US3434810A - Nickel-base dispersion hardened alloy - Google Patents

Description

United States Patent 3,434,810 NICKEL-BASE DISPERSION HARDENED ALLOY William J. Barnett, Brandywine Hundred, Del., assignor by mesne assignments, to Fansteel Inc., a corporation of New York No Drawing. Filed June 30, 1965, Ser. No. 468,592 Int. Cl. B22f 1/00, 9/00 US. Cl. 29-182.5 6 Claims ABSTRACT OF THE DISCLOSURE Nickel-molybdenum alloys, which are modified with certain dispersed, particulate refractory oxides and contain from 0.002 to 0.5 percent total carbon, are given improved ductility and high temperature strength properties by incorporating therein from 0.1 to 1.0 percent of zirconium or hafnium, of which greater than 0.02% is soluble in bromine-methanol solution.

in bromine-methanol solution, 0.002 to 0.5 percent total carbon, about from 1 to 6 percent by volume of a refractory oxide filler, said oxide having a free energy of formation at 1000 C. greater than 106 kilocalories per gram atom of oxygen, the balance of the compositions being nickel or a mixture of nickel with up to 40 percent of cobalt by weight, based on said nickel component, said oxide filler being in the form of particles in the size range of to 250 millimicrons, the average being less than about 100 millimicrons, and said particles being pervasively dispersed in the metal components of the alloys, the average minimum diameter of the grains in said alloy being greater than 10 microns. The invention is further particularly directed to the steps, in a process for making the novel alloys, comprising forming by powder metallurgy a consolidated body having the chemical composition desired, and containing the refractory oxide dispersed in the nickel, cobalt or molybdenum or in two or more of these components, cold-working said consolidated body at a temperature of up to 2000 F. to density it substantially to 100 percent density and to store energy therein sufficient to permit recrystallization, and heat-treating said cold-worked body by heating it to a temperature in the range of 1850 to 2400 F.

In Alexander et al., US. Patent 3,180,727 there is described a novel system of alloys which are dispersionhardened and which are adapted for use in high temperature applications such as in aircraft gas turbines. The alloys therein described have outstanding high temperature properties in that they retain their strengths well beyond the temperature limits at which ordinary metals or alloys become unusable. In certain special applications, however, the problem is not so much the retention of strength at the highest temperatures, but rather this in combination with the adequate strength at the intermediate temperatures for use under very high stresses. Thus, in the manufacture of turbine blades, the base or root section of the turbine blade operates at somewhat lower temperatures 3,434,810 Patented Mar. 25, 1969 than the air foil section but operates under higher stresses. In this and similar applications the alloys heretofore described, even When dispersion-modified, leave much to be desired.

There is, moreover, a need for a material which has an optimum relationship between creep and rupture ductility. Materials of construction lacking such ductility, such as cermets, may fail without warning. On the other hand, materials having adequate rupture ductility will creep sufficiently that the imminence of failure can be detected by suitable inspection during service life. Ideally, for use in a turbine blade assembly, an alloy should have a very low creep rate in the early stages of its service life, but when failure is imminent it should have sufficient ductility that failure is not instantaneous and catastrophic.

Now, according to the present invention, it has been found that when the composition of certain dispersionhardened alloys is carefully controlled within specified, rather narrow limits, alloys can be produced which have adequate rupture ductility, i.e., greater than 2 percent elongation, and at the same time have a rupture strength, at 1400 F. and hours life, which is greater than 32,000 pounds p.s.i. It has been found that the molybdenum content of nickel or nickel-cobalt base alloys should be carefully controlled within the limits of 12 to (22+8 times the wt. percent carbon) percent, and that such alloys should contain small but critical amounts of carbon and zirconium or hafnium. The total carbon content of such alloys must be in the range from 0.002 to 0.5 percent by weight. The zirconium or hafnium content should be from 0.1 to 1.0, the alloys containing zirconium being a strongly preferred embodiment of the invention. The soluble zirconium or hafniumthat is, the amount soluble in bromine-methanol solution-should be greater than 0.02 percent based on the total weight of the composition. The compositions must, of course, be dispersion-hardened by the presence of about 1 to 6 percent by volume of a very refractory metal oxide in particulate form, the high degree of refractoriness of the oxide being indicated by the fact that its free energy of formation at 1000 C. is greater than 106 kilocalories per gram atom of oxygen in the oxide. The average minimum diameter of the grains in the alloys is about from 10 to 100 microns.

