US3390983A - Tantalum base alloys - Google Patents

Description

July 2, 1968 R. L. AMMON ETAL 3,390,983

TANTALUM BASE ALLOYS Filed April 20, 1964 0 l4 W/O TOTAL ALLOY ADDITION :1 ---IO 'W/O TOTAL ALLOY ADDITION u O: D Y E m 200 41' E DUCTILE 5 RT h 5 o .2. (I, Z 4 5-200 {l4 BRITTLE (21') BRITTLE we I l o 2 a 4 5 e 1 TUNGSTEN-HAFNIUM mmo WITNESSES: INVENTORS Robert L. Ammon 0nd Righurd T. Begley United States Patent 3.390983 TANTALUM BASE ALLOYS Robert L. Ammon, Baldwin, and Richard T. Begiey, Penn Hills, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Fiied Apr. 20, 1964, Ser. No. 361,175 9 Claims. (Cl. 75-174) The present invention relates to tantalum base alloys which are suitable for use in applications wherein high strength at elevated temperatures is required or wherein ductility at sub-zero temperatures, or wherein both characteristics are required. More particularly, the invention relates to alloys of the character described which are in addition readily fabricable and weldable.

Fabricable and weldable alloys possessing strength and oxidation resistance at elevated temperatures have many industrial, military, and aerospace applications. Obviously, advances in many areas of technology are dependent upon or closely related to the availability of alloys possessing these properties. For example, the development of improved rocket nozzles and of improved blades for gas turbines is attendant upon the development of improvement of such alloys.

A number of tantalum base alloys have been developed prior to the present invention. Nearly all of these alloys, however, exhibit poor welding or fabricability properties or have only moderate high temperature strength, and in some cases suffer from both of these shortcomings.

The present invention is an improvement upon the alloys disclosed in US. application Ser. No. 208,617,- filed July 9, 1962, now Patent No. 3,166,414.

In accordance with the present invention, it has been found that fabricable and weldable alloys possessing strength at temperatures above 2000 F. and exhibiting sub-zero temperature ductility can be produced by alloying tantalum, tungsten, and hafnium in specified proportions together with minor amounts of one or more interstitial elements.

In view of the foregoing, it is an object of the invention to provide workable alloys which possess strength at elevated temperatures and which exhibit good sub-zero temperature ductility, comprising predetermined proportions of tungsten and hafnium with one or more interstitial elements and the balance being tantalum, with incidental amounts of impurities.

Another object of the invention is the provision of tantalum base alloys to which the hafnium and tungsten are added in a predetermined ratio by weight so as to produce the maximum sub-zero ductility.

Other objects, features and advantages of the invention will be elaborated upon during the forthcoming description of illustrative embodiments thereof, when taken in conjunction with the accompanying drawing, wherein:

The figure is a graphical representation illustrating the effects of varying the ratio by weight of the tungsten and hafnium additions to the alloy.

Tests for ductility of a metal sheet are commonly made by bending the sheet about a mandrel having a radius of four times the sheet thickness, the sheet being bent about 90 around the mandrel, both being cooled to a given temperature and noting if any rupture or crack appears on the metal sheet. This test is defined by the 4T bend test. For some cases, an application of the same test is applied by employing a mandrel whose radius is twice that of the sheet thickness, and this is known as the 2T ice bend test. Welded areas in the bending zones successfully subjected to such tests are an indication of good weld ductility. Cracks or breaks in the bent sheet indicate lack of sufiicient ductility at the test temperature.

In accordance with the present invention, ternary tantalum base alloys are produced comprising from 8 to 11% tungsten, from 1.5 to 3% by weight hafnium, the total being from 10% to 14%, carbon up to 0.05%, nitrogen up to 0.07%, oxygen up to 0.07% and the balance being tantalum, with the ratio by weight of tungsten to hafnium being in the range of 3:1 to 5:1 and preferably about 4:1 for sheets meeting the 2T test, and 2.521 to 5.5:1 for the 4T test. Incidental amounts of impurities and other metallic additives to a total of up to 1% of a maximum may be present. Contemplated by the invention are the ternary tantalum base alloys having the aforementioned ranges of tungsten and hafnium together with minor amounts of interstitial elements comprising carbon in an amount of at least 0.005% and nitrogen in an amount of at least 0.005%. t

