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NBSIR 80-2058 (ONR)

Studies of Microscopic Aspects of

Wear Processes in Metals

A. W. Ruff

P. J. Blau

Metallurgy Division

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

April 1, 1979-December 31, 1979

Annual Report

N0001 4-79-F-0034

NR 091 -01 1 /2-1 4-79(473)

Issued June 1 980

100

,U56

80-2058

1980

for:

f Naval Research

rient of the Navy

n, VA 22217

c.2 X.

NBSIR 80-2058 (ONR)

i • • STUDIES OF MICROSCOPIC ASPECTS OF

WEAR PROCESSES IN METALS

A. W. Ruff

P. J. Blau

NATIONAL BUREAU

OJT STANDARDS

LIBRARY $EP 1 9 1980

(kt O-Ci. - Cjt

aaoD

/4 0O

A r-N C v <r

Metallurgy Division

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

April 1, 1979-December 31, 1979

Annual Report

N0001 4-79-F-0034

NR 091-011/2-14-79(473)

Issued June 1 980

Reproduction in whole or in part is permitted for any prupose of the United States Government

Prepared for: Office of Naval Research

Department of the Navy

Arlington, VA 22217

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick. Secretary

Luther H. Hodges. Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and Innovation

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
-

•-

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: ’ jwr.|

-- 6 f
Abstract

Wear experiments have been conducted in copper alloys and steels

under dry sliding conditions in order to study the microscopic aspects

of wear and the mechanisms involved. Two experimental wear test systems

have been developed: a linear sliding tester and a block-on-ring computer

controlled tester. Preliminary findings have compared the wear rates

of three different steels, one a high strength-low alloy "dual phase"

steel, and two copper-aluminum alloys. Worn surface and subsurface

morphologies have been studied using optical and scanning electron

microscopy. Wear debris particles have been recovered from the tests

and compared in morphological characteristics between the materials.

Mechanical properties measurements of two of the steels were carried

out to determine strain hardening characteristics for comparison with

wear behavior. Micro-hardness measurements have also been made. Initial

wear rate and friction transients for tests in laboratory air and argon

have been examined to study processes involved in the early stages of

sliding.
TABLE OF CONTENTS

Introduction

I . Experimental Approach

A. Wear Test Systems

1. Block-on-ring system

2. Linear tribometer system

I I . Materials Considerations

III . Results and Discussion

A. Wear Experiments

1. Break-in studies

(a) Linear tribometer results

(b) Block-on-ring results

2. Wear studies

(a) Steel alloys

( b) Copper al loys

B. Mechanical Properties Measurements

IV. Summary and Plans

Acknowledgement s
Introduction

This annual report will describe the findings in a project concerned

with microscopic aspects of wear processes in metals. The initial phase of

research has been concerned with establishing a wear testing and wear

measurement capability, obtaining wear data in two different alloy systems

(iron-based and copper-based alloys), and obtaining microscopic evidence

on significant wear factors from surface, sub-surface and wear debris studies.

Mechanical properties data have also been obtained for examination of

materials parameter effects in wear. Plans for continued research into

the questions opened here will be described at the conclusion of this report.

The presently inadequate state of quantitative understanding of

material wear is due in large measure to the complexity of the subject.

Research studies have identified several different wear mechanisms and

wear processes that may combine or appear at different times in a practical

situation. However, an adequate understanding even of the separate wear

mechanisms already identified does not exist in most cases. This is

particularly true with regard to material parameter effects on wear. Therefore the prospects for extending the knowledge from simple wearing situations

to complex ones are not promising at the present time. In principle such

an approach should be possible. It is believed that an improved quantitative

understanding of basic wear processes should result from properly designed

experimental and theoretical investigations. Emphasis at this time is

needed from the viewpoint of metallurgy and materials science, particularly in

focusing on the microscopic scale of basic wear interactions as well as on

materials properties in the surface and the near-surface regions.

1
This research project is studying three specific aspects of the wear

problem: wear mechanisms, wear debris formation processes and material

parameter effects on wear. Attention will be directed to both initial

phases and steady-state phases of the wear process. Prior to the onset

of a steady-state wear condition (i.e. constant rate of wear), a characteristic behavior in numerous metallic sliding systems occurs known as the

run-in, or break-in, period. During this period initial surface finishes,

oxide and contaminant effects, and changing geometric loading conditions

may produce significant friction and wear transients. The break-in stage

establishes the conditions for steady state that follows. Below the metal

contact surfaces during break-in, initial microstructures are subjected to

directional surface tractions which may result in the formation of highly

strained and crystallographical ly textured zones. The nature of such

deformed zones is not well understood. Metallographi c studies are underway in this project to examine some of the microstructural evolutionary

processes which may affect the tribological response of the system,

including friction transients, during the break-in period. The role of

the surface and near-surface material in steady state wear is also being

examined. Attention here is being directed toward the development of

subsurface strains, subsurface microstructure , voids, cracks, etc., below

the contact surface as a result of sliding wear. The significance of

fatigue and fracture also are being examined in the different phases of

wear.

The wear mechanism that operates under a specific set of experimental

conditions will lead to wear debris formation as well as the establishment

of a particular surface morphology, structure, and deformation substructure

in the specimen. The microscopic processes by which debris particles are

formed are being studied in this project through a series of controlled

2
experiments involving changes in materials, environment and loading

conditions. Debris particles are being characterized with respect to size,

shape and morphology. Those observations when compared with wear surface

structures will enable us to develop conclusions regarding the debris

formation process involving plastic elongation and ductile failure of

surface microfeatures.

This project will also examine the effect on wear of limited changes

in certain material parameters, such as fatigue resistance, toughness,

ductility, strain hardening coefficient, and environmental sensitivity.

It is believed that a proper combination of measurable material parameters

can be shown to strongly influence wear rates, at least under certain

conditions. One example of a potentially significant material parameter

concerns the plastic strain hardening characteristic which can be altered

through alloying changes within one crystal system (and also varied among

alloys of different crystal structure). Significant changes in the formability of steels are known to result from minor changes in alloying

additions and processing conditions. Experiments involving microalloyed

steels are being undertaken to indicate whether the microalloying

approach to provide improved mechanical properties can also offer wear

benefits.

I . Experimental Approach

A. Wear test systems

1 . Block-on-ring system

Two wear test systems were developed for use in this study.

One involved a test configuration of conventional block-on-ring

geometry utilizing a variable speed 1/4 h.p. electric motor

with a replaceable standard wear ring (3.49 cm diameter, 8.7 mm

wide) attached to the motor shaft to provide sliding motion for

3
V.

the wear test (Fig. 1). The test specimen was loaded on top of this ring

and was held in place on an instrumented arm which was free to pivot in a

vertical plane. The holder used for the rectangular block specimens

(0.63x1.27x2.54 cm) was designed so that weights could be placed

over the contact in order to vary the load. A load of 10 N was used

in all tests with this system. A clear plastic enclosure around the wear

contact region was used to maintain a flowing argon atmosphere and a low

humidity level during the dry wear tests. A cam surface on the wear ring

holder on the motor shaft was used to open and close a switch in a D.C.

circuit, once per cycle. This switch was used to synchronize data sampling

with the motor shaft position to reduce the contribution to displacement

due to the wear ring surface run-out. Surface run-out was typically

10 pm, however, this data sampling method reduced the effect by a factor of

100. Wear debris was collected on a clean glass slide positioned below the

wear contact. All the experiments carried out with this system used a

sliding speed of 20 cm/s (110 RPM).