The major metallic component of the novel alloys is nickel, although the nickel may contain substantial but minor proportions of cobalt. Thus, the nickel may contain up to about 40 percent of its weight of cobalt, although normally the cobalt, if present, will be less than this amount. The molybdenum is a minor component but one which contributes substantially to the strength of the alloys at intermediate temperatures.

The carbon and zirconium or hafnium, although minor constituents, are critically important in providing ductility and workability to the alloys. They also appear to contribute to the unusually high rupture strengths at intermediate temperatures. Thus, an alloy containing 17.5 percent molybdenum 'but without zirconium or carbon present, for instance, and dispersion-strengthened with 2 percent thoria, might show a 1400 'F./ 100 hour rupture strength of say 28,000 p.s.i., whereas with both carbon and zirconium present, as required according to this invention, such rupture strength is in excess of 32,000 p.s.i. It will be understood that a combination of zirconium and hafnium can be used in the alloy, provided the total proportion of these two elements is within the range given for either alone. The alloys containing zirconium alone are greatly preferred.

Processes for dispersing refractory oxides such as thoria in matrix metals such as nickel and nickel-molybdenum alloys are already well known in the art and are described, for instance, in Alexander et al. US. Patent 3,087,234. It is extremely important to have the refractory oxide Well dispersed in the matrix metal. In describing the present invention, the oxide is said to be pervasively dispersed-that is, it is dispersed throughout the product, rather than being clustered together in a few areas at high concentration and being absent or substantially so in other areas. Moreover, the refractory oxide is present within the grains as well as being observable at the grain boundaries.

In preparing dispersion-modified nickel and nickel alloys a preferred process is to precipitate the refractory oxide in particulate form together with the oxides of the matrix metals and then reduce the metal matrix oxides to met-a1 by such methods as dry hydrogen reduction. It is important to effect complete reduction at this stage. The reduced powder is compacted to the form of a green billet, and this billet is then consolidated to a solid body which can serve as a starting material in a process of the present invention.

In a preferred embodiment of the invention, the starting material is prepared as a particulate solid comprising a compound of each metal of the group nickel and cobalt which is to be present in the final alloy, this solid having the refractory oxide dispersed in it; the particulate solid is dispersed in an aqueous ammonium molybdate solution at a pH of 5.5 to 8.5 whereby a molybdenum-containing coating is deposited on its surface, the coated solid is separated from the solution and calcined at 100 to 550 C., and the calcined product is heated at 450 to 1200 C. in contact with hydrogen, carbon, carbon monoxide or a hydrocarbon gas, whereby the particulate solid and its molybdenum-containing coating are reduced to their component metals and these metals are alloyed with each other, the refractory metal oxides remaining unreduced and dispersed therein.

The carbon and zirconium or hafnium in a process of the present invention are introduced into the powder of matrix metal containing thoria before such powder is consolidated. The carbon can advantageously 'be introduced in its powdered elemental form. The zirconium or hafnium can also be introduced as an elemental powder or it can be added as zirconium or hafnium hydride, a master alloy composition of zirconium or hafnium with a metal of the matrix, or a hydride of such master alloy.

It is important that the carbon, zirconium or zirconiumoontaining material, or hafnium or hafnium-containing material, and the refractory oxide-filled matrix metal be mixed together in the form of very fine powders. Thus, the particle size of zirconium or hafnium powder preferably should be less than microns, the carbon particle size preferably should be minus about 200 mesh, and the refractory oxide-filled molybdenum nickel matrix metal should preferably have a size less than 100 percent minus 200 mesh and 50 percent minus 325 mesh. In any event, the mixing should be extremely thorough, and the particle size and mixing should be such as to elfect very intimate contact between the various components. Moreover, the mixing methods and the choice of materials should be such as to provide uniform dispersion of the additives with respect to the matrix alloy.