The alloy may be melted by one of several procedures which will insure homogeneity and a minimum of contamination. For example, unalloyed, high purity, tantalum together with the proper amounts of pure tungsten and hafnium can be fed into a conventional non-consumable arc melting furnace containing an inert atmosphere such as argon or in a furnace in which a vacuum can be maintained. Desirably, the resulting ingot should be remelted several times, for example by non-consumably arc-melting it using a tungsten electrode to achieve the requisite homogeneity; and then may be hot worked to the desired shape. The alloy can also be prepared by levitation melting of a ball or rod compressed from wire, pellets or powders of components of the alloy, using induction heating techniques. Electron beam melting and consumable arc melting of the alloys are also satisfactory techniques.

Referring now to FIG. 1 of the drawing, the graphical representation therein illustrates the unique sub-zero characteristics of the alloys produced in accordance with this invention. In FIG. 1, variations in tungsten-hafnium ratio of the alloys are plotted against the respective transition temperature in degrees Fahrenheit. The curves 10 and 12 respectively represent the result of weld bend tests for the 2T and the 4T conditions. Data for the curves 10 and 12 are obtained from four alloy compositions each of which contains a total of 14 weight percent of combined tungsten-hafnium additions. 0n the other hand, the single point 14 represents an alloy having a combined total of 10 weight percent of tungsten-hafnium addition. The same test curve values are obtained when the alloys contain carbon up to 0.04%, nitrogen up to 0.02% and oxygen up to 0.02%. At 0.05% carbon the 4T test for the 8% tungsten 2% hafnium alloy results in a 200 F. transition temperature.

An inspection of FIG. 1 indicates that the ductility, as represented by the respective transition temperatures, exhibits a pronounced maximum effect at a tungsten to hafnium ratio of approximately 4:1. The corresponding brittle and ductile areas of the graph are indicated thereon, the brittle area being below the respective curves. For many applications involving sub-zero conditions, as evidenced from the graph, tungsten to hafnium ratios of between 3:1 and 5:1 can be produced and utilized advantageously, particularly for the 4T condition. For less rigorous cold conditions a ratio in the range of 2.5:1 to :1 is suitable.

The compositions of the alloys utilized for the prep- The alloys of Tables I and II are markedly improved aration of FIG. 1 are shown in the following Table I: by adding carbon, nitrogen and oxygen as interstitial TABLE I.TENSILE PROPERTIES OF TA-W-HF ALLOYS Tungsten to Ultimate Yield Heat Hainium Temperature Tensile Strength Elongation Remarks Ratio F.) Strength 0.2% Offset (Percent) (K s.i.) (K s.i.)

Ta-8W2Hf 4:1 320 147. 5 131.0 31 Material reduced recrystallized 75 84. 0 68. 6 31 1 hr. at 3,000 13. 2, 400 38.0 26. 4 29 3,000 15. 6 14.5 31

Ta-8W-6Hi 1. 33:1 -320 172. 0 157.0 25 Material reduced 80%; recrystallized 75 106. 8 06. 2 32 1 hr. at 3,000 F. 2, 400 52.3 39. 7 23 3,000 20.0 18.6 81

Ta-10W-4Ht 2. :1 320 172. 0 163.8 23 Material reduced 80%; recrystallized 75 106. 0 97. 2 26 1 hr. at 3,000 F. 2, 400 49. 6 37.0 32 3,000 25.8 25. 3 67 Ta-11,2W-2.8Hf 4:1 320 Material reduced 70%; recrystallized 75 104.3 97. 6 *14 1 hr. at 3,000 F. 2, 400 42. 2 29. 3 31 3, 000 20. 1 20. 1 38 Ta-12W-2Hf 6:1 320 172. 5 159. 0 29 Material reduced 80%, recrystallized 75 105. 4 06. 8 32 1 hr. at 3,000 F. 2, 400 56. 3 40. 0 36 3, 000 24. 2 23. 3 57 *Equipment maltunctioned. Test stopped after ultimate was reached. K s.c.=Thousa11ds of pounds per square inch. Strain rate 0.005 in./in./1m'n. at low temperatures. Strain rate 0.05 in./in./mi11. at high temperatures.

