for most material/indenter systems.

However, the strain rate of the material under the indenter during the indentation creep test has not

been accurately determined. It would be useful to extend the concept of representative strain under

an indenter to define a representative strain rate for the material undergoing indentation creep. The

representative strain rate could then be related to the indentation su-ain rate as e,^p = CjE/.

Newtonian viscous materials have a constant stress exponent of 1.0, irrespective of the stress and

strain rate applied. The relationship between stress and strain rate for a viscous material is

s = ^

(2)

3r7

which is similar to the power law creep equation with a stress exponent of 1.0. Using the

relationships shown above, the coefficient relating indentation strain rate to the representative strain

rate in a viscous material can be found from the following equation

c. = 7^ (3)

Indentation creep data on amorphous selenium at temperatures of 32.1 and 34.3 °C with a Berkovich indenter have been obtained.^ Creep data were obtained from a step load procedure, in

which a load of 10 mN was applied to the indenter in less than a second and held constant for 1 hour. Load and displacement as a function of time were monitored, from which hardness and

indentation strain rate were calculated. Hardness was calculated as the load divided by the

projected area of the indentation, while indentation strain rate was calculated as

h dt

where h is the current displacement. Indentation strain rate versus hardness curves for these

procedures are shown in Figure 1 . It can be seen that there are two regions to these curves - a

linear region at low hardness levels, and a non-linear region at higher hardness values. The non35
linear region is due to two effects. When the load is suddenly applied to the indenter, the

deformation of the material is initially dominated by the elastic and delayed elastic response of the

material. In addition, amorphous selenium exhibits non-Newtonian viscous flow for high stress, or hardness, levels.^ Once deformation is occurring only due to Newtonian viscous flow, the log

£/ - log H curves become linear with a slope of 1.0. Using experimental values of hardness and

indentation strain rate, c\ equal to 3, and published viscosity values,^-' Equation 3 results in a

coefficient ci of 0.09, or =0.09e, (5)

The coefficient relating indentation strain rate to strain rate should vary with the power-law creep

exponent as jc^''".'" Therefore, as n increases the representative strain rate will approach the

indentation strain rate.

Equation 3 can now be rewritten to obtain the viscosity as a function of hardness and indentation

strain rate during a constant load indentation creep test, or

^7 = — (6)

9(0.09)£;

The constant load indentation creep test has been shown to be characterized with a constant strain

of approximately 10%.'' Therefore, the constant load indentation creep procedure is equivalent to a

stress relaxation test. The relaxation function for a stress relaxation test can be defined as the

instantaneous stress divided by the initial su^ess applied. For an instrumented indentation test, this

can be expressed as ^ = ^

(7)

//(O)

where H{t) is the hardness at a given time and //(O) is the initial hardness. The relaxation function

of linear viscous materials can be well described by

T = exp

' t

V

_ X _ J

(8)

where x is the relaxation time for the material/temperature and ^ is a constant usually between 1/3

and 1/2." Equation 8 has been fit to the experimental relaxation function, as defined in Equation

7, for the 34.3 °C data with x and b as adjustable parameters. The resulting curve fit is shown as

the dashed line in Figure 2, with curve fit parameters 1 = 7 seconds and b = 1/3. The calculated

relaxation time is of the right order of magnitude for an amorphous material above its glass

transition temperature, and b is in the range found previously for oxide Newtonian materials. It can be seen that the fit is quite good, especially considering that some of the non-Newtonian data is included in the curve for the experimental relaxation function.

Indentation creep experiments on amorphous selenium has led to a better understanding of the

relationship between indentation and compression creep. Indentation creep procedures can also be

used to obtain viscoelastic parameters of materials, especially viscosity and relaxation functions.

36
10"

10"'

10'

10^

T I I—I I I I 1 1 r I -1—I—mn

/ 32.1 "C

slope = 1.0

' I

0.001 0.01 0.1 1 Hardness (GPa)10

Figure 1. Indentation strain rate versus hardness for amorphous selenium at the temperatures

indicated. The slope of the curves are equal to 1.0 at low hardness values, indicating

that deformation is occurring due to viscous flow.

0.7

C

o

a

u

c

3

c

o

•aa

X

0.6 -

0.5

0.4

0.3

0.2

0.1

-rrp I I 1

1

1 1—I—I I I 1

_l ' ' t I

10 100 1000 10^ Time (sec)

Figure 2. Experimentally determined relaxation function for indentation at 34.3 °C (solid line) and

a fit to the experimental data using Equation 8 (dashed line). Curve fit parameters are x = 7 seconds and b = 0.33.

37
References

1. A.G. Atkins, A. Silverio, and D. Tabor, "Indentation Hardness and the Creep of Solids,"

Journal of the Institute of Metals, 94 (1966) 369-378.

2. T.O. Mulhearn and D. Tabor, "Creep and Hardness of Metals: A Physical Study," Journal of

the Institute of Metals, 89 (1960) 7-12.

3. M.J. Mayo and W.D. Nix, "A Micro-Indentation Study of Superplasticity in Pb, Sn, and Sn38 wt% Pb," Acta Metallurgical 36 [8] (1988) 2183-2192.

4. B.N. Lucas and W.C. Oliver, "The Elastic, Plastic, and Time Dependent Properties of Thin

Films as Determined by Ultra Low Load Indentation," pp. 337-341 in Thin Films: Stresses and

Mechanical Properties III, Edited by W.D. Nix, J.C. Bravman, E. Arzt, and L.B. Freund.

Materials Research Society, Pittsburgh, PA, 1992. (Materials Research Society Symposium

Proceedings, 239).

5. P.M. Sargent and M.F. Ashby, "Indentation Creep," Materials Science and Technology, S

(1993) 594-601.

6. B. Roebuck and E.A. Almond, "Equivalence of Indentation and Compressive Creep Tests on a WC/Co Hardmetai," Journal of Materials Science Letters, 1 (1982) 519-521.

7. W.H. Poisl, W.C. Oliver, and B.D. Fabes, "The Relationship Between Indentation and

Uniaxial Creep in Amorphous Selenium," Journal of Materials Research, in press.

8. M. Cukierman and D.R. Uhlmann, "Viscous Flow Behavior of Selenium," Journal of NonCrystalline Solids, 12 (1973) 199-206.

9. R.B. Stephens, "The Viscosity and Structural Relaxation Rate of Evaporated Amorphous

Selenium," Journal ofApplied Physics, 49 112] (1978) 5855-5864.

10. A.F. Bower, N.A. Fleck, A. Needleman, and N. Ogbonna, "Indentation of a Power Law

Creeping Solid," Proceedings of the Royal Society of London, A441 (1993) 97-124.

11. G.W. Scherer, "Relaxation in Glass and Composites," J. Wiley, New York, 1986.

38
EFFECTS OF RESIDUAL STRESS ON THE MEASUREMENT OF

MECHANICAL PROPERTIES USING INSTRUMENTED INDENTATION*

George M. Pharr, Ting Y. Tsui, and Alexei Bolshakov

Rice University, Department of Materials Science, Houston, TX 77251-1892

Warren C. Oliver

Nano Instruments, Inc., Knoxville, TN 37914

The effects of stress on the measurement of hardness and elastic modulus using instrumented

indentation have been studied experimentally and by finite element simulation for a rapidly

solidified aluminum alloy (alloy 8009). The experiments were performed by making a linear array

of nanoindentations on the side of a stressed bend bar, sampling regions of high uniaxial tension,

high uniaxial compression, and a variety of stresses in between. When analyzed according to

standard methods, the nanoindentation data reveal a decrease in both hardness and modulus with

increasing stress from compression to tension. While the decrease in hardness is consistent with

previous observations made in conventional hardness testing, the modulus decrease was

unexpected

Finite element simulation revealed that the decreases in hardness and modulus are not real, but

occur because the procedure for determining contact area from the nanoindentation loaddisplacement data does not account for pileup around the indentation. The simulation shows that

large compressive stresses enhance pileup while tensile stresses reduce it, and this must be

properly accounted for if accurate hardnesses and moduli are to be obtained Re-evaluation of the

experimental results based on the finite element simulation further supports this point of view.

References

George M. Pharr, Ting. Y.Tsui, Alexei Bolshakov, and Warren C. Oliver, "Effects of Residual

Stress on the Measurement of Hardness and Elastic Modulus Using Nanoindentation", in Materials

Reliability in Microelectronics. Materials Research Society Symposium Proceedings Volume 338,

edited by P.Borgesen, J.C. Cobum, J£. Sanchez, Jr., K.P. Rodbell, and WJ. Filter, Materials

Research Society, Pittsburgh, pp. 127-134 (1994).