Having prepared a powder blend containing the desired constituents, the powder blend is compacted to a consolidated body having greater than 60 percent density. This can be accomplished quite easily by hydrostatic compaction. In this way a so-called green billet is obtained. In a preferred embodiment this billet is then sintered in hydrogen at temperatures below about 900 P. so as to remove any surface oxygen which has formed during the handling after the original reduction. This precaution is taken to minimize the formation of zirconium oxide in subsequent steps of the process. The temperature is then increased stepwise to about 1650 F. maintaining the dew point of the eflluent gas being used in the reduction at below 90 F. This sintering operation is carried out in a can or within a protective environment. In a particularly preferred embodiment the sintering is continued under vacuum at about 1650 'F. and a pressure less than 20 microns. After this hydrogen sinter under vacuum the billet is cooled to room temperature and sealed under this vacuum. Alternatively, the billet can be cooled under hydrogen or pure argon. In any event, oxygen contamination is to be avoided.

The sintered billet is then extruded to consolidate it. The density is thereby increased to about 99 percent of theoretical.

If the extrusion operation leaves in sufficient residual stored energy, such as if the recrystallization temperature is less than about 2400 F. for two hours, the consolidated product is recrystallized. Otherwise the product is worked at temperatures below 2000 F. by swaging, forging, bar-rolling, etc. This results in a reduction of the recrystallization temperature to the range of 1850 to 2200 F. for alloys with less than 3 percent thoria. With alloys containing more than 3 percent thoria the recrystallization temperature may remain above this figure. In a process of the invention the worked product is recrystallized at appropriate temperature.

For compositions of this invention containing about .1 to .3 percent carbon a further step may advantageously be employed consisting of heating to approximately 2200 F. to cause any carbides present to dissolve, and then quenching the system to retain the carbon in solution. The product thus obtained can advantageously then be aged at a temperature in the range of 1400 to 1800" F. for times from 4 to 24 hours. It will be understood that this solution heat-treatment can be combined with the aforementioned final recrystallization step.

The novel compositions of the invention which can be prepared by the processes above described are particularly well adapted for use as a material of construction in any situation where retention of high strength at intermediate temperatures-say 1000 to 1500 F.are encountered in service. The products also have high utility at very high temperaturessay 1800 F. and above. At 1800 to 1900 F. their strengths surpass the so-called superalloys. Thus, they are well adapted for use in gas turbines where portions of the structure must have high strength at very elevated temperatures and other portions must have good strength at somewhat lower temperatures.

The invention will be better understood by reference to the following illustrative examples:

EXAMPLE 1 A thoriated nickel-15 percent molybdenum alloy powder was prepared by adsorbing molybdate on a nickel carbonate-thoria coprecipitate, and reducing the resulting product with hydrogen. The nickel carbonate-thoria coprecipitate was prepared using the technique of Example 5 of U.S. Patent 3,019,103 except that twice as much thoria was used, and the thoria was introduced as Th(NO solution. The coprecipitate was filtered and washed, and then treated with a solution of ammonium molybdate, whereupon molybdate adsorbed on the nickel carbonate. The resulting product was filtered and dried at 400 C., and then reduced with hydrogen by treating the dried mass for 2 hours at 400 C., 2 hours at 650 C. and finally for 6 hours at 850 C.

The chemical composition of the thoriated nickelmolybdenum alloy powder was, by weight percent: 1.84% T 14.98% Mo, 0.0028% C, less than 0.001% S. One hundred percent of the resultant powder would pass a 200 mesh screen.

Three tenths percent by weight of zirconium hydride and five one-hundredths percent by weight of Darco carbon, the average particle size of each additive being less than ten microns, was cone-blended for two hours. A billet was prepared by hydrostatically compacting the powder blend at 60,000 p.s.i. The billet was machined to a right circular cylinder and was welded into a mild steel can containing entrance and exit tubes for passing Stress rupture properties of samples cut from the annealed bar were:

Specimens from the swaged bar which were annealed at 1850 F. for 2 hours plus 2200 F. for 2 hours yielded the following rupture properties:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs. percent of Area,

