Synthesis and Dynamic Compaction of

Titanium Boride and Titanium Carbide

by Liya Wang and Levi T. Thompson

prepared by

T/J Technologies, Inc.

3850 Research Park Drive

P.O. Box 2150

Ann Arbor, MI 48106

under contract

DAAA-1591-C-0088

.

I l

Approved for public release; distribution is unlimited.
The findings in this report are not to be construed as an official

Department of the Amy position unless so designated by other

authorized documents.

Citation of manufacturer’s or trade names does not constitute an

official endorsement or approval of the use thereof.

Destroy this report when it is no longer needed. Do not return

it to the originator.
.

.

Army Research Laboratory

Aberdeen Proving Ground, MD 2 1005-5066

ARL-CR-440 April 1999

Self-Propagating High-Temperature

Synthesis and Dynamic Compaction of

Titanium Boride and Titanium Carbide

Liya Wang and Levi T. Thompson

T/J Technologies, Inc.

prepared by

T/J Technologies, Inc.

3850 Research Park Drive

P.O. Box 2150

Ann Arbor, MI 48106

under contract

DAM-15-91-C-0088

Approved for public release; distribution is unlimited.
Abstract

Titanium carbide (Tic) and titanium diboride (TiB,) ceramic disks, with diameters of

100 mm and thicknesses of 25 mm, were fabricated with densities above 95% and 98% of

theoretical, respectively, using a self-propagating high-temperature synthesis/dynamic

consolidation (SHS/DC) process. First, an SHS reaction was initiated in a green body made from

precursor powders. Second, after the completion of the SHS reaction, the freshly synthesized

ceramic product was densified to near-full density by the action of the detonation of an

explosive. With a focus on potential military and civilian applications, the structural and

mechanical properties of the products were evaluated. Furthermore, the relationship between

process conditions, microstructure development, and mechanical properties was investigated.

Finally, correlations of the properties with key processing conditions were used to establish

guidelines for the fabrication, scale-up, and commercialization of the process.

ii
Table of Contents

.

1.

2,

3.

4.

4.1

4.2

4.3

4.4

4.4.1

4.4.2

4.4.3

4.4.4

4.4.5

4.4.6

5.

5.1

5.1.1

5.1.2

5.1.3

5.1.4

5.i.5

5.1.6

5.1.7

5.2

5.2.1

5.2.2

5.2.3

List of Figures...............................................................................................................

List of Tables.................................................................................................................

Introduction ..................................................................................................................

Literature Survey .........................................................................................................

Technical Objectives ....................................................................................................

Experimental.................................................................................................................

Raw Materials ..........................................................................................................

Mixing and Greenfom Preparation.........................................................................

SHS Reaction and DC..............................................................................................

Characterization .......................................................................................................

Density ................................................................................................................

Composition .......................................................................................................

Microstructure ...................................................................................................

Microhardness ...................................................................................................

Young’s Modulus ...............................................................................................

Compressive Strength ........................................................................................

Results and Discussion.................................................................................................

TiB2...........................................................................................................................

Physical Appearance of Compacts ....................................................................

Density ................................................................................................................

Composition .......................................................................................................

Microstructure and Grain Size ..........................................................................

Microhardness ...................................................................................................

Young’s Modulus ...............................................................................................

Compressive Strength ........................................................................................

Tic ............................................................................................................................

Physical Appearance of Compacts ....................................................................

Density ................................................................................................................

Composition .......................................................................................................

5.2.4 Microstructure and Grain Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

V

Vii

1

2

5

5

5

6

6

9

9

10

11

11

11

12

12

12

12

13

14

15

18

20

22

22

22

24

24

25

. . . 111
52.5 Microhardness ................................................................................................... 26

52.6 Young’s Modulus ............................................................................................... 28

52.7 Compressive Strength ........................................................................................ 28

6. summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Distribution List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Report Documentation Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

iv
List of Figures

.

Fiaure

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

Experimental Setup for the SHS Reaction and DC .......................................................

Illustration of Four Major Areas From Which Samples Were Obtained to Evaluate

the Uniformity in Microstructure and Properties...........................................................

Photographs of the TiB2 Samples Showing Impact Surfaces........................................

Intrusion Volume Against Pore Diameter for TB9225 Determined by Mercury

Porosimetry Analysis......................................................................................................

XRD Patterns..................................................................................................................

An SEM of TB9225 .......................................................................................................

Effect of Test Load on Measured Hardness...................................................................

Microcrack Along a Boundary Between Two TiB2 Grains...........................................

Effect of Annealing Temperature on Hardness of TB9225 Measured Under

Different Loads...............................................................................................................

A Cleavage Surface of the Sample TB9225 After the Compression Test....................

Photographs of the Impact Surfaces...............................................................................

XRD Pattern of TC9223 .................................................................................................

An SEM of TC9223 .......................................................................................................

Effects of Test Load on the Hardness of Tic Samples..................................................

Effect of Annealing Temperature on the Hardness of TC9223 Under Different

Loads...............................................................................................................................

A Cleavage Surface of TC9223 After the Compression Test .......................................

PaJ.g

7

10

13

15

16

17

20

21

21

23

23

25

26

27

28

29

V
INTIDTIONALLY LEFT BLANK.

vi
List of Tables

1. Specifications of the Starting Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2. Experimental Conditions for the SHS/DC of TiB2 and Tic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3. Density, Grain Size, Hardness, Young’s Modulus, and Compressive Strength

of SHSLDC TiB2............................................................................................................. 14

4. Density, Grain Size, Hardness, Young’s Modulus, and Compressive Strength of

SHWDC Tic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

vii
&lTJZNTIONALLY LEFT BLANK.

. . .

Vlll
1. Introduction

There is great interest in the development of light armor for improving the performance of

armored vehicles and for using in some domestic applications. The major requirements for an

armor material include high compressive strength, high elastic impedance, and low specific gravity

[ 1,2]. Titanium diboride (TiB$ and titanium carbide (Tic) possess these characteristics and are

ideal candidates for applications in armor. In addition, they are refractory (melting points for TiB2

and Tic are 2,980” C and 3,067” C, respectively), ultmhard (hardnesses for TiB2 and Tic are

3,400 kg/mm2 and 3,200 kg/mm2, respectively), wear resistant, thermal shock resistant, chemically

stable, and lightweight (densities of TiB2 and Tic are 4.571 kg/cm3 and 4.911 kg/cm3,

respectively) [3-51. These properties make TiB2 and Tic attractive for other applications, including

use in cutting tools, wear-resistant components, rocket nozzles, and jet engine components.

The fabrication of TiB2 and Tic ceramics by conventional sintering, hot-pressing, or

hot-isostatic pressing (HIPing) of TiB2 and TiC powders is costly because of the time-intensive and

facility-intensive nature of these processes. The application of TiB2 and Tic ceramics has thus

been limited. The development of the self-propagating high-temperature synthesis (SHS)

technique, however, may provide an economical method for producing TiB2 and Tic ceramics.

The SHS process takes advantage of the extreme heat generated during the formation of some

refractory materials. When a mixture of the constituent elements is ignited at one end, the highly

exothermic reaction propagates spontaneously and rapidly and converts the reactants into a

refractory product. The reaction temperature can exceed 2,500” C. The SHS technique has

attracted attention as a route to a variety of refractory materials, including borides, carbides,

nitrides, silicides, and intermetallic compounds [6-211.

The SHS products cannot be used directly as structural materials because they are generally

quite porous (the porosity can be as high as 50 volume-percent). This porosity can be reduced by

compressing the SHS product while it remains at a temperature above its ductile-brittle transition

point. A number of methods that combine a compaction step with the SHS process have been

1
developed in order to exploit the high post-reaction temperature. Among these are

SHShot-pressing [22, 231, SHSElIPing [24, 251, SHS/hot-forging [26, 271, SHS/hot-rolling [28],

and SHS/dynamic compaction (DC) 129-321. These methods hold promise for the economical

synthesis of armor materials due to their low costs and high productivity, as compared to

hot-pressing and HIPing. While the costs of products generated using the SHS-based techniques

are yet to be compared, the SHS/DC method is the least facility-intensive and time-intensive

process. This technique has been employed for the synthesis of TiB2, Tic and hafnium carbide

(HfC) by scientists at the U.S. Army Ballistic Research Laboratory (BRL)* [29-31,33-371.