The 52100 steel ring and specimen block were fastened in place

after cleaning in hexane and acetone. The alloy blocks were previously

metal 1 ographi cal ly polished through 600 grit SiC paper (through 1 ym diamond

polishing for the copper alloys). The block specimens were aligned using

two set screws in the specimen holder. A small light was used to illuminate

the contact area between the block and the ring and a magnifier was

used to inspect the contact for parallel surfaces. When the specimen was

properly aligned, argon was introduced into the chamber for wear tests.

After about 5-10 minutes of argon flow the test was begun. When the test was

completed the wear debris slide and specimen were removed and the ring was

4
cleaned with hexane and acetone to remove loose wear debris. Test rings were

changed whenever a new type of specimen was tested or when the rings began

to show significant wear. Typically two to four tests were conducted on

one 52100 steel ring.

The block-on-ring wear test system was interfaced to a mini-computer

system for control and data acquisition purposes. Four parameters were

measured: contact friction, contact displacement, enclosure or specimen

(bulk) temperature, and time, in a repeating cycle. Contact displacement

was measured with a linear variable differential transducer (LVDT) which

monitored the change in height of the specimen holder relative

to the ring surface. Friction was monitored through the use

of two strain gauges attached to the pivoting arm; the resulting

signal was directed to an amplifier. Temperature was measured by a thermocouple placed within the enclosure or welded to the specimen. Running

time was determined by the computer internal clock. The input signals

were directed to an addressable switch scanner (100 Hz switching rate)

and then to a programmabl e digital voltmeter (25 Hz reading rate). Program

control enables the computer to select a scanner channel, set the range

and operating mode for the voltmeter and then read a value from the voltmeter. Data were printed as needed during the wear test; usually the average

of 10 readings at a 2 Hz rate. Data were also recorded for processing

using the computer and a plotter. Processing software was developed to

examine and plot friction vs^ time, wear displacement vs time, and wear

volume V£ time. The wear displacement and wear volume plots could be made

with either the raw data or with averaged data.

5
2. Linear tribometer system

A schematic representation of the second wear system, a ball-on- flat

linear tribometer, is shown in Fig. 2. In the figure, A is the flat specimen

being tested (mechanically polished through 1 ym diamond paste), B is a

52100 steel ball bearing (0.635 cm diam.) mounted on a brass stub, C is a

drill rod guide pin through a high precision linear ball bushing and D is a

304 stainless steel proving ring containing a strain gauge (not shown)

mounted on the outside surface. The arrow shows the movement of Specimen

A, relative to the ball, B. The friction head was mounted above

the traversing table of a bench-top milling machine. The sliding

velocity was 0.45 cm/s in all tests and the loads on the ball

were 250 g and 500 g (2.45 N and 4.91 N). Loading weights were placed

directly above the ball on the protruding end of the ball mounting stub.

Prior to testing, each specimen and ball surface was cleaned in hexane,

acetone, and methanol. Tests were conducted in laboratory air environments. An enclosure is being constructed for future tests in argon gas.

A "dummy" rider stub containing a pulley-mounted wire was substituted for

the rider ball in order to calibrate friction force. Weights were

applied to give a hori zonal deflection of the proving ring. The strain

gauge output was fed to a strain gauge conditioner, and then to the Y

drive of an X-Y recorder. Calibration was performed before and after each

track was worn. The recorder X axis was set at a constant time-base scan

rate so that it represented the position of the ball rider along the wear

track (at constant sliding velocity). In this way frictional force (hence,

friction coefficient) was plotted as a function of position along the

track. Multi-pass experiments were performed in a unidirectional sliding

mode with the rider manually reset between subsequent passes.

6
B. Meohanioal Testing

Tensile deformation characteristics of two of the steels studied here

were carried out using a commerical screw- type tensile machine. Tests were

conducted at a cross head extension rate of 0.5 mm/min at room temperature.

The yield stress was determined at 0.2% plastic elongation, and the tensile

strength at fracture. The reduction-in-area was determined using traveling

microscope measurements of the initial and final cross-section of each

specimen. The tensile specimens were machined by milling from the 1015

steel material and the dual phase steel. Prior to testing the specimens

were lightly polished to remove residual machining marks from the 2.5 cm

gauge length. True stress-true strain data were obtained from each test

and will be described later.

II . Materials Considerations

Two alloy systems are being studied in this project. Iron-based

alloys of three types are included at present: a plain carbon steel,

a type of microalloyed (dual phase) steel and a tool steel. Pure copper

and copper-based alloys containing aluminum as a solute are also under

investigation. These two alloy systems are in extensive use in tribological

applications; therefore, improved wear data and an increased understanding

of the mechanisms involved should have a demonstrable impact on applications.

Plain carbon steels are utilized in many wearing situations, involving

both dry and lubricated environments, since they offer a low cost materials

option. For simplicity and purposes of comparison, a low carbon AISI 1015

type steel has been selected for study here. The composition was

0.14% C, 0.4% Mn, 0.04% P, 0.05% S, the balance being iron. The material

was obtained in strip form, 3.2 mm thick and 19 mm wide. Specimens for

wear testing and for tensile testing were machined from this strip and

7
normalized at 925°C in evacuated glass vials prior to testing. The microstructure prior to wear testing is shown in Fig. 3a.

Microalloyed high-strength steels are currently available [1]* with a

broad range of characteri sti cs for many structural applications including

buildings, bridges, pilings and pressure vessels. Yield strengths in the ashot-rolled condition range up to about 550 MPa, about twice that of

conventional mild steels that are customarily used for structural purposes.

The so-called high strength, low alloy (HSLA) or microalloyed steels

contain small amounts of alloy elements such as copper, chromium, columbium,

silicon, vanadium and others, and a relatively low carbon content of about

0.2%. Strengthening is achieved by grain size refinement along with solidsolution and precipitation hardening. A recent development of ferritemartensite steels, so-called dual phase (DP) steels [1-4] are a special

class of microalloyed steels that offer improved formability at the same

strength levels. They are obtained by re-heating the HSLA steel in the

ferri te-austeni te region ( i ntercri ti cal annealing) to develop a structure

of about 80% ferrite and 20% martensite (with some retained austenite).

These dual phase steels are finding application in several product areas

[1 ] where improved strength/weight ratios and formability are required.

Studies of the wear performance of DP steels have not yet been reported;

however, certain characteri sti cs (e.g. strength, ductility) of this alloy

class suggests the potential for effective wear performance. Several

commercial DP steels have been obtained in sheet form for this study.

One such alloy (DP 80) will be reported on here; the indicated composition was

0.13% C, 1.56% Mn, 0.63% Si, 0.06% A1 , 0.036% V, 0.01% P, 0.01% S,

0.014% Ce, 0.008% N. Wear specimens were machined from this sheet after removing

*Numbers in brackets indicate references.

8
about 0.1 mm from the surface but were not heat treated prior to testing.

