Gamma titanium aluminum alloys modified by carbon, chromium and niobium

A TiAl composition is prepared to have high strength and to have improved ductility by altering the atomic ratio of the titanium and aluminum to have what has been found to be a highly desirable effective aluminum concentration by addition of chromium, carbon and niobium according to the approximate formula Ti.sub.51-43 Al.sub.46-50 Cr.sub.2 Nb.sub.1-5 C.sub.0.1.

CROSS REFERENCE TO RELATED APPLICATIONS 
The subject application relates to copending applications as follows: Ser. 
Nos. 138,407, 4,836,983, 138,408, 138,476, 4,857,268, 138,481, 4,842,819, 
138,486, filed Dec. 28, 1987; 4,842,820 Ser. No. 201,984, filed Jun. 3, 
1988; 4,879,902 Ser. Nos. 252,622, 253,659, filed Oct. 3, 1988; Ser. No. 
293,035, filed Jan. 3, 1989. 
The texts of these related applications are incorporated herein by 
reference. 
BACKGROUND OF THE INVENTION 
The present invention relates generally to alloys of titanium and aluminum. 
More particularly, it relates to gamma alloys of titanium and aluminum 
which have been modified both with respect to stoichiometric ratio and 
with respect to addition of a combination of additive elements. 
It is known that as aluminum is added to titanium metal in greater and 
greater proportions the crystal form of the resultant titanium aluminum 
composition changes. Small percentages of aluminum go into solid solution 
in titanium and the crystal form remains that of alpha titanium. At higher 
concentration of aluminum (including about 25 to 35 atomic %) an 
intermetallic compound Ti.sub.3 Al is formed. The Ti.sub.3 Al has an 
ordered hexagonal crystal form called alpha-2. At still higher 
concentrations of aluminum (including the range of 50 to 60 atomic % 
aluminum) another intermetallic compound, TiAl, is formed having an 
ordered tetragonal crystal form called gamma. 
The alloy of titanium and aluminum having a gamma crystal form, and a 
stoichiometric ratio of approximately one, is an intermetallic compound 
having a high modulus, a low density, a high thermal conductivity, 
favorable oxidation resistance, and good creep resistance. The 
relationship between the modulus and temperature for TiAl compounds to 
other alloys of titanium and in relation to nickel base superalloys is 
shown in FIG. 2. As is evident from the figure, the TiAl has the best 
modulus of any of the titanium alloys. Not only is the TiAl modulus higher 
at higher temperature but the rate of decrease of the modulus with 
temperature increase is lower for TiAl than for the other titanium alloys. 
Moreover, the TiAl retains a useful modulus at temperatures above those at 
which the other titanium alloys become useless. Alloys which are based on 
the TiAl intermetallic compound are attractive lightweight materials for 
use where high modulus is required at high temperatures and where good 
environmental protection is also required. 
One of the characteristics of TiAl which limits its actual application to 
such uses is a brittleness which is found to occur at room temperature. 
Also, the strength of the intermetallic compound at room temperature needs 
improvement improvement before the TiAl intermetallic compound can be 
exploited in certain structural component applications. Improvements of 
the TiAl intermetallic compound to enhance ductility and/or strength at 
room temperature are very highly desirable in order to permit use of the 
compositions at the higher temperatures for which they are suitable. 
With potential benefits of use at light weight and at high temperatures, 
what is most desired in the TiAl compositions which are to be used is a 
combination of strength and ductility at room temperature. A minimum 
ductility of the order of one percent is acceptable for some applications 
of the metal composition but higher ductilities are much more desirable. A 
minimum strength for a composition to be useful is about 50 ksi or about 
350 MPa. However, materials having this level of strength are of marginal 
utility for certain applications and higher strengths are often preferred 
for some applications. 
The stoichiometric ratio of gamma TiAl compounds can vary over a range 
without altering the crystal structure. The aluminum content can vary from 
about 50 to about 60 atom percent. However, the properties of gamma TiAl 
compositions are, however, subject to very significant changes as a result 
of relatively small changes of one percent or more in the stoichiometric 
ratio of the titanium and aluminum ingredients. Also, the properties are 
similarly significantly affected by the addition of relatively similar 
small amounts of additive elements. 
I have now discovered that further improvements can be made in the gamma 
TiAl intermetallic compounds by incorporating therein a combination of 
additive elements so that the composition contains a combination of these 
additive elements. 
Furthermore, I have discovered that the composition including the 
combination of additive elements has a uniquely desirable combination of 
properties which include appreciably strength, a significantly higher 
ductility and a valuable oxidation resistance. 
PRIOR ART 
There is extensive literature on the compositions of titanium aluminum 
including the Ti.sub.3 Al intermetallic compound, the TiAl intermetallic 
compounds and the TiAl.sub.3 intermetallic compound. A patent, U.S. Pat. 
No. 4,294,615, entitled "TITANIUM ALLOYS OF THE TiAl TYPE" contains an 
extensive discussion of the titanium aluminide type alloys including the 
TiAl intermetallic compound. As is pointed out in the patent in column 1, 
starting at line 50, in discussing TiAl's advantages and disadvantages 
relative to Ti.sub.3 Al: 
"It should be evident that the TiAl gamma alloy system has the potential 
for being lighter inasmuch as it contains more aluminum. Laboratory work 
in the 1950's indicated that titanium aluminide alloys had the potential 
for high temperature use to about 1000.degree. C. But subsequent 
engineering experience with such alloys was that, while they had the 
requisite high temperature strength, they had little or no ductility at 
room and moderate temperatures, i.e., from 20.degree. to 550.degree. C. 
Materials which are too brittle cannot be readily fabricated, nor can they 
withstand infrequent but inevitable minor service damage without cracking 
and subsequent failure. They are not useful engineering materials to 
replace other base alloys". 
It is known that the alloy system TiAl is substantially different from 
Ti.sub.3 Al (as well as from solid solution alloys of Ti) although both 
TiAl and Ti.sub.3 Al are basically ordered titanium aluminum intermetallic 
compounds. As the '615 patent points out at the bottom of column 1: 
"Those well skilled recognize that there is a substantial difference 
between the two ordered phases. Alloying and transformational behavior of 
Ti.sub.3 Al resemble those of titanium, as the hexagonal crystal 
structures are very similar. However, the compound TiAl has a tetragonal 
arrangement of atoms and thus rather different alloying characteristics. 
Such a distinction is often not recognized in the earlier literature." 
The '615 patent does describe the alloying Of TiAl with vanadium and carbon 
to achieve some property improvements in the resulting alloy. 
The '615 patent also discloses in Table 2 alloy T.sub.2 A-112 which is a 
composition in atomic percent of Ti-45Al-5.0Nb but the patent does not 
describe the composition as having any beneficial properties. 
A number of technical publications dealing with the titanium aluminum 
compounds as well as with the characteristics of these compounds are as 
follows: 
1. E. S. Bumps, H. D. Kessler, and M. Hansen, "Titanium-Aluminum System", 
Journal of Metals, June 1952, pp. 609-614, TRANSACTIONS AIME, Vol. 194. 