Table I also lists the tensile properties of the alloys components, in amounts not exceeding 0.05% carbon, shown graphically in FIG. 1. The data of Table I shows 0.07% oxygen and 0.07% nitrogen. the significant improvement in tensile properties when 30 The advantageous addition of a minor amount of an the total tungsten and hafnium concentration is raised interstitial element such as carbon is illustrated by the from to 14 weight percent. The alloys represented by following Table III:

TABLE III.COHPARATIVE TENSILE PROPERTIES Tenzpelrafure Ultimate Yield Strength Elongation Total Tung- Alloy Strength 0.2% Oflset (percent) stenHa[nium (K s.i.) (K s.i.) Solute (w/o) Tit-SW-Zllf 320 147. 5 131. 0 31 10 Ta-9.GW-2.4HI0.01C 320 184. 6 175.0 28 12 Strain Rate 0.005 in./in./1nin. at low temperatures. Strain Rate 0.05 in./in./min. at high temperatures.

Table I have been found to exhibit excellent fabricability,

elevated temperature strength and in those alloys having a In the foregoing table, the tensile properties of the tungsten to hafnium ratio of between 3:1 and 5:1, excelalloy Ta-9.6W-2.4Hf-0.01C is compared with one of the lent weldability. Additionally, it has been found that tanalloys, Ta-SW-ZHf, which is plotted in FIG. 1 and listed talum base alloys containing up to 14 weight percent in the preceding Tables I and II. For the alloy Ta-8W- additions of tungsten-hafnium in ratios ranging from 2.511 2Hf, the same data are used in Table III as in Table I, to 5.5 :1 have been melted and processed to sheet without save that data for the temperature condition 3500 F. difliculty. are added. By cross referring to Tables I, II and III, the The following Table II lists the one and ten hour stress alloy Ta-9.6W-2.4Hf-0.01C can also be compared as to rupture properties of the various tantalum ternary alloys tensile properties with the other alloys described herein at 2400 F., in accordance with the invention: for the temperature range 320 to 3000 F.

TABLE II Stress for Stress for Tungsten- Total Solute Heat N0. 1 hour life 10 hour life Hainium (w/o) (K s.i.) (K s.i.) Ratio 'IBM-2, Ta8W-6Hi- 35. 3 25. 3 1. 33:1 14 TBu-a, Pa-10W-4Hf- 36. 5 2s. 0 2. .51 14 TBM-14, Ta11.2W-2.8Hf. 39. 0 32. 5 4; 1 14 TBM-4, Ta12W-2Hf 38.0 29.5 6:1 14 T111,Ta8W-2Hf 33.5 20.0 4:1 10

Table II exemplifies the improved stress rupture properties of the tantalum alloys of the invention as the total The addition of the interstitial element, carbon, pro- Weight percentage of the tungsten-hafnium solute is induces a significant improvement in tensile properties as creased from 10% to 14%. Table II also indicates that compared to the other alloys noted herein, and partiularly the aforementioned stress rupture properties are optimized to Ta-8W-2Hf. At the same time, the sub-zero ductility with tungsten-hafnium ratios in the neighborhood of 3:1 of the alloy Ta-9.6W-2.4Hf-0.01C is improved by utilizing to 5 :1. an intermediate total solute addition of 12%.

TABLE IV.STRESS RUPTURE PROPERTIES Alloy Stress For One Stress For 10 Hour Liie (K s.i.) Hours Life (K s.i.

Ta-BW-2Hi 33. 5 26. Ta-9.6W2.5, Iii-0.010 44.0 35.0

By cross referring to Tables II and IV, the Ta-9.6W- 2.5Hf-0.01C alloy of the invention can likewise be compared as to comparative stress rupture properties with the other tantalum alloys disclosed herein. It is seen that the tantalum alloy Ta-9.6W-2.4Hf-0.01C exhibits a marked improvement over the alloy Ta-SW-ZI-If and significant improvement in stress rupture properties over the remaining alloys. The effect of the carbon addition upon tensile and stress rupture properties is particularly significant when comparing the alloy Ta-9.6W-2.4Hf-0.01C with the alloy Ta-8W-2I-If and Ta-11.2W-2.8Hf, all three alloys have a 4:1 tungsten to hafinum ratio, but the latter two alloys having correspondingly lesser and greater total solute additions than the first alloy.