2. Literature Survey

While the SHS technique was developed more than a century ago, it did not receive much

attention until the mid-1960s, when Merzhanov [38, 391 (in the former Soviet Union) used this

technique to produce powders of refractory compounds. Today, the total number of materials that

can be prepared by this technique exceeds 500, covering a wide range of materials, including

carbides, box-ides, nitrides, silicides, and intermetallic compounds [6-371. This progress has

generated a great deal of interest around the world, and a number of research efforts have been

initiated in the U.S. and Japan in the past few years.

Advantages of the SHS process are as follows [ 11, 131: (1) the materials are usually purer

because the extremely high reaction temperatures cause the expulsion of volatile contaminates and

no catalysts or other compounds are involved, (2) this process has a high energy efficiency since no

heat is needed except for the ignition, (3) the process has the potential for high production

efficiencies due to the very quick processing times (on the order of seconds instead of hours and

days for competing techniques), (4) the capital investment is low compared to conventional

techniques, and (5) it is possible to produce metastable materials due to the fast cooling rates.

Materials prepared by the SHS process can easily be crushed to form powders; however, they

*BRL was deactivated on 30 September 1992 and subsequently became a part of the U.S. Army Research Laboratory

(ARL) on 1 October 1992.

2

l HIPing - The reactant mixture is vacuum-sealed in a glass envelope. The envelope is then

embedded in a combustion reagent in a crucible. The assembly is placed inside a

high-pressure vessel. When the combustion reagent is ignited, the heat generated sets off .

the reaction of the powder mixture inside the envelope. During the process, an isostatic

pressure, which mechanically compacts the sample into a dense body, is .

maintained [24,25].

l Hot-Forging - The SHS reaction is combined with a forging process so that the hot porous

reaction products are forged into dense ceramics immediately after the reaction [26,27].

l Hot-Rolling - Mixed reactants encased in insulated tubes are ignited and continuously

compacted in a rolling mill immediately following passage of the reaction front [28].

l DC - Hot porous ceramic bodies formed during the SHS reactions are consolidated to high

density by the action of a pressure wave from the detonation of a high explosive or impact

of an explosively driven flyer plate [29-321.

While the costs and structural properties of the products prepared by these methods have not

been compared, the DC technique has the merit of being less dependent on expensive facilities and

higher in productivity. This method has been extensively studied by Niiler and coworkers at BRL

[29-3 11. They have demonstrated that, under the appropriate conditions, near fully dense TiB2,

Tic, and HfC ceramics could be prepared by this technique. Their work has also provided insight

into the SHS/DC process. Valuable information regarding the effects of the powder characteristics,

inert diluent, impurities, delay time, and (ratio of the explosive charge [C] mass to the metal driving

plate mass [Ml) on the synthesis and compaction was obtained. The results suggested that a pure

starting powder; an appropriate delay time and C/M ratio; and a future, including a strong container

and a thermal insulator with outgasing vent holes, were essential for the successfi.rl synthesis and

consolidation of TiB2 and Tic. The microhardness and ballistic performance of SHS/DC-prepared

TiB2 and TiC were comparable to those of the hot-pressed materials.

4
Thadhani and coworkers at the Center for Explosives Research and Technology at New Mexico

Tech, continued the SHWDC effort [32,43, 441, based on results reported by Niiler and coworkers

[29-311. They modified the explosive loading assembly to obtain a more uniform compression of

the samples. Dense TiB2 (98% of theoretical) and Tic (95%) compacts were synthesized.

Additional understanding of the process was obtained through both experiments and theoretical

modeling.

T/J Technology, Inc., in response to a solicitation from the U.S. Department of Defense (DOD),

completed a Phase I small business innovative research (SBIR) contract aimed at synthesizing near

fully dense TiB2 and Tic plates. This information is used to determine the feasibility of developing

a commercial process based on the SHWDC technique. The results are presented in this final

report.

3. Technical Objectives

The primary objective of this project was to use the SHS/DC technique to fabricate

100~mrn-diameter by 25-mm-thick plates of TiB2 and Tic with densities greater than 98% and 95%

of their theoretical values, respectively. The secondary objective was to evaluate the structural and

mechanical properties of the synthesized TiB2 and Tic and assess the feasibility of applying these

ceramics in military and civilian uses. Finally, a desire existed to investigate the relationship

between the processing conditions, microstructure development, and mechanical properties of TiB2

and Tic. Of particular interest was the effect of precursor powder purity on the mechanical

properties because pure boron (B) is very expensive. Correlations of the properties with the

processing conditions provide guidelines for scaling-up and commercializing this process.

4. Experimental

4.1 Raw Materials. The starting materials were elemental powders of titanium (Ti),

carbon (C), and B. The purity, particle size, and suppliers of the powders are summarized in

5
Table 1. Two different B powders were used. The B-l powder contained l-5% C, whereas the

B-2 powder was ultrapure. The particle sixes were selected as a compromise between the reduced

reaction rate of larger particles and the inconvenience of handling smaller particles [ 301 o

Table 1. Specifications of the Starting Materials

Material

Ti

B-l

B-2

C

Purity

(%)

99.5

>95

99.5

99.9

Particle Size Supplier

- 325 mesh Micron Metals

-325 mesh Aldrich

-325 mesh Atlantic

2um Consolidated Astronautics

4.2 Mixing and Greenform Preparation. The B/Ti atomic ratio of 2: 1 and C/Ti atomic ratio

of 0.95:1 were selected based on reports in the literature. A stoichiometric ratio of B/Ti has been

widely used, whereas a range of C/Ti atomic ratios have been employed (0.7-1.19) [9,29, 30, 401.

Several researchers have reported that the optimum C/Ti atomic ratio is 0.95 for SHS/DC [40,45].

There are at least two reasons for the use of substoichiometric C/Ti ratios [27]. First, the violent

release of impurities can cause expulsion of Ti from the compact 1341. Second, at the elevated

temperatures at which compaction occurs, nonstoichiometric Tic has a lower yield strength than

stoichiometric Tic [46].

The Ti-B and Ti-C powders were dry-mixed under an argon (Ar) atmosphere for 12 hr in a

V-shaped plastic mechanical blender. Since no milling media was used, the possibility of

contamination during mixing was minimal. The mixtures were uniaxially pressed into disk-shaped

greenforms (100 mm in diameter with 40 mm thickness) using a hydraulic press. The greenforms

were stored in a vacuum chamber to prevent oxidation.

4.3 SHS Reaction and DC. The experimental setup for the SHS/DC is shown in Figure 1.

This is a modified version of the BRL design 130, 32,401. The system was made up of layers of

gypsum wallboard, which were center-cored to a diameter slightly larger than that of the reactant

6
r l3fmm

I 19.09 mm

I

aA9 mm

f

19.0s mm

ANFO E?iPLOSIVE

9 mm PVC lube

SEEL COMPRESSION PLATE -I

2 mm Zirconio

\

0.6mm Gdoil CL___

Figure 1. Experimental Setup for the SHS Reaction and DC.

greenforms. Two telescoping, mild steel rings of equal height were placed between the greenform

and the gypsum to serve as lateral containment during the reaction and subsequent compaction.

The bottom ring and the gypsum block had four matching holes to vent gases released during the

reaction. A Grafoil strip was placed between the steel ring and the greenform to provide thermal

insulation and prevent impurities from diffusing into the reacted compact, Circular driver plates

and momentum traps made of high-hardness steel [47] were epoxied into wooden frames and lined

with zirconia felt and a Grafoil sheet.

The explosive loading assembly consisted of a poly vinyl chloride (PVC) tube into which a

120” gypsum cone was cast. The apex of the cone was lined with a Detasheet booster and filled

with ammonium nitrate mixed with 6-weight-percent fuel oil (ANFO) explosive with a density of

0.9 g/cm3 and detonation velocity of 3,480 m/s. Such a cone-initiated explosive charge assembly

provided a much more uniform pressure loading in comparison to that generated using

sweeping-wave initiation of the explosive charge [32,40].

7
Loose powder of the same composition as that of the reactant mixture was placed on the top of

the greenform. The powder was ignited by an electric match using a 115-V source; this, in turn, set

off the reaction between Ti and B or Ti and C in the greenform. The combustion wave traveled

down toward the bottom surface of the greenform, and the completion of the reaction was verified

using a chromel-alumel thermocouple attached to the surface of the momentum trap. Time to

detonation (time delay between reaction completion and explosive compaction) was varied in an

attempt to enhance the densities of the compacts. The same experimental setup was used for the

synthesis of both TiB2 and Tic.