13. percent Stress rupture strength of a specimen of the extruded bar after annealing at 2200 F. for 16 hours was:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs. percent of Area, F. percent EXAMPLE 3 A thoriated nickel-18 percent molybdenum alloy powder was prepared by the method described in Example 1. The chemical composition of the thoriated nickel-molybdenum alloy powder was, by weight percent: 1.91% ThO 17.58% Mo, 0.009% C, 0.00l1% S. Thoria size as measured by X-ray techniques was 13 millimicrons. One hundred percent of the resultant powder would pass a 200 mesh screen. Three-tenths perment by weight of zirconium hydride and five-tenths percent by weight of ground and sized -200/ +325 mesh spectro-graphic stick carbon, the average particle size of the ZrH additive being less than ten microns, was cone-blended for 2 hours.

From this powder a billet was prepared, canned, and reduced with dry hydrogen, all as described in Example 1, the reduction conditions being as follows:

The billet was heated slowly to 490 F. under a flow of about 7 cubic feet per hour of said hydrogen. After about 16 hours at temperature the dewpoint of the effluent hydrogen was less than '90 F. The temperature was then increased to 760 F. for 4 hours, then to 1000 F. for 2 hours, then to 1625 F. for 2 hours, the dewpoint of the effluent hydrogen after each heating period being below '90 F.

After the reduction was completed, hydrogen flow was terminated, and the canned billet was evacuated at temperature. After about 1% hours at temperature under vacuum an ultimate pressure of about 8 microns was attained. The canned billet was slowly cooled to room temperature under vacuum.

The exit and entrance tubes were then forge-welded shut. The canned billet was extruded at 1700 F. to a reduction ratio of 8/1. After extrusion the mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed less than 0.001 weight percent sulfur, and 0.456 weight percent carbon.

By digesting the extruded bar in a bromine-methanol solution and analyzing the soluble fraction for zirconium it was found that over 34 percent by weight of the zirconium added remained as zirconium alloyed in the nickel-molybdenum alloy matrix. The remaining approximately 66 percent (approximately 0.16 weight percent of product) was in the form of ZrO Zr(CN) or similar compounds insoluble in the digestion medium.

The thoriated nickel-molybdenum alloy bar was then canned in stainless steel tubing of about & wall thickness, heated to 1500 F. for 2 hours and swaged from 1500 F. with reheating after each pass, to a reduction of about 63.9 percent in cross-sectional area. After swaging the stainless steel can was removed by pickling.

The swaged bar was annealed at 2200" F. for 2 hours. Metallographic examination of the annealed bar revealed a relatively uniform, fine-grained, recrystallized micro structure.

Stress rupture properties of samples cut from the annealed bar were:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs. percent of Area,

F. percent Other specimens from the swaged bar were solution treated at 2200 F. for 2 hours, quenched in water and aged at 1650 F. for 16 hours. Stress rupture properties of these solution treated and aged specimens were:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs. percent of Area, F. percent EXAMPLE 4 The Ni-Mo-Th0 powder of Example 2 was used in this example. T hree-tenths percent by weight each of zirconium hydride and ground and sized 200/+325 mesh spectrographic stick of carbon, the average particle size of the ZrH additive being less than 10 microns was cone-blended with this starting powder for two hours.

From this powder a billet was prepared, canned and reduced with dry hydrogen, all as described in Example 1, the reduction conditions being as follows:

The billet was heated slowly to about 440 F. under a flow of about 7 cubic feet per hour of said hydrogen. After about 16 hours at temperature the dewpoint of the effiuent hydrogen was less than F. The temperature was then increased to about 800 F. for 3 hours, then to 1000 F. for 2 hours, then to 1610 F. for 4 hours, the dewpoint of the effluent hydrogen after each heating period being below 90 F.

After the reduction was completed, hydrogen flow was terminated, and the canned billet was evacuated at temperature. After about 2 hours at temperature under vacuum an ultimate pressure of about 2 microns was attained. The canned billet was cooled to room temperature under vacuum.

