Ceramic tantalum carbide artifacts with high thermal shock and mechanical erosion resistance are provided by incorporating tungsten-rhenium and carbon particles in a tantalum carbide matrix. The mix is sintered by hot pressing to form the ceramic article which has a high fracture strength relative to its elastic modulus and thus has an improved thermal shock and mechanical erosion resistance. The tantalum carbide is preferable less than minus 100 mesh, the carbon particles are preferable less than minus 100 mesh, and the tungsten-rhenium particles are preferable elongate, having a length to thickness ratio of at least 2/1. Tungsten-rhenium wire pieces are suitable as well as graphite particles

Honeycutt, L., III

Manning, C. R.

English

NASA Technical Reports Server

United States Patent 
Fletcher et al. 
[111 4,067,742 
[45] Jan. 10, 1978 
[54] THERMAL SHOCK AND EROSION 
RESISTANT TANTALUM CARBIDE 
CERAMIC MATERIAL 
[76] Inventors: James C. Flctckr, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Leroy Honeycutt, 111, 
Winston-Salem; Charles R. Man- 
ning, Jr., Raleigh, both of N.C. 
[21] Appl. No.: 672,695 
[22] Filed: Apr. 1, 1976 
[51] Int. Cl.2 .............................................. W B  35/52 
[52] U.S. Cl. ................................... 106/43; 60/200 A, 
75/229; 75/239; 75/241 
l[58] Field of Search ............................. 106/43, 55, 56; 
29A82.7, 182.8; 75/203, 204, 174, 229, 239, 
241; 60/200 A 
1561 References Cited 
U.S. PATENT DOCUMENTS 
1,936,435 11/1933 Kelley ................................. 29A82.7 
2,021,576 11/1935 McKenna ............................ 29A82.7 
2,039,822 5/1936 McKenna ....................... 29A82.7 X 
3,226,929 1/1966 McKenna ............................... 75/241 
3,379,520 4/1%8 Chang et al. ........................... 75/174 
3,779,716 12/1973 Riley et al. ........................ 75/204 X 
FOREIGN PATENT DOCUMENTS 
1,384,013 11/1964 France ................................ 29A82.7 
Primary Examiner-Helen M. McCarthy 
Attorney, Agent, or Firm-Howard J. Osborn; Wallace 
J. Nelson; John R. Manning 
[57l ABSTRACT 
Ceramic tantalum carbide artifacts having high thermal 
shock and mechanical erosion resistance are provided 
by incorporating tungsten-rhenium and carbon particles 
in a tantalum carbide matrix. The mix is sintered by hot 
pressing to form the ceramic article which has a high 
fracture strength relative to its elastic modulus and thus 
has an improved thermal shock and mechanical erosion 
resistance. The tantalum carbide is preferable less than 
minus 100 mesh, the carbon particles are preferable less 
than minus 100 mesh, and the tungsten-rhenium parti- 
cles are preferable elongate, having a length to thick- 
ness ratio of at least 2/1. Tungsten-rhenium wire pieces 
are suitable as well as graphite particles. 
14 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19780009263 2020-03-20T12:47:16+00:00Z
4,067,742 
1 
THERMAL SHOCK AND EROSION RESISTANT 
TANTALUM CARBIDE CERAMIC MATERIAL 
ORIGIN OF THE DISCLOSURE 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 STAT 435; 42 USC 2457). 
BACKGROUND OF THE INVENTION 
This invention relates to ceramic articles and to meth- 
ods of making same. More particularly, the invention 
relates to tantalum carbide articles and to methods of 
making same. 