The experimental conditions employed for the Ti-B and Ti-C systems are summarized in

Table 2. The fixture used for the Ti-B system was 200 mm in diameter, whereas both 200~mm and

300~mm fixtures were used for the Ti-C system. Both the C/M ratio and delay time had significant

influences on the product quality. The C/M ratio reflects the pressure applied to the samples during

the explosion. While a low C/M ratio might not generate a pressure sufficient to fully compact the

sample, a high C/M ratio could cause severe cracks and delamination in the sample due to strong

rarefaction forces and edge effects from the shock waves. The C/M ratio suggested in reports by

Niiler et al. [30] was 0.22 for the Ti-B system and 0.44 for the Ti-C system. The difficulty of

compacting Tic compared to TiBz is reflected in the higher C/M ratio. Since the compressive yield

strength at 1,800” C is 50 MPa for Tic [46] and 441 MPa for TiB2 [48], a mechanism other than

plastic deformation was probably involved. It has been postulated by Niiler et al. [30] that the

melting point of TiB2 was exceeded during the SHS process, whereas that of Tic was not. This

implies that TiB2 can be compacted more easily than Tic during SHWDC because of the presence

of some liquid phase. A C/M ratio of 0.2 was used for the Ti-B system, and two C/M ratios, 0.4

and 0.6, were used for the Ti-C system in this research.

The delay time influences the temperature at which the sample is compacted. A longer delay

time usually means a lower temperature. If the delay time is too long, the compaction of the sample

would be difficult due to the lack of plasticity at low temperatures. If, however, the delay time is

too short, delamination of the sample could occur due to the after-burn phenomenon, leading to a

8
Table 2. Experimental Conditions for the SHS/DC of TiB2 and TiC

TC9243 1 C/Ti = 0.95: 1 0.6 5 300 I

-

low density [32]. The optimum delay time depends on the system. Generally, the higher the

reaction temperature, the longer the optimal delay tune. The delay time was varied from 5 to 20 s

in the present experiments.

4.4 Characterization. Samples for analysis were cut using a diamond saw from four areas

within the compacts to examine the uniformity of the microstructural and mechanical properties. A

schematic illustrating the locations of the four areas from which specimens were taken is given in

Figure 2. Three specimens were taken from the center of the compact at varying distances from the

impact surface compact top (CT), compact center (CC), and compact bottom (CB). Another

specimen was taken from the area halfway between the compact center and the edge, middle

center (MC). These specimens permitted an assessment of the transverse and radial uniformity.

4.41 Density. Density was measured for specimens cut from the central region using the

Archimedes water displacement technique. The specimens were boiled in water for at least 2 hr to

ensure that all open pores were filled with water. The displacement of water by each specimen was

used to calculate the volume of the specimen. The density of stoichiometric TiB2 (4.57 kg/cm3) and

that of TiCo.9 (4.88 kg/cm3) [27] were used to calculate the relative densities of the TiBz and Tic

samples, respectively.

9
The second letter refers to the vertical position

Top

Center

Botom

Impact Surface

Non-impact Surface

The first letter refers/to the radial position

Figure2. Illustration of Four Major Areas From Which Samples Were Obtained to

Evaluate the Uniformity in Microstructure and Properties.

The pore sizes of selected samples were analyzed using a Micromeritics Model 93 10 pore sizer.

Mercury porosimetry is based on the capillary law governing liquid penetration into small pores.

This law, in the case of nonwetting liquids like mercury and cylindrical pores, is expressed by the

following equation [49],

d = -(l/p)4ycos~ , (1)

where d is the pore diameter, p is the applied pressure, y is the surface tension (485 dynkm), and 0

is the contact angle (130’).

4.4.2 Composition. Phase constituents in the SHS reacted, and explosively densified compacts

were determined by x-ray diffraction (XRD) using a Rigaku diffractometer. An energy-dispersive

spectrometer attached to a Hitachi S-800 scanning electron microscope (SEM) was used to

qualitatively analyze the composition of each phase, especially that of any secondary phases or

impurities. The compositions of selected phases were quantitatively analyzed by electron

microprobe analysis using a low-Z window detector capable of detecting B and C. The Ti content

in each phase was assayed against a pure Ti standard. The B/Ti and C/Ti atomic ratios were

calculated by assuming that the only other element was B in the TiB2 grams and C in the Tic

grains.

10
4.4.3 Microstructure. Specimens were polished sequentially using diamond pastes with grit

sizes of 45,30,15,6, and 1 pm. The polished samples were etched prior to microstructural analysis

using a solution of two parts HNOs, one part CHsCOOH, and one part HF. The microstructure was

examined using an SEM. Gram sizes were determined from the SEM micrographs using the linear

intercept technique developed by Mendelson [50], according to the following equation:

D = 1.57 C/O, (2)

where D is the gram size, C is the length of the test line, M is the magnification of the micrograph,

and N is the number of grain boundary intercepts. The proportionality constant relates the grain

size to the intercept length of a random section though a space-filling array of grains. At least four

micrographs were taken from each area in the compact. Ten lines were drawn randomly on each

micrograph. The average gram size was obtained from over 40 line measurements, which included

several hundred grains and therefore provided a statistically reliable value.

4.4.4 Microhardness. Microhardness was measured by the Knoop indentation technique with

a load of 0.1 kg. The hardness tests were performed on the specimens from all four areas in the

compact. Between 20 and 30 indentations were made in each area to obtain a statistically

significant result. The effect of grain boundary strength on hardness was examined by increasing

the load to 5 and 10 kg.

4.4.5 Young’s Modulus. The Young’s moduli of selected materials were measured based on

the velocity of sound through the specimens. The device used for the measurements consisted of a

pulse circuit, transducer, and oscilloscope. A trigger generator in the system activated an electric

switch, which produced large amplitude pulses. These pulses were applied to a transducer, which

converted them into short ultrasonic pulses. The pulse wave bounced back and forth within the

specimen. Each of the reflections was received by the transducer, and a train of echoes could be

observed on the oscilloscope. The velocity of sound in the specimen was obtained by dividing

11
twice the thickness of the specimen by the time between two successive reflections. The Young’s

modulus, E, was calculated using the following equation [5 11:

E=pu2 9 (3)

where p is the density of the specimen and u is the sound velocity in the specimen.

4.4.6 Compressive Strength. The compressive strength of selected samples was measured

using an INSTRON system. The specimens, with dimensions of 3.6 x 3.6 x 7.2 mm, were prepared

using a surface grinder. The two ends of the specimens were carefully ground so that they were

parallel to each other. Two larger blocks of the same material were used as spacers between the

rams and the test bar. A spherical seat was used to ensure good alignment.

5. Results and Discussion

5.1 TiB2.

5.1.1 Physical Appearance of Compacts. The SHS reacted and explosively compressed

compacts were usually recovered as single piece plates 100 mm in diameter with 25 mm thickness.

A photograph of the impact surface of TB9225 is shown in Figure 3(a). The surface was smooth.

The steel ring maintained its shape with no signs of melting or failure. No major cracks were

observed, but some edge delamination occurred. For some samples synthesized from the ultrapure

B-2 powder (like TB9246, which is shown in Figure 3@]), the surfaces were much rougher and the

steel rings were distorted or partially melted. Severe cracks were observed in these samples.

The results indicated the effect of the powder composition on the synthesis and consolidation of

the samples. The TB9244 sample was synthesized using the same processing condition as those

used for TB9224 except that the former used the B-2 powder rather than the B-l powder. The

TB9244 sample showed severe cracks and was blown into pieces. This might be related to the

12
_. _-

8 r, Lx- :! :i .J ‘1 .a 2

_ y -. ^.. _ - -. .-

..-_ _--- _

(a) TB9225. (b) TB9246.

Figure 3. Photographs of the TiB2 Samples Showing Impact Surfaces.

different reactivities and, hence, different temperatures generated using the two powders Since the

heat of reaction is lower for Tic, C in the B-l powder may have acted as a diluent and reduced the

violence of the reaction. A 5-s delay time seemed adequate for successful compaction of the

samples when using the B-l powder. For the samples prepared using the B-2 powder, a 15-s delay

time yielded the best results. A shorter (TB9244) or longer (TB9246) delay time caused severe

CEiCkS.