Research sponsored by the Division of Materials Sciences, U.S. Department of Energy, under

contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc., and through the

SHaRE Program under contract DE-AC05-76OR00033 with the Oak Ridge Institute for Science

and Education.

39
MEASURING THE INDENTATION MODULUS

OF ELASTICALLY ANISOTROPIC SOLIDS

Joost J. Vlassak and W.D. Nix

Department of Materials Science and Engineering

Stanford University

Palo Alto, CA 94305

Nanoindentation testing is one of the most popular methods for measuring the mechanical

properties of materials that are difficult to test with more conventional techniques. It has been

used successfiilly to study hard coatings, ceramics and thin films used in microelectronic devices

and for magnetic data storage. The indentation process is well understood for elastically isotropic

materials and simple formulae can be derived to determine the elastic modulus of a material. We

have studied the indentation of elastically anisotropic materials. The modulus measured in an

indentation experiment is then a weighted average of the elastic properties of the material and is

very different from Young's modulus in the direction of the indentation. We define the

indentation modulus for anisotropic materials and show how it can be calculated for arbitrary

anisotropic solids. We present the results from calculations for materials with cubic and

hexagonal crystal symmetry and for textured films. We have calculated the contact stiffness for

a flat triangular indenter on a half space for various anisotropic materials. The indentation

modulus for a triangular indenter is typically 5--6% higher than that for an axisymmetric indenter

and varies only slightly with the orientation of the indenter in the plane of the indentation. We

have also conducted nanoindentation experiments in various single crystals. Results are in good

agreement with theoretical calculations.

Barnett, D.M. and Lothe, J. (1975) Line force loadings on anisotropic half spaces and wedges.

Physical Norvegica 8, 13-22.

King, R.B., Elastic analysis of some punch problems for a layered medium. Int. J. Solids

Structures 23, 1657-1664.

Vlassak, J.J. and Nix, W.D. (1993) Indentation modulus of elastically anisotropic half spaces.

Phil. Mag. A 67, 1045-1056.

Vlassak, J.J. and Nix, W.D. (1994) Measuring the elastic properties of anisotropic materials by

means of indentation experiments. J. Meek. Phys. Solids 42, 1223-1245.

Willis, J.R. (1966) Hertzian contact of anisotropic bodies. J. Meek Phys. Solids 14, 163-176.

Willis, J.R. (1967) Boussinesq problems for an anisotropic half space. J. Mech Phys. Solids 15,

331-339.

40
THREE-DIMENSIONAL FINITE ELEMENT MODELING

OF SHARP INDENTATIONS

A. E. Giannakopoulos

Department of Solid Mechanics

Royal Institute of Technology

Stockholm S- 10044, Sweden

In recent years, pyramid micro and nano-indentation tests have been used on materials such as metals, polymers, ceramics and glasses and were found to give valuable mechanical and other

physical information which may be otherwise difficult to obtain. The present talk concerns

analysis of the commonly used Vickers and Berkovich tests [1,2], as well as the cone indentation

test, of homogeneous, isotropic materials that are initially stress free. The mechanical information

included in the experimental observations was explored with the finite element method in

combination with theoretical results. A large strain elasto-plastic formulation was used, assuming

small elastic strains. Contact with a rigid indenter with and without friction was accounted for.

Different degrees of material strain hardening were examined. The material pressure sensitivity

(e.g., compaction, transformation) was modeled according to the classic Drucker-Prager plastic

potential [3]. The results concern the indentation force-depth curve for a complete load-unload

cycle, the imprint morphology (i.e., sinking-in, elastic rebound, surface lift and contact area),

stress and strain 3-D distributions and macro-cracking commencement. The results are presented

in compact universal forms and 3-D maps which can be used for the inverse mechanical problems

of finding the mechanical properties of materials (e.g. elastic modulus, yield and ultimate stress,

toughness) given the output of their indentation test.

[1] A.E. Giannakopoulos, P.-L. Larsson and R. Vestergaard (1994). "Analysis of Vickers

Indentation", Int. J. Solids and Structures 31 (19), pp. 2679-2708.

[2] P.-L. Larsson, E. Soderlund, A.E. Giannakopoulos, D.J. Rowcliffe and R. Vestergaard

(1995). "Analysis of Berkovich Indentation", to appear in Int. J. Solids and Structures.

[3] A. E. Giannakopoulos and P.-L. Larsson (1995). "Analysis of Pyramid Indentation of

Pressure Sensitive Hard Metal and Ceramic Materials", in final preparation.

41
MODELING STRESSES AT THE FILM-SUBSTRATE INTERFACE - SIGNIFICANCE TO INDENTATION TESTING

S. Ramalingam and Lanshi Zheng

Department of Mechanical Engineering

University of Minnesota

MinneapoHs, MN 55455

Differences in displacements within the substrate and the coating are common when coated solids are loaded, due to differences in elastic constants. This is usually a serious problem when

compliant solids are covered with hard coats, since hard compounds used for protection are invariably much stiffer than the common substrate materials. The problem is especially serious

in concentrated contacts where Hertz-like contact conditions prevail and hard coats are employed

to secure wear protection. Integrity of the coated composite then depends on flexure stress in the

film, shear stress at the film-substrate interface or the film lift-off stress at or close to the contact.

This presentation is concerned with the modeling of film-matrix interface stresses and the

computation of stresses at and close to a two-dimensional or axisymmetric, high stress contact

in a thin-film coated solid.

Earlier work is first reviewed. Approaches based on Fourier Transform of the stress function

have been used widely. Notable works include those of Gupta and Walovit, Kennel and Dow,

Ling, and Wu and Ling. Focus in these and other studies has principally been on contact stress

calculations. Wu and Ling have determined the von Mises stresses at and below an axisymmetric

contact. Keer and co-workers have recently made an important contribution using the transform

(stress function) method.

Since the stress function transform method originally introduced by Sneddon leads to severe convergence problems when very thin coatings (sub-micron coating thickness) are modeled,

(noted by Gupta and Walovit), a displacement formulation is developed and applied

systematically to a number of contact problems in the present work. Navier equations of

elasticity are solved for single and multi-layer composites with very thin coatings. The

displacement field is first determined and the stresses are then calculated from the displacement

derivatives. It is shown that the flexure stress in the film and the lift-off stress at the film-matrix

interface close to the contact can lead to coating failure in many combinations of contact

geometry, loading and contact friction conditions. Modeling results also indicate that the likely

problems can be avoided with a judicious combination of film and substrate materials, choice of

coating thickness and film deposition conditions (control of residual stresses during film

deposition). Calculated results support the views advanced and discussed. It is suggested that

an analytical basis is now available to design coatings for a range of loaded contact applications.

Approaches to model and analyze instrumented indentation are noted. It is noted that geometric

similarity, which holds in frictionless contact, no longer holds in indentation testing. Significance

of stick and slip zones at the contact is recognized. Attention is also called to the importance of

Dunder's constant.

42
The presentation is concluded by postulating possible film failure modes during indentation

testing based on the von Mises stresses calculated at and close to an indent. Results presented

were obtained by modeling a two-dimensional contact - a cylindrical indentor acting on a semi-infmite coated composite. It is suggested that the plastic collapse is initiated on the upper

surface of the film and grows beneath the contact and into the substrate. Shear mode failure

appears to prevail during growth of plastic volume. Initial results of axisymmetric modeling

(sphere on a semi-infinite coated composite) tend to support this view as well. Since

elastic-plastic transition is initiated at small strains, it is noted that there is a need for relatively

high precision calculations to model the indentation process.

43
NANOINDENTATION USING THE AFM: CONSIDERATIONS FOR THE

QUANTITATIVE MEASUREMENT OF MECHANICAL PROPERTIES

Steven Hues

Code 6177, Naval Research Laboratory

Washington, D.C. 20375-5342

The useful application of a material depends, in many cases, on the mechanical properties of

those few nanometers comprising the surface or surrounding an internal interface. Examples of

this would include material failure due to grain boundary embrittlement and polymer surface

coating delamination. Nanoindentation provides us for the first time with a window through

which we may view the mechanical properties of these nanometer-scale volumes. Nanoindentation using an atomic force microscope (AFM) allows us the highest degree of both force

and penetration depth resolution.'