2. H. R. Ogden, D. J. Maykuth, W. L. Finlay, and R. I. Jaffee, "Mechanical 
Properties of High Purity Ti-Al Alloys", Journal of Metals, February 1953, 
pp. 267-272, TRANSACTIONS AIME, Vol. 197. 
3. Joseph B. McAndrew, and H. D. Kessler, "Ti-36 Pct Al as a Base for High 
Temperature Alloys", Journal of Metals, October 1956, pp. 1348-1353, 
TRANSACTIONS AIME, Vol. 206. 
The McAndrew reference discloses work under way toward development of a 
TiAl intermetallic gamma alloy. In Table II, McAndrew reports alloys 
having ultimate tensile strength of between 33 and 49 ksi as adequate 
"where designed stresses would be well below this level". This statement 
appears immediately above Table II. In the paragraph above Table IV, 
McAndrew states that tantalum, silver and (niobium) columbium have been 
found useful alloys in inducing the formation of thin protective oxides on 
alloys exposed to temperatures of up to 1200.degree. C. FIG. 4 of McAndrew 
is a plot of the depth of oxidation against the nominal weight percent of 
niobium exposed to still air at 1200.degree. C. for 96 hours. Just above 
the summary on page 1353, a sample of titanium alloy containing 7 weight % 
columbium (niobium) is reported to have displayed a 50% higher rupture 
stress properties than the TiAl-36 %Al used for comparison. 
4. Patrick L. Martin, Madan G. Mendiratta, and Harry A. Lispitt, "Creep 
Deformation of TiAl and TiAl +W Alloys", Metallurgical Transactions A, 
Volume 14A (October 1983) pp. 2171-2174. 
5. P. L. Martin, H. A. Lispitt, N. T. Nuhfer, and J. C. Williams,"The 
Effects of Alloying on the Microstructure and Properties of Ti.sub.3 Al 
and TiAl", Titanium 80. (Published by American Society for Metals, 
Warrendale, PA), Vol. 2, pp. 1245-1254. 
6. Tokuzo Tsujimoto,"Research, Development, and Prospects of TiAl 
Intermetallic Compound Alloys", Titanium and Zirconiummm, Vol. 33, No. 3, 
159 (July 1985) pp. 1-19. 
7. H. A. Lipsitt,"Titanlum Aluminides--An Overview", Mat.Res.Soc. Symposium 
Proc., Materials Research Society, Vol. 39 (1985) pp. 351-364. 
8. S. H. Whang et al., "Effect of Rapid Solidification in Ll.sub.o TiAl 
Compound Alloys", ASM Symposium Proceedings on Enhanced Properties in 
Struc.Metals Via Rapid Solidification, Materials Week (October 1986) pp. 
1-7. 
9. Izvestiya Akademii Nauk SSSR, Metally. No. 3 (1984) pp. 164-168. 
10. P. L. Martin, H. A. Lipsitt, N. T. Nuhfer and J. C. Williams, "The 
Effects of Alloying on the Microstructure and Properites of Ti.sub.3 Al 
and TiAl", Tittanium 80 (published by the American Society of Metals, 
Warrendale, PA), Vol. 2 (1980) pp. 1245-1254. 
U.S. Pat. No. 3,203,794 (Jaffee) discloses many TiAl compositions. A carbon 
containing TiAl is indicated to be much harder than the base composition 
(320 vs. 200 Vickers hardness) and consequently to be much less ductile. 
As Jaffee states, starting at column 3, line 59: 
"Carbon, oxygen and nitrogen have a potent hardening action when present 
even in small amounts. Thus, the hardness of the Ti-37.5%Al is increased 
from about 200 to 320 Vickers by additions of 0.25% of each of C, O and 
N." 
U.S. Pat. No. 4,661,316 (Hashimoto) teaches doping TiAl with 0.1 to 5.0 
weight percent of manganese, as well as doping TiAl with combinations of 
other elements with manganese. At column 2, line 58, Hashimoto suggests 
adding 0.02 to 0.12% carbon to the manganese doped TiAl. However, at line 
63, Hashimoto indicates ductility is decreased in stating: 
"The addition of carbon increases high-temperature strength although 
decreasing ductility." 
Accordingly, the prior art teaches that the addition of carbon to a ductile 
TiAl composition decreases ductility. 
BRIEF DESCRIPTION OF THE INVENTION 
One object of the present invention is to provide a method of forming a 
titanium aluminum intermetallic compound having greatly improved 
ductility, and related other properties at room temperature. 
Another object is to improve the ductility properties of titanium aluminum 
intermetallic compounds at low and intermediate temperatures. 
Another object is to improve the combination of ductility of TiAl base 
compositions together with a set of other favorable properties. 
Yet another object is to make improvements in a set of ductility and 
strength properties. 
Other objects will be in part apparent, and in part pointed out, in the 
description which follows. 
In one of its broader aspects, the objects of the present invention are 
achieved by providing a nonstoichiometric gamma TiAl base alloy, and 
adding a relatively low concentration of chromium; a low concentration of 
niobium and a lower concentration of carbon to the nonstoichiometric 
composition. Addition of chromium in the order of approximately 1 to 3 
atomic percent; of niobium to the extent of 1 to 5 atomic percent and 
carbon to the extent of 0.05 to 0.3 percent is contemplated. 
As used herein, the term "gamma TiAl base alloy" designates a base alloy 
including titanium and aluminum and which may include also, in addition to 
designated additives, other additives in kind and amount which do not 
interfere with or detract from the good combination of properties of the 
base alloy. 
If the composition is rapidly solidified, it may be consolidated as by 
isostatic pressing and extrusion to form a solid composition of the 
present invention. However, the alloy of this invention may be produced in 
ingot form and may be processed by ingot metallurgy to achieve highly 
desirable combinations of ductility, strength and other beneficial 
properties.

DETAILED DESCRIPTION OF THE INVENTION 
There are a series of background and current studies which led to the 
findings on which the present invention, involving the combined addition 
of carbon, niobium and chromium to a gamma TiAl are based. The first 
twenty five examples deal with the background studies and the later 
examples deal with the current studies. 
EXAMPLES 1-3 
Three individual melts were prepared to contain titanium and aluminum in 
various stoichiometric ratios approximating that of TiAl. The 
compositions, annealing temperatures and test results of tests made on the 
compositions are set forth in Table I. 
For each example, the alloy was first made into an ingot by electro arc 
melting. The ingot was processed into ribbon by melt spinning in a partial 
pressure of argon. In both stages of the melting, a water-cooled copper 
hearth was used as the container for the melt in order to avoid 
undesirable melt-container reactions. Also, care was used to avoid 
exposure of the hot metal to oxygen because of the strong affinity of 
titanium for oxygen. 
The rapidly solidified ribbon was packed into a steel can which was 
evacuated and then sealed. The can was then hot isostatically pressed 
(HIPped) at 950.degree. C. (1740.degree. F.) for 3 hours under a pressure 
of 30 ksi. The HIPping can was machined off the consolidated ribbon plug. 