The last disclosed tantalum alloy, Ta-9.6W-2.4Hf- 0.01C, is readily fabricable; for example, it can be fabricated to sheet from three inch diameter are cast ingots without difficulty. In addition to the improved elevated temperature properties and stress rupture properties, this alloy, as in the case of the other alloys disclosed herein possesses excellent sub-zero weld bend ductility. This alloy is completely ductile, for example, over 2.5T at 250" F. for both stress-relieved and recrystallized base metal.

Accordingly, the present invention comprises broadly, the ternary tantalum-tungsten-hafnium alloy comprising a total W-Hf solute addition in the prescribed range of 10% to 14% and with the tungsten to hafnium being in the preferred ratio range of between 3:1 and :1; wherein the alloys include with small additions of carbon, nitrogen and oxygen as interstitial components.

In the course of investigating tantalum base alloys containing tungsten and hafnium, alloys with a nominal composition of Ta-8W-2Hf together with individual additions of up to 0.05 w./o. carbon, 0.07 w./o. oxygen, 0.07 w./o. nitrogen and with multiple additions of up to 0.01 w./o. of each interstitial element carbon, oxygen and nitrogen have been found to possess desirable qualities of fabricability, weldability, and attractive high temperature properties. These tantalum base alloys containing the aforementioned concentrations of interstitial elements, respectively, can be processed to sheet from are cast ingots without difiiculty. Additionally, sheet material of the aforementioned alloys can be welded without difficulty.

The efiect of various interstitial additions on the weld bend transition temperature for the 2T and 4T bend conditions is illustrated in the following table:

TABLE V.-WELD BEND DUCTILITY 0F INTERSTITIAL- CONTAINING TANTALUM ALLOYS From the foregoing Table V, it will be seen that all of the interstitial alloys noted therein exhibit weld bend ductility at 320 F. with the exception of the alloy containing 0.5 w./o. carbon. The weld bend transition for this alloy was raised to room temperature for the 2T condition and to 200 F. for the 4T condition.

The tensile properties of the tantalum interstitial containing alloys are shown in the following table:

TABLE VI.LOW AND HIGH TEMPERATURE TENSILE PROPERTIES OF INTERSTITIAL-CONTAINING T-111 ALLOYS Ultimate Yield Heat No. Temperature Tensile Strength Elongation Remarks F.) Strength 02% Offset (percent) (K s.i.) (K s.i.) TBM-lO, T111+0.02C 230 171. 2 153.8 23 Material reduced 70%; recrystallized 75 108. 7 98. 75 26 1 hr. at 3,000 F. 2, 400 53. 7 35. 7 34 3, 000 20. 4 19. 7 78 TBM-le, T111+0.05C 320 170. 4 148.6 26 Material reduced 68%; recrystallized 75 108. 7 82. 4 29 1 hr. at 3,000 F. 2, 400 54. 0 35. 3 23 3, 000 21. 4 21.4 68 TBM-ll, T111+0.02C 320 148. 25 137. 8 33 Material reduced 70%; recrystallized 75 88.8 78. 7 32 1 hr. at 3,000 F. 2,400 41. 7 25. 8 38 3, 000 15. 6 14. 9 52 TBM-17, T-111+0.05C 320 152. 7 140. 3 34 Material reduced 68%; recrystallized 75 88. 7 78.0 32 1 hr. at 3,000 F. 2, 400 39. 7 26. 4 3, 000 18. 0 17. 8 58 TBM-12, T-111+0.02N 320 187. 2 178. 3 25 Material reduced recrystallized 112. 2 105. 7 29 1 hr. at 2,000 F. 2, 400 58. 0 41. 9 14 3,000 18. 9 18. 4 43 TBM-18, T-l11+0.05N 320 224. 9 225. 2 18 Material reduced 75%; recrystallized 75 133. 8 132. 3 20 1 hr. at 3,000 F. 2, 400 56. 5 36. 3 24 3, 000 TBM-15, 'l111+0.01C+0.010+0.01N 320 188. 8 186.0 24 Material reduced 70%; recrystallized 75 117.3 115.0 25 1 hr. at 3,000 F. 2, 400 55. 0 37.9 45 3, 000 19.7 19. 5 122 Low Interstitial, T-lll, Pa-34 320 147. 5 13 .0 31 Material reduced recrystallized 75 84.0 68. 6 31 1 hr. at 3,000 F. 2,400 38.0 26. 4 29 3, 000 15. 6 14. 5 31 Strain rate 0.005 in./in.lmin at low temperatures. Strain rate 0.05 in./in./min. at high temperatures.