5.1.2 Density. The density, grain size, hardness, Young’s modulus, and compressive strength

of the TiB2 samples are presented in Table 3. The relative density of TB9225 was 99.3% of the

theoretical density. This result indicated that it was not necessary to use ultrapure B powders to

achieve high density. The target density for TiB2 in this Phase I project was 98% of the theoretical

density. The lowest density was obtained for TB9246 (~85% of the theoretical density). While the

diminished density for TB9246 compared to the other specimens may have been a consequence of

using the purer B powder (a more violent reaction and failure of the steel containment), it is

believed that the primary reason was that the delay time (20 s) was too long, resulting in sample

compaction at a relatively low temperature.

13
Table 3. Density, Grain Size, Hardness, Young’s Modulus, and Compressive Strength of

SHSIDC T&

Relative Young’s Compressive

Sample Density Grain Sizea Hardnessa Modulus Strength

(%) (Pm) (kg/mm2) (Gpa) (Gpa)

CT: 20+4 CT: 3351 z!z 443 548 z!z 18 1.8 zk 0.5

TB9224 97.2 cc: 19+4 cc: 3291+310 -

-

CB: 16+3 CB: 3309+274 -

-

MC: 17f3 MC: 3193+375 -

-

CT: 18+4 CT: 33562 438 -

-

CC: 18+3 CC: 3387f405 -

-

TB9225 99.3 CB: 17+4 CB: 3354 zk 431 -

-

MC: 17k4 MC: 3265+349 -

-

CT: 23+4 CT: 3273+610 -

-

-

TB9246 84.6 cc: 29+5 CC: 3277+393 -

CB: 29f7 CB: 3297+385 -

-

MC: 3029 MC: 3213+474 -

-

IT, CC, CB, and MC refer to the positions illustrated in Figure 2.

A comparison of the experimental results for TB9224 and TB9225 clearly demonstrated the

effect of delay time on the synthesis and compaction. The higher density for TB9225 relative to

TB9224 was probably due to compaction of the former, while the sample was at a higher

temperature (a shorter delay time), thus enhancing the densification through plastic deformation.

The density measured by the Archimedes immersion technique for TB9225 was further

confirmed by a porosity measurement, which showed a porosity of 0.4 volume-percent. The results

of mercury porosimetry analysis are shown in Figure 4. The total pore volume was 0.0008 cm3/g,

with l-, 4,12-, and 93-m-pore diameters, each accounting for 25% of the total pore volume.

5.1.3 Composition. XRD indicated that TB9225 consisted primarily of TiB2, with a small

amount of Tic (Figure 5[a]). There was no evidence of residual elemental Ti or B, indicating that

the synthesis reaction proceeded to completion. The Tic was the result of C impurity in the

precursor B powder (recall that B-l contained l-5% C). Electron microprobe analysis of the TiB2

14
I l

$ 2

“0

x

- 1.5

fz 1

>

.-6 0.5

i

E 0

Figure 4. Intrusion Volume Against Pore Diameter for TB9225 Determined by Mercury

Porosimetq Analysis.

grains showed that the B/Ti atomic ratio was 1.75. This corresponds to a B atomic fraction of 0.64,

which is within experimental error of the lower limit of the stoichiometric range for TiB2 (0.65), as

given in the Ti-B phase diagram [52].

The XRD pattern of TB9246 is shown in Figure 5(b). Again, TiB2 was the major phase, with

Tic being a minor constituent. The Tic content in TB9246 was much lower than that in the

samples prepared using the B-l powder. One of the peaks in the diffraction pattern has been

attributed to titanium carbonitride (TiCN). The formation of TiCN is possible because Tic and

titanium nitride (TiN) can form an infinite solid solution

5.1.4 Microstrwcture and Grain Size. Figure 6 shows an SEM micrograph of TB9225, the

densest TiB2 produced in this research. It shows a microstructure relatively free of porosity. This

observation further supported the density and porosity measurements. It should be pointed out that

pores larger than 10 pm were not observed by microscopy. The “large pores” revealed by mercury

porosimetry might actually be cracks in the sample. This would explain the absence of evidence of

large pores in the micrographs.

Figure 6. An SEM of TB9225.

The dark phase in the micrograph was due to TiB2 grams with shapes that were consistent with

a section cut through randomly oriented hexagonal single crystals. This supported the postulation

that the melting point of TiB2 was exceeded during the synthesis since single-crystal formation

could only occur during cool-down from a liquid phase [30].

The light gray phase in Figure 6 was identified as Tic with a C/Ti atomic ratio of 0.80 by

electron microprobe analysis. Some small but very bright white phases were also observed. These

were found, by energy dispersive spectrum analysis, to be an ahoy containing mainly Ti and iron

(Fe) with small amounts of nickel (Ni), vanadium (V), and chromium (Cr). These metal impurities

were probably present in the starting materials. The amount of the alloy phase was much less than

that of Tic. Both Tic and the metallic alloy were present primarily at the junctions of the TiB2

glXi.TlS.

The TiB2 grains in samples prepared using the B-l powder (II39224 and TB9225) were

relatively uniform in size, with diameters between 15 and 20 pm, depending on their location in the

17
compacts. It should be pointed out that almost every line drawn for grain size analysis intercepted

some secondary-phase particles. In order to avoid an inaccurate determination of the TiBs grain

size, the length intercepted by these secondary-phase particles was subtracted from the total length

so that the presence of the secondary phase did not alter the TiB2 grain size measurement.

For TB9246, which was prepared using the B-2 powder, no secondary phases were observed.

The average grain size for TB9246 was greater than those for TB9225 and TB9224 (prepared using

B-l powder). This seemed reasonable, considering that the delay time for TB9246 was 20 s,

whereas those for TB9224 and TB9225 were 10 and 5 s, respectively. Longer delay times would

permit the growth of larger grains. Furthermore, the reaction temperature for TB9246 may also

have been higher since the B-2 powder was purer than B-l. This was supported by the observation

that the steel rings used for containing the samples prepared using the B-2 powder always showed

some signs of melting. In contrast, the steel rings used for the samples prepared using the B-l

powder were intact after the reaction.

5.15 Microhardness. The values of Knoop microhardness measured for the three TiB2

samples were between ~3,200 and 3,400 kg/mm2. The hardness values measured on samples from

different areas were not significantly different. With such a low load (0.1 kg) and careful selection

of locations, indentations were made within TiB2 grains so that the effect of the grain boundaries on

the hardness was greatly reduced. The reported hardness for TiB2 ranges from 2,710 to

3,900 kg/mm2, depending on the microstructure of the specimen and test conditions [53]. The

hardness given in the literature measured under the same load (0.1 kg) was between 1,800 to

3,500 kg/mm2. Riley and Niiler [29] reported hardness values between 1,800 and 2,600 kg/mm2 for

SHS/DC TiB2, and between 2,500 and 3,500 kg/mm2 for hot-pressed TiB2. The hardness of TiB2

measured by Honak [54] under a load of 0.1 kg was 3,400 kg/mm2. Therefore, the microhardness

of the TiB2 compacts prepared in this research was in excellent agreement with the values reported

in the literature. Furthermore, the microhardness of the SHS/DC TiB2 was comparable to that of

the hot-pressed TiB2.

18
The effects of test load on the hardness were also examined. The results are shown in Figure 7.

When the test load was increased from 0.1 to 5 kg, the measured hardness of TB9225 and TB9224

decreased from 3,300 to 1,200 kg/mm2. Under a large load, the indentation covered more than

1 grain. The collapse of the gram boundaries resulted in a low value of the measured hardness.

This suggested weak grain boundary bonding. The weak gram boundary bonding might have been

caused by several factors. First, the individual particles produced by the SHS reaction were

randomly oriented. Although the high dynamic pressure could press them into dense body, there

was very little atomic-level bonding between grains since the cooling rate was so rapid that the

atoms at the gram boundaries did not have an opportunity to adjust

cooling rate could cause microcracks along the grain boundaries.

observed in the high-magnification micrographs. A microgap is

neighboring TiB2 grains in Figure 8.

themselves. Second, the rapid

These microcracks were often

clearly evident along the two

While the weak grain boundary bonding reduced the macrohardness, it may be beneficial for the

fracture toughness since debonding of the gram boundaries can effectively deflect cracks. This is

one of the major toughening mechanisms for ceramic materials. The measurement of fracture

toughness was not successful because there were usually no major cracks present when Vickers

indentations were made on these samples. The effect of grain boundary strength on the hardness

and toughness will be addressed during the Phase II effort. Perhaps a relationship between hardness

and fracture toughness can be developed.

