US3384479A - Columbium-base alloys - Google Patents

Description

United States Patent 3,384,479 COLUMBlUM-BASE ALLOYS Winston H. Chang, Cincinnati, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Filed July 8, 1965, Ser. No. 470,560 3 Claims. (Cl. 75-174) ABSTRACT OF THE DISCLOSURE columbium-base alloys consisting essentially of, by weight, about 30% W, ODS-0.12% C, 05-60% of Ti, Zr, or Hf, or combinations thereof have been found to have very high creep and tensile strengths at elevated temperatures and are ductile and fabricable at low temperatures.

This invention relates to high strength workable columbium-base alloys, and more particularly to such alloys which are capable of possessing significant tensile ductility at room temperature.

Over the past decade, many improvements have been made in columbium-base alloys resulting in higher strength combined with workability, oxidation resistance and other desirable factors. Naturally, further significant improvements that can be made in these areas will continue to be desirable. However, it has come to be accepted that significant increases in high temperature strength are generally accompanied by diminishing or disappearing low temperature ductility and its concomitant characteristic--workability.

Although increasing amounts of highly refractory solid solution alloy additives were found to be useful in increasing strength in the lower alloy ranges such as up to about or it was generally expected that significantly higher amounts of solute metals such as tungsten would be quite harmful to ductility and workability. Indeed, it was considered by some that increases beyond tungsten in carbide strengthened columbium-base alloys would not result in increased strengthening. (Percentages herein are by weight except where indicated otherwise.)

It is a principal object of the present invention to provide columbium-base alloys having significantly higher levels of strength at elevated temperatures such as 2400 F. to 3000 F. than previously available in combination with workability and low temperature ductility in a fabricated condition.

Another object of the invention is to provide such alloys that also possess useful oxidation resistance so that they might be used in oxidizing atmospheres with appropriate coatings, and might be useful in nonoxidizing atmospheres containing small amounts of residual oxidizing impurity gases even without coatings.

Briefly stated, the present invention in one aspect provides columbium-base alloys consisting essentially of, by weight, about 30% W, -0.05-0.12% C, 0.56.0% total reactive metal selected from the group consisting of Ti, Zr and Hf and combinations thereof, the balance essentially all columbium and residual impurities. Aside from carbon, other interstitial elements including oxygen and nitrogen may be useful in stabilizing precipitates, or, alternatively, they might be considered as residual impurities having no great effect on the properties of the alloy, de-

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TABLE I.CHEMICAL ANALYSES Analysis, Weight Percent Alloy Item 1 Ti Zr 0 0 N H CIH {N 30.0 1.0 0.1

1 N =uominal; A =analyzed.

Cb-l and Cb-2 were consolidated by pressing together well-blended metal powders in the proportions in the nominal compositions to form electrodes which were then sintered and vacuum-arc melted. Based on heat-treatment results of as-cast materials, the ingots were extruded at 3750 F. for Cb-l and 3500 F. for Cb2. Both ingots were extruded, jacketed in molybdenum cans, at a ratio of about 9: 1, resulting in significant hot-work with incipient recrystallization. Swagin-g was then performed on the Cb-l extruded bar at 2750 F. for a 50% reduction in cross section, followed by swaging for a total of 93% reduction in area (from extrusion) at 500 F. The same swaging treatment was successfully performed on extrusions of both alloys following aging at 2-700 F. for one hour.

The one-hour complete recrystallization temperatures were determined to be 3200 F. for Cb-l and 2900 F. for Cb-2.

My studies have shown that the Cb-l alloy contains a face-centered-cubic (FCC) phase (Zr, Cb, W)C which may also contain substantial amounts of oxygen and nitrogen as the stable precipitate below about 3000" F. Above that temperature, Cb C and ZrO also exist. Apparently due to the additional presence of Ti, alloy Cb-2 contains as its precipitate the FCC phase (Zr, Cb, Ti, W)C exclusively, except for small amounts of ZrO The Ti content and especially the ratio of (Ti+Zr)/C seem to suppress the formation of Cb C.