ERTIES OF INTERSTITIAL-CONTAINING TANTALUINI ALLOYS AT 2400 F.

Stress for 1 Hr. Stress for 10 Hr.

Material Rupture Lite Rupture Life (K s.i.) (K s.i.)

Ta8W2Hf, Low Interstitial 5 26.

+0.01 C+0.01 O+0.0l N 40.0 30. 5

Interstitial amounts of carbon and nitrogen have a pronounced effect on rupture stress for One and ten hour rupture life. On the other hand, oxygen additions do not particularly benefit the stress rupture properties.

The addition of carbon and nitrogen to 0.02 w./o. either individually or in combination does not adversely affect the fabricability or weldability of the ternary alloy Ta8W2Hf, while producing a significant improvement in tensile and stress rupture properties. In certain applications, the addition of either carbon or nitrogen alone in amounts above 0.02% and up to 0.05 w./o. results in improved properties.

The following examples are illustrative of the manner of preparing alloys disclosed by the present inventiornln these examples, the percentages given for the composition are by weight (w./o.) and the hardness values are diamond pyramid hardness (d.p.h.).

EXAMPLE I An alloy of the following composition was prepared by non-consumable arc melting: 86% tantalum, 11.2% tungsten and 2.8% hafnium. The resulting ingot was reduced 70% into sheet and samples of the sheet were recrystallized by heating for one hour at 3000 F. When tested at a temperature of 3000 F., the ultimate tensile strength and the 0.2% offset yield strength were both 20,100 p.s.i. and the resulting elongation was 38%. The samples had an average hardness of 240 d.p.h. in the cast condition and 230 d.p.h. after reduction to sheet and annealing at 1 hr./3000 F.

EXAMPLE II An ingot of three inches diameter of an alloy of the following composition was prepared by non-consumable arc melting: 88% tantalum, 9.6% tungsten, and 2.4 hafnium (nominal). Interstitial carbon in an amount of 0.011% was added. The ingot heated to 2200 F, was broken down by high energy forging. This forged alloy has been found to exhibit a 0.2% offset yield strength of 15,800 p.s.i. and an ultimate strength of 15,900 p.s.i. at 3500 F., with an elongation of 37%. Sheets 6 inches by 24 inches were produced from the foregoing by cold rolling. The samples had an average hardness of 292 d.p.h. in the as cast condition and 286 d.p.h. after reduction to sheet and 1 hr. anneal at 3000 F. This example illustrates the beneficial effect of the small amount of carbon.

Both single and double arc melting using consumable arc melting were employed to produce other ingots. The double arc melted ingot gave better results on high ternperature (3000 F. and over) tests, though both were essentially similar in 2400 F. tests.

EXAM PLE l l l.

An alloy of the following composition was prepared by non-consumable arc melting: tantalum, 8% tungsten and 2% hafnium. In addition, an interstitial amount, 0.02% of nitrogen was introduced in the form of a master alloy. Samples Were removed from the resulting ingot after it was reduced 70% and recrystallized for one hour at 3000 F. The alloy exhibited an ultimate tensile strength of 18,900 p.s.i. and a 0.2% offset yield strength of 18,400 p.s.i. at 3000 F. with an elongation of 43%. In addition, the alloy exhibited an excellent sub-zero at 320 F. ultimate tensile strength of 187,200 p.s.i., elongation of 25%, and a 0.2% offset yield strength of 178,300 p.s.i. The average hardness of the samples has been found to be 285 d.p.h. in the as cast condition and 270 d.p.h. after reduction to sheet and annealing 1 hr. at 3000 F. The rupture strength of this alloy was found to be 43,500 p.s.i. and 32,500 p.s.i. for one hour and ten hours stress rupture lives respectively.

Sheets and other members of the alloys of these xamples were readily cut into desired shapes by machining, and were weldable into assemblies.

