GB2266315A - Manganese and tungsten-modified titanium aluminium alloys - Google Patents

Abstract

A gamma TiAl composition is prepared to have high strength and to have improved ductility by altering the atomic ratio of the titanium and aluminium to have what has been found to be a highly desirable effective aluminum concentration by addition of a combination of manganese and tungsten according to the formula: Ti52-44Al46-50W1-3Mn1-3.

Description

MANGANESE AND TUNGSTEN-MODIFIED TITANIUM ALUMINUM ALLOYS CROSS-REFERENCE TO RELATED APPLICATIONS The subject application relates to copending applications as follows: Serial Nos. 138,408, 138,476, 138,486, 138,481, and 138,407, filed concurrently December 28, 1987. It also relates to Serial No. 201,984, filed June 3, 1988; Serial Nos. 252,622 and 253,649, filed October 3, 1988; Serial No. 293,035, filed January 3, 1989; and Serial No. (Attorney Docket RD-18,642) filed .

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 alloys of titanium and aluminum which have been modified both with respect to stoichiometric ratio and with respect to manganese and tungsten addition.

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 concentrations of aluminum (including about 25 to 35 atomic %) an intermetallic compound Ti3Al is formed. The Ti3Al 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, good oxidation resistance, and good creep resistance. The relationship between the modulus and temperature for TiA1 compounds to other alloys of titanium and in relation to nickel base superalloys is shown in Figure 1. As is evident from the figure, the TiA1 has the best modulus of any of the titanium alloys. Not only is the TiAl modulus higher at 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 before the TiAl intermetallic compound can be exploited in 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 compositión to be useful is about 50 ksi or about 350 MPa.

However, materials having this level of strength are of marginal utility and higher strengths are often preferred for some applications.

The stoichiometric ratio of 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. The properties of TiAl compositions are 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 affected by the addition of relatively similar small amounts of ternary 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 not only contains a ternary additive element but also a quaternary additive element.

Furthermore, I have discovered that the composition including the quaternary additive element has a uniquely desirable combination of properties which include a desirably high ductility and a particularly valuable oxidation resistance.

PRIOR ART There is extensive literature on the compositions of titanium aluminum including the Ti3Al intermetallic compound, the TiAl intermetallic compounds and the TiAl3 intermetallic compound. A patent, U.S. 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 Ti3Al: "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 10000C. 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 200 to 5500C. 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 Ti3Al (as well as from solid solution alloys of Ti) although both TiAl and Ti3Al 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 Ti3Al 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 does describe the alloying of TiAl with vanadium and tungsten to achieve some property changes in the resulting alloy.

In Table 2 of the '615 patent, two TiAl compositions containing tungsten are disclosed. Alloy T2A128 is disclosed to contain Ti-48Al-1.0W and alloy T2A-127 is disclosed to contain Ti-48Al-l.OV-1/1.0W.

In the text below Table 2, it is pointed out that "the effects of the alloying additions are summarized in Figure 3 for Ti-48Al. Referring to Figure 3, it can be seen that all additions increased creep life but it is seen that tungsten lowers ductility while vanadium raises or preserves it: compare alloy 128 with 125." The influence of tungsten in lowering ductility is pointed out further in column 5 starting at line 51 in the statement that "most elements such as Mo and W tend to lower ductility somewhat and may reduce creep rupture properties." The negative influence of tungsten on ductility at room temperature is evident from Figure 3. From Figure 3 it is evident that the "RT % Elong." of alloy 128 containing 1% tungsten in the base alloy is less than half that of the base Ti-Al 48 alloy. The ductility of alloy 127 containing 1% tungsten and 1% vanadium in the base alloy is even lower.

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.

4. S.M.L. Sastry, and H.A. Lipsitt, "Plastic Deformation of TiAl and Ti3Al", Titanium 80 (Published by American Society for Metals, Warrendale, Pennsylvania), Vol.

2 (1980) page 1231.

U.S. Patent 4,661,316 discloses titanium aluminide compositions which contain manganese as well as manganese plus other speculative ingredients including a speculative content of tungsten.

Two additional papers deal with titanium aluminides. These are: 5. 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.

6. P.L. Martin, H.A. Lispitt, N.T. Nuhfer, and J.C.

Williams, "The Effects of Alloying on the Microstructure and Properties of Ti3Al and TiAl", Titanium 80, (Published by American Society for Metals, Warrendale, PA), Vol. 2, pp.

1245-1254.