Initially, the nanoindentation measurements which were obtained via the AFM were qualitative

only. That is, the mechanical properties derived from the force versus penetration depth curves

were higher for stiffer materials, but the actual measurements for a given material varied over

a fairly large range. Upon further study, it was determined that this lack of precision was due

to large degrees of hysteresis and creep in the lead zirconia titanate piezoceramic actuators used

to translate the sample during the measurement. Upon replacing the piezoelectric actuators with

electrostrictive lead magnesium niobate actuators, the hysteresis and creep effects were

eliminated.^ This resulted in highly reproducible measurements which allowed us to

quantitatively compare the relative magnitudes of surface mechanical properties, i.e., one surface

was 2.3 time stiffer than another.

The next evolution of this technique involved the determination of absolute mechanical properties

without regard to a reference surface, i.e., surface A has an elastic modulus of 4.3 GPa.

Determinations of this type require knowledge of the magnitude of the contact area between the

indentor tip and the surface. Spherical indentors have several advantages for nanoindentation.^

Among these is an easily characterized contact area. Through the use of spherical glass indentors

we have been able to quantify the absolute elastic modulus of highly-orientated pyrolytic graphite

(HOPG) and commercial polycarbonate as a function of strain. Our measurements have excellent

agreement with those taken on the same samples using the commercial UMIS-2000 instrument."*

'S.M. Hues, R.J. Colton, E. Meyer, and H.-J. Giintherodt, MRS Bulletin XVIII 1, 41 (1993)

^S.M. Hues, C.F. Draper, K.P. Lee, and R.J. Colton, Rev. Sci. Instrum. 65, 1561 (1994).

^J.S. Field and M.V. Swain, J. Mater. Res. 8, 297 (1993).

"^C.F. Draper, D.M. Schaefer, R.J. Colton, S.C. Webb, and S.M. Hues, J. Mater. Res., submitted.

44
INTERFACIAL FORCE MICROSCOPY MEASUREMENTS

OF THE NANOMECHANICAL PROPERTIES OF MATERIALS

J.E. Houston and T.A. Michalske

Sandia National Laboratories

Albuquerque, NM

Scanning probe techniques have shown dramatic growth over the last several years and are presently making a significant impact on surface and interfacial problems in material science.

The most widely used of these techniques is Atomic Force Microscopy (AFM), which can

measure interfacial forces down to the molecular level and which is applicable to virtually all

materials. In its present embodiment, however, the AFM is limited in applicability by its use of

a deflection force sensor which is mechanically unstable under rapidly varying interfacial forces

and which has a very large compliance when measuring repulsive contact forces. In contrast,

Interfacial Force Microscopy (IFM) utilizes a self-balancing force sensor which eliminates the

instability and permits operation in both the attractive and repulsive modes with effectively a zero compliance. In recent studies, we have taken advantage of these unique sensor properties and

applied the IFM to the study of the mechanical properties of materials at the nano-meter scale.

In this presentation, we show results demonstrating the enhanced capabilities of the IFM in

application to studies of the elastic and plastic deformation of single nano-scale grains in

polycrystalline films of Au deposited on various substrates. The probes consisted of characterized

W tips and the Au surfaces were all passivated by a single monolayer of self-assembling

alkanethiol molecules. These molecules eliminate the adhesive interaction of the tip and substrate

and permit a classical Hertzian analysis of the loading data. Interestingly, we are able to create

significant indentations in the Au surfaces without detecting any tip/substrate bonding interaction.

The molecular monolayers have a truly impressive breakdown resistance.

Loading data for single grains, along with repulsive-force images of the surface before and after

loading, permit a quantitative evaluation of the effective local elastic modulus, the shear-stress

threshold for plastic deformation and various modes of grain-boundary slipping. The results show

a considerable variation in values obtained for the various substrates. However, the modulus and

threshold shear-stress values vary in a consistent way such that the ratio of the latter divided the

former is a constant 4%. The implication of this constant ratio is that the deformation to plastic

threshold should be a constant 12 nm (for the 200 nm tip radius used), which is confirmed

experimentally. We discuss these curious results in terms of the structural properties of the

films - average grain size, substrate adhesion, etc.

In addition, we present preliminary studies of the affect of probe radius on the threshold shear

stress for plastic deformation for W probes on thiol-passivated single-crystal Au(lll) surfaces.

We find that for tip radii less than about 400 nm the shear stress at threshold is not constant but

rises sharply with decreasing radius. These findings will be discussed in terms of defect

nucleation. Finally, we include a brief discussion of projected future work using the IFM in

application to studies of the mechanical properties of materials.

This work is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences

under contract DE-AC04-94AL85000.

45
DEVELOPMENT OF TRACEABLE CALIBRATION GUIDELINES FOR

LOAD DISPLACEMENT INSTRUMENTS, AND THEIR VALIDATION BY

AN INTERCOMPARISON TEST

S R J Saunders, ^ G Shafirstein, ^ J Meneve, ^ J F Smith, ' T Dietz, * and E Mattaei-Schultz *

^ National Physical Laboratory, UK * VITO, Belgium ' MicroMalerials, UK

* IWT, Germany

The results of a research project partly funded by the European Commission on the

"Measurement of Hardness (Mechanical Properties) of Surfaces" are described. The objective

of the study was to develop calibration procedures for measurement of the mechanical

properties of surfaces using load displacement indentation instruments; both nano- and

micro-range instruments were included in the project.

The work was carried out in three phases:

i) development of calibration procedures;

ii) production and homogeneity testing of reference samples for an interlaboratory test,

and;

iii) conducting an intercomparison using the agreed procedures and samples.

A primary objective in the calibration phase of the work was only to use methods that were

traceable to primary standards. While for the intercomparison, the following reference

materials were produced: single crystal tungsten and fused silica (isotropic materials) and

single crystal aluminium (anisotropic) and 2 |im thick TiN coated tool steel was also used to

examine the behaviour of a bilayer system.

Load calibration procedures for all types of instrument used in this study were relatively

straightforward, with the use of calibrated weights. In some cases the weights were

suspended on the indenter holder, while in others it was possible to introduce a calibrated

top loading balance into the system and thus measure the load directly. Displacement

calibration was carried out using a laser interferometer or a linear variable displacement

transducer (LVDT) which had been previously calibrated using traceably calibrated slip

gauges.

Calibration of the frame stiffness was more complex and consisted of measuring the

composite stiffness as a function of load and determining the intercept at zero load in the

manner described by Oliver and Pharr, for example. For this work the single crystal tungsten

samples were used. There was some evidence that the expected linear behaviour was not

found, and in that case the intercept was determined from the extrapolation of the best fit

to the data. The departure from linearity may be related to instrument derived thermal drift

during loading or use of the flat punch model (at low displacements)

46
Calibration of the indenter tip shape was carried out using a calibrated AFM and by

indentation into fused silica. Both methods agreed at contact depths greater than about

200 nm, but the divergence increased up to 10 % at about 20 nm. This result was considered

very satisfactory. Possible reasons for this discrepancy were related to uncertainty about the

AFM/indenter tip interactions, and the assumption of lack of pile-up or dishing during the

indentation method, and, of course, the assumption of depth independent property behaviour

of the silica.

A round-robin was carried out on three types of instrument, two nano-scale and one microscale. When all participants have completed the tests, it is hoped that up to 14 data sets will

be available. The results of three, are, however, presented. These data showed that for the

isotropic materials reproducibility was such that the one standard deviation of the mean of

five measurements fell within 10%. A complete error analysis considering both calibration

(systematic) and measurement (random) errors showed that in the best case hardness and

Young's modulus values could be obtained to 15% uncertainty for a confidence of probability

of not less than 95% (2 sigma).

47
Abstracts for Poster Presentations

48
DETERMINATION OF THERMODYNAMIC RESPONSE OF POLYMERS BY MICROINDENTATION RATE CHANGES

W.R. Newson and S. Saimoto

Department of Materials and Metallurgical Engineering, Queen's University, Kingston Ontario

Canada.

The characterization of polymers by thermodynamic response via direct activation volume

measurements can be performed by means of strain rate change tests. The difficulty in

performing these tests has been to make the measurement without inelastic strain transients. This

has been accomplished by the use of a step-ramp procedure and validated by measuring the

unrelaxed modulus of polymers during tensile testing. This step-ramp technique has been adapted

for micro-indentation testing of polymers such that thermodynamic response from small volumes

can be measured. The use of this technique to examine Polyethylene resins and polyester paints

will be demonstrated.