The HIPped sample was a plug about one inch in diameter and three inches 
long. 
The plug was placed axially into a center opening of a billet and sealed 
therein. The billet was heated to 975.degree. C. (1787.degree. F.) and was 
extruded through a die to give a reduction ratio of about 7 to 1. The 
extruded plug was removed from the billet and was heat treated. 
The extruded samples were then annealed at temperatures as indicated in 
Table I for two hours. The annealing was followed by aging at 1000.degree. 
C. for two hours. Specimens were machined to the dimension of 1.5 .times.3 
.times.25.4 mm (0.060 .times.0.120 .times.1.0 in.) for four point bending 
tests at room temperature. The bending tests were carried out in a 4-point 
bending fixture having an inner span of 10 mm (0.4 in.) and an outer span 
of 20 mm (0.8 in.). The load-crosshead displacement curves were recorded. 
Based on the curves developed, the following properties are defined: 
(1) Yield strength is the flow stress at a cross head displacement of one 
thousandth of an inch. This amount of cross head displacement is taken as 
the first evidence of plastic deformation and the transition from elastic 
deformation to plastic deformation. The measurement of yield and/or 
fracture strength by conventional compression or tension methods tends to 
give results which are lower than the results obtained by four point 
bending as carried out in making the measurements reported herein. The 
higher levels of the results from four point bending measurements should 
be kept in mind when comparing these values to values obtained by the 
conventional compression or tension methods. However, the comparison of 
measurements'results in many of the examples herein is between four point 
bending tests, and for all samples measured by this technique, such 
comparisons are quite valid in establishing the differences in strength 
properties resulting from differences in composition or in processing of 
the compositions. 
(2) Fracture strength is the stress to fracture. 
(3) Outer fiber strain is the quantity of 9.71hd, where"h" is the specimen 
thickness in inches, and"d" is the cross head displacement of fracture in 
inches. Metallurgically, the value calculated represents the amount of 
plastic deformation experienced at the outer surface of the bending 
specimen at the time of fracture. 
The results are listed in the following Table I. Table I contains data on 
the properties of samples annealed at 1300.degree. C. and further data on 
these samples in particular is given in FIG. 3. 
TABLE I 
______________________________________ 
Gam- Outer 
ma Anneal 
Yield Fracture 
Fiber 
Ex. Alloy Composit. Temp Strength 
Strength 
Strain 
No. No. (at. %) (.degree.C.) 
(ksi) (ksi) (%) 
______________________________________ 
1 83 Ti.sub.54 Al.sub.46 
1250 131 132 0.1 
1300 111 120 0.1 
1350 * 58 0 
2 12 Ti.sub.52 Al.sub.48 
1250 130 180 1.1 
1300 98 128 0.9 
1350 88 122 0.9 
1400 70 85 0.2 
3 85 Ti.sub.50 Al.sub.50 
1250 83 92 0.3 
1300 93 97 0.3 
1350 78 88 0.4 
______________________________________ 
* No measurable value was found because the sample lacked sufficient 
ductility to obtain a measurement 
A plot of the crosshead displacement in mils against applied load in pounds 
for these three alloys in relation to an alloy containing chromium 
additive is given in FIG. 3. 
It is evident from the data of this Table and from FIG. 3 that alloy 12 for 
Example 2 exhibited the best combination of properties. This confirms that 
the properties of Ti-Al compositions are very sensitive to the Ti/Al 
atomic ratios and to the heat treatment applied. Alloy 12 was selected as 
the base alloy for further property improvements based on further 
experiments which were performed as described below. 
It is also evident that the anneal at temperatures between 1250.degree. C. 
and 1350.degree. C. results in the test specimens having desirable levels 
of yield strength, fracture strength and outer fiber strain. However, the 
anneal at 1400.degree. C. results in a test specimen having a 
significantly lower yield strength (about 20% lower); lower fracture 
strength (about 30% lower) and lower ductility (about 78% lower) than a 
test specimen annealed at 1350.degree. C. The sharp decline in properties 
is due to a dramatic change in microstructure due, in turn, to an 
extensive beta transformation at temperatures appreciably above 
1350.degree. C. 
EXAMPLES 4-13 
Ten additional individual melts were prepared to contain titanium and 
aluminum in designated atomic ratios as well as additives in relatively 
small atomic percents. 
Each of the samples was prepared as described above with reference to 
Examples 1-3. 
The compositions, annealing temperatures, and test results of tests made on 
the compositions are set forth in Table II in comparison to alloy 12 as 
the base alloy for this comparison. 
TABLE II 
__________________________________________________________________________ 
Outer 
Gamma Yield 
Fracture 
Fiber 
Ex. 
Alloy Composition 
Anneal Strength 
Strength 
Strain 
No. 
No. (at. %) Temp (.degree.C.) 
(ksi) 
(ksi) (%) 
__________________________________________________________________________ 
2 12 Ti.sub.52 Al.sub.48 
1250 130 180 1.1 
1300 98 128 0.9 
1350 88 122 0.9 
4 22 Ti.sub.50 Al.sub.47 Ni.sub.3 
1200 * 131 0 
5 24 Ti.sub.52 Al.sub.46 Ag.sub.2 
1200 * 114 0 
1300 92 117 0.5 
6 25 Ti.sub.50 Al.sub.48 Cu.sub.2 
1250 * 83 0 
1300 80 107 0.8 
1350 70 102 0.9 
7 32 Ti.sub.54 Al.sub.45 Hf.sub.1 
1250 130 136 0.1 
1300 72 77 0.2 
8 41 Ti.sub.52 Al.sub.44 Pt.sub.4 
1250 132 150 0.3 
9 45 Ti.sub.51 Al.sub.47 C.sub.2 
1300 136 149 0.1 
10 57 Ti.sub.50 Al.sub.48 Fe.sub.2 
1250 * 89 0 
1300 * 81 0 
1350 86 111 0.5 
11 82 Ti.sub.50 Al.sub.48 Mo.sub.2 
1250 128 140 0.2 
1300 110 136 0.5 
1350 80 95 0.1 
12 39 Ti.sub.50 Al.sub.46 Mo.sub.4 
1200 * 143 0 
1250 135 154 0.3 
1300 131 149 0.2 
13 20 Ti.sub.49.5 Al.sub.49.5 Er.sub.1 
+ + + + 
__________________________________________________________________________ 
* See asterisk note to Table I 
+ Material fractured during machining to prepare test specimens 
Measurement of the properties of alloy 45 of Example 9 demonstrated that 
the addition of carbon to a ductile TiAl drastically reduced the ductility 
by about 90%. 
For Examples 4 and 5, heat treated at 1200.degree. C., the yield strength 
was unmeasurable as the ductility was found to be essentially nil. For the 
specimen of Example 5 which was annealed at 1300.degree. C., the ductility 
increased, but it was still undesirably low. 
For Example 6, the same was true for the test specimen annealed at 
1250.degree. C. For the specimens of Example 6 which were annealed at 
1300.degree. and 1350.degree. C. the ductility was significant but the 
yield strength was low. 