There has long been a need for refractory materials 
‘capable of use in high temperature environments. Most 
recently, refractory materials have been developed for 
space applications. Typically, materials have been de- 
veloped for throat areas of solid propellant rocket noz- 
zles. These throat areas are subject not only to high 
temperatures and pressures but to severe thermal shock, 
to mechanical erosion, and to chemical erosion. Materi- 
als developed in the past for this application include 
graphite, tungsten, alumina, zirconia, and hafnia. How- 
ever, each of these materials lacks resistance to one or 
more of the above areas of degradation. Zirconia, hafnia 
and graphite, which having excellent thermal shock 
resistance, has poor chemical and mechanical erosion 
resistance. Tungsten is heavy, hard to fabricate, and has 
poor chemical erosion resistance. Alumina, on the other 
hand has poor thermal shock resistance. Applicants’ 
prior invention disclosed in U.S. Pat. No. 3,706,583, 
while adequate for the purposes intended, did not pro- 
vide the improved thermal, mechanical and chemical 
‘erosion resistance as the present invention disclosed and 
claimed herein. 
It is therefore an object of the present invention to 
provide an improved ceramic article having high ther- 
mal shock resistance. It is a further object to produce 
such an article having good mechanical and chemical 
erosion resistance at elevated temperatures. It is still a 
further object to provide such an article including tanta- 
lum carbide. 
BRIEF SUMMARY OF THE INVENTION 
The foregoing and other objects which will be appar- 
ent to those of ordinary skill in the art are achieved 
according to the present invention by providing a ce- 
ramic artifact comprising a tantalum carbide matrix and 
from one to five percent by weight for each addition 
based on the weight of the article, of either tungsten or 
tungsten-rhenium particles and carbon or graphite par- 
ticles distributed throughout said matrix. The article is 
made by providing a mixture of particles or tantalum 
carbide and from one to five percent by weight for each 
addition of tungsten or tungsten-rhenium particles and 
carbon or graphite particles, and hot pressing the mix- 
ture at a sintering temperature and pressure sufficient to 
produce an article of at least 85 percent of theoretical 
density . 
DETAILED DESCRIPTION 
There follows a detailed description of a preferred 
embodiment of the invention. However, it is to be un- 
derstood that the detailed description is solely for the 
purpose of illustrating a preferred embodiment and that 
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the invention is capable of numerous modifications and 
variations apparent to those skilled in the art without 
departing from the spirit and scope of the invention. 
EXAMPLES 
Tantalum carbide specimens were fabricated by a 
vacuum hot pressing technique. Cylindrical specimens 
varying in diameter from $ inch to 4 inch and height 
from one inch to inch were formed by induction heat- 
ing in conventional graphite dies. Contoured specimens 
averaging one inch in diameter (O.D.) and height vary- 
ing from one inch to 14 inches with an entrance inside 
diameter averaging C inch and exit inside diameter aver- 
aging 8 inch diameter were formed by induction heating 
in conventional graphite dies. The temperature is main- 
tained at or near 2150” C .  in a vacuum of less than 10 
microns of mercury. Pressures up to 8,000 pounds per 
square inch are applied during hot pressing. 
The graphite dies are machined from Carborundum 
Graphatite A or G for pressures to four thousand 
pounds per square inch and Poco Graphite HPD-1 for 
pressures above those. All rams and plugs are fabricated 
from Poco Graphite HPD-1 or HPD-3 graphite. Tanta- 
lum end shields are placed between the ram and speci- 
men to facilitate removal and to reduce carbon diffusion 
into the specimen. 
Pressure is supplied by a conventional hydraulic press 
through a bellows assembly into a vacuum body which 
is evacuated by a 6-inch diffusion pump backed by a 750 
standard cubic foot per minute mechanical pump. The 
graphite die is located inside a graphite and silica cloth 
lined induction coil within the vacuum chamber. The 
vacuum chamber is cooled by conventional water cir- 
culation in 3 inch tubing attached to the outside surface 
of the vacuum chamber. The temperature of the outside 
surface of the graphite die is read by a calibrated optical 
pyrometer through a series of sight ports through the 
vacuum chamber, coil and insulation. Die displacement 
readings for determination of densification termination 
is measured by a variable differential transducer and the 
output is read on a strip chart recorder. 