ARTIFACTS IN NANOINDENTATION PROCEDURES

L. Riester and M.K. Ferber

Mechanical Properties User Center, Oak Ridge National Laboratory, Oak Ridge, TN 3783 1-6069.

Mechanical Properties Microprobes (MPM) have become a useful means of measuring hardness

and elastic moduli in materials. Precision positioning tables on these devices allow the user to assess small changes in mechanical properties over predetermined distances and locations in a sample. Some MPMs have sophisticated options and allow the user to vary parameters such as load/unload rate, depth of penetration and length of hold segments which opens new possibilities

for investigators. The versatility of controls on these MPMs may, on the other hand, lead

inexperienced users to obtain erroneous microhardness measurements. Not only may their results

differ from standard Vickers or Knoop hardness values, but variations in hardness measurements

which are solely dependent on the indentation procedures programmed by the user of the MPM

may be observed. This study addresses the effects of the manipulation of the operating parameters

of an MPM on the microhardness and elastic modulus of a number of material systems.

Research sponsored by the U. S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy,

Office of Transportation Technologies, as part of the High Temperature Materials Laboratory User Program, under

contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.

49
DEVELOPMENT OF STANDARDS FOR THE VALIDATION OF HARD THIN COATINGS

Th. Dietz, A. Schulz, H. Vetters, and P. Mayr

Institut fur Werkstofftechnik, Bremen; Badgasteiner Str. 3, 28359 Bremen; Germany.

In Round-Robin-Experiments the qualification of thin hard coatings for the standardisation of

chemical analysis and hardness tests was investigated. PVD-TiNx-coatings of different

compositions were proofed. The coating thickness amount to 10 fj.m. Substrate types were M2

and 1015. After finishing these investigations samples will certificate as standards. These

standards then are provided for the calibration of instruments by end users.

The integral coating composition was obtained by wet chemical analysis. Element-depth profiles

have been tested by several spectroscopic techniques (GDOS, AES, XPS, etc.).

The quantification of the results of the spectroscopic techniques shows systematic deviations in

the concentrations of nitrogen and titanium. These deviations were determined by the used

technique and increases with increasing distance to the stoichiometric composition of TiN. The

results of the investigations were located by the mean value of the quantificated results of the

spectroscopic techniques.

The hardness of the coated samples was examined by optical methods inspecting the indentation

profile. Furthermore the load-indentation depth-technique was tested by round robin trials.

The intercomparison of hardness measurements of thicker coatings (10 |j.m), deposited on

polished M2-substrates, showed good reproducibility. Nevertheless, by lower loads the roughness

of the coating leads to increasing error paths of the results. Coated 1015-substrates are not

suitable for standard samples, because of the soft substrate.

GROWTH AND MECHANICAL ANISOTROPY OF TiN THIN FILMS

W.J. Meng and G.L. Lesley

General Motors Research and Development Center, Warren, Michigan 48090.

We have grown TiN thin films on Si(lOO) and Si(lll) substrates by ultra high vacuum dc

reactive sputtering. TiN grows on Si(l 11) epitaxially while almost completely textured growth

of TiN on Si(lOO) is achieved. Elastic constants of TiN are measured by measuring the

longitudinal sound velocity in these TiN films using a time resolved transient piezoreflectance

technique. The mechanical response of these TiN films was further measured with a sub-micron

depth-sensing indentation technique. Measured hardness and indentation modulus as a function

of indentation depth are compared with existing theories.

50
ADHESION OF METAL INTERCONNECTS BY MICROWEDGE INDENTATION

M.P. de Boer, and W.W. Gerberich

Dept. of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN

55455.

Indentation in thin film fine lines such as metal interconnects is most conveniently analyzed by

using a sharp wedge-shaped probe as opposed to a tip which comes to a point as in the case of

planar thin films. Two new techniques for obtaining the interfacial work of adhesion, G^,, using

microwedge probes are compared in this work. In the first, microwedge indentation, we present

the mechanics for adhesion, and compare the resuhs to experiment. The system of choice is a tungsten thin film on SiOj, commonly used in the microelectronics industry. The mechanics

show that compared to axisymmetric analysis of a planar film, the microwedge technique has

much higher driving force. This allows for good accuracy in measuring crack lengths using

Nomarski microscopy, because crack lengths on the order of 1 0 to 40 microns are predicted and

measured. A crack stability analysis is performed, and the effect of buckling during and after

indentation is analyzed. The experiment shows an unexpected dependence of crack length versus

metal line linewidth at a given indentation depth, which is resolved by accounting for

microwedge tilt. Spallation of the fine lines at larger indentation depths can be detected in the

indentation curves. This result is used to calculate critical bending strains in the thin films.

While reasonable values of G^. are found by this technique, accuracy depends on measuring the

indentation volume V^, precisely, which is best achieved by AFM. In order to improve on the

accuracy of G^., a procedure which directly measures the driving lateral force has been developed.

In this technique, precracked fine lines are probed by microwedge scratching at the end of a fine

line. By taking lateral load cell measurement data, G^ is well known, and compared to the result

from the indentation technique.

ASSORTMENT OF TECHNIQUES IN INSTRUMENTED INDENTATION

K.B. Yoder, M.F. Tambwe, and D.S. Stone

Department of Materials Science and Engineering, University of Wisconsin, Madison, WI 53706.

In this poster we review experimental techniques we have developed for: (1) calibrating both

machine compliance and tip shape without having to directly image indents in the microscope;

(2) performing experiments and analyzing data characterizing the creep properties of the material;

and (3) performing experiments and analyzing data characterizing the hardnesses and moduli of

thin coatings.

51
IN SITU IMAGING OF ULTRA-LIGHT LOAD INDENTS INTO GaAs AND Fe-3wt% Si

E.T. Lilleodden, W. Bonin*, J. Nelson, J.T. Wyrobek*, and W.W. Gerberich

Department of Chemical Engineering and Materials Science, University of Minnesota,

Minneapolis, MN 55455. *Hysitron, Inc., Minneapolis, MN.

Nanomechanical devices constitute an important and growing field, as they allow for new

understanding of the mechanical properties at interfaces and surfaces. As an example, a newly

developed nanoindentation device has been used to accomplish ultra-light load indents into GaAs

and iron single crystals. This unique force/displacement transducer designed by Hysitron

Incorporated, Minneapolis, MN, allows STM or AFM imaging directly before and after

indentation, and force/displacement measurements during indentation. It is shown here that a

plastic zone can be measured and is comparable to theory. Also, it is shown that the rate of

indentation affects both the depth and upset zone of low load indents, implying a strain-rate

sensitivity effect at room temperature. The unique problems this presents with regard to

assessment of tip shape and penetration on hardness measurements of metallic surfaces is

discussed. This is reinforced by observation of what appears to be a glide-based relaxation

process.

MODIFICATION OF THE NIKON QM HIGH TEMPERATURE MICROHARDNESS TESTER

TO OBTAIN LOAD-DEFLECTION CURVES

D. Zirkin, B. Farber and A. Heuer

Department of Materials Science and Engineering, Case Western Reserve University, Cleveland

OH 44106.

Micro indentations will be made on a grown single crystal of zirconia at temperatures up to

300 °C. The crystal grown by the flux method at Case, presumably monoclinic, will be cut in

to bend bars. Indentations will be made on certain crystallographic planes, primarily the {100}

planes, based on recent studies done at Case. The bend bars will then be bent and released prior

to fracture. T.E.M. analysis of the indent area should reveal patterns of dislocation motion and

generation. A secondary goal based on modifications done to a hot furnace Nikon micro indenter

will enable the generation of load verses displacement curves done during the indentation. Such

curves won't be affected by elastic recovery and thereby provide true hardness measurements.

A load cell and displacement gages connected to an I.B.M. acquisition system will provide and

record the data.

52
NEW ANALYTICAL PROCEDURE TO DETERMINE STRESS-STRAIN CURVE AND

ELASTIC MODULUS FROM INSTRUMENTED BALL INDENTATION

B.Taljat*, P.M. Haggag^ and T. Zacharia^

*Faculty of Mechanical Engineering, Askerceva 6, 61000 Ljubljana, Slovenia. ^Advanced

Technology Corporation, 115 Clemson Dr, Oak Ridge, TN 37830, USA. ^Oak Ridge National

Laboratory, Metals and Ceramics Division, Oak Ridge, TN 37831-6140.