None of the test specimens of the other Examples were found to have any 
significant level of ductility. 
It is evident from the results listed in Table II that the sets of 
parameters involved in preparing compositions for testing are quite 
complex and interrelated. One parameter is the atomic ratio of the 
titanium relative to that of aluminum. From the data plotted in FIG. 3, it 
is evident that the stoichiometric ratio or nonstoichiometric ratio has a 
strong influence on the test properties which formed for different 
compositions. 
Another set of parameters is the additive chosen to be included into the 
basic TiAl composition. A first parameter of this set concerns whether a 
particular additive acts as a substituent for titanium or for aluminum. A 
specific metal may act in either fashion and there is no simple rule by 
which it can be determined which role an additive will play. The 
significance of this parameter is evident if we consider addition of some 
atomic percentage of additive X. 
If X acts as a titanium substituent, then a composition Ti.sub.48 Al.sub.48 
X.sub.4 will give an effective aluminum concentration of 48 atomic percent 
and an effective titanium concentration of 52 atomic percent. 
If, by contrast, the X additive acts as an aluminum substituent, then the 
resultant composition will have an effective aluminum concentration of 52 
percent and an effective titanium concentration of 48 atomic percent. 
Accordingly, the nature of the substitution which takes place is very 
important but is also highly unpredictable. 
Another parameter of this set is the concentration of the additive. 
Still another parameter evident from Table II is the annealing temperature. 
The annealing temperature which produces the best strength properties for 
one additive can be seen to be different for a different additive. This 
can be seen by comparing the results set forth in Example 6 with those set 
forth in Example 7. 
In addition, there may be a combined concentration and annealing effect for 
the additive so that optimum property enhancement, if any enhancement is 
found, can occur at a certain combination of additive concentration and 
annealing temperature so that higher and lower concentrations and/or 
annealing temperatures are less effective in providing a desired property 
improvement. 
The content of Table II makes clear that the results obtainable from 
addition of a ternary element to a nonstoichiometric TiAl composition are 
highly unpredictable and that most test results are unsuccessful with 
respect to ductility or strength or to both. 
EXAMPLES 14-17: 
A further parameter of the gamma titanium aluminide alloys which include 
additives is that combinations of additives do not necessarily result in 
additive combinations of the individual advantages resulting from the 
individual and separate inclusion of the same additives. 
Four additional TiAl based samples were prepared as described above with 
reference to Examples 1-3 to contain individual additions of vanadium, 
niobium, and tantalum as listed in Table III. These compositions are the 
optimum compositions reported in copending applications Ser. Nos. 138,476, 
138,408, and 138,485, respectively. 
The fourth composition is a composition which combines the vanadium, 
niobium and tantalum into a single alloy designated in Table III to be 
alloy 48. 
From Table III, it is evident that the individual additions vanadium, 
niobium and tantalum are able on an individual basis in Examples 14, 15, 
and 16 to each lend substantial improvement to the base TiAl alloy. 
However, these same additives when combined into a single combination 
alloy do not result in a combination of the individual improvements in an 
additive fashion. Quite the reverse is the case. 
In the first place, the alloy 48 which was annealed at the 1350.degree. C. 
temperature used in annealing the individual alloys was found to result in 
production of such a brittle material that it fractured during machining 
to prepare test specimens. 
Secondly, the results which are obtained for the combined additive alloy 
annealed at 1250.degree. C. are very inferior to those which are obtained 
for the separate alloys containing the individual additives. 
In particular, with reference to the ductility, it is evident that the 
vanadium was very successful in substantially improving the ductility in 
the alloy 14 of Example 14. However, when the vanadium is combined with 
the other additives in alloy 48 of Example 17, the ductility improvement 
which might have been achieved is not achieved at all. In fact, the 
ductility of the base alloy is reduced to a value of 0.1. 
Further, with reference to the oxidation resistance, the niobium additive 
of alloy 40 clearly shows a very substantial improvement in the 4 
mg/cm.sup.2 weight loss of alloy 40 as compared to the 31 mg/cm.sup.2 
weight loss of the base alloy. The test of oxidation, and the 
complementary test of oxidation resistance, involves heating a sample to 
be tested at a temperature of 982.degree. C. for a period of 48 hours. 
After the sample has cooled, it is scraped to remove any oxide scale. By 
weighing the sample both before and after the heating and scraping, a 
weight difference can be determined. Weight loss is determined in 
mg/cm.sup.2 by dividing the total weight loss in grams by the surface area 
of the specimen in square centimeters. This oxidation test is the one used 
for all measurements of oxidation or oxidation resistance as set forth in 
this application. 
For the alloy 60 with the tantalum additive, the weight loss for a sample 
annealed at 1325.degree. C. was determined to be 2 mg/cm.sup.2 and this is 
again compared to the 31 mg/cm.sup.2 weight loss for the base alloy. In 
other words, on an individual additive basis both niobium and tantalum 
additives were very effective in improving oxidation resistance of the 
base alloy. 
However, as is evident from Example 17, results listed in Table III alloy 
48 which contained all three additives, vanadium, niobium and tantalum in 
combination, the oxidation is increased to about double that of the base 
alloy. This is seven times greater than alloy 40 which contained the 
niobium additive alone and about 15 times greater than alloy 60 which 
contained the tantalum additive alone. 
TABLE III 
__________________________________________________________________________ 
Outer 
Gamma Yield 
Fracture 
Fiber 
Weight Loss 
Ex. 
Alloy 
Composit. 
Anneal 
Strength 
Strength 
Strain 
After 48 hours 
No. 
No. (at. %) Temp (.degree.C.) 
(ksi) 
(ksi) 
(%) @ 98.degree. C. (mg/cm.sup.2) 
__________________________________________________________________________ 
2 12 Ti.sub.52 Al.sub.48 
1250 130 180 1.1 * 
1300 98 128 0.9 * 
1350 88 122 0.9 31 
14 14 Ti.sub.49 Al.sub.48 V.sub.3 
1300 94 145 1.6 27 
1350 84 136 1.5 * 
15 40 Ti.sub.50 Al.sub.46 Nb.sub.4 
1250 136 167 0.5 * 
1300 124 176 1.0 4 
1350 86 100 0.1 * 
16 60 Ti.sub.48 Al.sub.48 Ta.sub.4 
1250 120 147 1.1 * 
1300 106 141 1.3 * 
1325 * * * * 
1325 * * * 2 
1350 97 137 1.5 * 
1400 72 92 0.2 * 
17 48 Ti.sub.49 Al.sub. 45 V.sub.2 Nb.sub.2 Ta.sub.2 
1250 106 107 0.1 60 
1350 + + + * 
__________________________________________________________________________ 
* Not measured 
+ Material fractured during machining to prepare test specimen 
The individual advantages or disadvantages which result from the use of 
individual additives repeat reliably as these additives are used 
individually over and over again. However, when additives are used in 
combination the effect of an additive in the combination in a base alloy 
can be quite different from the effect of the additive when used 
individually and separately in the same base alloy. Thus, it has been 
discovered that addition of vanadium is beneficial to the ductility of 
titanium aluminum compositions and this is disclosed and discussed in the 
copending application for patent Ser. No. 138,476. Further, one of the 
additives which has been found to be beneficial to the strength of the 
TiAl base and which is described in copending application Ser. No. 