BRIEF DESCRIPTION OF THE INVENTION One object of the present invention is to provide a method of forming a titanium aluminum intermetallic compound having improved ductility, and related properties at room temperature.

Another object is to improve the properties of titanium aluminum intermetallic compounds at low and intermediate temperatures.

Another object is to provide an alloy of titanium and aluminum having improved properties and processability at low and intermediate temperatures.

Another object is to improve the combination of ductility and particularly oxidation resistance of TiAl base compositions.

Still another object is to significantly improve the oxidation resistance of TiAl compositions.

Yet another object is to make improvements in a set of strength, ductility together with oxidation resistance 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 TiAl base alloy, and adding a relatively low concentration of manganese and a low concentration of tungsten to the nonstoichiometric composition. The addition may be followed by rapidly solidifying the manganese- and tungsten-containing nonstoichiometric TiAl intermetallic compound. Addition of manganese in the order of approximately 1 to 3 atomic percent and of tungsten to the extent of 1 to 3 atomic percent is contemplated.

The rapidly solidified composition may be consolidated as by isostatic pressing and extrusion to form a solid composition of the present invention.

The alloy of this invention may also be produced in ingot form and may be processed by ingot metallurgy.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a graph illustrating the relationship between modulus and temperature for an assortment of alloys.

FIGURE 2 is a graph illustrating the relationship between load in pounds and crosshead displacement in mils for TiAl compositions of different stoichiometry tested in 4point bending.

FIGURE 3 is a graph similar to that of Figure 2 but illustrating the relationship of Figure 2 for Ti52Al46Mn2.

FIGURE 4 is a graph displaying comparative oxidation resistance properties.

FIGURE 5 is a bar graph displaying strength in ksi for samples given different heat treatments.

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 tungsten and manganese to a gamma TiAl are based. The first twenty one 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 9500C (17400F) 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 9750C (17870F) 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 10000C for two hours.

Specimens were machined to the dimension of 1.5 x 3 x 25.4 mm (0.060 x 0.120 x 1.0 in.) for four point bending tests at room temperature. The bending tests were carried out in a 4point 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 13000C and further data on these samples in particular is given in Figure 2.

TABLE I Outer Gamma Yield Fracture Fiber Ex. Alloy Composit. Anneal Strength Strength Strain No. No. (at.%) Temp (OC) (ksi) (ksi) (%) 1 83 Ti54A146 1250 131 132 0.1 1300 111 120 0.1 1350 * 58 0 2 12 Ti52A148 1250 130 180 1.1 1300 98 128 0.9 1350 88 122 0.9 1400 70 85 0.2 3 85 Ti50Al50 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 measure ment It is evident from the data of this table 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 12500C and 13500C results in the test specimens having desirable levels of yield strength, fracture strength and outer fiber strain. However, the anneal at 1400do 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 13500C. 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 13500C.

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( C) (ksi) (ksi) (%) 2 12 Ti52A148 1250 130 180 1.1 1300 98 128 0.9 1350 88 122 0.9 4 22 Ti50Al47Ni3 1200 * 131 0 5 24 Tis2Al46Ag2 1200 * 114 0 1300 92 117 0.5 6 25 Ti50Al48Cu2 1250 * 83 0 1300 80 107 0.8 1350 70 102 0.9 7 32 Ti54Al45Hfl 1250 130 136 0.1 1300 72 77 0.2 8 41 Ti52Al44Pt4 1250. 132 150 0.3 9 45 Ti51A147C2 1300 136 149 0.1 10 57 . Ti5oAl48Fe2 1250 * 89 0 1300 * 81 0 1350 86 111 0.5 11 82 Ti50Al48Mo2 1250 128 140 0.2 1300 110 136 0.5 1350 80 95 0.1 12 39 Ti50A146Mo4 1200 * 143 0 1250 135 154 0.3 1300 131 149 0.2 13 20 Ti49.5Al49.5Erl + + + + * - See asterisk note to Table I + - Material fractured during machining to prepare test specimens For Examples 4 and 5, heat treated at 12000C, the yield strength was unmeasurable as the ductility was found to be essentially nil. For the specimen of Example 5 which was annealed at 13000C, the ductility increased, but it was still undesirably low.

For Example 6, the same was true for the test specimen annealed at 12500C. For the specimens of Example 6 which were annealed at 1300 and 13500C 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 Figure 4, 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 Ti48Al48X4 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.