The exit and entrance tubes were forge-welded shut, and the canned billet was extruded at 1700 F. to a reduction ratio of 8/1. After extrusion the mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed 16.6 weight percent molybdenum, less than 0.001 weight percent sulfur, and 0.262 weight percent carbon. By digesting the extruded bar in a bromine-methanol solution and analyzing the soluble fraction for zirconium it was found that over about 19 percent by weight of the zirconium added remained as zirconium alloyed in the nickel-molybdenum alloy matrix. The remaining approximately 81 percent (approximately 0.222 weight percent of product) was in the form of ZrO Zr(CN) or similar compounds insoluble in the digestion medium.

The thoriated nickel-molybdenum alloy bar was then canned in stainless steel tubing of about wall thickness, heated to 1500 F. for 2 hours and swaged, with reheating after each pass, to a reduction of about 62.3 percent in cross-sectional area. After swaging the stainless steel can was removed by pickling.

The swaged bar was annealed at 2200 F. for 2 hours. Metallographic examination of the annealed bar revealed a relatively uniform, fine-grained, recrystallized microstructure.

hydrogen over the billet and for evacuation. The canned billet was evacuated at room temperature to a pressure of less than about 50 microns and back-filled with pure dry (dew point less than 90 F.) hydrogen. The billet was heated slowly to 400 F. under a flow of about 7 cubic feet per hour of said hydrogen. After about 2 hours at temperature the dew point of the effiuent hydrogen was less than 90 F. The temperature was then increased to 700 F. for about 2 hours, then to 900 F. for 1 hour, then to 1650 F. for 2 hours, the dew point of the eiiluent hydrogen after each heating period being below 90 F.

After 2 hours at 1650 F., hydrogen flow was terminated, and the canned billet was evacuated at temperature. After about /1 hours at temperature under vacuum an ultimate pressure of about microns was attained. The canned billet after having been cooled to ambient temperature under vacuum exhibited a leak rate as indicated by pressure rise in the system of less than 1 micron in 60 minutes. The exit and entrance tubes were forgewelded shut. The canned billet was extruded at 1700 F. to a reduction ratio of After extrusion, the mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed 14.5 weight percent molybdenum, less than 0.001 weight percent sulfur, and 0.025 weight percent carbon. By digesting the extruded bar in a bromine-methanol solution and analyzing the soluble fraction for zironium it was found that over about 48% by weight of the zirconium added remained as zirconium alloyed in the nickel-molybdenum alloy matrix. The remaining approximately 52 percent (approximately 0.142 weight percent of product) was in the form of ZrO Zr(CN) or similar compounds insoluble in the digestion medium.

The thoriated nickel-molybdenum alloy bar was then heated to 1500 F. and swaged, with reheating after each pass, to a reduction of about 60.9 percent in cross-sectional area. The swaged bar was annealed at 1850 F. for 2 hours. Metallographic examination of the annealed bar revealed a relatively uniform, fine-grained, recrystallized microstructure.

Thoria particle size in the swaged bar was 18 m This was calculated from surface area after extraction of the thoria, as follows:

The metal component of a powder product of the invention is dissolved in an acid, or in bromine-methanol, leaving the filler oxide particles, which are recovered by coagulating, centrifuging, washing and drying.

The Br -CH 0H extraction procedure is as follows: Calculate the weight of metal for extraction required to give approximately 0.2 gm. ThO residue. Thus, 10 gm. of a metal containing 2 percent ThO are required. For each 10 gram portion of metal, prepare 500 ml. of solution containing 5.3 percent Br by volume in dry methanol. subdivide the metal. If dense, machine to chips. Add the metal slowly with stirring to the Br -CH OH solution. Place the solution in a water bath, and cool during the addition. (Temperature should be 35 C.) Avoid frothing caused by excessive gas evolution. After all the metal is added, remove the solution from the water bath, and allow to stand 24 hours with occasional stirring. Allow the residue to settle. Carefully decant the clear supernatant. Centrifuge the remaining residue. Wash and centrifuge the solid residue repeatedly with dry methanol until the supernatant liquor is colorless. Retain all decants and washings for 24 hours to see if additional residue settles out. If so, repeat the centrifuging and washing procedure so as to include this material with the original residue. If, during washing, the ThO residue begins to peptize, fioc the material by adding 2 to 3 drops of concentrated HNO then continue centrifuging. Dry the final, washed residue and weigh.