The initial microstructure is shown in Fig. 3b.

Tool steel alloys are also used extensively in wear situations and

are characterized by high hardness and wear resistance. An oil-hardening

tool steel, AISI type 0-2, was studied here In both annealed and hardened

states. The nominal composition was 0.90% C, 1.6% Mn, and 0.25% Si. This

steel is relatively inexpensive and the high carbon content produces good

wear resistance in cutting operations that do not involve high temperatures

.

The material was obtained in bar form; wear specimens were machined from

the bar and annealed at 815°C in sealed glass vials. One group of wear

specimens was hardened by oil quenching from 802 °C followed by tempering

for 1 hour at 275°C. The resulting microstructure is shown in Fig. 4.

Two copper-aluminum single phase alloys were obtained for study,

Cu-3.5wt%Al and Cu-7.0wt%Al. The alloys were vacuum cast. They were then

annealed 3 hours at 800°C and hot rolled from 5.0 to 1.55 cm thickness

in 5 passes. Wear block specimens were obtained by machining (fly cutting)

from the rolled bar stock.

All wear tests reported here utilized bearing quality AISI type 52100

steel surfaces as the counterfaces. A bearing ball (6.35 mm diameter) was

used in the linear tribometer where a new contact area was used for each

independent test. Tapered rings (roller bearing cups) were used in the blockring wear test system. Typically two to four tests were carried out with each

ring, although a new ring was used for each change of material or specimen.

9
III. Results and Discussion

A. Wear Experiments

1 . Break-i n studi es

The break-in process, in the context of this report, will be defined

as that set of changes in the tribological behavior which occur in a newly

established solid contact prior to the establishment of constant average

friction coefficient and/or constant wear rate (refered to as "steady tate").

Furthermore, a distinction will be made here between friction and wear breakin behavior. The purpose of this phase of the project was to examine the

initial stages of mi crostructura 1 response to applied surface tractions.

The following materials were studied:

1) normalized 1015 steel

2) dual phase steel (DP 80)

3) oxygen free high conductivity (OFHC) copper

4) Cu-3.5wt%Al

5) Cu-7.0wt%Al

Table I lists basic character!' sti cs of these materials.

Two experimental apparatus were used in determining break-in behavior:

the block-on-ring tribometer and the linear tribometer as described earlier.

The latter device provided information on the initial friction transients

at various locations on the wear track.

(a) Linear tribometer results

Pass-by-pass studies were performed in laboratory air on the materials

summarized in Table II. Flats were given a final mechanical polish

through 1 ym diamond paste the day of the test and both ball and flat were

degreased in hexane, acetone and methanol before installation in their

10
TABLE I. MATERIALS STUDIED IN BREAK-IN TESTS

Material Condi tion

Mi cro hardness

KHN

20Q

( kg/mm

2

)

Average

Grain Intercept

Length (ym)

SAE 1015 steel Normal i zed 1 78±8 49±7

DP-80 steel As-recei ved 235±8 8±3

OFHC Cu As-received

rod

5.1 cm round 1 1 4± 5 39±20

Cu-3. 5wt%Al As-recei ved (see text) 131 ±9 (See Note)

Cu-7. 0wt%Al n n

1 69±1

2

(See Note)

Note:

As-received Cu-Al alloys had a partially (about 50 vol. %) recrystallized

microstructure consisting of regions of large grains with deformation

twins (exceeding 250 ym diameter) and small recrystallized grains

(averaging about 10 ym diameter).

11
TABLE II. PASS-BY-PASS FRICTION TEST CONDITIONS

Material

of FI a

t

%RH

Lab.

Track

Number

New or Used BallLoad

(N)

Total No.

Passes

on Track

1 01 5 Steel 35 1 N 2.5 5 2 U 2.5 4

3 N 4.9 9

4 U 4.9 4

5 U 2.5 8

DP80 24 1 N 4.9 3

2 U 4.9 4

3 N 2.5 13

4 U 2.5 4

OFHC Cu 52 1 N 4.9 22

2 N 2.5 57

3 N 4.9 5 4 U 2.5 4

12
test fixtures. Initial surface roughness values were approximately 0.03 ym

R^. Riders were lowered slowly onto the starting point of each pass,

the recorder X -axis motion was started and then the table traverse was

set in motion.

A typical set of friction traces for 1015 steel is shown in Fig. 5.

The general appearance of the traces was similar for all three materials,

but the time of development of the larger peaks and troughs as well as the

magnitudes of the friction coefficients differed.

Figure 6 compares the maximum value, the minimum value and the

difference between maximum and minimum values of friction coefficients for

each separate pass for the three materials indicated in tests using a

2.5 N load. As shown, once the friction force began to change the

maximum recorded friction climbed rapidly from pass to pass.

The DP80 and 1015 steel data also show that the friction range

tended to maximize at some point in the transition process. Initial

optical studies of wear tracks show that track features at specific

positions tended to correspond with specifc variations in friction coefficient. For example, smooth-appearing track portions showed less

variation in friction coefficient while rapid drops in friction corresponded to areas of the tracks where large debris fragments had become dislodged.

Figure 7 is an optical photomicrograph of a portion of the wear track

on a 1015 steel specimen where the friction trace showed a marked drop.

A portion of the friction trace showing this feature is presented in

Figure 7. During the next reporting period such friction behavior will

be linked to surface and subsurface microstructural details for linear tests

conducted in an argon atmosphere. The present set of linear tribometer

"lab air" results will serve primarily as a guide to break-in track

development and as an added basis for evaluating argon test results.

13
(b) Block-on-Ri ng Results

These break-in studies were concerned with the analysis of the early

portions of the block-on-ring wear - and friction - vs^ - time curves on

all the metals studied. Surface preparation techniques described earlier

led to initial surface roughness values in the range of 0.03 ym to 0.08 ym R . M

Two examples of break-in for DP80 steel specimen are shown in Fig.. 8. Two

features of break-in were of particular interest: 1) the general shape of

the friction and wear curves and 2) the time required to reach steady state

conditions for friction coefficient and wear rate. Figure 9a depicts four

basic friction curve shapes observed for the specimens studied here.

Figure 9b shows several curves for the DP80 steel alloy in particular.

Table III lists break-in behavior for all materials tested. The friction

symbols used in Table III refer to those symbols defined on Fig. 9a.

The friction break-in of the five alloys studied are plotted in the

histogram in Fig- 10- For Cu-Al alloys the use of previsouly unworn test rings

generally resulted in longer friction break-in periods. However, for the

steel specimens this was not always the case.