EXAMPLS 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 Serial 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 13500C 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 12500C 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/cm2 weight loss of alloy 40 as compared to the 31 mg/cm2 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 9820C 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/cm2 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 13250C was determined to be 2 mg/cm2 and this is again compared to the 31 mg/cm2 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 (OC) (ksi) (ksi) (%) 980c(mg/crn2) 2 12 Ti52A148 1250 130 180 1.1 * 1300 98 128 0.9 * 1350 88 122 0.9 31 14 14 Ti49A148v3 1300 94 145 1.6 27 1350 84 136 1.5 * 15 40 Ti50A146Nb4 1250 136 167 0.5 * 1300 124 176 1.0 4 1350 86 100 0.1 * 16 60 Ti48A148Ta4 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 Ti49A145V2Nb2Ta2 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 Serial 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 Serial No. 138,408, filed December 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 Serial 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 21: Four 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 (OC) (ksi) (ksi) (%) 2 12 Ti52Al48 1250 130 180 1.1 1300 98 128 0.9 1350 88 122 0.9 18 37 Ti52Al46Mn2 1250 111 167 1.6 1300 98 143 0.8 1350 70 90 0.2 19 54 Ti50A148Mn2 1250 106 125 0.5 1300 95 111 0.3 1350 -* 63 0 20 50 Ti52Al44Mn4 1250 72 90 0.2 21 61 Ti48Al48Mn4 1250 109 136 0.6 1300 97 132 0.8 1350 92 120 0.7 * - No measurable value was found because the sample lacked sufficient ductility to obtain a measurement From the results listed in Table IV, it is evident that, based on the four-point bend testing the manganese additive has an influence on the strength and ductility properties of the resultant alloys. Alloy 37 shows a distinct improvement in ductility when annealed at 12500C without a loss of strength which compares in percentage to the 60% gain in ductility.

For the most part, the values of strength and ductility of the other alloys of the series of tests of Table IV are lower than those of the base Ti52Al48 alloy.

The above samples were prepared as described in Examples 1-3. Also, the above samples of Examples 1-21 were tested by the four-point bending test.

EXAMPLE 22: An additional alloy sample identified as Alloy 142, for Example 22, was prepared by ingot metallurgy processing.

The ingot metallurgy processing is different from the processing which is described with reference to Examples 1-3 above. The alloy was first melted by electro arc melting and was then cast into an ingot about 2 inches in diameter and about one half inch thick. The ingot was homogenized for two hours at 12500C. The homogenized ingot was then enclosed in a steel ring and after being so enclosed was heated to 9750C.

The heated ingot and the containing ring assembly was then forged to a thickness of approximately half that of the original thickness. The ingot was annealed at temperatures as set forth in Table V below for two hours for each sample.

After annealing at the individual temperatures, indicated in Table II, each of the samples was aged at 10000C for two hours. Specimens of the cast and forged sample thus prepared were machined into tensile bars for tensile tests at room temperature.

Selected heat treated samples were also exposed to static air at the temperature of 9820C for 48 hours. The oxide scale formed on the sample was removed and the amount of metal weight loss was measured. The weight loss when divided by the specimen surface area is an indication of the rate of oxidation. The weight loss for the samples tested are listed in Table V in the last column of the table.

TABLE V Room Temperature Tensile Rar Tensile Tent Plastic Weight Loss Anneal Yield Fracture Elon- After 48 hrs.

Ex. Alloy Composition Temp. Strength Strength gation 8 9820C No. No. (at.%) (OC) (ksi) (ksi) (%) (mg/cm2) 2A 12A Ti52A148 1300 54 73 2.6 53 1325 50. 71 2.3 1350 53 72 1.6 22 142 Ti4gAl48Mn2W2 1300 83 91 1.3 5 1325 82 89 1.2 1350 77 85 0.7 The Table V immediately above includes two sample listings to provide a basis for comparison. Sample 12A of Example 2A corresponds exactly to Example 2 as set forth in the tables above with the exception that the alloy was prepared by the ingot metallurgy processing as described above with reference to Alloy 142. Further, the tensile data and weight loss data for Alloy 12A was obtained with tensile bars and with alloy specimens corresponding to those employed in the tests made of Alloy 142.

From the data presented in Table V, it is evident that there is a very significant gain in yield strength for Alloy 142 containing the manganese and tungsten additives when compared to the TiAl base alloy of Alloy 12A.

Further, the ultimate tensile strength listed in the table as fracture strength, is also significantly higher for the Alloy 142 as compared to the base Alloy 12A. The tensile elongation values are of Alloy 12A are significantly higher than those of Alloy 142 and, in general, are roughly twice as high as the elongation values for Alloy 142.