138,408, filed Dec. 28, 1987, as discussed above, is the additive niobium. 
In addition, it has been shown by the McAndrew paper discussed above that 
the individual addition of niobium additive to TiAl base alloy can improve 
oxidation resistance. Similarly, the individual addition of tantalum is 
taught by McAndrew as assisting in improving oxidation resistance. 
Furthermore, in copending application Ser. No. 138,485, it is disclosed 
that addition of tantalum results in improvements in ductility. 
In other words, it has been found that vanadium can individually contribute 
advantageous ductility improvements to gamma titanium aluminum compound 
and that tantalum can individually contribute to ductility and oxidation 
improvements. It has been found separately that niobium additives can 
contribute beneficially to the strength and oxidation resistance 
properties of titanium aluminum. However, the Applicant has found, as is 
indicated from this Example 17, that when vanadium, tantalum, and niobium 
are used together and are combined as additives in an alloy composition, 
the alloy composition is not benefited by the additions but rather there 
is a net decrease or loss in properties of the TiAl which contains the 
niobium, the tantalum, and the vanadium additives. This is evident from 
Table III. 
From this, it is evident that, while it may seem that if two or more 
additive elements individually improve TiAl that their use together should 
render further improvements to the TiAl, it is found, nevertheless, that 
such additions are highly unpredictable and that, in fact, for the 
combined additions of vanadium, niobium and tantalum a net loss of 
properties result from the combined use of the combined additives together 
rather than resulting in some combined beneficial overall gain of 
properties. 
However, from Table III above, it is evident that the alloy containing the 
combination of the vanadium, niobium and tantalum additions has far worse 
oxidation resistance than the base TiAl 12 alloy of Example 2. Here, 
again, the combined inclusion of additives which improve a property on a 
separate and individual basis have been found to result in a net loss in 
the very property which is improved when the additives are included on a 
separate and individual basis. 
EXAMPLES 18 thru 23: 
Six additional samples were prepared as described above with reference to 
Examples 1-3 to contain chromium modified titanium aluminide having 
compositions respectively as listed in Table IV. 
Table IV summarizes the bend test results on all of the alloys, both 
standard and modified, under the various heat treatment conditions deemed 
relevant. 
TABLE IV 
__________________________________________________________________________ 
Outer 
Gamma Yield 
Fracture 
Fiber 
Ex. 
Alloy Composition 
Anneal Strength 
Strength 
Strain 
No. 
No. (at. %) 
Temp (.degree.C.) 
(ksi) 
(ksi) (%) 
__________________________________________________________________________ 
2 12 Ti.sub.52 Al.sub.48 
1250 130 180 1.1 
1300 98 128 0.9 
1350 88 122 0.9 
18 38 Ti.sub.52 Al.sub.46 Cr.sub.2 
1250 113 170 1.6 
1300 91 123 0.4 
1350 71 89 0.2 
19 80 Ti.sub.50 Al.sub.48 Cr.sub.2 
1250 97 131 1.2 
1300 89 135 1.5 
1350 93 108 0.2 
20 87 Ti.sub.48 Al.sub.50 Cr.sub.2 
1250 108 122 0.4 
1300 106 121 0.3 
1350 100 125 0.7 
21 49 Ti.sub.50 Al.sub.46 Cr.sub.4 
1250 104 107 0.1 
1300 90 116 0.3 
22 79 Ti.sub.48 Al.sub.48 Cr.sub.4 
1250 122 142 0.3 
1300 111 135 0.4 
1350 61 74 0.2 
23 88 Ti.sub.46 Al.sub.50 Cr.sub.4 
1250 128 139 0.2 
1300 122 133 0.2 
1350 113 131 0.3 
__________________________________________________________________________ 
The results listed in Table IV offer further evidence of the criticality of 
a combination of factors in determining the effects of alloying additions 
or doping additions on the properties imparted to a base alloy. For 
example, the alloy 80 shows a good set of properties for a 2 atomic 
percent addition of chromium. One might expect further improvement from 
further chromium addition. However, the addition of 4 atomic percent 
chromium to alloys having three different TiAl atomic ratios demonstrates 
that tee increase in concentration of an additive found to be beneficial 
at lower concentrations does not follow the simple reasoning that if some 
is good, more must be better. And, in fact, for the chromium additive just 
the opposite is true and demonstrates that where some is good, more is 
bad. 
As is evident from Table IV, each of the alloys 49, 79 and 88, which 
contain "more" (4 atomic percent) chromium shows inferior strength and 
also inferior outer fiber strain (ductility) compared with the base alloy. 
By contrast, alloy 38 of Example 18 contains 2 atomic percent of additive 
and shows only slightly reduced strength but greatly improved ductility. 
Also, it can be observed that the measured outer fiber strain of alloy 38 
varied significantly with the heat treatment conditions. A remarkable 
increase in the outer fiber strain was achieved by annealing at 
1250.degree. C. Reduced strain was observed when annealing at higher 
temperatures. Similar improvements were observed for alloy 80 which also 
contained only 2 atomic percent of additive although the annealing 
temperature was 1300.degree. C. for the highest ductility achieved. 
For Example 20, alloy 87 employed the level of 2 atomic percent of chromium 
but the concentration of aluminum is increased to 50 atomic percent. The 
higher aluminum concentration leads to a small reduction in the ductility 
from the ductility measured for the two percent chromium compositions with 
aluminum in the 46 to 48 atomic percent range. For alloy 87, the optimum 
heat treatment temperature was found to be about 1350.degree. C. 
From Examples 18, 19 and 20, which each contained 2 atomic percent 
additive, it was observed that the optimum annealing temperature increased 
with increasing aluminum concentration. 
From this data it was determined that alloy 38 which has been heat treated 
at 1250.degree. C., had the best combination of room temperature 
properties. Note that the optimum annealing temperature for alloy 38 with 
46 at.% aluminum was 1250.degree. C. but the optimum for alloy 80 with 48 
at.% aluminum was 1300.degree. C. The data obtained for alloy 80 is 
plotted in FIG. 3 relative to the base alloys. 
These remarkable increases in the ductility of alloy 38 on treatment at 
1250.degree. C. and of alloy 80 on heat treatment at 1300.degree. C. were 
unexpected as is explained in the copending application for Ser. No. 
138,485, filed Dec. 28, 1987. 
What is clear from the data contained in Table IV is that the modification 
of TiAl compositions to improve the properties of the compositions is a 
very complex and unpredictable undertaking. For example, it is evident 
that chromium at 2 atomic percent level does very substantially increase 
the ductility of the composition where the atomic ratio of TiAl is in an 
appropriate range and where the temperature of annealing of the 
composition is in an appropriate range for the chromium additions. It is 
also clear from the data of Table IV that, although one might expect 
greater effect in improving properties by increasing the level of 
additive, just the reverse is the case because the increase in ductility 
which is achieved at the 2 atomic percent level is reversed and lost when 
the chromium is increased to the 4 atomic percent level. Further, it is 
clear that the 4 percent level is not effective in improving the TiAl 
properties even though a substantial variation is made in the atomic ratio 
of the titanium to the aluminum and a substantial range of annealing 
temperatures is employed in studying the testing the change in properties 
which attend the addition of the higher concentration of the additive. 