Small amounts of zirconium, preferably not exceeding /2% by weight, may be present in the alloys of this invention. In amounts substantially above /z%, the zirconium raises the weld bend transition temperature and induces hot tearing during welding. If the alloy members are not to be welded, then the alloy may include up to a maximum of 2% of zirconium.

It Will be understood that the foregoing description is only exemplary and not limitative of the invention.

Accordingly what is claimed as new is:

1. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content of said alloy ranges between 10% and 14%, from 0.005% to 0.05% carbon, from 0.005% to 0.07% nitrogen and up to 0.07% oxygen, up to 0.5% zirconium, and the balance being tantalum except for small amounts of incidental impurities and wherein the ratio of tungsten to hafnium varies between 2.5 :1 and 5.5 :1.

2. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 12 and 14% by weight, from 0.005 to 0.5% carbon, from 0.005% to 0.07% nitrogen and up to 0.07% oxygen, and the balance being tantalum except for small amounts of incidental impurities and wherein the ratio of tungsten to hafnium ranges between 2.5:1 and 5.5: 1.

3. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 10 and 14% by weight, from 0.005% to 0.05% carbon and 0.005% to 0.07% nitrogen, and up to 0.07% oxygen and the balance tantalum except for incidental impurities and wherein the ratio of tungsten to hafnium ranges between 3:1 and 5:1.

4. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 10% and 14%, from 0.005% to 0.05% carbon, from 0.005% to 0.07% nitrogen and up to 0.07% oxygen, and the balance being tantalum except for small amounts of incidental impurities wherein the ratio of tungsten to hafnium is about 4:1.

5. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 10% and 14%, from 0.01 to 0.05% by weight of at least one of the group consisting of carbon and nitrogen, up to 0.5% zirconium, and the balance tantalum, the ratio of tungsten to hafnium being from 2.5:1 to 5.5: 1.

6. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 10 and 14% and wherein the ratio of tungsten to hafnium ranges between 2.5:l and 5.5: 1, and the balance tantalum, and from 0.01

to 0.05% by weight of at least one of the group consisting of carbon and nitrogen.

7. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 10 and 14% and wherein the ratio of tungsten to hafnium ranges between 2.5:-1 and 5.511, and the balance tantalum and from 0.01 to 0.05% by weight of carbon.

8. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium, wherein the total tungsten and hafnium content ranges between 10 and 14% and wherein the ratio of tungsten to hafnium ranges between 2.5 :1 and 55:1, and the balance tantalum and from 0.01 to 0.05 by weight of nitrogen.

9. A tantalum base alloy consisting essentially of tantalum, tungsten and hafnium wherein the total tungsten and hafnium content ranges between 10 and 14% by weight and wherein the ratio of tungsten to hafnium is about 4:1 with the balance being tantalum, together with 10 from 0.005 to 0.05% by weight of at least one of .the group consisting of carbon and nitrogen.

References Cited UNITED STATES PATENTS 3,243,290 3/1966 Clark et a1. 75-174 3,113,863 12/1963 Chang et a1 75174 3,166,414 1/1965 France et al. 75174 OTHER REFERENCES Columbium-Base Alloys, General Electric Company, February 1962.

Temperature Dependence of the Tensile Properties of Tantalum, Pugh, Transactions of ASM, vol. 48, pp. 677 688.

CHARLES N. LOVELL, Primary Examiner.

DAVID L. RECK, Examiner.

Claims (1)

1. A TANTALUM BASE ALLOY CONSISTING ESSENTIALLY OF TANTALUM, TUNGSTEN AND HALNIUM, WHEREIN THE TOTAL TUNGSTEN AND HAFNIUM CONTENT OF SAID ALLOY RANGES BETWEEN 10% AND 14%, FROM 0.005% TO 0.05% CARBON, FROM 0.005% TO 0.07% NITROGEN AND UP TO 0.07% OXYGEN, UP TO 0.5% ZIRCONIUM, AND THE BALANCE BEING TANTALUM EXCEPT FOR SMALL AMOUNTS OF INCIDENTAL IMPURITIES AND WHEREIN THE RATIO OF TUNGSTEN OF HAFNIUM VARIES BETWEEN 2.5:1 AND 5.5:1.

Images