A multiple ball indentation process performed at a single penetration location was analyzed by

finite element method. The response surface methodology was implemented to analyze the

influence of various material properties on load-displacement (P-h) curve. A new analytical

approach for relating the ball indentation data to the true-stress/true-plastic-strain (a,-8p) curve,

where Sp could be also higher than 0.2, is presented. Also, a new correlation between P-h curve,

after indenter compliance subtraction, and material elastic modulus was obtained. The correlation

was verified by experimental data measured by the automated ball indentation technique, for

several metallic materials (Al, Cu, Steel) and the results were within ±5%.

DYNAMIC HARDNESS TESTING OP INPRARED MATERIALS

S. Joshi and K.A. Richardson

Center for Research and Education in Optics and Lasers (CREOL), University of Central Plorida.

Dynamic hardness represents a novel form of material property evaluation where the hardness of

the sample is calculated based on the depth of indenter penetration while the test piece is still

under load. Since this form of testing yields information about the resistance of a material to

both elastic and plastic deformation and the property measurement is carried out at the time of

point load application, the data obtained is highly relevant to the grinding mechanisms of these

materials. Dynamic hardness measurements have been carried out for a host of infrared materials

like ZnS, ZnSe, Si, Ge, etc. The hardness variation at low loads which are pertinent in the

grinding process, has been examined and various possible causes for this behavior have been

investigated. The influence of the surface preparation on the dynamic hardness due to various

modes of grinding operations has also been investigated.

This work was carried out with the support of the Center of Optics Manufacturing (COM), American Precision Optics

Manufacturers Association (APOMA) and the University of Central Florida

53
EFFECT OF INDENTER SHAPE, YIELD STRESS AND MODULUS ON THE

INDENTATION PROCESS

Kangjie Li and J.C.M. Li

Materials Science Program, Department of Mechanical Engineering, University of Rochester,

Rochester, NY 14620.

The indentation process is simulated by finite element analysis using the elastic/perfect plastic

constitutive relation and the ABAQUS software. Conical indenters of different included angles

are used. To correlate with the yield stress, the hardness should be calculated by dividing the

applied force to the projected area (rather than the contact area used in some conventional

hardness tests) measured by including the pileup of the indentation (similar to the area observed

in the optical microscope). The area determined by using the plastic depth, namely, the

extrapolated depth from the initial part of the unloading curve is about 72% of the projected area

just mentioned. The estimation of Young's modulus from the slope of the initial part of the

unloading curve is better if the projected area is used instead of the area determined by the plastic

depth. The ratio of hardness to yield stress decreases with the ratio of yield stress to Young's

modulus if the area determined by the plastic depth is used.

This work was supported by NSF through DMR 9221326 monitored by Dr. Bruce MacDonald and by the Manufacturing

Sciences Group in the Center for Optics Manufacturing at the University of Rochester.

VISCOSITY MEASUREMENT BY IMPRESSION TEST

F. Yang and J.C.M. Li

Materials Science Program, Department of Mechanical Engineering, University of Rochester,

Rochester, NY 14620.

A new method of measuring Newtonian viscosity is proposed. In this method, a flat cylindrical

punch is pressed onto the surface of a semi-infinite medium by a small load. The relationship

between the steady penetration velocity and the applied load is independent of the slip or stick

boundary condition at the punch-material interface. In this relation, the steady state punch

velocity is proportional to the punching stress and, for the same stress, it is proportional to the

punch diameter and inversely proportional to the viscosity. By using this method, the viscosity

of amorphous Se was measured in the temperature range of 29.2 to 50.7 °C and under the

punching stress of 0.25 to 15 MPa. The viscosity of amorphous Se obtained this way is

comparable to the literature data and its flow behavior under these conditions is Newtonian.

This work was supported by NSF through DMR 9221326 monitored by Dr. Bruce MacDonald.

54
CONTACT STRESS ANALYSIS OF A LAYERED SOLID UNDER A RIGID INDENTER

L. Zheng and S. Ramalingam

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455.

The problem of a layered elastic solid indented by a rigid body involves mixed boundary

conditions. The distributed tractions between two bodies and contact length are determined by

the geometries and material properties of the punch, films coated and substrate. An approach

based on the displacement formulation is used. The contact pressure and contact length are calculated from the governing integral equations. The problem then becomes that of a layered

solid under boundary tractions. Calculated results of stresses within film and substrate are to be

presented. The effects of the elastic modulus and Poisson's ratios of film and substrate are investigated and discussed.

MEASUREMENT OF STRAIN-RATE SENSITIVITY BY NANOINDENTATION

TECHNIQUES

R. Upadhyaya, S. Saimoto* and R.S. Timsit

AMP of Canada Ltd., 20 Esna Park Drive, Markham, ON, Canada L3R lEl. *Department of

Materials and Metallurgical Engineering, Queen's University Kingston, ON, Canada K7L 3N6.

For this work, the nanoindentation device uses a piezoelectric transducer to drive the indenter and

a double spring system to measure mechanical load. The instrument is characterized by a displacement resolution of 0.4 nm and a load resolution of 5 |iN. The indenter system was

modified to perform strain-rate sensitivity measurements by a software-driven step ramp

technique. The procedure involves the application of an indenter-displacement step in the ramp

while changing the indentation rate. The magnitude of the displacement step is selected to

compensate the elastic response of the indenter system and to eliminate any transient in

indentation rate. The change in load response is then truly material dependent and provides

information on microstructural properties of the specimen.

55
ANALYSIS OF NANOINDENTATION LOAD-DISPLACEMENT LOADING CURVES

S.V. Hainsworth, H. Sjostromt, J.-E. Sundgrent, H.W. Chandler & T.F. Page

Materials Division, Dept. of Mechanical, Materials and Manufacturing Engineering, University

of Newcastle upon Tyne, Newcastle upon Tyne, NEl 7RU, UK.

t Thin Film Division, Dept of Physics, Linkoping University, S-581 83 Linkoping, Sweden.

Nanoindentation load-displacement curves provide a 'mechanical fingerprint' of a materials

response to deformation. Over the last few years, much attention has been focused on

understanding the shape of the unloading curve to obtain values for true contact area. Young's

modulus and hardness. When the unloading curve is well behaved, i.e. approximates to linear

behaviour or alternatively fits a power-law relationship then this approach can be very

succesful. However, when the material is very stiff and hard (such as for many thin hard

coatings), the unloading curve fits neither of these two models particularly well. Therefore,

there can be considerable difficulty in obtaining an accurate final plastic depth from which the

area of contact between the coated system and the indenter can be calculated. Thus it can be

extremely complex to calculate meaningful mechanical property data (i.e. E and H numbers) for

these types of material.

Recently, an alternative approach has been to try and understand the shape of the

nanoindentation loading curve and the relationship between modulus, hardness, indenter

geometry and the resultant maximum displacement for a given load. This used an original

model by Loubet ^ who proposed the relationship P = K^^h" for describing the shape of loading

curves, where K^^ is a constant which describes the elasto-plastic nature of the loading curve.

This model was used to predict the rank position of loading curves for a range of materials

including a TiN coating on Si and a CNx coating on Si ^.

However, when compared to real nanoindentation loading curves it was found that there was

some discrepancy between the rank order of the actual loading curves and those predicted by

the Loubet model. The Loubet model used a power law fit to the loading curves, which gave

indexes of usually < 2. For indentation by a cone however, the relationship between the load

and displacement is predicted to follow the relationship P <^5^ and therefore we chose to plot P

versus 6'^ to see if this relationship holds. The plots of load versus displacement squared

showed excellent correlation over the whole loading range. This correlation then formed the

basis for our analysis. We followed a similar approach to Loubet et al where we decomposed

56
the total deformation into elastic and plastic parts. The plastic and elastic contributions can be

represented by

H

and

For these two equations 5 is the displacement, ^ and y are constants, P is the load, H the

hardness and E the Young's modulus. Summing these two parts and a little manipulation of the

equation gives the relationship

This equation is of the form

P = K^5'

We found the gradients, m, of the load versus displacement squared plots from nanoindentation

data for a number of materials and compared this to the value of Ki predicted from their modulus

and bulk hardness values. This allowed us to determine the constants given below

This equation was found to reliably predict the loading curves of a wide range of materials with

varying combinations of modulus and hardness.

This model therefore, helps to analyse and understand the fundamental factors which control the

shape of the loading curve during nanoindentation experiments with a pointed (Berkovich)

indenter. This is particularly valuable for assessing the mechanical properties of systems with

thin hard coatings, where there are difficulties in estimating the real plastic depth.