EXAMPLE 24: 
Samples of alloys were prepared which had a composition as follows: 
EQU Ti.sub.52 Al.sub.46 Cr.sub.2. 
Test samples of the alloy were prepared by two different preparation modes 
or methods and the properties of each sample were measured by tensile 
testing. The methods used and results obtained are listed in Table V 
immediately below. 
TABLE V 
__________________________________________________________________________ 
Plastic 
Process- Yield 
Tensile 
Elon- 
Ex. 
Alloy 
Composition 
ing Anneal 
Strength 
Strength 
gation 
No. 
No. (at. %) 
Method 
Temp (.degree.C.) 
(ksi) 
(ksi) 
(%) 
__________________________________________________________________________ 
18 38 Ti.sub.52 Al.sub.46 Cr.sub.2 
Rapid 
1250 93 108 1.5 
Solidifi- 
cation 
24 38 Ti.sub.52 Al.sub.46 Cr.sub.2 
Ingot 
1225 77 99 3.5 
Metallur- 
1250 74 99 3.8 
gy 1275 74 97 2.6 
__________________________________________________________________________ 
In Table V, the results are listed for alloy samples 38 which were prepared 
according to two Examples, 18 and 24, which employed two different and 
distinct alloy preparation methods in order to form the alloy of the 
respective examples. In addition, test methods were employed for the metal 
specimens prepared from the alloy 38 of Example 18 and separately for 
alloy 38 of Example 24 which are different from the test methods used for 
the specimens of the previous examples. 
Turning now first to Example 18, the alloy of this example was prepared by 
the method set forth above with reference to Examples 1-3. This is a rapid 
solidification and consolidation method. In addition for Example 18, the 
testing was not done according to the 4 point bending test which is used 
for all of the other data reported in the tables above and particularly 
for Example 18 of Table IV above. Rather the testing method employed was a 
more conventional tensile testing according to which a metal samples are 
prepared as tensile bars and subjected to a pulling tensile test until the 
metal elongates and eventually breaks. For example, again with reference 
to Example 18 of Table V, the alloy 38 was prepared into tensile bars and 
the tensile bars were subjected to a tensile force until there was a yield 
or extension of the bar at 93 ksi. 
The yield strength in ksi of Example 18 of Table V, measured by a tensile 
bar, compares to the yield strength in ksi of Example 18 of Table IV which 
was measured by the 4 point bending test. In general, in metallurgical 
practice, the yield strength determined by tensile bar elongation is a 
more generally used and more generally accepted measure for engineering 
purposes. 
Similarly, the tensile strength in ksi of 108 represents the strength at 
which the tensile bar of Example 18 of Table V broke as a result of the 
pulling. This measure is referenced to the fracture strength in ksi for 
Example 18 in Table V. It is evident that the two different tests result 
in two different measures for all of the data. 
With regard next to the plastic elongation, here again there is a 
correlation between the results which are determined by 4 point bending 
tests as set forth in Table IV above for Example 18 and the plastic 
elongation in percent set forth in the last column of Table V for Example 
18. 
Referring again now to Table V, the Example 24 is indicated under the 
heading"Processing Method" to be prepared by ingot metallurgy. As used 
herein, the term "ingot metallurgy" refers to a melting of the ingredients 
of the alloy 38 in the proportions set forth in Table V and corresponding 
exactly to the proportions set forth for Example 18. In other words, the 
composition of alloy 38 for both Example 18 and for Example 24 are 
identically the same. The difference between the two examples is that the 
alloy of Example 18 was prepared by rapid solidification and the alloy of 
Example 24 was prepared by ingot metallurgy. Again, the ingot metallurgy 
involves a melting of the ingredients and solidification of the 
ingredients into an ingot. The rapid solidification method involves the 
formation of a ribbon by the melt spinning method followed by the 
consolidation of the ribbon into a fully dense coherent metal sample. 
In the ingot melting procedure of Example 24 the ingot is prepared to a 
dimension of about 2"in diameter and about 1/2 thick in the approximate 
shape of a hockey puck. Following the melting and solidification of the 
hockey puckshaped ingot, the ingot was enclosed within a steel annulus 
having a wall thickness of about 1/2 and having a vertical thickness which 
matched identically that of the hockey puckshaped ingot. Before being 
enclosed within the retaining ring the hockey puck ingot was homogenized 
by being heated to 1250.degree. C. for two hours. The assembly of the 
hockey puck and containing ring were heated to a temperature of about 
975.degree. C. The heated sample and containing ring were forged to a 
thickness of approximately half that of the original thickness. 
Following the forging and cooling of the specimen, tensile specimens were 
prepared corresponding to the tensile specimens prepared for Example 18. 
These tensile specimens were subjected to the same conventional tensile 
testing as was employed in Example 18 and the yield strength, tensile 
strength and plastic elongation measurements resulting from these tests 
are listed in Table V for Example 24. As is evident from the Table V 
results, the individual test samples were subjected to different annealing 
temperatures prior to performing the actual tensile tests. 
For Example 18 of Table V, the annealing temperature employed on the 
tensile test specimen was 1250.degree. C. For the three samples of the 
alloy 38 of Example 24 of Table V, the samples were individually annealed 
at the three different temperatures listed in Table V and specifically 
1225.degree. C., 1250.degree. C., and 1275.degree. C. Following this 
annealing treatment for approximately two hours, the samples were 
subjected to conventional tensile testing and the results again are listed 
in Table V for the three separately treated tensile test specimens. 
Turning now again to the test results which are listed in Table V, it is 
evident that the yield strengths determined for the rapidly solidified 
alloy are somewhat higher than those which are determined for the ingot 
processed metal specimens. Also, it is evident that the plastic elongation 
of the samples prepared through the ingot metallurgy route have generally 
higher ductility than those which are prepared by the rapid solidification 
route. The results listed for Example 24 demonstrate that although the 
yield strength measurements are somewhat lower than those of Example 18 
they are fully adequate for many applications in aircraft engines and in 
other industrial uses. However, based on the ductility measurements and 
the results of the measurements as listed in Table 24 the gain in 
ductility makes the alloy 38 as prepared through the ingot metallurgy 
route a very desirable and unique alloy for those applications which 
require a higher ductility. Generally speaking, it is well-known that 
processing by ingot metallurgy is far less expensive than processing 
through melt spinning or rapid solidification inasmuch as there is no need 
for the expensive melt spinning step itself nor for the consolidation step 
which must follow the melt spinning. 
EXAMPLE 25: 
Samples of an alloy containing both chromium additive and niobium additive 
were prepared as disclosed above with reference to Examples 1-3. As 
reported in copending application Ser. No. 201,984, filed Jun. 3, 1988, 
tests were conducted on the samples and the results are listed in Table VI 
immediately below. 