The friction break-in time is expected to reflect the block and ring

interactions including material transfer character!" sti cs, work-hardening,

debris accumulation and texturing of the materials. In the case of

previously worn ring surfaces, the steady state wear surface microgeometry and

surface composition did not require as much time to reform in subsequent

tests (even though rings were solvent cleaned with hexanes, acetone and

methanol between runs). The behavior of certain steels was

not easy to understand. The microstructural features of the

14
TABLE III. BREAK-IN DATA FOR BLOCK-ON-RING TESTS

BLOCK

New or

Used Ring

Test

Code y o

FRICTION

COEFFICIENT

y* y ss

Cycles

t0

^ss

Type of

Break-in

Cycles to

Constant

Wear Rate

1015 N SI -1 .33 .67 2290 a 'bO U S 1 - 2 .35 - .80 2020 a 600

U S 1 - 3 .28 - .70 1790 a 370

u S 1 - 4 .27 - .55 1500 a 990

N S2-1 .30 - .65 2310 a 820

U S2-2 .32 - .77 2560 a 1650

U S2-3 .39 .60 .82 1810 c 880

DP80 N DPI1

.28 .63 .50 820 b 460

U DP 1 — 2 .31 .72 .53 550 b 640

U DPI -3 .25 .53 .50 450 b 270

N DP 1-4 .36 .67 .55 1010 b 550

U DP1-5 .33 .75 .72 990 d 1650

N DP2-1 .32 .34 .51 1500 d 1010

U DP2-2 .25 - .45 1 500 a 330

U DP2-3 .40 .47 .42 910 d 910

0-2 N R1 .46 .67 .52 270 b 500

U R2 .53 .66 .56 640 b 730

U R3 .46 .74 .55 460 b 730

U R4 .53 (Note 1

)

.55 (Note 2) (Note 2) 910

CU-3.5A1 N 3.5A1-1 .34 .50 .86 1650 c 640

U 3.5A1-2 .26 - .85 640 a (Note 3)

Cu-7. 0A1 N 7A1-1 .30 .45 .76 1470 d no

U 7A1-2 .51 .82 .70 1100 b (Note 4)

U 7A1-3 .33 .68 500 a 'bO

Table Notes : IT) See Fig. 9a for definition of friction coefficients.

(2) No observed break-in in friction trace.

(3) Erratic wear curve.

(4) No observed break-in in wear trace.

15
steel may play a role in this case, and will be a subject of continuing

analysis in the next reporting period.

A final observation on the friction and wear break-in lengths is

represented by the "break-in map" in Fig. 11. Break-in types indicated

for each marked region refer to Fig. 9a. Here, it will be noted that

wear and friction break-in periods did not always coincide, and

that break-in types and specific materials tended to cluster in certain

areas of the map . It should also be noted that data for the 0-2 tool

steel, which exhibited the anomalous frictional break-in with new and

used rings, lay entirely in the region where wear break-in exceeded

friction break-in. The microstructural and surface film implications

of the "break-in map" will be further considered as more metal lographic

studies are carried out on these metals.

2 . Wear Studies

(a) Steel alloys

Wear and friction measurements were carried out on the alloys using

the block-on-ring tester. The experiments were conducted using a 52100

steel ring as the counterface, 10 N load, and 20 cm/s sliding speed

in an argon atmosphere at about 23°C. Sliding distances of either 363 m

(1800 seconds time) or 726 m (3600 seconds time) were used. Both new

rings and rings previously used for the same alloy were employed and are

identified in this discussion.

Examples of the friction curves and wear curves obtained from several

experiments on the DP80 steel and the 1015 steel are shown in Figs. 8, 12,

and 13. These data show some of the variations encountered in the wear

experiment results. Figures 8a and 8b show different trends in the wear

16
volume change with time. The steady state wear rate on both examples

is, however, in agreement as determined from the last 25% to 50% of the

run time. While the friction- time curves in these cases are of a similar

type, the beginning friction peak in Fig. 8a is more pronounced, possibly

reflecting the nature of the break-in processes for this particular

specimen-ring combination. The decreasing slope of the wear volumetime curve for early times in Fig. 8a may also result from this same

effect. In both curves the depth of the wear scar measured after the

experiment was completed is indicated on the wear axis at the point P.

A stylus profilometer was used to obtain this value. In this way an

absolute measure of wear scar depth is obtained for comparison with the

wear depth values obtained during the experiment using the LVDT system.

The profilometer measured wear scar depth was usually 10% to 20% greater

than that measured by the LVDT system. This difference is attributed to the

effect of wear debris in the contact zone and metal transfered to the

ring surface, both cases leading to a reduced displacement value measured

by the LVDT system.

The results of another experiment using a DP80 steel specimen and a

new ring for a longer running time (sliding distance of 726 m) are

shown in Fig. 12. The wear curve here is not statistically smoothed

before plotting as was done in Fig. 8, and shows the extent of a measured

variation in the wear contact position. The wear volume-time curve in

Fig. 12 shows a significant transition in slope at about 2400s (480 m

sliding distance). The initial wear rate (wear rolume per unit sliding distance)

is linear but is considerably smaller than the final wear rate. This

effect was reproduced in several additional experiments with the DP80

alloy and apparently reflects an actual change in wear process in the

17
latter portion of the experiments. In view of this finding two average

wear rate values are reported for the DP80 steel, one for 360 m sliding

distance experiments and one for 720 m sliding distance experiments.

This effect was not found for either the 1015 steel or the 0-2 tool

steel and will be explored further in order to identify the causes.

Two experimental wear and friction curves for 1015 steel specimens

are shown in Fig. 13. In Fig. 13a the wear data are averaged over 5 second

intervals for a smoothing effect. Both experiments produced reasonably

linear wear volume - time (sliding distance) curves, although both showed

a lower wear rate for the initial 300 seconds (60 meters). There was

consistent behavior for this alloy in experiments involving the two sliding

distances, in contrast to the DP80 steel.

A summary of wear measurements for the 1015 and DP80 steels is shown

in the Tables IV and V. The 1015 steel specimens showed fairly consistent

friction coefficient and wear rate values. The DP80 steel results indicate

a transition in both friction and wear rate over the two distances studied.

The wear rate initially (up to 363 m) is about 25% of that found for the

sliding distance interval of 363 m to 726 m. The reasons for the sharp

transition are not yet understood. The DP80 steel wear rates are significantly lower than those measured for the 1015 steel; a factor of 1/8 to

1/2 lower depending on the sliding distance accumulated. As indicated in

Table I the hardness values measured for these two steels are in the ratio

18
TABLE

IV

.

WEAR

AND

FRICTION

RESULTS

ON

THE

DP

80

ALLOY

CO

at

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19

(

3)

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over

last

one-third

of

experiment

.
TABLE

V.

WEAR

AND

FRICTION

RESULTS

ON

1015

STEEL

O CD

i- +-> 4- O3 s I i 1 | o i | 1 CD 1—- E o o o O r— o o o +-> v. I 1 r— i— X ,— t— r—

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HK( DP80)/HK(1 01 5) = 1.32 for annealed material (and 1.14 for deformed

material, measured using tensile specimens, see Table IX later). Hence, the

hardness ratios are not sufficient to account for the observed wear rate

ratios

.

Scanning electron microscope studies have been carried out on the worn

surfaces and on debris particles recovered from the steel specimen wear

tests. A schematic representation of the block-on-ring geometry is shown

in Fig. 14 for use in this discussion. Examples of debris particles recovered as they fell from the 1015 steel block during wear experiments are shown

in Fig. 15. Generally, two types of particles are found; large flat particles

such as (A) and much smaller, equiaxed particles. Figure 16 shows other

examples of this wear debris. In the lower photograph one of the large,

flat particles (A) appears to be partly fractured. The smaller particles

(less than 1 ym in size) are frequently found clinging to the larger

particles and also clumped themselves into a larger agregate such as at

(B). Examination of the entrance zone of the wear scar on the block

revealed a similar collection of debris particles. The exit zone of the

wear scar on the block showed a different morphology as indicated in Fig. 17.