References

Page, T. F. Hainsworth, S.V,. Surface and Coatings Technology, 61, 1993, 201-208.

Doemer, M. F., Nix, W. D., Journal of Materials Research, 1, 1986, 601-609.

Oliver, W. C, Pharr, G. M., Journal of Materials Research, 7, 1992, 1564-1583.

Loubet, J. L., Georges, J. M., Meille, G., In Microindentation Techniques in Materials Science

and Engineering: ASTM, Philadelphia: 1986; pp 72-89.

Sjostrom, H.; Hultman, L.; Sundgren, J.-E.; Hainsworth, S. V.; Page, T. F.; Theunissen, G. S. A.

M. Submitted to Phys. Review B, 1995

57
MEASUREMENT AND THEORY OF THE ORIENTATION DEPENDENCE OF KNOOP

MICROHARDNESS IN A LAYERED SINGLE CRYSTAL

J. Marschall* and F. Milstein

Departments of Materials and Mechanical Engineering, University of California, Santa Barbara,

CA 93106.

The room-temperature red phase of mercuric iodide crystallizes in a layered structure, with

monoatomic planes of iodine (I) and mercury (Hg) atoms stacked perpendicular to the [001] (or

c) axis in the sequence ..THglIHglIHgl.... Each mercury atom is covalently bonded to two

iodine atoms in the layer below and two iodine atoms in the layer above; bonding between

adjacent iodine layers is van der Waals in nature. Because of its unusual bonding characteristic

and resulting high anisotropy, single crystal mercuric iodide provides an interesting system for

studying fundamental deformation processes. The scientific interest in mercuric iodide's behavior

is enhanced by its technological importance as a wide band-gap, high atomic mass semiconductor

which finds application as a room-temperature detector material for gamma-ray, X-ray and visible

radiation. In the present work, measurements were made of the orientation dependence of the

Knoop microhardness on faces of single crystals of red (tetragonal) mercuric iodide that were

vapor-grown for use in radiation detectors. Theoretically, the size of a microhardness indention

is presumed to depend on the volume of material in which appropriate slip systems are stressed

sufficiently to cause appreciable slip. To test this concept and determine which particular slip

systems dominate the indention process, the "infinite flat punch" model was used to calculate the

orientation and volumetric variations of shear stress on various potential slip systems in mercuric

iodide. Excellent agreement was obtained between theory and experiment.

'Present address: NASA Ames Research Center, Mail Stop 234-1, Moffett Field, CA 94035.

INDENTATION AND STRENGTH OF FIBER-REINFORCED AEROGELS

K.E. Parmenter and F. Milstein

Departments of Mechanical Engineering and Materials, University of California, Santa Barbara,

CA 93106.

Aerogels are extremely low density solids that are characterized by a high porosity and by pore

sizes on the order of nanometers. Their low thermal conductivity and sometimes transparent

appearance make them desirable for applications such as insulation in cryogenic vessels and

between double paned glass in solar architecture. An understanding of the mechanical properties

of aerogels is necessary before aerogels can be used in load bearing applications. Experiments

to test the resistance to indentation (hardness) and the compressive strength of various types of

fiber-reinforced silica aerogels have been undertaken. The indentation pressures of traditional

techniques such as Vickers and Knoop were too large for the fragile aerogels. An alternative

approach using an Instron 1123 testing machine equipped with a 19.05 mm steel ball as the

indenter proved successful. Initial results of measurements of hardness, compressive strength, and

stiffness, and their dependence on processing variables and fiber percentage, are presented. For

specimens tested to date, the addition of fibers to the aerogel matrix resulted in weaker materials.

58
STUDY OF ROCK INDENTATION FRACTURE IN MECHANICAL

EXCAVATION

Yousof Abd Al-Jalil, Ph. D. candidate

Dr. Priscilla Nelson, Associate Professor

Geotechnical Engineering Program,

Department of Civil Engineering,

University of Texas,

Austin, Texas 78712

This paper represents part of research effort to establish a method for prediction of penetration rate

of tunnel boring machines (TBMs). Focus is on single disc cutters working in medium to very

high strength rock (uniaxial compressive strength 20 to more than 200 MPa) . The objective is to

relate achieved penetration rate to geometry and material properties of the disc cutter, and

mechanical properties of the intact rock; effects of discontinuities on penetration rate will be

investigated once the model is working for intact rock. Our proposed work will focus on basics of

indentation fracture and rock crushing.

Indentation of brittle materials using sharp indentors leads to inelastic deformation beneath the

indentor, and radial-median cracks during loading. Lateral cracks grow from the area of inelastic

deformations and propagate toward free surface upon unloading (Lawn, 1993). Similar

observations have been made during linear cutter tests (Snowdon etal, 1982, Nelson, 1986).

Proposed methodology contains three phases: identification of the potentially most important

factors in disc-rock interaction, developing analytical solution(s) to determine state of stress under

cutter, and a finite-element model to model rock crushing and crack propagation from contact zone. A simple two-dimensional indentation problem will be modeled, in conjunction with laboratory

experiments. In this problem, four distinct substructures can be identified: cutter and machine,

crushed rock, moderately-cracked rock, and intact rock. Interface elements will be used between

elements of different substructure types. Data from similar loading conditions are sought even if tests done on other brittle materials.

The model needs then to be extended to three-dimensional, dynamic problems in order to be able to

predict penetration of cutters. This is left as a future project once the two-dimensional, static model

gives insight into the mechanics of problem and provides good answers.

References:

Lawn, B. (1993), Fracture of Brittle Solids, 2nd ed., Cambridge University Press.

Nelson, P. P. (1983), Tunnel boring machine performance in sedimentary rock. Ph. D.

dissertation. School of Civil and Environmental Engineering, Cornell University.

Snowdon, R. A., Ryley, M. D., and J. Temporal (1982), "A study of disc cutting in selected

British rocks". Int. J. Rock Mech. Min. Sci. & Geomech. Abstr., Vol. 19, pp. 107-121.

59
INDENTATION TESTING OF THE MAGNETIC THIN-FILM HEAD ALUMINA

SUBSTRATE

A.S. Chekanov, T.S. Low, S. Alii and B. Liu

Magnetic Technology Center, National University of Singapore, Singapore.

The complex layered structure of the thin-film head contains many materials and interfaces.

Interaction of the head with the rotating disk surface causes the crack initiation which leads to

the head failure. We report on the application of the microindentation technique for the

characterization of the crack resistance of the head alumina substrate. Effects of the head current,

laser processing on the fatigue crack location and geometry discussed.

BULK AND INTERFACIAL CRACK-PROPAGATION BEHAVIOR IN CVD DIAMOND

A. Kant, R.O. Ritchie, M.D. Drory*, R.H. Dauskardt^ and I.G. Brown

Center for Advanced Materials, Materials Sciences Division, Lawrence Berkeley Laboratory, and

Department of Materials Science and Mineral Engineering, University of California, Berkeley,

CA 94720. *Crystallume, 3506 Bassett Street, Santa Clara, CA 95054. ^Department of

Materials Science and Engineering, Stanford University, Stanford, CA 94305.

The fracture toughness, stress corrosion and cyclic fatigue properties of CVD polycrystalline

diamond have been investigated on thick (100 to 300 \im) free-standing films. Since all reported

toughness and crack growth measurements on CVD diamond to date have been derived using

approximate indentation techniques, in the present study ASTM-standard compact-tension

(fracture-mechanics) specimens were tested in addition to indentation methods. Resulting values

of the fracture toughness, Kj^, for the free-standing films were found to be of the order of 5

MPav/m. Preliminary studies on subcritical crack growth under sustained load indicate that CVD

diamond is essentially immune to stress-corrosion cracking, although more sophisticated

experiments need to be tried out in order to prove this definitively. Fatigue tests are currently

being conducted by loading indentation-precracked free standing CVD diamond cantilever beams

in three point bend. Indentation techniques have also been applied to measure and compare the

interfacial adhesion and toughness of thin (~2 |a.m) CVD diamond films deposited on various

metallic substrates such as molybdenum and titanium.

60
RESIDUAL STRESS FIELDS AT INDENTATIONS

K. Zeng, D.J. Rowcliffe and P. Meier

Materials Science and Engineering, Royal Institute of Technology, S-100 44 Stockholm, Sweden.