TABLE VI* 
__________________________________________________________________________ 
Plastic 
Wt. Loss 
Yield 
Tensile 
Elon- 
After 48 
Ex. 
Alloy 
Composition 
Anneal 
Strength 
Strength 
gation 
hrs @ 980.degree. C. 
No. 
No. (at. %) Temp (.degree.C.) 
(ksi) 
(ksi) 
(%) (mg/cm.sup.2) 
__________________________________________________________________________ 
2A** 
12A Ti.sub.52 Al.sub.48 
1300 77 92 2.1 + 
1350 + + + 31 
15 40 Ti.sub.50 Al.sub.46 Nb.sub.4 
1300 87 100 1.6 4 
19 80 Ti.sub.50 Al.sub.48 Cr.sub.2 
1275 + + + 47 
1300 75 97 2.8 + 
25 81 Ti.sub.48 Al.sub.48 Cr.sub.2 Nb.sub.2 
1275 82 99 3.1 4 
1300 78 95 2.4 + 
1325 73 93 2.6 + 
__________________________________________________________________________ 
+ Not measured. 
*The data in this Table is based on conventional tensile testing rather 
than on the four point bending as described above. 
**Example 2A corresponds to Example 2 above in the composition of the 
alloy used in the example. However, Alloy 12A of Example 2A was prepared 
by ingot metallurgy rather than by the rapid solidification method of 
Alloy 12 of Example 2. The tensile and elongation properties were tested 
by the tensile bar method rather than the four point bending testing used 
for Alloy 12 of Example 2. 
It is known from Example 17, in Table III above, that the addition of more 
than one additive elements, each of which is effective individually in 
improving and in contributing to an improvement of different properties of 
the TiAl compositions, that nonetheless, when more than one additive is 
employed in concert and combination, as is done in Example 17, the result 
is essentially negative in that the combined addition results in a 
decrease in desired overall properties rather than an increase. 
Accordingly, it is very surprising to find that by the addition of two 
elements and specifically chromium and niobium to bring the additive level 
of the TiAl to the 4 atomic percent level and employing a combination of 
two differently acting additives that a substantial further increase in 
the desirable overall property of the alloy of the TiAl composition is 
achieved. In fact, the highest ductility levels achieved in all of the 
tests on materials prepared by the Rapid Solidification Technique are 
those which are achieved through use of the combined chromium and niobium 
additive combination. 
A further set of tests were done in connection with the alloys and these 
tests concern the oxidation resistance of the alloys. In this test, the 
weight loss after 48 hours of heating at 982.degree. C. in air were 
measured. The measurement was made in milligrams per square centimeter of 
surface of the test specimen. The results of the tests are also listed in 
Table VI. 
From the data given in Table VI, it is evident that the weight loss from 
the heating of alloy 12 was about 31 mg/cm.sup.2. Further, it is evident 
that the weight loss from the heating of alloy 80 containing chromium 
above was 47 mg/cm.sup.2. By contrast, the weight loss resulting from the 
heating of the alloy 81 annealed at 1275.degree. C. was about 4 
mg/cm.sup.2. This decrease in the level of weight loss represents an 
increase in the oxidation resistance of the alloy. This is a very 
remarkable increase of about seven fold from the combination of chromium 
and niobium additives in the alloy 81. Accordingly, what is found in 
relation to the chromium and niobium containing alloy is that it has a 
very desirable level of ductility and the highest achieved together with a 
very substantial improvement and level of oxidation resistance. 
The alloy is suitable for use in components such as components of jet 
engines which display high strength at high temperatures. Such components 
may be, for example, swirlless, exhaust components, LPT blades or vanes, 
components, vanes or ducts. 
The alloy may also be employed in reinforced composite structures 
substantially as described in copending application Ser. No. 010,882, 
filed Feb. 4, 1987, and assigned to the same assignee as the subject 
application the text of which application is incorporated herein by 
reference. 
EXAMPLE 26: 
The alloy described in Example 25 was prepared by rapid solidification. By 
contrast, the alloy of this example was prepared by ingot metallurgy in a 
manner similar to that described in Example 24 above. 
The specific preparation method is important in achieving an improvement in 
properties over the properties of the composition as described in 
copending application Ser. No. 201,984, filed Jun. 3, 1988. 
The proportions of the ingredient of this alloy are as follows: 
EQU Ti.sub.48 Al.sub.48 Cr.sub.2 Nb.sub.2. 
The ingredients were melted together and then solidified into two ingots 
about 2 inches in diameter and about 0.5 inches thick. The melts for these 
ingots were prepared by electro-arc melting in a copper hearth. 
The first of the two ingots was homogenized for 2 hours at 1250.degree. C. 
and the second was homogenized at 1400.degree. C. for two hours. 
After homogenization, each ingot was individually fitted to a close fitting 
annular steel ring having a wall thickness of about 1/2 inch. Each of the 
ingots and its containing ring was heated to 975.degree. C. and was then 
forged to a thickness about half that of the original thickness. 
Both forged samples were then annealed at temperatures between 1250? C. and 
1350? C. for two hours. Following the annealing, the forged samples were 
aged at 1000? C. for two hours. After the aging, the sample ingots were 
machined into tensile bars for tensile tests at room temperature. 
Table VII below summarizes the results of the room temperature tensile 
tests. 
TABLE VII* 
______________________________________ 
Room Temperature Tensile Properties of Cast-and-Forged 
Ti.sub.48 Al.sub.48 Cr.sub.2 Nb.sub.2 
Ingot Tensile 
Homo- Specimen Plastic 
genizatn Heat Treat- 
Yield Fracture 
Elon- 
Temperature 
ment Temp. Strength 
Strength 
gatn 
Ex. (.degree.C.) 
(.degree.C.) 
(ksi) (ksi) (%) 
______________________________________ 
26A 1250 1275 61 70 1.4 
1300 67 74 1.5 
1325 62 76 2.1 
1350 65 61 1.3 
26B 1400 1275 64 77 2.7 
1300 63 77 2.8 
1325 60 76 2.9 
______________________________________ 
*-The data in this Table is based on conventional tensile testing rather 
than on the fourpoint bending as described in Examples 1-23 above 
From the data included in Table VI above an in Table VII here, it is 
evident that it has been demonstrated experimentally that a strong ductile 
TiAl base alloy having high resistance to oxidation has been prepared by 
cast and wrought metallurgy techniques. 
The yield strengths are in the 60 to 67 ksi range and it is noteworthy that 
these yield strengths are quite independent of homogenization and heat 
treatment temperatures which were applied. By contrast, the ductilities 
are seen to be strongly dependent on the homogenization temperatures used. 
Thus, when the 1250.degree. C. homogenization temperature is used, the 
ductilities measured range from 1.3 to 2.1% depending on the heat 
treatment temperature. 
However, when the homogenization is performed at 1400.degree. C., the 
ductilities achieved in the samples are at the higher values of 2.7 to 
2.9%. These ductilities are significantly higher and, furthermore, are 
significantly more consistent than those found from measurements of the 
materials homogenized at the lower temperature. 