The lower half of Fig. 17a is a portion of the wear scar while the upper

half is unworn, original surface. There is some plastic flow of the

steel out of the wear scar region causing the irregular edge, approximately

perpendicular to the sliding direction (shown by the arrow). One of the

plastically deformed protrusions is seen in more detail in Fig. 17b. Clearly

some evidence is present suggesting tearing of this material at the edges

formed during the mi crodeformati on process. Stereo scanning electron

microscope studies of the morphology present provided convincing evidence

for debris formation at many of these protrusions.

21
Studies of the wear scar surface within the contact zone also revealed

evidence for considerable plastic deformation. Figure 18 shows two regions

(A) within the wear scar where particles of size 3 ym to 10 ym appear to

be forming by a parti cally ductile tearing process. Stereo- viewing of

micrographs taken from the wear scar region suggests that the normal

load at any time is carried by only a small fraction of the apparent area

and that plastic flow both in the direction of sliding (arrow) and transverse to that direction is probably significant in forming the ridges

and lips of material, as well as forming debris particles.

Wear debris was also recovered from experiments involving the DP80

alloy. One collection of particles is shown in Fig. 19. Three different

classes of parti cles were found; further details are presented in Fig. 20.

Relatively large flat particles (A) were found that frequently show cracklike features (arrows). Comparably large particles of a distinctly

different morphology (B)werealso found. Further, much smaller (< 1 ym)

wear particles of roughly equiaxed dimensions were always present. One

area in the entry region of the wear scar is shown in Fig. 21a. Wear

debris particles found in that region (Fig. 21b) were similar to those

recovered after falling from the wearing contact. Again score lines and

crack-like features are seen (A). The morphology at the exit side of the

wear scar is seen in Fig. 22. There is considerable evidence for plastic

flow of material. In Fig. 22b, the lip of metal shown has numerous cracklike features at the edges as well as transverse ripple markings that

suggest constrained plastic deformation. Studies using stereo scanning

electron microscopy of the wear scar surface within the contact zone

(such as Fig. 23) showed that the normal load was probably carried by a

22
small fraction of the apparent area as evidenced by flat ridges of metal

(A) extended in the sliding direction. Irregular edges of these ridges

were commonly found. In most of the micrographs obtained, the surface

regions within the contact zone that were depressed away from contact

with the ring surface appear to have collected quantities of the small

debris particles (such as at B inFigs.22a, 23). This process of fine

debris collection and compaction within the wear gap may in fact produce

the porous appearing debris particles typified by the example in Fig. 20b.

Similar features were observed on the wear scars on the copper-aluminum

blocks to be discussed next.

(b) Copper alloys

Wear and friction measurements were carried out on the Cu-3.5wt%Al

specimens and the Cu-7.0wt%Al specimens. The first tests on each alloy

used a new 52100 steel ring; subsequent tests of each alloy were conducted using the same ring after ultrasonic cleaning (in acetone and

methanol). Table VI summarizes the Cu-Al test results. With the

exception of the last test of Cu-7.0wt%Al which ran twice as long as the

others, all tests were performed under similar conditions. Figure 24

shows a representative wear and friction plot for one of these alloys. As

shown in Table VI, steady state sliding friction was lower for the higher

A1 content. Initial frictional behavior was discussed in the section

dealing with break-in studies. Based on the data in Table VI it is

found that higher aluminum content led to higher wear volume and wear

rates. Further, the alloys with lower friction coefficients also had

higher wear values.

23
TABLE

VI.

WEAR

AND

FRICTION

RESULTS

FOR

THE

Cu-Al

ALL

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24

(3)

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over

last

one-third

of

experiment.

(4)

Erratic.
Specimens of the Cu-Al alloys have been examined by optical microscopy and SEM. Such studies can help clarify the fracture processes

involved in debris formation and establish the role of debris in promoting

further surface degradation.

Figure 14 showed a typical block wear scar schematically. It is

appropriate to discuss the observations made on these alloys in the context

of the three zones shown; entrance, contact and exit. Some features of

these regions in the Cu-Al alloys are delineated below.

1 Entrance zone :

Powdery debris which is carried by the turning ring is deposited

here and compressed into compacts with varying degrees of mechanical

strength. Compacts closer to the scar tend to be stronger. Figure 25a

shows this zone on a Cu-7A1 specimen. Most loose debris came free

upon probing with a camel s-hair brush leaving the island near the

center of the view. Figure 25b shows the leading edge of the island

which may be a region where micrometer-sized debris are trapped and

compacted into the island mass. Beneath the looser debris (not present

on this sample any longer) there is localized cratering of the flat

surface showing an appearance similar to that observed in erosive wear.

The possibility of a small additional contribution to wear in the blockon-ring geometry by particles generated ahead of the main scar should

be considered based on this evidence.

Contact zone :

The main contact zone of the scars consisted of deep grooving with

occasional darker appearing patches covering the grooves. The patches

25
(see Fig. 26) were often gray with some brighter metallic areas.

Preliminary cross-sectioning indicates that they may be "marble

cake"-like compacts of oxide and metal. Further metallography is

planned to examine the role of oxides. Various bands of color

(i.e. black, orange-brown, coppery and bulk alloy colored) were

observed by naked eye lying in the direction of sliding. Their

widths and location across the scars varied from test to test.

Exit zone :

Evidence for the significance of subsurface deformation

in wear was observed in this zone where extensive slip line fields

appeared. As shown in Fig. 27a, the surface distortions followed

the wear groove pattern closely and extended about 50 micrometers

beyond the contact interface. Fig. 27b shows some additional details

of the parallel slip line morphology in this region on the Cu-7.0wt%Al,

low stacking fault energy, alloy.

Initial results concerning the subsurface structure for a Cu-7.0wt%Al

worn block are shown in the photomicrographs in Fig. 28. Figure 28a shows

a longitudinal cross section (sliding direction right to left) of a wear

surface in the polished, unetched condition (copper plated before sectioning).

The dark gray regions at the copper plating/sample interface have the

appearance of a "marbleized" mechanical mixture of bright metal and oxide

debris. This is consistent with the mottled appearance of patches observed

on the sliding surface of this alloy. Light etching* by swabbing revealed

the thin (approximately 4 ym) deformed layer below the sliding surface (Fig. 28b),

but it also resulted in a loss of interface material and oxide-metal details.

*2 g K

2

Cr

2

0

7

, 1.5 g NaCl , 18 ml H

2 S0

4

, 1 00 ml H

2 0.

26
This phenomenon was discussed in a recent paper by Ahn et al. [6].

Further subsurface studies are planned for the other wear tested materials.

Characterization of the dimensions and structure of such sliding weardeformed constituents is felt to be central to developing a valid structure/

properties relation for friction and wear.

B. Mechanical Properties Measurements

Measurements have been carried out on 1015 steel and the DP80 steel

specimens to determine certain bulk mechanical properties that may be

relevant to the wear characteristics of those alloys. Figure 29 shows the

configuration of the tensile specimens used in these experiments. The

relevant dimensions are listed in Table VIII. True stress-true strain

analysis of the data from these tensile tests was carried out in order

to obtain strain hardening coefficients for the two materials studied.