This presentation outlines an indentation method to measure residual stress in ceramics. The

analysis is based on the premise that the observed lengths of radial cracks at Vickers indentations

depend on the residual stress due to the indentation and a component due to any imposed residual

stress field. The expressions to evaluate the imposed residual stress are:

1- (c / c ) Or = ^— (tensile stress)

1 - { C / C ) = ^— (compressive stress)

where K^. is the fracture toughness, c^ is the unstressed crack size and c, and Cj are crack sizes

in the stress field.

The technique is used to explore residual stress fields around Vickers, Berkovich and Knoop

indentations made in glass and several ceramics. The data are presented as isostress contour maps

for both the tensile and compressive components of the biaxial stress fields. In general the fields

are not axisymmetric but reflect the shape of the indenter and the influence of cracking. The

toughness of the material appears to be an important factor influencing the residual stress field

produced by sharp indentation.

Reference: K. Zeng and D.J. Rowcliffe, J. Hard Mater. 5, 239, 1994.

61
INTERFACIAL FORCE MICROSCOPY STUDY OF THE NANOMECHANICAL

PROPERTIES OF THIN FILMS FORMED ON CARBON STEEL FROM ZINC DIALKYL

DITHIOPHOSPHATE ANTIWEAR/EXTREME PRESSURE OIL ADDITIVES

O.L. Warren, P.R. Norton, W.K. Wan, J.E. Houston*, C.A. DiRubio*, and T.A. Michalske*

Tribology Research Center, The University of Western Ontario, London, Ontario, Canada.

'Surface and Interface Sciences Department, Sandia National Laboratories, Albuquerque, New

Mexico, USA.

Zinc dialkyl dithiophosphates (ZDDPs) are the most commonly used antiwear/extreme pressure

additives in commercial motor oils. These compounds break down under conditions of sliding

contact, and form thin antiwear films on carbon steel surfaces from the decomposition products.

The chemical makeup of the antiwear films has not been elucidated to any great extent, nor has

the mechanism by which ZDDPs dramatically decrease the wear rate.

In this study, we have used the interfacial force microscope (IFM) to investigate the

nanomechanical properties of thin films formed on carbon steel from decomposition of ZDDPs

in base oil. Films formed by thermal means only and films formed in the presence of sliding

contact have been examined. Preliminary results indicate that these two methods of preparation

result in vastly different mechanical properties on the nanometer scale. In the case of the thermal

samples, the elastic portion of the loading curve can be interpreted in terms of Hertzian contact

mechanics for a parabolic probe. Both the indentation modulus of the film and the maximum

shear stress at the onset of plastic deformation have been determined. The sliding contact

samples, on the other hand, exhibit a range of indentation behavior that suggests the presence of

three distinct materials. Two of these are likely to be exposed steel and material quite similar

to the thermal films, but the third is unique to the sliding contact samples. The latter material

is particularly exciting as its force-displacement curve is elastic to high peak loads, although not

in a Hertzian manner. These observations allow us to speculate that the material unique to the

sliding contact samples may come about by transformation of thermal film material under the

influence of high local stress and temperature at contact asperities. This is an important statement

in that it contradicts the belief held by some researchers that the two methods of preparation

result in identical films.

62
List of Attendees

Abd Al-Jalil, Yousof Q.

Univ. of Texas

ECJ 9.227

Austin, TX 78712

Baxter, William J. General Motors

R&D Center

30500 Mound Road, Box 9055

Warren, MI 48090

Behncke, Hans-Hermann

Helmut Fischer Co.

Inst. f. Elektronik und Mebtechnik

71 069 Sindelfmgen

Industriestrasse 21, Germany

Biederman, Ronald R.

Worcester Polytech. Inst.

Matls. Sci. & Eng.

100 Institute Road

Worcester, MA 01 609

Bonin, Wayne A.

Hysitron Inc.

2010 E. Hennepin Ave.

Minneapolis, MN 55413

Bowden, Craig C.

British Aerospace Defence Ltd.

Military Aircraft Div., Matls. Eng.

Brough N. Humberside HU 15 lEQ, U.K,

Carey, Colleen

Nano Instruments

1001 Larson Drive

Oak Ridge, TN 37830

Chaudhuri, Dilip K.

Tennessee State Univ.

3500 John A. Merritt Blvd.

Nashville, TN

Chen, Ming Y.

Wright Lab, USAF

2941 P. St. Ste 1 WPAFB, OH 45433

Cheng, Yang T.

General Motors

R&D Center

30500 Mound Road

Warren, MI 48090

Christoph, Rainer

CSEM

Jaquet Droz 1 Neuchatel CH-2007

Switzerland

Cogdell, J. David

The Timken Co.

Timken Research, RES-09

FOB 6930

Canton, OH 44706

Cooper, Clark V.

United Tech. Res. Cntr.

411 Silver Lane, MS 129-24

East Hartford, CT 6108

Crowell, Jeffrey A.

Univ. of Wisconsin

Nuclear Eng. Dept. Room 142

1500 Johnson Drive,

Madison, W 53706

De Boer, Maarten

Univ. of Minnesota

Dept. of Chem. Eng. & Mat. Sci.

421 Washington Ave. S.E.

Minneapolis, MN 55455

Deng, Hong

Univ. of Alabama

Box 870209/233 Bevill Bldg.

Tuscaloosa, AL 35487

63
Dietz, Thornas Hainsworth A. M.\^XM.M.»J T T VyX l>XX^ Sarah k^fc4X WU,X VT •

Inst. f. Werkstofftechnik Univ. of Newcastle

Badgasteiner Str. 3 Matls X T XV^VX ky • DivX T •« Herschel X. XVrX k.yV'XXWX Bide i^XVXC^s Bremen 28359 Germany Newcastle Upon Tyne

Nel 7RU UK

Digiorgio, Anthony

SKF USA Inc. Hannula X. x.^p€x XXX v»x Simo-Pekka i>..^xxxxvy x xyx^xx.vx

1 1 00 First Avenue VTT T X X. Manufacturing X XVXXX VAXC^V V \>XX XXXC^ Tech X WVXX> King of Prussia, PA 19406 PO Box 1703

Fin-02044 VTT, Finland

Elings, Jeff R.

Digital Instruments Houston, Jack E.

520 E. Montecito St. Sandia Natl. Lab.

Santa Barbara, CA 93103 Dept. 1114 PO Box 5800

Albuquerque, NM 87185

Fu Zezhons

Intel Comoration Hues X X VX%^ ky * SteveT ^/ MX T X 5000 W. Chandler Blvd. Naval Research Lab

Chandler, AZ 85226 Code 6170

Washington, DC 20375

Fujimoto, Harry H.

Intel Comoration Inturi, Rama B.

3065 Bosers Ave SCI -03 Univ. of Alabama

Santa Clara CA 95054 Dentxy V • ofvy X Metallursical x * xx/ ^v^x x vxx x xy v^x and v^x xxx Matls x * xv^ liX i.y » Ene x-^xxc^ * Tuscaloosa X v«-k.y xy vxx xy vy ALx xj y 35487 ^y i v_y / Gerberich, William W.

Univ v.^ XXX T • ofX Minnesota X T X X XXX x^^ k.^ \^ Jacobs v v^x/ X/ ' ky * David -A S^ k^ T X XX *—z • Dept. of Chem. Eng. & Mat. Sci. Norton Company

421 Washington Ave. SE 1 Goddard Road

Minneapolis, MN 55455 Northboro, MA 01532

GiannakoDoulos X w^xxx xv^xvvy L./ vy v&x vy %-j * Antonios x xx x x xx \^ Joshi V xy kyxxx « Somit \^ xy xx xx \r Royal Inst, of Tech. CREOL

Dept. of Solid Mechanics Suite 400

Osquours Backe 1 Research Parkway

Stockholm kw/ L vy xxj. X \-/ X X X X 100 X \y vy 44i i Sweden *^ v \^ x x Orlando x^ X X ^xx XXXxy ^ FLx * * 32826 vy x/

Graham X ^AX XW^X XX ^ Michael X T XX WXX^.^^^ X E' ^ * Kant, Avinash

BIRL, Northwestern Univ. Lawrence Berkeley Lab

1801 Maple Avenue Matls. Sci. Division

Evanston, IL 60201 1 Cyclotron Road, MS 62-203

Berkelev x^^ x/x xx%y xxy T ^ CAx_y x x 94720 ^ i / \j Gupta, Bal Kishan

The .1. xxw Ohio v^xxxvy Stat k.y wi.xv Univ XXX v Lad \ J ^xxx ^ Robert X xxy xyx v Jv « Dept. of Mech. Eng. Univ. of Maine

206 West 18th Avenue 5764 Sawyer Research Center

Columbus, OH 43210 Orono, ME 04469

64
Lahres, Michael

Daimler-Benz AG

89013 Ulm

Wilhelm-Runge Str. 1

Germany

Leroux, Pierre

Micro Photonics Inc.