These tests demonstrate that the ductility of a Ti.sub.48 Al.sub.48 
Cr.sub.2 Nb.sub.2 composition prepared by cast-and-forged metallurgy 
techniques are greatly improved by homogenization at 1400.degree. C. 
The foregoing example demonstrates the preparation of a composition having 
a unique combination of ductility, strength and oxidation resistance. This 
example is disclosed in copending application Ser. No. 354,965, filed May 
22,1989. 
Moreover, the preparation is by a low cost ingot metallurgy method as 
distinct from the more expensive melt spinning method used in Example 25. 
The method is unique to the composition doped with the combination of 
chromium and niobium. The concentration ranges of the chromium and niobium 
for which the subject method of this example will produce advantageous 
results is as follows: 
Ti.sub.48 Al.sub.48 Cr.sub.2 Nb.sub.2. 
The homogenization of the ingot prior to thickness reduction is preferably 
carried out at a temperature of about 1400.degree. C. but homogenization 
at temperatures above the transus temperature in practicing the method is 
feasible. It will be realized that the transus temperature will vary 
depending on the stoichiometric ratio of the titanium and the aluminum and 
on specific concentrations of the chromium and niobium additives. For this 
reason, it is advisable to first determine the transus temperature of a 
particular composition and to use this value in carrying out the method. 
Homogenization times may vary inversely with the temperature employed but 
shorter times of the order of one to three hours are preferred. 
Following the homogenization and enclosing of the ingot, the assembly of 
ingot and containing ring are heated to 975.degree. C. prior to the 
reduction in thickness through forging. Successful forging can be 
accomplished without any containing ring and with samples heated to 
temperatures between about 900.degree. C. and the incipient melting 
temperature. Temperatures above the incipient melting point should be 
avoided. 
The reduction in thickness step is not limited to a reduction to one half 
the original thickness. Reductions of from about 10% and higher produce 
useful results in practicing the present invention. A reduction above 50% 
is preferred. 
Annealing, following the thickness reduction, can be carried out over a 
range of temperatures from about 1250.degree. C. to the transus 
temperature, and preferably from about 1250.degree. C. to about 
1350.degree. C., and over a range of times from about one hour to about 10 
hours, and preferably in the shorter time ranges of about one to three 
hours. Samples annealed at higher temperatures are preferably annealed for 
shorter times to achieve essentially the same effective anneal. 
Aging may be carried out after the annealing. Aging is usually done at a 
lower temperature than the annealing and for a short time in the order of 
one or a few hours. Aging at 1000.degree. C. for one hour is a typical 
aging treatment. Aging is helpful but not essential to practice of the 
present invention. 
The foregoing was explained in the copending application Ser. No. 354965 
filed May 22,1989 which application is incorporated herein by reference. 
EXAMPLE 27: 
A sample of an alloy containing carbon additive in addition to chromium and 
niobium was prepared according to the formula: 
EQU Ti.sub.47.9 Al.sub.48 Cr.sub.2 Nb.sub.2 C.sub.O.1. 
The composition was prepared and tested as described in Examples 24 and 
26A. This included electro arc melting and casting into an ingot about 2 
inches in diameter and 1/2 inch thick. The cast ingot was homogenized for 
2 hours at 1250.degree. C. and then enclosed in a steel ring. The ingot 
and ring were heated to 975.degree. C. and the ingot and ring were then 
forged to a thickness approximately half that of the original thickness. 
After annealing at temperatures between 1200.degree. and 1400.degree. C. 
for 2 hours, and aging at 1000.degree. C. for 2 hours, specimens were 
machined for tensile tests at room temperature. The results of the tests 
are contained in the Table VIII immediately below together with the 
results of the tensile testing of alloy 81 of Example 26A. These two sets 
of test data are included in Table VIII as the two alloys had been 
prepared and processed through the same set of processing steps so that 
the results of their respective tests are quite closely comparable. 
TABLE VIII 
__________________________________________________________________________ 
Room Temperature Tensile Properties of Cast-and-Forged Alloys 
Gamma Yield 
Fracture 
Plastic 
Ex. 
Alloy 
Composition 
Anneal 
Strength 
Strength 
Elongtn 
No. 
No. (at. %) Temp (.degree.C.) 
(ksi) 
(ksi) 
(%) 
__________________________________________________________________________ 
26A 
81 Ti.sub.48 Al.sub.48 Cr.sub.2 Nb.sub.2 
1275 61 70 1.4 
1300 67 74 1.5 
1325 62 76 2.1 
1350 65 71 1.3 
27 185 Ti.sub.47.9 Al.sub.48 Cr.sub.2 Nb.sub.2 C.sub.0.1 
1275 64 77 2.7 
1300 63 81 3.2 
1325 64 82 3.0 
__________________________________________________________________________ 
From the results tabulated in Table VIII, it is evident that the addition 
of carbon to the chromium and niobium doped gamma TiAl produced most 
remarkable increases in ductility. These results are plotted in FIG. 1. 
What is evident from Table VIII and FIG. 1 is that the remarkably good 
ductility of the alloy 81 annealed at 1275.degree. and 1300.degree. C. and 
containing the combination of the chromium and niobium additives was 
incredibly doubled by the further addition of 0.1 atom percent of carbon. 
Clearly, this is a most unusual and unexpected result. 
Accordingly, from the foregoing, it is evident that there are a plurality 
of ways of providing improvements in the ductility of a TiAl composition 
which has chromium and niobium additives included therein. 
A first way is through the use of rapid solidification processing. By 
itself the rapid solidification route of preparing a Ti.sub.48 Al.sub.48 
Cr.sub.2 Nb.sub.2 composition favors the development of higher ductility. 
A second method is the method of Example 26B which involves homogenization 
at 1400.degree. C. 
The third method is the one taught herein and specifically the inclusion of 
carbon along with chromium and niobium in the TiAl composition. 
As indicated from the foregoing, each of these techniques are effective in 
improving the ductility of the TiAl. 
Regarding the precise composition containing carbon where a composition 
such as 
EQU Ti.sub.47.9 Al.sub.48 Cr.sub.2 Nb.sub.2 C.sub.0.1 
is provided, the carbon substituent and the base composition TiAl into 
which the carbon is substituted may be expressed as fixed and certain. 
However, this is not equally true in a composition such as: 
EQU Ti.sub.52-42 Al.sub.46-50 Cr.sub.1-3 Nb.sub.1-5 C.sub.0.05-0.2 
where there are many variables for each constituent. For convenience of 
notation in such a composition, the decimal values of the titanium 
ingredient are not indicated. Rather, reliance is placed on the clear 
designation of the carbon constituent with the understanding that the 
concentration value of the titanium constituent will be the complement of 
whatever carbon value is designated. Thus, if the carbon value is 0.2 the 
titanium value will be [(52 to 42)-0.2]. Where the carbon concentration 
value is 0.05 the titanium concentration value will be [(52 to 42)-0.05].