According to this analysis, the stress-strai n relation

„ _ v

n

is fitted to the observed data, as shown in Fig. 30 for one specimen.

This method derives two parameters, K, the strength coefficient, and n,

the strain-hardening coefficient, that describe the plastic response of the

material to uniaxial tensile loads. A summary of the results are shown in

Fig. 31 and Table VIII.

The lower value of strain hardening coefficient measured for the DP80

steel is characteristic of such materials. While the yield stress of the

DP80 steel is only slightly greater than that for the 1015 carbon steel

(353 MPa ys_ 309 MPa, respectively, about 14%), the tensile strengths

differed considerably (682 MPa v^ 500 MPa, about 36%). This increased

27
O0

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00 c

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Q.X

cn lu cc

cu TO

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L- CU

+-> -r- O0 O£4-

<uooc a>

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T3 +>

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a)

L-03

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CL) • £

CM CO

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LO LO

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Q.N

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C

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28 I
strength level arises from the hardening effect of the microalloyed solutes

rather than the carbon content which is actually slightly reduced in the DP80

steel. Equally significant is the increased ability of the DP80 steel to

withstand greater reductions in area than the plain carbon steel (about 58%

greater, see Table VIII).

Microhardness measurements were carried out on both these steels and

on the 0-2 tool steel; the results are shown in Table IX. Considering

first the values for the annealed specimens, the DP80 steel and the 0-2

tool steel showed comparable microhardness values. Both were about 32%

greater than that measured for the 1015 carbon steel. This difference was

reduced by about 1/2 for the deformed materials. Grain intercept lengths

were measured for all three steels and are shown in Table IX. The DP80

steel has a significantly smaller grain size which probably contributed

to the higher yield stress values.

While these tensile measurements were obtained under uniaxial tensile

loading conditions, and the microscopic deformation conditions at wearing

contacts are almost certainly multiaxial with both tensile and compressive

components, it is interesting to compare the differences in mechanical

behavior of the steels with their measured wear performance. The comparison

between DP80 steel and the 1015 carbon steel indicates that both the

higher tensile strength values and the greater potential ductility of DP80

steel probably contribute to its greater wear resistance, since plastic

deformation effects have been shown earlier to be a prominent feature of

the wear process. Tensile data were not obtained for the 0-2 tool steel;

however, the microhardness measurements suggest comparable strength levels

29
TABLE IX. MICROHARDNESS RESULTS ON STEELS

Metal Descri ption

Grain Intercept

Length (ym)

Hardness

Knoop (500 g)

Hardness 00 o

CL. Q

Hardness [metal

)

1015 anneal ed 49±7 1 7 8± 8 1.32

1015 deformed - 244±10 1.14

DP80 annealed 8±3 235±8 1

DP80 deformed - 279±1

0

1

0-2 annealed 30±7 2 33± 5 1.01

30
with DP80 steel. The somewhat greater wear resistance of the DP80 steel

relative to the 0-2 tool steel that was previously described may be due

principally to the greater ductility of DP80 steel. Additional

mechanical properties measurements on the steels are planned to

further explore this matter. Multi axial deformation data will be sought

since such conditions are more closely related to the conditions in the

wearing contact.

IV. Summary and Plans

Initial results are presented on the wear of three steels and two

copper-aluminum alloys. The wear experiments were carried out in two

ways: first, the break-in wear and friction processes were studied using

a linear ball-on-flat system and a block-on-ring wear system, and second,

the steady-state wear processes were studied using a computer-interfaced

block-on-ring system.

The break-in studies were designed to examine trends in friction

coefficient and worn surface morphology on a pass-by-pass basis for the

first 10 to 50 passes for the alloys. Rapid changes in friction values

were measured and in some cases correlated with changes in wear track

morphology. In longer time experiments, four types of characteristic

friction curves were identified. The number of cycles (distance of

sliding) that were required to achieve constant friction or constant wear

response were measured and compared among the alloys using a "map"

representing friction v£ wear break-in behavior. Each of the alloy

systems produced data that clustered in particular regions of this map.

This is interpreted to result from a characteristic combination of

significant parameters such as oxide type and thickness, subsurface

31
deformation modes, and to an unknown extent the kinetic relations between

the mechanical and chemical processes involved.

Steady-state wear studies were carried out for total sliding distances

of both 363 m and 726 m. Wear depth values were obtained continually

(2 Hz rate) through the course of each experiment using the LVDT system.

In this way the time periods required for steady state wear could be

determined and changes in wear rate during the experiment could be measured.

In all experiments the generation of wear debris and the transfer of metal

and oxide between the contacting surfaces was noted. Accumulation of

debris at the entrance edge of the wear scar was a major factor. In approximate terms about one- half of the debris typically fell from the block-ring

combination onto the debris collecting surface, the balance remaining on

the ring or block. Microscopic studies of the contacting surfaces after

the experiments showed evidence for wear debris accumulation within the

contact gap at locations where surface depressions existed.

Three characteristic types of wear debris particles were identified.

Flat metallic particles were prominant in the debris with major axis

dimensions from about 1 urn to 40 ym and thicknesses up to about 1 ym.

Examination of the worn surfaces revealed many features resulting from

plastic deformation both within the contact gap and at the exit end of the

wear scar. The size and features of these deformed ridges and lips

suggested that production of flat debris particles could be explained by

ductile failure processes on a microscopic scale. A second type of large

particle was clearly the result of compaction of much smaller particles,

presumably occurring within the contact gap or possibly at the entrance

edge. The third type were small particles about 0.1 to 1 ym in all

dimensions that may have been formed by elementary rubbing processes between

the surfaces. These smallest particles were compacted into one type of the

32
larger particles as noted above. Xray diffraction studies have been

initiated to identify the oxides and metals present in the wear debris

collections since it seems plausible that the smallest particles are

largely composed of oxides.

The wear rate measurements of the two types of steels revealed

some interesting differences. In particular, the DP80 steel wear rate

while initially about 1/8 that of the 1015 steel, increased for longer

sliding distances until it was about 1/2 that of the 1015 steel.

Clearly a change of this magnitude reflects a change in the dominant

wear process. The measured coefficients of friction as well showed a

corresponding change for the DP80 alloy. The two copper alloys also

showed significant trends in both friction coefficient and wear rate.

The wear rate doubled with a two-fold increase in aluminum concentration

while the steady-state friction coefficient decreased with that change.

No particular trends with composition in the principal wear debris particle

characteristics were noted, but further studies into this question are

in progress.

The mechanical properties measurements on the two steels revealed

some significant differences that were generally expected. The DP80

steel alloy exhibited a slower work-hardeni ng rate than that for the

1015 carbon steel specimens under uniaxial tensile deformation. The

greater formability of the DP80 alloy is consistent with in such

behavior. In contrast, the microhardness values for the 1015 steel in

the deformed condition were only about 15°/ lower than for the DP80

alloy. Thus the difference in microhardness is probably only a small

factor in the overall difference in mechanical behavior of the two types

33
of steel and hence in the contrasting wear resistance.