In order to examine the effect of gram boundary bonding on the hardness, TB9225 was

annealed at 1,500 and 2,000” C in Ar for 7.5 hr. Boron nitride crucibles were used. The effect of

annealing on the hardness under different loads is shown in Figure 9. Annealing at 1,500” C

increased the hardness from about 1,100 to over 1,300 kg/mm2, whereas annealing at 2,000” C

further improved the hardness to 1,550 k@rnm2. Clearly, the grain boundary strength was improved

by annealing, although the improvement was not enough for the grain boundaries to withstand a

high load (i.e., 10 kg). Nevertheless, the results are promising and the concept of improving grain

boundary strength to produce engineering materials with high bulk hardness was demonstrated.

19
3600

w; 3200

E

2 2800

Y

‘;;

zi

2400

-s

;;i

2000

=: 1600

g 1200

800

0 2 4 6 8 10

Load (kg)

(a) TB9225.

3600 L

"E 3200

E

& 2800

Y

cn 2400

$

s 2000

ii

-L 1600

i?

g 1200

4

Load (kg:

8

(b) TB9224

F’igure 7. Effect of Test Load on Measured Hardness.

5.1.6 Young’s Modulus. The Young’s modulus of the TiB2 samples prepared by the SHS/DC

technique was comparable to or greater than that of the hot-pressed TiBi. The results are presented

in Table 3. The average of nine measurements was 54.8 zk 18 GPa. The Young’s modulus for

hot-pressed TiB2, reported by Koteh&ov et al. [55] and Samsonov [56], was 529 GPa.

20
Figure 8. Microcrack Along a Boundary Between Two TiBz Grains.

4 5 6 7 a 9

Load (kg)

Figure 9. Effect of Annealing Temperature on Hardness

Different Loads.

10 11

of TB9225 Measured Under
5.1.7 Compressive Strength. The compressive strength of the TiB2 prepared by the present

SHYDC technique was comparable to or in excess of hot-pressed TiB2. The value presented is the

average of three measurements. The compression test was diffkult because it required near-perfect

alignment of the test system. Any point contacts between the specimen and spacers, or between the

spacers and rams, could cause a local failure of the specimen or spacers, resulting in a false

measurement. Furthermore, internal defects in the specimens such as cracks could also affect the

test results. Therefore, it was expected that the measured compressive strength would vary. The

maximum value obtained was 2.51 GPa, while the average was 1.84 GPa. For the sample for

which the maximum compressive strength was recorded, failure was accompanied by a loud

explosion-like sound, much stronger than that for the other samples. The samples were usually

blown into pieces as a result of the sudden release of energy. The compressive strength of

hot-pressed TiB2 measured by Kotelnikov et al. [SS] was 1.62 GPa, whereas that reported by

Samsonov [56] was 1.32 GPa.

Figure 10 shows a cleavage surface for TB9225 after the compression test. It shows both

intergranular and transgranular fracture. It is interesting to note that, during the hardness test, the

fracture mode was observed to be predominantly intergranular. The existence of the transgranular

fracture in the compression-ruptured samples might be related to the sudden release of the high

energy stored in the sample during the test. This, in addition to the fact that the compressive

strength of the SHS-prepared Ti& was comparable to that of the hot-pressed TiB2, suggested that

the relatively weak grain boundaries did not result in a reduction in the compressive strength.

5.2. TIC.

5.2.1 Physical Appearance of Compacts. As was the case for the TiB2 compacts, the

SHS reacted and explosively compressed Tic compacts were recovered as single piece plates

(100 mm in diameter with 25 mm thickness). Photographs of the impact surfaces of TC9223 and

TC9242 are shown in Figure 11. The surfaces of the samples were smooth, and the steel rings

usually were not distorted. Two types of cracks were observed for the Tic samples: (1) major

22
Figure 10. A Cleavage Surface of the Sample TB9225 After the Compression Test. It Shows

Both Intergranular and Transgranular Fracture.

(a) 9223. (b) 9242.

Figure 11. Photographs of the Impact Surfaces.

23
cracks, often going through the samples, and (2) smaller cracks, with a much higher number

density. The cracks resulted from residual strains, which may have been caused by the temperature

gradients within the compacts during cooling. It is expected that the outer surfaces of the compacts

cooled at faster rates than did the cores. Should the residual thermal stresses not be released by

plastic deformation, cracks would form as a result. Potential reasons that Tic was more prone to

cracking than TiB2 are its lower heat of reaction and higher thermal expansion coefficient [40].

5.2.2 Density. Samples TC9223 and TC9242 were analyzed for density, composition, grain

size, and microhardness. Sample TC9223 was further analyzed to determine its Young’s modulus

and compressive strength. Some of the results are presented in Table 4. The density was 96.7% of

the theoretical density for Tic0.90. The target density for Tic in this Phase I project was 95% of the

theoretical density.

Table4. Density, Grain Size, Hardness, Young’s Modulus, and Compressive Strength of

SHSLDC TiC

3, CC, CB, and MC refer to positions given in Figure 2.

5.2.3 Composition. The XRD pattern of TC9223 is shown in Figure 12. The only phase

present was Tic. There was no evidence of residual elemental Ti or C, indicating that the synthesis

reaction proceeded to completion. No secondary phases were observed, perhaps due to the use of

pure starting materials. Electron probe microanalysis of the Tic grains showed that the C/Ti atomic

24
10. 20. 30. 40. 50. 60. 70. 80.

TWO THETA ANGLE

Figure 12. XRD Pattern of TC9223.

ratio was 0.85 + 0.04. This corresponds to a C atomic fraction of 0.46, which is within the

stoichiometric range for Tic, as given in the Ti-C-phase diagram [52].

5.2.4 Microstructure and Grain Size. Figure 13 shows an SEM of TC9223. The Tic grains

were more equiaxed than the TiB2 grains; however, the Tic grains were not of uniform size, as was

the case for the TiBz samples. The Tic grains in some areas were coarse (~100 p), whereas those

in other areas were fine (~20 p). The average was between 35 and 43 p. The average grain size

in the area close to the impact surface was slightly larger than that in the area close to the nonimpact

surface.

Most of large pores (up to several micrometers in diameter) were on the grain boundaries. They

were most likely residual pores from the greenfonn. The small pores (ccl p) were

25
Figure 13. An SEM of TC9223.

predominantly within the Tic grains. They might have resulted from the formation of volatile

products during the reaction.

52.5 Microhardness. The Knoop microhardness values of TC9223 and TC9242 were

approximately 3,000 kg/rnm2. As was the case for the TiB2 samples, the hardness measured for the

TIC sample from different areas was similar. The microhardness measured for the present

TiCcompacts was generally in agreement with those reported in the literature. More importantly,

the microhardness of the SHWDC TiC was comparable to that of the hot-pressed Tic. The

reported hardness for Tic ranges from 1,500 to 3,200 kg/mm2. The hardness reported by Kieffer

and Kiilbl [57], for the same load used in this research (0.1 kg), was 3,200 kg/mm2. Riley and

Niiler [29] reported values between 1,500 and 2,700 kg/mm2 for SHWDC Tic, and between 2,400

and 3,100 kg/mm2 for hot-pressed Tic. The discrepancy between reported values has been

attributed to differences in the microstructures of the specimens and/or the test conditions [5].

The effects of test load on the hardness were also examined for TC9223 and TC9242. The

results are shown in Figure 14. The hardness decreased from 3,000 to 1,500 kg/rnm2, as the test

load was increased from 0.1 to 5 kg. Further increases in the load did not result in a significant

26
; 2500

t!

$ 2000

I

1000 i

,

3600

q 3200

5 2800

Y

i 2400

i 2000

; 1600

Y

s 1200

800

0 5

Load (kg)

(a) TC9223,

I , 1 I , , , , , , ( ( , , ,

0 2 4

hati (kg;

8 10

(b) TC9242

Figure 14. Effects of Test Load on the Hardness of TiC Samples.

further reduction in the hardness. This reduction in hardness with test load was related to weak

grain boundaries; however, it was noticed that the decrease in hardness with test load was less

dramatic for Tic than for TiB2. The hardness of TiB2 measured under a test load of 5 kg was only

1,200 kg/mm2, whereas that for Tic was 1,500 kg/mrn2. Note that the hardness of TiB2 measured

under a load of 0.1 kg was higher (=3,400 kg/mrn2) than that of Tic (~3,000 kg/mm2). These

results suggest that the grain boundary strength in Tic was greater than that in TiB2 and that Tic

might be superior to TiB2 for some hardness applications.
The sample TC9223 was annealed at 1,500 and 2,000” C for 7.5 hr in an Ar atmosphere to

examine the effect of grain boundary strength on the hardness measured under different loads. The

result is shown in Figure 15. Annealing at 1,500” C did not increase the hardness (the exceptional

data point under a test load of 10 kg might be due to the nonuniformity of the Tic microstructure).