The tantalum carbide used in these examples as the 
matrix material is minus 325 mesh (Tyler) particle size 
and preferably of reactor grade although commercial 
grade may be used. 
Density determinations are by ASTM designation 
B311-58 entitled “Standard Method of Test for Density 
of Cemented Carbides” with no modifications. This 
technique is the immersion technique and distilled water 
is the immersion fluid used. 
Specimens having a diameter of one-half inch and a 
height varying from 4 inch to # inch are used to deter- 
mine the apparent modulus of elasticity and compres- 
sive fracture strength. The small height to diameter 
ratio is employed to reduce the effect of barreling on 
strain measurements obtained by SR-4 strain gages ce- 
mented to each specimen. 
Specimens are loaded in compression with a conven- 
tional tensile compressive testing machine. Strain is 
measured at intervals of 100 pounds static loading be- 
tween 500 and 2000 pounds load. Strain in micro inches 
per inch is read from 120 ohm gages having a gage 
factor of 2.01 by use of a balanced bridge potentiometer. 
Polyester films are placed between the specimen ends 
and the compressive platens to reduce sliding friction 
on the self-alining platens. Loading is cycled a minimum 
of three times with the specimen in three positions (9 
cycles total) to achieve reproducibility of strain read- 
4,067.742 
4 
ings. The values of stress are plotted against strain to 
assure linearity. Compressive fracture stress is given as 
that stress at which the first crack is observed to cause 
a discontinuity in the loading. 
Specimens are tested for thermal shock resistance by 
exposing them to an oxygen-acetylene flame at a tem- 
perature of approximately 5000" C. for a period of 30 
seconds and subsequently submerging them in stirred 
room temperature distilled water. The specimens nomi- 
nally one-half inch in diameter and varying from $ inch 
to inch in height, are heated from one end by the 
oxygen-acetylene flame. Specimen temperature aver- 
ages 2000" C .  before quenching. The difference in tem- 
tungsten-rhenium particles with the tantalum carbide 
particles. 
As shown in the following table, thermal shock resis- 
tance indicated by the ratio of compressive fracture 
5 stress to the modulus of elasticity, and the erosion resis- 
tance, indicated by the weight loss per 2.2 lbs of AI2O3 
is increased by the addition of tungsten or tungsten- 
rhenium and carbon or graphite particles. In addition, 
no specimens containing tungsten or tungsten-rhenium 
10 particles exhibited thermal spalling, thermal cracking or 
cracking from erosion. No specimen containing carbon 
or graphite was cracked by either thermal exposure or 
erosion. 
TABLE 1 
Wt % Ratio of compressive Wt. loss % Change 
Sample Wt % Carbon or fracture stress to per 2.21b in exit 
Number Tunesten eraohite modulus of elasticitv AI,O, diameter - - .  . >  
I 0 I 5.8 x lo-' ,458 I .6 
2 0 2 3.4 x lo-' ,283 2. I 
,283 1.6 3 0 3 2.6 x IO-' 
4 I I 5.3 x 10-3 ,246 0.5 
5 3 I 7.5 x lo-' ,153 0.5 
6 I 2 4.6 x IO-' .I96 1.4 
7 3 2 7.0 x 10-3 ,115 0.5 
8 5 2 2.1 x IO-'  .539 0.8 
9 0 0 1.6 x lo-' .483 1.8 
perature (AT) for thermal shock testing was approxi- Similar results are obtained by substituting a tung- 
mately 1900" C. The criteria for failure is either total sten-rhenium alloy for the tungsten shown in the above 
disintegration of the specimen or the presence of one or table and in essentially the same quantities. The term 
more macroscopic cracks traversing a portion or all of 'tungsten-rhenium' as used hereinafter denotes a tung- 
the specimen. The specimens were tested on both a one 30 sten wire alloyed with 25 weight percent of rhenium 
cycle and repeated cycle basis. based on the total wire weight. 