Aging studies were performed on specimens .of swaged Ob-l and C b-2 solution treated at 3500 F. and then aged for one hour at various temperatures in the range of 1500-3000 F. Maximum hardness aging peaks occur at about 2100 F. for Cb-l and 1750 F. for Cb-2. The age hardening of Cb-l appears to be accompanied by dissolution of the Cb C phase and precipitation of FCC (Zr, Cb, W)C phase. Within the 2000-2250 F. range of peak hardening, however, the precipitating FCC phase could not be discerned under optical examination. In alloy Cb-Z, the (Zr, Ob, Ti, W)C precipitated directly from the matrix in the absence of any pre-existing Cb C.

These studies indicate that carbide dispersion strengthening is most effective in these alloys at temperatures below about 2200 F., although some strain-induced precipitation may persist up to 250 F. Thus, solution strengthening becomes more effective and more necessary for retaining strength at higher temperatures. I have discovered that about 30% tungsten in combination with thestated amounts of carbide-precipitating additives results in considerably stronger alloys than previously available postion than in a stress-relief condition, particularly in alloy sessing workability and low temperature ductility in an Cb-l. as-Worked condition and when stress-relieved. An alloy of the prior art with which Cb-l can be comhaving a nominal composition of 15% W, 5% Mo, 1% Zr, .1% C, the balance columbium. Table III presents a comparison of the tensile properties showing that Cb-l is considerably temperatures, while still retaining superior ductility even at room temperature.

d 4 4% F a y a 0 d H mt a a S 1 .1 am. m m a f nu OS 5 a f md a n a y fin s Be r t S r u Tensile testing of specimens in various heat-treated condition-s has shown that alloy Cbroom-temperature ductility after one-h 2500 R, either directly swaged or aged before being swaged, and alloy Cb-Z possesses such ductilit stress-relief treatment at 2200 F.

TABLE III.-TENSILE PROPERTY COMPARISON 013-] vs. F-48 Test Tensile Elongation, Alloy Temp., Strength, percent F. K s.i.

1 Table IV compiles tensile properties of the Cb2 alloy ged at as swaged after having been aged at 2750 F. for one hour. S.R. means stress relief for one hour at 2200 F., and R means recrystallized at 2900 F. for one hour. A it did for Cb-l, recrystallization of Cb-2 raises the ten- TABLE IV.-TENSILE PROPERTIES OF Ola-2 ALLOY Heat Tensile 0.2% Yield Elongation, Reduction Test Temp, F. Treatment Strength, Strength, percent in Area, K s.i. K s.i. percent Table II presents data on the tensile properties of Cb directly swaged and as swaged after having been a 2750 F. for one hour. The column on heat treatment involves three treatments for one hour: SR. 1 is a stress gth than that pared with prior art a nominal composition of 15% Ti, 0.1% C, the balance columbium.

sile transition temperature (in this case to about 300 and results in somewhat higher tensile stren or the stress-relieved condition.

Likewise, alloy Cb-2 can be com in Area, percent alloy F-SO, having 75 5% Mo, 1% Zr, 5%

. aeutaLaaZow B MWW N1112 1 164 gation, Reduction percent 013-1 ALLOY 0.2% Yield Elon gth, Strength, 5 i K s.i.

Tensile Stren K [A. Directly swaged] 2 2 2 2 2 2 1 2 .1 a ma. S SSSSSS m SS S TABLE II.TENSILE PROPERTIES OF Heat Treatment Although recrystallization raises the ductile-to-brittle transition temperature, it is accompanied by strain-induced precipitation, resulting in considerably higher strengths at temperatures above 1000 F in the recrystallized COI'lCllrelief at 2200 F., SR. 2 is a stress relief at 2500 F., and R is a recrystallization treatment at 3200 F.; K s.i. means thousands of pounds per square inch.