Annealing at 2,000” C for 7.5 hr significantly increased the hardness measured under a test load of

5 kg but did not increase the hardness measured under a test load of 10 kg. The less dramatic effect

of annealing on the hardness of Tic compared to TiB2 might be due to the higher melting

temperature of TiC and the stronger initial grain boundary bonding for Tic.

7 800

ti$- 1700

g 1600

5 1500

1 1400

g 1300

z1200

8 1100

1000

*As-synthesized

~1000 “C 7.5

4 5 6 7 8 9 10 11

bad (kg)

Figure 15. Effect of Annealing Temperature on the Hardness of TC9223 Under Different

Loads.

5.2.6 Young’s Modulus. The Young’s modulus of Tic prepared by SHS/DC was 548 + 14.

This value is the average of seven measurements. The elastic moduli reported by Samsonov [58],

were 45 1 GPa; that by McMurtry et al. [59] were 531 GPa; and that by Kingery, Bowen, and

Uhlmann [60] were 310 GPa. The present result was in good agreement with the Young’s modulus

reported by Samsonov.

5.2.7 Compressive Strength. The compressive strength of Tic was 1.0 + 0.2 GPa (average of

three measurements). The measured compressive strength was lower than the value reported by

Samsonov (1.35 GPa) [SS]. This might be due to the extensive cracks present in our TiC

*

28
samples. The cracks could cause local failures in the samples, resulting in lower compressive

strengths. Figure 16 is a cleavage surface of the sample TC9223 after the compression test. Similar

to observations for TB9225, a mode including both intergranular and transgranular fractures was

observed for TC9223. The transgranular fracture might be due to the sudden release of strain

energy stored in the sample.

F’igure 16. A Cleavage Surface of TC9223 After the Compression Test,

6. Summary

The primary objective of this Phase I effort was to produce plates of TiB2 at 98% of theoretical

density and Tic at 95% of theoretical density using the SHS and DC technique. The compositional,

microstructural, and mechanical properties of these materials were evaluated.

29
TiB2 and Tic compacts with diameters of 100 mm and thicknesses of 25 mm were fabricated

successfully. Theoretical densities of 99% for TiB2 and almost 97% for Tic were achieved, thus

satisfying the primary goal of this research. The hardnesses measured using a load of 0.1 kg for

SHS/DC TiB2 and Tic averaged 3,286 and 2,975 kg/mm2 (32.2 and 29.2 GPa), respectively. The

hardness decreased as the applied load was increased, indicating that the grain boundaries were

relatively weak. Annealing in Ar at temperatures greater than or equal to 1,500” C increased the

hardness measured at a load of 5 kg. The Young’s moduli were 548 GPa for TiB2 and 458 GPa for

Tic, and the compressive strengths were 1.8 GPa for TiB2 and 1.0 GPa for Tic. The mechanical

properties of these SHSAX ceramics were comparable to or greater than those reported for

materials prepared by conventional hot-pressing methods.

It was found that the TiB2 plates prepared using the less-pure B powders (l-5% C impurity) had

mechanical properties comparable to those of plates prepared using the pure powders. According to

projections by Niiler et al. [30], the raw materials costs could account for 66% of the total

production cost for SHWDC TiB2 and about 23% for SHS/DC Tic, if pure precursors are

employed. If, as indicated by the present experimental results, high-quality TiB2 and Tic plates can

be produced from less-pure powders or mixtures of B and C without sacrificing the density and/or

mechanical properties, the total production costs could be greatly reduced.

30
I .

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11,

12.

7. References

Wilkins, M. L. “2nd Progress Report of Light Armor Program.” UCRL-50349, Lawrence

Radiative Laboratory, University of California, Livermore, CA, 1976.

Wilkins, M. L., R. L. Landingham, and C. A. Honodel. “5th Progress Report of Light

Armor Program. UCRL-50349, Lawrence Radiative Laboratory, University of California,

Livermore, CA, 1976.

Samsonov, G. V., and B. A. Kovenskaya. Boron and Refractory Borides. P. 5,

V. I. Matkovich (editor), Berlin, Germany: Springer-Verlag, 1977.

Toth, L. E. Transition Metal Carbides and Nitrides. New York, NY: Academic Press,

1971.

Storms, E. K. The Refractory Carbides. New York, NY: Academic Press. 1967.

Yamada, O., Y. Maimed, and M. Koizumi. “High Pressure Self-Combustion Sintering of

Silicon Carbide.” American Ceramic Society Bulletin, vol. 64, no. 2, pp. 319-321, 1985.

Holt, J. B., D. D. Kingman, and G. M. Bianchini. “Kinetics of Combustion Synthesis of

TiB2.” Materials Science and Engineering, vol. 71, pp. 321-327, 1985.

Rice, R. W., and W. J. McDonough. “Intrinsic Volume Changes of Self-Propagating

Synthesis.” Journal of American Ceramic Society, vol. 68, no. 5, pp. C122-Cl23, 1985.

Holt J. B., and Z. A. Munir. “Combustion Synthesis of Titanium Carbide: Theory and

Experiment.” Journal of Materials Science, vol. 21, no. 1, pp. 251-259,1986.

Hirao, K., Y. Maimed, and M. Koizumi. “Sintering of S&N4 Powders Synthesized by a

Combustion Reaction.” Yogyo Kyokai Shi, vol. 95, no. 10, pp. 955-960,1987.

Munir, Z. A. “Synthesis of High Temperature Materials by Self-Propagating Combustion

Methods.” American Ceramic Society Bulletin, vol. 67, no. 2, pp. 342-348, 1988.

Dunmead, S. D., D. W. Ready, and C. E. Semler. “Kinetics of Combustion Synthesis in the

Ti-C and Ti-C-Ni Systems.” Journal of American Ceramic Society, vol. 72, no. 12,

pp. 23 18-2324,1989.

.

.3. Munir, Z. A., and U. Ansehni-Tamburini. ‘Self-Propagating Exothermic Reactions: The

Synthesis of High Temperature Materials by Combustion.” Materials Science Report,

vol. 3, no. 7-8, pp. 277-365,1989.

31
14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

Choi, Y., M. E. Mullins, K. Wijayatilleke, and J. K. Lee. “Processing Effects on the

Morphology of Titanium Carbide in Self-Propagating High-Temperature Synthesis.” High

Temperature Technology, vol. 8, no. 3, pp. 227-229, 1990.

Trambukis, J., and 2. A. Munir. “Effect of Particle Dispersion on the Mechanism of

Combustion Synthesis of Titanium Silicide.” Journal of the American Ceramic Society,

vol. 73, no. 5, pp. 1240-1245, 1990.

Eslamloo-Grami, M., and Z. A. Munir. “Effect of Porosity on the Combustion Synthesis of

Titanium Nitride.” Journal ofthe American Ceramic Society, vol. 73, no. 5, pp. 1235-1239,

1990.

Agrafiotis, C. C., J. Lis, J. A. Puszynski, and V. Hlavacek. “Combustion Synthesis of

Silicon Nitride-Silicon Carbide Composites.” Journal of the American Ceramic Society,

vol. 73,no. ll,pp. 3514-3517,199O.

Yi, H. C., and J. J. Moore. “Self-Propagating High-Temperature Combustion Synthesis

(SHS) of Powder-Compacted Materials.” Journal of Materials Science, vol. 25, no. 2B,

pp. 1159-l 168,199O.

Deevi, S. C. “Structure of the Combustion Wave in the Combustion Synthesis of Titanium

Carbide.” Journal of Materials Science, vol. 26, no. 10, pp. 2662-2670,1991.

Rice, R. W. “Microstructural Aspects of Fabricating Bodies by Self-Propagating Synthesis.”

Journal of Materials Science, vol. 26, no. 24, pp. 6533-6541, 1991.

Zeng, J., Y. Maimed, and 0. Yamada. “Combustion Synthesis of SisNd-Sic Compisite

Powders.” Journal of the American Ceramic Society, vol. 74, no. 9, pp. 2197-2200, 1991.

Richardson, G. Y., R. W. Rice, W. J. McDonough, J. M. Kunetz, and T. Schroeter. “Hot

Pressing of Ceramics Using Self-Propagating Synthesis. “Ceramic Engineering and Science

Proceedings, vol. 7, no. 7-8, pp. 761-770,1985.