Specimens are tested for erosion resistance by expos- In view of the foregoing results, it is preferred to use 
ing them to an oxygen-acetylene flame until a tempera- from about 1 to about 5 percent by weight of tungsten 
ture of approximately 1800' C .  and subjecting them to or tungsten-rhenium and from about 1 to about 3 per- 
vertical impingement by 2.2 pounds of minus 325 mesh 35 cent by weight of carbon or graphite to achieve a sub- 
(Tyler) alumina particles at a velocity of 400 feet per stantial increase in the ratio of compressive fracture 
second. The specimens nominally one inch in outside stress to modulus of elasticity to substantially improve 
diameter and height varying from one inch to 14 inch thermal shock and erosion resistance. It is preferred to 
with an entrance diameter of inch and an exit diameter also use from about 1 to about 3 percent by weight of 
of inch, are heated on the inside contoured surface by 40 carbon or graphite to substantially improve thermal 
the oxygen-acetylene flame. Specimen temperature shock and erosion resistance. Erosion resistance mea- 
averages 1400" C. during the erosion testing. The crite- sured as the weight loss per 2.2 Ibs of A1203 or percent 
ria for failure is either total fracture by one or more change in exit diameter. Still more preferably, tungsten 
macroscopic cracks traversing a portion or all of the or tungsten-rhenium is used in an amount of from about 
specimen or a change in the exit diameter of more than 45 1 to about 3 percent by weight and carbon or graphite 
5%. Due to the phenomenal characteristics of erosion, a in an amount of from about 1 to about 2 percent by 
change in specimen weight of more than 0.50 grams was weight. 
used as a criteria for failure. The specimens were tested Thermal shock resistance is also related to density, 
on both a one-cycle and repeated-cycle basis. lower density articles having less thermal shock resis- 
Initially, base materials of the high density (98 per- 50 tance. In general, the density will be at least 80 percent 
cent of theoretical) and low density (80 percent of theo- of theoretical for most applications, with densities of 
retical) are exposed to the described thermal stress and about 85 percent of theoretical being preferred. 
erosion environments. Of these materials, the higher The tungsten and tungsten-rhenium particles are pref- 
density specimens exhibit the best thermal shock and erably elongate, having a lengthhhickness ratio of at 
erosion resistance. No spalling was evident in any speci- 55 least about 2/1. The size of the particles can vary 
mens. widely and is generally chosen for ease of blending 
The tungsten or tungsten-rhenium added to the tanta- uniformly with the tungsten carbide particles. In gen- 
lum carbide is in form of wire, 0.005 inches in diameter, eral, the thickness of the pieces will be up to about 0.05 
cut to a length of approximately one-quarter inch. The inches. The lengthkhickness ratio will generally be up 
tungsten or tungsten-rhenium are mechanically mixed 60 to about 100/1 and will be somewhat related to diame- 
with the tantalum carbide particles using a conventional ter. Wire pieces are preferred and wire having a diame- 
mixer. The carbon or graphite added to the tantalum ter of up to about 0.05 inches and a length/diameter 
carbide is in less than minus 200 mesh (Tyler) particles. ratio of 5/1 to 100/1 are preferred. The particle size of 
The carbon or graphite particles are mechanically the carbon or graphite is conventional and is preferably 
mixed using a conventional liquid to create a slurry and 65 at least minus 100 mesh, more preferably minus 200 
then dried. The carbon or graphite particles are wet mesh, and even more preferably less than minus 325 
mixed with the tantalum carbide particles and allowed mesh for most applications, particularly where high 
to dry before mechanically dry mixing the tungsten or density is concerned. 