However, the plastic elongation values for Alloy 142 are totally adequate for many application purposes and there is a significant gain in the strength of the alloy containing manganese and tungsten additives.

Lastly, the weight loss which represents the resistance to oxidation is about ten-fold lower in the case of the manganese and tungsten containing alloy when compared to the base TiAl alloy of Example 2A.

Regarding the testing of oxidation resistance, it has been found that test results vary from day to day due in part to changing humidity or other changing test conditions.

In order to avoid any such variation the oxidation resistance test data for any table is required from a series of tests performed on the same day with the same furnace and other equipment. Accordingly, from table to table the oxidation resistance test values may vary, but the values given in any one table are valid and reliable relative to other values given in the same table.

Claims (20)

What is claimed is:

1. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the following approximate atomic ratio: Ti52-44Al46-5oWl-3Mnl-3

2. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the approximate atomic ratio: Ti51~45A14 6-soW2Mnl-3

3. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the following approximate atomic ratio: Ti51-45A146-50W1-3Mn2

4. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the approximate atomic ratio: Ti50-46A146-50W2Mn2

5.A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the following approximate atomic ratio: Ti4947Al4749W2Mn2

6. The alloy of claim 1, said alloy having been rapidly solidified from the melt and consolidated.

7. The alloy of claim 2, said alloy having been rapidly solidified from the melt and consolidated.

8. The alloy of claim 3, said alloy having been rapidly solidified from the melt and consolidated.

9. The alloy of claim 4, said alloy having been rapidly solidified from the melt and consolidated.

10. The alloy of claim 5, said alloy having been rapidly solidified from a melt and consolidated.

11. The alloy of claim 1, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

12. The alloy of claim 2, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment between 13000C and 1350 C.

13. The alloy of claim 3, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

14. The alloy of claim 4, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

15. The alloy of claim 5, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

16. The method of improving the oxidation resistance of a structural member formed of TiAl which comprises adjusting the stoichiometric ratio of Ti to Al and incorporating manganese and tungsten in the member according to the following approximate atomic formula: Tis2-44A146-soW1-3Mn1-3

17. The method of claim 16, in which the formula is Ti51-45Al46-50W2Mn1-3

18. The method of claim 16, in which the formula is Tisl-4sAl46-soWl-3Mn2

19. The method of claim 16, in which the formula is Ti50-46Al46-50W2Mn2

20. A structural member, said member being formed of an alloy having the following composition in atomic percent: Ti52-44Al46-50W1-3Mn1-3

20. A structural member, said member being formed of an alloy having the following composition in atomic percent: Ti52-44Al46-5oWl-3Mnl-3 Amendments to the claims have been filed as follows 1.A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the following atomic percentages: Ti52-44A1 46-50WI-3Mnl-3

2. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the atomic percentages: Ti 51-45A146-50W2MnI-3

3. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the following atomic percentages: Ti 51-45A146-50W1-3Mn2

4. A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the atomic percentages Ti50-46Al46-50W2Mn2 5.A tungsten and manganese modified titanium aluminum alloy consisting essentially of titanium, aluminum, tungsten and manganese in the following atomic percentages Ti49-47Al47-49W2Mn2

6. The alloy of claim 1, said alloy having been rapidly solidified from the melt and consolidated.

7. The alloy of claim 2, said alloy having been rapidly solidified from the melt and consolidated.

8. The alloy of claim 3, said alloy having been rapidly solidified from the melt and consolidated.

9. The alloy of claim 4, said alloy having been rapidly solidified from the melt and consolidated.

10. The alloy of claim 5, said alloy having been rapidly solidified from a melt and consolidated.

11. The alloy of claim 1, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

12. The alloy of claim 2, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment between 13000C and 13500C.

13. The alloy of claim 3, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

14. The alloy of claim 4, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500C.

15. The alloy of claim 5, said alloy having been rapidly solidified from the melt and then consolidated and given a heat treatment at a temperature between 13000C and 13500.

16. The method of improving the oxidation resistance of a structural member formed of TiAl which comprises adjusting the stoichiometric ratio of Ti to Al and incorporating manganese and tungsten in the member according to the following atomic percentages: Ti52-44A1 46-50WlqMnl-3

17. The method of claim 16, in which the atomic percentages are: Ti51-45A46-50W2Mn1-3

18. The method of claim 16, in which the atomic percentages are: Ti51-45Al46-50W1-3Mn2 19. The method of claim 16, in which the atomic percentages are: Ti50-46Al46-soW2Mn2