Zavitsanos, P. D., J. J. Gebhardt, and A. Gatti. “The Use of Self-Propagating

High-Temperature Synthesis of High-Density Titanium Diboride.” Combustion and Plasma

Synthesis of High Temperature Materials, pp. 170-178, Z. A. Munir and J. B. Holt (editors),

New York, NY: VCH Publishers, 1990.

Miyamoto, Y. “New Ceramic Processing Approaches Using Combustion Synthesis Under

Gas Pressure.” American Ceramic Society Bulletin, vol. 69, no. 4, pp. 686-690,1990.

Hirao, K., Y. Miyamoto, and M. Koizumi. “Synthesis of Silicon Nitride by a Combustion

Reaction Under High Nitrogen Pressure.” Journal of the American Ceramic Society,

vol. 69, no. 4, pp. C60-C61, 1986.

32
I

26,

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

Vecchio, K., J. C. LaSalvia, M. A. Meyers, and G. T. Gray, III. “Microstructural

Characterization of Self-Propagating High-Temperature Synthesis/Dynamically Compacted

and Hot-pressed Titanium Carbides.” Metallurgical Transactions A, vol. 23A, no. 1,

pp. 87-97,1992.

LaSalvia, J. C., L. W. Meyer, and M. A. Meyers. “Densification of Reaction-Synthesized

Titanium Carbide by High-Velocity Forging.” Journal of the American Ceramic Society,

vol. 75, no. 3, pp. 592-602, 1992.

Rice, R. W., W. J. McDonough, G. Y. Richardson, J. M. Kunetz, and T. Schroeter, “Hot

Rolling of Ceramics Using Self-Propagating High-Temperature Synthesis.” Ceramic

Engineering and Science Proceedings, vol. 7, no. 7-8, pp. 751-760, 1985.

Riley, M. A., and A. Niiler. “Low Pressure Compaction of SHS (Self-Propagating

High-Temperature Synthesis) Prepared Ceramics.” BRLMR-3574, U.S. Army BaIlistic

Research Laboratory, Aberdeen Proving Ground, MD, 1987.

Niiler, A., L. J. Kecskes, T. Kottke, P. H. Netherwood, Jr., and R. F. Benck, “Explosive

Consolidation of Combustion Synthesized Ceramics: Titanium Carbide (Tic) and Titanium

Diboride (TiBz).” BRL-TR-2951, U.S. Army Ballistic Research Laboratory, Aberdeen

Proving Ground, MD, 1988.

Niiler, A., L. J. Kecskes, and T. Kottke. “Shock Consolidation of Combustion-Synthesized

Ceramics.” Combustion of Plasma Synthesis of High Temperature Materials, pp. 309-3 14,

Z. A. Munir and J. B. Holt (editors), New York, NY: VCH Publishers, 1990.

Grebe, H. A. Private communication. New Mexico Institute of Mining and Technology,

Socorro, NM, 1991.

Kottke, T., L. J. Kecskes, and A. Niiler. “Control of Titanium Diboride SHS Reactions by

Inert Dilutions and Mechanical Constraint.” American Institute of Chemical Engineers

Journal, vol. 36, no. 10, pp. 1581-1584,199O.

Kecskes L. J., and A. Niiler. “Impurities in the Combustion Synthesis of Titanium

Carbide.” Journal of the American Ceramic Society, vol. 72, no. 4, pp. 655-661,1989.

Kecskes, L. J., T. Kottke, and A. Niiler. “Microstructural Properties of

Combustion-Synthesized and Dynamically-Consolidated Titanium Boride and Titanium

Carbide.” Journal of the American Ceramic Society, vol. 73, no. 5, pp. 1274-1282,199O.

Kottke, T., L., J. Kecskes, and A. Niiler. “Combustion Synthesis Dynamics Modeling.”

Combustion and Plasma Synthesis of High Temperature Materials, p. 238, Z. A. Munir and

J. B. Holt (editors), VCH, NY, 1990.

33
37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

47.

Kecskes, L. J., R. F. Benck, and P. H. Netherwood. “Dynamic Compaction of Combustion

Synthesized Hafnium Carbide.” Journal of the American Ceramic Society, vol. 73, no. 2,

pp. 383-387,199O.

Merzhanov, A. G. and I. P. Borovinskaya. “Self-Propagating High-Temperature Synthesis

of Refractory Inorganic Compounds.” Doklady Chemistry, vol. 204, no. 2, pp. 429-432,

1972.

Crider, J. F. “Self-Propagating High Temperature Synthesis - A Soviet Method for

Producing Ceramic Materials.” Ceramic Engineering Science Proceedings, vol. 3,

no. 9-10, pp. 519-537,1982.

Grebe, H. A. “High-Rate Chemical Reaction and Dynamic High-Pressure Processing of

Titanium Carbide Ceramics.” Ph.D. Thesis, New Mexico Institute of Mining and

Technology, Socorro, NM, 1996.

Cutler R. A., A. V. Virkar, and J. B. Holt. “Synthesis and Densification of Oxide-Carbide

Composites.” Ceramic Engineering and Science Proceedings, vol. 6, no. 7-8, pp. 715-728,

1985.

McCauley, J. W., N. D. Corbin, T. M. Resetar, and P. Wong. “Simultaneous Preparation

and Self-Sintering of Materials in the Titanium-Boron-Carbon System.” Ceramic

Engineering and Science Proceedings, vol. 3, no. 9-10, pp. 504-511, 1982.

Advani, A. H., N. N. Thadhani, H. A. Grebe, R. Heaps, C. Coffm, and T. Kottke. “Dynamic

Modelling of Material and Process Parameter Effects on Self-Propagating

High-Temperature Synthesis of Titanium Carbide Ceramics.” Journal of Materials Science,

vol. 27, no. 12, pp. 3309-3317, 1992.

Advani, A. H. Private communication. University of Texas at El Paso, El Paso, TX, 1991.

Yamada, O., Y. Maimed, and M. Koizumi. “High-Pressure Self-Combustion Sintering of

Titanium Carbide.” Journal of the American Ceramic Society, vol. 70, no. 9,

pp. C206-C208,1987.

Miracle, D. B., and H. A. Lips&. “Mechanical Properties of Fine-grained Substoichiometric

Titanium Carbide.” Journal of the American Ceramic Society, vol. 66, no. 8, pp. 592-597,

1983.

U.S. Army Research Laboratory. “Armor, Plate, Steel, Wrought, High-Hardness.”

Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD, 29 June

1990.

34
48.

L 49.

50.

51. Kittel, C. Introduction to Solid State Physics. New York, NY: John Wiley Sons, 1953.

52. Massalski, T. B., (editor-in chief). Binary Alloy Phase Diagrams. Vol. 1. Metals Park,

OH: American Society for Metals, 1986.

53.

54.

55.

56.

57.

58.

59.

60.

Ramberg, J. R., and W. S. Williams. “High Temperature Deformation of Titanium

Diboride.” Journal of Materials Science, vol. 22, no. 5, pp. 1815-1826, 1987.

Caste&n, G. W. Physical Chemistry. Reading, MA: Addison-Wesley, 1971.

Mendelson, M. I. “Average Grain Size in Polycrystalline Ceramics.” Journal of the

American Ceramic Society, vol. 52, no. 8, pp* 443-446, 1969.

McCohn, I. J. Ceramic Hardness. New York, NY. Plenum Press, 1990.

Honak, E. R. “Ueber Hochschmelzende Boride der Uebergangsmetalle und ein Neues

Darstellungsverfabren von Titan- und Zirkondiborid.” Thesis, Technische Hochschule,

Graz, Austria, 195 1.

Kotelnikov, R. B., N. Bashlykov, Z. G. Galiachbarov, and A. J. Kashtanov. Especially High

Melting Elements and Compounds. Isdatel’stvo Metallurgija, Moscow, 1969.

Samsonov, G. V. Refractory Compounds. Moscow, Russia: Mettalurgizdat, 1963.

Kieffer, R. and F. Kolbl. Powder Metallurgy Bulletin. Vol. 4, no. 1, pp. 4-17, Tungsten

Carbide-Free Hard Metals, 1949.

Samsonov, G. V. Plenum Press Handbook of High-Temperature Materials No. 2 Properties

Index. New York, NY: Plenum Press 1962.

McMurtry, C. H., W. D. G. Boecker, S. G. Seshadri, J. S. Zanghi, and J. E. Gamier.