4949 Liberty Lane

Suite 170 PO Box 3129

Allentown, PA 18106

Li, Kangjie

Univ. of Rochester

Dept. of Mech. Eng.

Rochester, NY 14627

Lilleodden, Erica T.

Univ. of Minnesota

Dept. of Chem. Eng. & Matls. Sci.

Minneapolis, MN 55455

Lin, Bo

Magnetics Tech. Cntr.

10 Kent Ridge Crescent

NUS 0511 Singapore

Liu, Chi-Wen

Natl. Chial-Tung Univ.

Dept. of Electronics Eng.

1001 Ta Hsueh Road

Hsinchu 30050 Taiwan

Loubet, Jean-Luc

Ecole Centrale de Lyon

URA CNRS 855

BP 163 36 Av Guy de Collongue

Cedex 69131 France

Lucas, Barry N.

Univ. of Term.

Oak Ridge Natl. Lab.

PO Box 2008, MS 6116

Oak Ridge, TN 37831

Lucas, Stephane

Cockerill Sambre Res. Cntr.

Boulevard de Colonster

B57 Domaine Univ.

Du Sart Tilman B-4000

Belgium

Marieb, Thomas N.D.

Intel Corporation

3065 Bowers Ave., SCI-03

Santa Clara, CA 95052

McHargue, Carl J. Univ. of Tenn.

Center for Matls. Processing

102 Estabrook Hall

Knoxville, TN 37996

Michalske, Terry A.

Sandia Natl. Lab.

MS 1413

Albuquerque, NM 87185

Molloy, John P.

Parteq Innovations

Queen's Univ.

Kingston, Ontario

K7L 3N6 Canada

Moody, Neville R.

Sandia Natl. Lab.

PO Box 969, Division 8312

Livermore, CA 94551

Newson, William R.

Queens Univ.

Dept. of Metall. & Matls. Eng.

Nicol Hall

Kingston, ON K7L 3N6 Canada

Nix, William D.

Stanford Univ.

Dept. Mat. Sci. & Eng.

Stanford, CA 94305

65
O'Connor, Kevin M.

Eastman Kodak Co.

Research Lab., Bldg. 82

Rochester, NY 14650

O'Hem, Michael E.

Nano Instruments, Inc.

1001 Larson Dr.

Oak Ridge, TN 37830

Oliver, Warren C.

Nano Instruments, Inc.

1001 Larson Dr.

Oak Ridge, TN 37830

Ottaviani, Robert A.

General Motors

R&D Center

30500 Mound Road

Warren, MI 48090

Page, Trevor F.

Department of Metallurgy and

Engineering Materials

Herschel Building, U. of Newcastle

Newcastle upon Tyne, NEl 7RU, England

Parmenter, Kelly E.

Univ. of CA

Dept. of Mech. & Env. Eng.

Santa Barbara, CA 93106

Pethica, John

Oxford University

Parks Road

Oxford 0X1 3PH U.K.

Pharr, George M.

Rice University

Dept. of Mech. Eng,

PO Box 1892

Houston, TX 77251

Poisl, W. Howard

Univ. of Arizona

Dept. of Matl. Sci. & Eng.

4715 E. Fort Lowell

Tucson, AZ 85712

Pryputniewicz, Richard J. Worcester Polytechnic Inst. Mech. Eng. Dept.

Cntr. for Holographic & Laser Tech.

Worcester, MA 01609

Ramalingam, Subbiah

Univ. of Minnesota

Dept. of Mech. Eng.

1 1 1 Church Street

Minneapolis, MN 55455

Ribaudo, Carl R.

The Timken Co.

PO Box 6930, Mail Code Res 09

Canton, OH 44706

Riester, Laura

Oak Ridge Natl. Lab.

PO Box 2008, MS 6069

Oak Ridge, TN 37831

Rodin, Gregory J. Univ. of Texas

302 WRW UT

Austin, TX 78712

Rouzaud, Andre

CEA/CEN-G

M2Ri/DEM/SGSA/LTS

17 Rue des martyrs

Grenoble 38054 France

Rowcliffe, David J. Royal Inst, of Tech.

SI 00-44 Stockholm, Sweden

Salmoto, Shigeo

Queens Univ.

Dept. of Matls. & Metall. Eng.

Nicol Hall

Kingston, ON K7L 3N6 Canada

Saunders, Stuart

Natl. Physical Lab.

Queens Road

Teddington, Middlesex

TWll OLW U.K.

66
Schaefer, David M.

Naval Research Lab

Code 6170

Washington, DC 20375

Shinozaki, Douglas M.

Univ. of Western Ontario

Dept. of Matl. Eng.

London, ON N6A 5B9 Canada

Singer, Irwin L.

Naval Research Lab

Code 6170

Washington, DC 20375

Skalak, Richard

Institute for Mechanics and Materials

9500 Oilman Drive

San Diego, CA 92093-0404

Smith, Douglas T.

NIST

Bldg. 223, Room A329

Gaithersburg, MD 20899

Stone, Donald S.

Univ. of Wisconsin

Dept. of Matls. Sci. & Eng.

1509 University Avenue

Madison, WI 53706

Sun, Bradford L.

Intel Corporation

M/S SC2-24

Santa Clara, CA 95052

Swain, Mike V.

CSIRO

Div. of Applied Physics

PO Box 218

Lindfield NSW 2070

Australia

Taljat, Bostjan

Oak Ridge National Lab.

Materials and Process Modelling Group

Oak Ridge, TN 37831-6140

Tambwe, M.F.

Univ. Wisconsin-Madison

Dept.of Matls. Sci. & Eng.

1509 University Ave.

Madison, WI 53706

Tchekanov, Albert

Magnetic Tech. Center

NVS Singapore

10 Kent Ridge Crescent

NVS, MTC Singapore 0511

Tendys, John

Australian Nuclear Tech. & Sci. Org.

Private Mailbag No.l, MENAl

NSW 2234 Australia

Tobolski, Edward L.

Wilson Instruments

Div. of Instron Corp.

100 Royall St. Canton, MA 02021

Tsui, Ting Y.

Rice University

Dept. of MEMS

PO Box 1892

Houston, TX 77251

Upadhyaya, Ramachandra K.

AMP of Canada

20 ESNA Park Drive

Markham ON L3R lEl Canada

Vlassak, Joost J. Stanford Univ.

Matls. Sci. & Eng., Bldg. 550

Stanford, CA 94305

Voevodin, Audrey A.

Wright Laboratory

WL/MLBT

2941 P. Street Ste.l

WPAFB, OH 45433

67
Warren, Oden L.

The Univ. of Western Ontario

Dept. of Chemistry, Chem. Bldg.

London, ON N6A 5B7 Canada

Webb, Stephen C.

Wilson Instruments/Instron

100 Royal St. Canton, MA 02021

White, Richard L.

IBM AdStar

Advanced Thin Film Matls. E32/502

5600 Cottle Road

San Jose, CA 95193

Whitmore, Lawrence C.

Univ. of Cambridge

Dept. of Matls. Sci.

Pembroke Street, Cambridge

Cambridgeshire CB2 3QZ U.K.

Wyrobek, Thomas J. Hysitron Inc.

2010 E. Hennepin Ave.

Minneapolis, MN 55413

Yang, Wuhua

General Motors

R&D Center

30500 Mound Road, Box 9055

Warren, MI 48090

Yang, Fuqian

Univ. of Rochester

Dept. ME

Rochester, NY 14627

Yoder, Karl B.

Univ. of Wisconsin

Dept. of Matls. Sci. & Eng.

1509 University Ave.

Madison, WI 53706

Zhang, Jian

Caterpillar Inc.

PO Box 1875 , Tech. Center - E.

Peoria, IL 61656

Zheng, Lanshi

Univ. of Minnesota

315 5th St. SE 103

Minneapolis, MN 55414

Zirkin, David L.

Case Western Reserv Univ.

Room 614 White Building

10900 Euclid Avenue

Columbus, OH 44106

68
Technical Publications

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active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement methodology and the basic technology

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official source of information in the Federal Government regarding standards issued by NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717 (38 FR 12315, dated May 1 1, 1973) and Part 6 of

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