5 
4,067,742 
6 
The hot pressing process of making the article is ness of up to about 0.05 inches and a length/thickness 
conventional and conventional temperatures and pres- ratio of at least 2/1. 
sures for the hot pressing of ceramic artifacts are em- 5. A ceramic artifact according to claim 4 wherein 
Wwed. In general, the temperature is at least 1700" C. the metal particles are wire pieces having a length- 
and a temperature of about 2150" C. is preferred. Con- 5 /diameter ratio of between 5/1 and 100/1. 
ventional pressures'required to achieve desired density 6. A ceramic artifact as in claim 1 wherein the carbon 
are employed, typical pressures being from to or graphite particles are between minus 100 mesh and 
10,ooO pounds per square inch. minus 
The particle size of the tantalum carbide is conven- a ceramic article having high 
tional and is preferably at least minus 100 mesh, more 10 resistance to thermal shock comprising the steps of 
a metal selected from the group consisting of tungsten where high density is desired. 
pansion, coefficient of heat transfer, and Poisson's Ratio 15 cent by weight of carbon or graphite particles and hot 
also affect thermal shock resistance. Factors such as pressing the mixture in the temperature range of from hardness, velocity of impinging particles, and particle 1700" c. to 2150" c. and at a pressure to pro- shape also affect erosion resistance. However, these are duce an article of at least to 85 percent of theoretical 'either affected favorably or only slightly unfavorably density. by the present invention. The major effect is a change in 20 8. A method according to claim 7 wherein the mix- the ratio of compressive fracture stress to modulus of ture is hot pressed at a pressure in the range of loo0 to elasticity which increases both thermal shock and ero- 
10,OOO pounds per square inch. sion resistance. 
What is claimed as new and desired to be secured by 9. A method according to claim 7 wherein the tanta- 
25 lum carbide particles are in the range of minus 100 mesh Letters Patent of the United States is: 
1. A ceramic artifact adaptable for use in throat areas 
,of rocket nozzles and the like which consists of a hot- 
pressed composite of at least 80 to 85 percent of theoret- 
ical density of a tantalum carbide matrix and from one 
to five percent by weight, based on the weight of the 30 a lengthithickness ratio Of at least 2/1- 
article, of particles of a metal selected from the group 
consisting of tungsten and tungsten-rhenium alloy, and 
from one to three percent by weight based on the 
weight ofthe article, ofcarbon or graphite particles and 
wherein the tantalum carbide matrix is formed from the 35 least 2/10 
group consisting of reactor grade and commercial grade 
particles. 
2. A ceramic artifact according to claim 1 wherein 
the metal is tungsten and the amount of tungsten is from 
one to three weight percent. 
3. A ceramic artifact according to claim 1 wherein 
the metal is tungsten-rhenium and the amount of tung- 
sten-rhenium alloy is from one to three weight percent. 
4. A ceramic artifact according to claim 1. wherein 
said metal particles are elongate pieces having a thick- 45 
7. A method of 
preferably minus 200 mesh and even more preferably 
particularly 
providing a mixture of particles of.commercia] grade 
tantalum carbide, from one to five percent by weight of 300 mesh for 
Other factors such as the coefficient Of ex- and tungsten-rhenium alloy, and from one to three per- 
and 
is tungsten and the tungsten particles are 
pieces having a thickness of up to about 0.05 inches and 
l1- A method according to claim 7 wherein the metal 
is tungsten-rhenium alloy and the tungsten-rhenium 
alloy particles are Wire pieces having a thickness Of up 
to about 0.05 inches and a lengthkhickness ratio of at 
12. A method according to claim 7 wherein the metal 
particles are elongate wire pieces having a length/diam- 
eter ratio of at least 5/1. 
13. A method according to claim 7 wherein the car- 
40 bon or graphite particles are in the size range of minus 
100 mesh to minus 325 mesh. 
14. A method according to claim 7 wherein the metal 
i s  tungsten wire alloyed with 25 percent weight of rhe- 
nium. 
300 mesh size. 
10. A method according to claim 7 Wherein the metal 
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Thermal shock and erosion resistant tantalum carbide ceramic material

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