“Microstructure and Material Properties of Sic-TiB2.” American Ceramic Society Bulletin,

vol. 66, no. 2, pp. 325-329, 1987.

Kingery, W. D., H. K. Bowen, and D. R. Uhlmann. Introduction to Ceramics. New York,

NY: John Wiley Sons, 1976.

35
blTENTIONALLYLEFTBLANK.

36
NO. OF

COPIES ORGANIZATION

2 DEFENSE TECHNICAL

INFORMATION CENTER

DTLC DDA

8725 JOHN J KINGMAN RD

STE 0944

FT BELVOIR VA 22060-62 18

1 HQDA

DAMOFDQ

D SCHMIDT

400 ARMY PENTAGON

WASHINGTON DC 20310-0460

1 OSD

OUSD(A&T)/ODDDR&E(R)

RJTREW

THEPENTAGON

WASHINGTON DC 20301-7100

1 DPTY CG FOR RDE HQ

usARMYMATERIELcMD

AMCRD

MG CALDWELL

5001 EISENHOWER AVE

ALEXANDRIA VA 22333-0001

1 INST FOR ADVNCD TCHNLGY

THE UNIV OF TEXAS AT AUSTIN

PO BOX 202797

AUSTIN TX 78720-2797

1 DARPA

B KASPAR

3701 N FAIRFAX DR

ARLINGTON VA 22203-1714

1 NAVAL SURFACE WARFARE CTR

CODE B07 J PENNELLA

17320 DAHLGREN RD

BLDG 1470 RM 1101

DAHLGREN VA 22448-5100

1 US MILITARY ACADEMY

MATH SC1 CTR OF EXCELLENCE

DEPT OF MATHEMATICAL SC1

MAJMDPHJLLIE’S

THAYERHALL

WEST POINT NY 10996-1786 ,

37

NO. OF

ORGANIZATION COPIES

1 DIRECTOR

US ARMY RESEARCH LAB

AMSRL D

RWWHALIN

2800 POWDER MJLL RD

ADELPHJ MD 20783-l 145

1 DIRECTOR

US ARMY RESEARCH LAB

AMSRLDD

J J ROCCHJO

2800 POWDER MILL RD

ADELPHI MD 20783-l 145

1 DIRECTOR

us ARMY RESEARCH LAB

AMSRL CS AS (RECORDS MGMT)

2800 POWDER MILL RD

ADELPHI MD 20783-I 145

3 DIRECTOR

USARMYRESEARCHLAB

AMSRL GILL

2800 POWDER MILL RD

ADELPHI MD 20783-l 145

ABERDEEN PROVING GROUND

4 DIR USARL

AMSRZ, CI LP (305)
NO. OF

COPIES ORGANIZATION

2 US ARMY ARDEC

D KAPOOR

S CYTRON

DOVER NJ 07801

NO. OF

COPIES

1

3 ARMY RSRCH OFFICE

A CROWSON

E CHEN 30

R REEBER

PO BOX 12211

RSRCH TRIANGLE PRK NC

22709-2211

1 BATTELLE PACIFIC NW

LABORATORIES

W GURWELL

PO BOX 999

RICHLAND WA 99352

1 PENNSYLVANIA STATE UNlV

DEPT ENGNR SCIENCES AND

MEcHANIcs

RGERMAN

227 HAMMOND BLDG

UNIVERSITY PARR PA

16802-1401

1 UNIV OF CALJFORNJA

SAN DIEGO

DEPT APPLIED MECHANICS

AND ENGNR SCIENCES

M MEYERS

MAIL CODE 0411

9500 GIL&IAN DRIVE

LA JOLLA CA 92093-0411

2 GEORGIA INST OF TECH

SCHL OF MTRL ENG

K LOGAN

NTHADHAN-I

ATLANTA GA 30332-0245

3 NEW MEXICO INST

OFMJNINGANDTECHCTR

FOR EXPLSV TECH AND RSRCH

AMBLER

P PERSSON

MTRLSANDMETENG

OINAL

SOCORRO NM 87801

ORGANIZATION

UNTV OF CALIFORNIA

COLLEGE OF ENGNRNG

ZMUNLR

DAVIS CA 95616

ABERDEEN PROVING GROUND

USARL

AMSRLWMTE

L KECSKES (15 CPS)

ANIILER

AMSRL WM TA

W GOOCH

W GILLICH

M BURIUNS

GHAUVER

THAVEL

E HORWATH

AMSRLWMTD

KFRANK

AMSRL WM TC

E KENNEDY

L MAGNESS

AMSRL WM MC

J LASALVIA

THYNES

J MCCAULEY

DVIECHNICKI

JWELLS

,

38
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 07040188

PuMlc reporting burden for this follecUon 01 lnlonnation Is ealimaed to dwage 1 hour pa raapomq Including the time for revvlswlng Inmtclfom. seaching e~sllng data SWSelf-Propagating High-Temperature Synthesis and Dynamic Compaction of

Titanium Boride and Titanium Carbide

C: DAAA 15-91-C-0088

Liya Wang and Levi T. Thompson

REPORT NUMBER

PO Box 2150

Ann Arbor, MI 48 106

9. SPONSORlNWMONlTORlNG AGENCY NAMES(S) AND ADDRESS 10.SPONSORlNG/MONITORlNG

AGENCY REPORT NUMBER

U.S. Army Research Laboratory

ATI’Nz AMSRL-WM-TE ARL-CR-440

Aberdeen Proving Ground, MD 210055066

11. SUPPLEMENTARY NOTES

Point of contact for this report is Dr. Laszlo Kecskes, U.S. Army Research Laboratory, ATIN A.MSRL-wM-T&

Aberdeen Proving Ground, MD 21005-5066.

12a. DISTRIBUTIONfAVAIlJBiLlTY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution is unilimited.

13. ABSTRACT(Maximum 200 words)

Titanium carbide (Tic) and titanium diboride (TiB,) ceramic disks, with diameters of 100 mm and thicknesses of 25 mm

vere fabricated with densities above 95% and 98% of theoretical, respectively, using a self-propagating high-temperature

:ynthesis/dynamic consolidation (SHS/DC) process. First, an SHS reaction was initiated in a green body made from

)recursor powders. Second, after the completion of the SHS reaction, the freshly synthesized ceramic product was

lensified to near-full density by the action of the detonation of an explosive. With a focus on potential military and

:ivilian applications, the structural and mechanical properties of the products were evaluated. Furthermore, the

elationship between process conditions, microstructure development, and mechanical properties was investigated. Finally,

:orrelations of the properties with key processing conditions were used to establish guidelines for the fabrication, scale-up,

nd commercialization of the process.

14. SUBJECT TERMS 15. NUMBER OF PAGES

titanium, carbon, boron, titanium carbide, titanium diboride, SHS, DC, 44

explosive compaction 16. PRICE CODE

17. SECURITY CLASSIRCATION 18. SECURlTY CLASSlFlCATlON 19. SECURlTY CLASSIFICATION 20. LIMITATION OF ABSTRACT

OF REPORT OF THIS PAGE OF ABSTRACT

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

NSN 7540-01-280-5500 39

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-l 8 298-l 02
INTENTIONALLY LEFT BLANK.

40
USER EVALUATION SHEET/CHANGE OF ADDRESS

This Laboratory undertakes a continuing effort to improve the quality of the reports it publishes. Your comments/answers

to the items/questions below will aid us-in our efforts.

1. ARL Report Number/Author ARL-CR-440 Cwanp; TPOC: Kecskesl) Date of Report Amill

2. Date Report Received

3. Does this report satisfy a need? (Comment on purpose, related project, or other area of interest for which the report will

be used.)

t

4. Specifically, how is the report being used? (Information source, design data, procedure, source of ideas, etc.)

5. Has the information in this report led to any quantitative savings as far as man-hours or dollars saved, operating costs

avoided, or efficiencies achieved, etc? If so, please elaborate.

6. General Comments. What do you think should be changed to improve future reports? (Indicate changes to organization,

technical content, format, etc.)

Organization

CURRBNT

ADDRESS

Name

Street or P.O. Box No.

E-mail Name

City, State, Zip Code

7. If indicating a Change of Address or Address Correction, please provide the Current or Correct address above and the Old

or Incorrect address below.

. Organization

OLD Name

> ADDRESS

Street or P.O. Box No.

City, State, Zip Code

(Remove this sheet, fold as indicated, tape closed, and mail.)

(DO NOT STAPLE)