Plans for the coming year in this project include the following

studies

• two other dual phase steel alloys will be examined in terms

of wear behavior and mechanical properties.

• microstructural studies of subsurface regions in worn specimens

will be emphasized.

• friction and wear break-in characteristics will be determined

for the alloys in different environments, particularly studying

the effect of water vapor and contaminants.

• an oil -free, ultrahigh vacuum pumpable wear system will be

constructed for studies in various controlled atmospheres.

• compression testing and multi-axial mechanical testing of the

different steels will be conducted for comparison with wear

performance.

• the complex wear rate characteristics of the DP80 alloy will

be closely examined.

• relevant wear mechanism differences among the iron-based and

copper- based alloys will be studied.

• the responsible wear debris formation processes in the alloys

will be further defined.

Acknowledgements

Considerable assistance has been provided in the experimental phases

of this work by Paul Boyer, David Cooper and Kirk Mettam. The copper

alloys used in this research were obtained through the cooperation of the

01 in Corporation.

34
References

1. "A Review of the Status, Selection and Physical Metallurgy of

High-Strength, Low-Alloy Steels", E. E. Fletcher, MCIC Report #79-39

(Battelle Columbus Laboratory, Ohio, March 1979).

2. "Molybdenum in Intercri tical ly Annealed Dual -Phase Steel Strip",

J. Morrow and G. Tither, J. Metals 30, 1 6 (1 978).

3. "Physical Metallurgy of Antomotive High-Strength Steels",

R. G. Davies and C. L. Magee, AIME publication in press, 1979.

4. "Dual-Phase Sheet Steels for Automotive Applications",

T. Furukawa, Metal Progress 116 , 36-39 (1979).

5. Mechanical Metallurgy, G. E. Dieter (McGraw-Hill Book Company, 1961)

p. 243.

6. "Metal lographic Techniques for Wear Test Specimens", T. M. Ahn,

P. J. Blau, K-L Hsu, D. A. Rigney and J. D. Schell, Wear 56,

409-413 (1979).

35

Fig. 1. Wear test apparatus showing motor (M), ring (R),

controller (C), specimen arm (A), enclosure (E).

Fig. 2. Schematic of the linear tribometer head: (A)

specimen, (B) ball rider on a brass stub,

(C) precision linear ball bushing, (D) strain

ring with gauges .
r

Fig. 3. (a) 1015 steel microstructure, etched in nital,

(b) DP80 steel microstructure, etched in nital.

Fig. 5. Observed variation of friction with position on track

during the first 5 passes on 1015 steel specimen.
Fig. 6. (a) Linear tribometer friction results for

a 1015

steel specimen.
Fig. 6. (b) Linear tribometer friction results for

a DP80 steel specimen.
Stroke Number

Fig. 6. (c) Linear tribometer friction results for a copper specimen.
between a drop off in friction and the beginning

of a deep groove in the wear track.
**E K

Q S S s S~\00

(0

LU-2.

Fig.

8.

(a)

Wear

depth

(W),

wear

volume

(WV)

and

friction

coefficient

(FC)

results

for

DP80

steel

specimen.
WEAR

VOL.

(mm )

FRICTION

COEF.

Specimen

DP

80

(l- 3>

WEAR

(pm)** 10_

0.

0100,

10. 0 a

aa

a • • • • 00 CD (M

(a

0081

0091

mvx

00SI

A

0001®0) v-/

LxJ 008 2

009

00V

00S

00 CD CM

a • • • • a a a a a

Fig.

8.

(b)

Wear

depth

(W),

wear

volume

(WV)

and

friction

coefficient

(FC)

results

for

DP80

steel

specimen.
t

Fig. 9. (a) Types of friction break-in curves observed

for block-on-ring tests.
0081

0091

00V I

003T

000 1

008

009

00V

003 0

0098

0883

0013

0VVI $ o

CO

Q_OO<4-uo

H03L

V)

a>>

s-3

<_> o

•I—s0091 <+-oc in 0091 o c

l/) cu r- E

S- -r- 00V I

fO o

cl a) E Q- o to 0031 C_) 1 a>

<u 0001 1£

-Q +J — to

003 . "

009

00V

003

CD

•r—

Ll. 0
Friction

BreakIn

(Cycles)

a>

Q> tn

too

4>

V)0

00

1 a.o

w

o

o

CM

i O

55*to

ro

t3

o

Fig. 10. Comparison of friction break-in characteristics

for five alloys.

Cu-7.0%

Al
CYCLES

TO

CONSTANT

FRICTION

CYCLES TO CONSTANT WEAR RATE

Fig. 11. Break-in map illustrating relationships between

friction and wear break-in periods. Letters

indicate break-in types from Fig. 9(a).
/~\ 0

(D0

V-/ LUI

c

<dE C T- o o

•r- cu 4-> Q. u to

•r*t- i—

4- CD

ai -a +-> c to

(0 o

.—-00 > CL 3 CO

s_ CD O i— to O 4-> > r-3

J- to

ra (D

CD s- 2• c_> 4-> -C c

-t-> CD Q.-ICD U

-a •—<4-

i- 4-

ra CD

CD

O 3 O

CMO0
** Q s s El s El s ej • s e! E3

cn cl C\J r-t

ION

COEF \

\- • _i 1 H —4

—i 

, , !=!s GO CD ro ei

cr

u. ^ El E) 9 El e3 eS

0081

0091

00M

0021

0001

008

009

00fr

002 0 o

(D

(0

LlI

If) •o r- c o

ta r— ,— s_ > o 3 <*-

i/i

CL) 4-> E r- 3 3 i— in O <D > Ss- ^ra o

O) u_ 3 —

« 4-> ^ c 3 <Uo

-M 4-

C

cl 4- <y

<U CUoo

TD

O -Is_fd

cu o

cuCL

in o cu -^•p- cu (B s-+) —4- m

ro

CD i 1
WEAR

VOL. E

/'N0©

(0

LU

CJl

(b)

Wear

depth

(W),

wear

volume

(WV)

and

friction

coefficient

(FC)

results

for

1015

steel

specimen.
BLOCK

SPECIMEN

CONTACT ZONE

Fig. 14. Schematic representation of block-on-ring

geometry.

Fig. 16. Wear debris particles recovered from test of

1015 steel specimen. Note partial fracture of

particles (A) in lower photograph. An agregate

of much smaller particles is seen at (B).
Fig. 17. Scanning electron micrograph of exit edge of

wear scar on 1015 steel specimen surface.

(a) arrow shows sliding direction, (b) evidence

of deformation and fracture at edges of displaced

material

.
Fig. 18. Central region of wear scar on 1015 steel

specimen. Wear particle formation appears

underway at locations (A) where heavily deformed

metal is present.

I

'
Fig. 19. Scanning electron micrograph of wear debris

particles collected from test of DP80 steel

specimen. Note scoring

flat particle (A)

.

lines on surface of
Fig. 20. Examples of large debris particles from DP80

wear tests having two different morphologies.

Note crack-like feature in (A) at arrow.
Fig. 21. (a) Entry region of wear scar on a DP80 specimen

with sliding direction indicated by arrow.