5 6 The same strength superiority accompanied by room- 29,000 p.s.i., corresponding to a 100-hour strength-totemperature ductility retention over F-SO is found with density ratio of 78,000 inches (0.371 1b./in. nominal). In Cb-2 as was found with Cb-l over F-48. addition to room-temperature ductility, rupture ductility TABLE V.TENSILE PROPERTY COMPARISON Cb-2 VS. F-50 All tensile testing of Cb-l and Cb-2 alloys was perof the C-b-l was characterized by about 20% elongation formed in vacuum (except at room temperature) at a 20 and 80% reduction of area. Due in part to overaging and nominal strain rate of 0.05/minute. The stress-relieved incipient recrystallization, the 100-1 Strength of ..2 tensile specimens were of the button-head type having a at 24000 F. was found to be about 14,500 psi The com of to of 0.125 inch diam ter by 0.33 inch length to assure the 25 meme relatonshlp suggests that the 20000 loo'hollf complete removal of surface defeda strength of Cb-1 and Cb 2 should be about 50,000 p.s.i.

Stress-rupture testing was performed at 2400 F. to and 401000 P- respectlvelybli h h 100-1 strength Th rupture Specimens Satisfactory oxidation-resistant characteristics of Cb-1 were identical to what was used for tensile testing, and and Cb-2 were found and are tabulated in Table VII TABLE VI.-CREEP-RUPTURE DATA ON STRESS-RELIEVED ALLOYS Stress, Life, MC R, Elongation, Reduction Alloy Condition 1 K s.i. Hrs. Percent [111. Percent in Area, Percent 35.0 14. 32 0.97 11. 1 77. 30.0 30.0 0. 70 17. 7 78. 4 Cb1- 30.0 137. 72 0.046 20. 4 77. 7 30. 0 54. 29 0. 122 22. 0 77. 0 27. 124. 05 0. 047 21. 7 81. 0 35.0 1. 76 23. 2 75. 5 30. 0 3. 70 22. 3 59. 4 Cb2 B 20.0 5. 34 1. 67 18. 5 69. 1 17. 5 28. 64 0. 44 47. 5 82. 0 15.0 71.8 0. 02 41. 2 82. 7

1 A directly swaged and stress relieved; B aged, swaged, and stress relieved.

testing was conducted by direct loading in a radiationbelow. Alloy Cb-2 is significantly superior to alloy Cb-l,

heated furnace evacuated by an ion pump to a vacuum of due in part to the titanium content of Cb-2.

torr. Data obtained are presented in Table VI above. Although the present invention has been described The data were consistent and well correlated by the 50 with respect to certain embodiments, it will be under- Larson-Miller parametric relationship of P=T(+log t) stood by those skilled in the art that certain changes, omiswhere T is temperature in degrees Rankine and t is hours. sions and substitutions may be made within the spirit and The 100-hour strength of Cb-l was found to be about scope of the invention as defined in the appended claims.

TABLE V1I.OXIDATION DATA 0F CB-BASE ALLOYS Weight Gain, Depth of Harden- Metal Loss,

Temp., F. 'lEme, mg. cm. ing, mils side mils side Cb-l (lb-2 Ob-l Cb-2 Cb-l Clo-2 1 Terminal air tests unless otherwise indicated.

2 Continuous weight-gain air test.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A columbium-base alloy consisting essentially of, by weight, about: 30% W, ODS-0.12% C, 0.56.0% total reactive metal selected from the group consisting of Ti, Zr and Hi and combinations thereof, the balance essentially all columbium and residual impurities.

2. A columbium-base alloy consisting essentially of, by weight, about: 30% W, ODS-0.1% C, 15% Ti, 0.84% Zr, and the balance essentially all columbium and residual impurities.

3. A columbium-base alloy consisting essentially of, by weight, about: 30% W, O.51.0% Zr, 0.050.1% C, the balance essentially all columbium and residual impurities.

8 References Cited UNITED STATES PATENTS 2,973,261 2/1961 Frank 75174 3,056,672 10/1962 Clark 75-l74 3,113,863 12/1963 Chang et al. 75-174 FOREIGN PATENTS 889,099 2/1962 Great Britain. 923,225 4/ 1963 Great Britain.

CHARLES N. LOVELL, Primary Examiner.