(b) Note crack in particle at (A) in one area of loose debris deposit.
Fig. 22. (a) Scanning electron micrograph of exit

edge of wear scar on a DP80 specimen.

(b) Details of deformation markings and

crack- like features. Arrow indicates sliding

distance.

I
Fig. 23. Central region of wear scar on a DP80 specimen.

Flat ridges of deformed metal (A) aligned in

sliding direction (arrow) appear to carry

imposed normal load.
WEAR

VOL.

(mm )

FRICTION

COEF.

Specimen

Cu-7A1“1

WEAR

(pm)

1.0_

0.

0150,

15. 0 SI

OJ

SI

CD

Si

CD s00

Si

si

/"N0

(D(0 Vw/

LlI

h-

*3-

CV1

CD

Wear

depth

(jW),

wear

volume

(WV),

and

friction

coefficient

(FC)

results

for

Cu-7.0A1

specimen.
r

Fig. 25. Scanning electron micrograph of a large patch

at the entrance edge of a wear scar on a Cu-7.0%A1

specimen. Sliding direction is left to right

(a) contact zone begins about one-third the

distance from the right edge of the photomicrograph. (b) Higher magnification view of the

leading edge of the patch. Small debris appears

to be in the process of compaction, as indicated

by the outlines on the patch surface at lower

right.
Fig. 26. Optical photomicrograph of an entrance edge

patch on Cu-7.0A1 showing gray (oxide) at A

and light (metal) regions at B. Sliding

direction is indicated by arrow.

1
Fig. 27 Interference-contrast photomicrograph of the

exit end of a Cu-7.0%A1 block scar (a) surface

topography reflects the deformation under the worn grooves (b) slip line fields at the exit

end of the wear grooves. Sliding direction

is given by arrows.
ifiWfWIai |

electrodeposit^

10 um

i 1

Fig. 28. (a) Cross section through Cu-7.0%A1 block wear

scar. Thickness of the lamellar zone is about

8 ym. Unetched. (b) Lightly etched microstructure. Ring surface moved from right to left.
Fig. 29. Tensile specimen configurations.
9.4

9.2

9.0

8.8

8.6

8.4

8.2

/

DP80 (Tl)

/ K=1110 MPa

/ n=0. 19

i i b CO LO CO CvJ -—i C53

I I I I I I

Log True Strain

Fig. 30. Example of true stress-true strain results for one DP80 steel specimen.
Log True Stress

Fig. 31. Summary of uniaxial tensile deformation results

on 1015 steel and DP80 steel specimens.

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SECURITY CLASSIFICATION OF THIS PAGE (Whin Data Entered) REPORT DOCUMENTATION PAGE READ INSTRUCTIONS

BEFORE COMPLETING FORM

1. REPORT NUMBER 2. GOVT ACCESSION NO. NBSIR 80- 2058 (ONR)

3. RECIPIENT’S CATALOG NUMBER

4. TITLE (and Subtitle) STUDIES OF MICROSCOPIC ASPECTS OF WEAR

PROCESSES IN METALS

5. TYPE OF REPORT A PERIOD COVERED

Annual Report

Jan. 1979 - Dec. 1979

6. PERFORMING ORG. REPORT NUMBER

7. AUTHORCaJ A. W. Ruff

P. J. Blau

8. CONTRACT OR GRANT NUMBERfaJ

N00014-79- F-0034

9. PERFORMING ORGANIZATION NAME AND ADDRESS

National Bureau of Standards

Washington, DC

10. PROGRAM ELEMENT. PROJECT, TASK

AREA A WORK UNIT NUMBERS

11. CONTROLLING OFFICE NAME AND ADDRESS

Dept, of Navy

Office of Naval Research - ATTN: R. Burton

Arlington, VA ???17

12. REPORT DATE

March 1980

13. NUMBER OF PAGES

34

<4. MONITORING AGENCY NAME a ADDRESSfi/ dltlerent irom Controlling Oflice) 15. SECURITY CLASS, (ot thle report)

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SCHEDULE

16. DISTRIBUTION STATEMENT (ol thle Report)

17. DISTRIBUTION STATEMENT (ol the ebetrect entered In Block 30, It dltlerent trom Report)

Uni imi ted

18. SUPPLEMENTARY notes

19. KEY WORDS (Continue on reveree elde It neceeemry end Identify by block number)

Copper; electron microscopy; friction; metals; plastic deformation;

steel; surfaces; wear; wear debris

20. ABSTRACT (Continue on reveree elde It neceeeery end Identity by block number)

Wear experiments have been conducted in copper alloys and steel

under dry sliding conditions in order to study the microscopic aspects

of wear and the mechanisms involved. Two experimental wear test systems

have been developed: a linear sliding tester and a block-on-ring computer

controlled tester. Preliminary findings have compared the wear rates

of three different steels, one a high strength-low alloy "dual phase"

DD 1 JAN^73 1473 EDITION OF I NOV 65 IS OBSOLETE

S/N 0102-LF-014-6601 SECURITY CLASSIFICATION OF THIS PAGE flWian Data Entered)
20. Abstract (continued)

steel, and two copper-aluminum alloys. Worn surface and subsurface

morphologies have been studied using optical and scanning electron

microscopy. Wear debris particles have been recovered from the tests

and compared in morphological characteristics between the materials.

Mechanical properties measurements of two of the steels were carried

out to determine strain hardening characteristics for comparison with wear behavior. Micro-hardness measurements have also been made. Initial wear rate and friction transients for tests in laboratory air and argon

have been examined to study processes involved in the early stages of

sliding.

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BIBLIOGRAPHIC DATA

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1. PUBLICATION OR REPORT NO.

NBSIR 80-2058 (ONR)

2. Gov't' Accession No.

; *0 Vc-K-.s.C

Z. Parent's Accession No.

4. TITLE AND SUBTITLE

Studies of Microscopic Aspects of Wear

Processes in Metals

5. Publication Date

June 1980

6. Performing Organization Code

7. AUTHOR(S)

A. W. Ruff and P. J. Blau

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No.

.

11. Contract/Grant No. N0001 4-79- F-0034

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, zip)

Office of Naval Research

Department of the Navy

Arlington, VA 22217

13. Type of Report & Period Covered Annual

i4. Sponsoring Agency Code

: 15. SUPPLEMENTARY NOTES

f~

|

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) Wear experiments have been conducted in copper alloys and steels

under dry sliding conditions in order to study the microscopic aspects

of wear and the mechanisms involved. Two experimental wear test systems

have been developed: a linear sliding tester and a block-on-ring computer

controlled tester. Preliminary findings have compared the wear rates

of three different steels, one a high strength-low alloy "dual phase"

steel, and two copper-aluminum alloys. Worn surface and subsurface

morphologies have been studied using optical and scanning electron

microscopy. Wear debris particles have been recovered from the tests

and compared in morphological characteristics between the materials.

Mechanical properties measurements of two of the steels were carried

out to determine strain hardening characteristics for comparison with

wear behavior. Micro-hardness measurements have also been made. Initial wear rate and friction transients for tests in laboratory air and argon

have been examined to study processes involved in the early stages of

si idi ng.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Copper; electron microscopy; friction; metals; plastic deformation; steel;

surfaces; wear; wear debris.

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