The surface area of the recovered oxide from the abovedescribed process is then measured by the conventional BET method or its equivalent. (P. H. Emmett in Symposium on New Methods for Particle Size Determination in the Subsieve Range, Philadelphia: ASTM, 1941, p. 95.) From this surface area measurement, the mean particle diameter, D, is calculated from the expression: D=6000/fA where f is the absolute density of the filler oxide particles in grams per milliliter and A, is their surface area in square meters per gram.

Stress rupture properties of samples cut from the annealed bar were:

A thoriated nickel-15 percent molybdenum alloy powder was prepared by the technique of Example 1. The chemical composition of the thoriated nickel-molybdenum alloy powder was, by weight percent: 1.91% ThO 17.58% Mo, 0.009% C. 0.00l1% S. Thoria size as measured by X-ray techniques was 13 millimicrons.

One hundred percent of the resultant powder would pass a 200 mesh screen. Three-tenths percent by weight of zirconium hydride and five one-hundredths percent by weight of Darco carbon, the average particle size of each additive being less than 10 microns, was cone-blended with this powder for two hours.

A billet was prepared, canned, and reduced with dry hydrogen, all as described in Example 1, the reduction conditions being as follows:

The billet was heated slowly to 400 F. under a flow of about 7 cubic feet per hour of said hydrogen. After about 15 hours at temperature the dew point of the efiiuent hydrogen was less than F. The temperature was then increased to 600 F. for 1 hour, to 800 F. for 3 hours, and to 1 650 F. for 2 hours, the dew point of the effluent hydrogen after each heating period being below 90 F.

After the reduction was completed, hydrogen flow was terminated, and the canned billet was evacuated at temperature. After about hours at temperature under vacuum an ultimate pressure of about 20 microns was attained.

The exit and entrance tubes were forge-welded shut. The canned billet was extruded at 1800 F. to a reduction ratio of 8/ 1. After extrusion the mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed 17.8 weight percent molybdenum, less than 0.001 weight percent sulfur, and 0.025 weight percent carbon. By digesting the extruded bar in a bromine-methanol solution and analyzing the soluble fraction it was found that about 50 percent by weight of the zirconium added remained as zirconium alloyed in the nickel-molybdenum alloy matrix. The remaining approximately 50 percent (approximately 0.12 weight percent of product) was in the form of ZrO Zr(CN) or similar compounds insoluble in the digestion medium.

The thoriated nickel-molybdenum alloy bar was then heated to 1500 F. for 2 hours and swaged from 1500 F. with reheating after each pass, to a reduction of about 62.9 percent in cross-sectional area.

The swaged bar was annealed at 1850 F. for 2 hours. Metallographic examination of the annealed bar revealed a relatively uniform, fine-grained, recrystallized microstructure.

Stress rupture properties of samples cut from the annealed bar were:

Elongation, Reduction Test Tempeature, Stress, p.s.l. Life, hrs. percent of Area,

percent 1, 400 35, 400 57. 1 8. 0 8. 7 1, 400 33, 500 136. 0 4. 0 7. 9

Other specimens from the swaged bar were solutiontreated at 2200 F. for 2 hours, quenched in water and aged at 1650 F. for 16 hours. Stress rupture properties of these solution-treated and aged specimens were:

A thoriated nickel-21 percent molybdenum alloy powder was prepared by the chemical method described in Example 1 and ball-milled to '200 mesh. The chemical composition of the thoriated nickel-molybdenum alloy powder was, by weight percent: 2.74% ThO 21.4% Mo, 0.0046% C, less than 0.001% S. Thoria size as measured by X-ray techniques was 12 millimicrons.

This powder was cone-blended with, by weight, 0.30% of zirconium hydride and 0.05% Darco carbon, and a billet was prepared, canned, and reduced with dry hydrogen, all as described in Example 1, the reduction conditions being as follows:

The billet was heated slowly to 480 F. under a flow of about 7 cubic feet per hour of said hydrogen. After about 16 hours at temperature the dewpoint of the effluent hydrogen was less than --90 F. The temperature was then increased to 800 F. for 2%. hours, then to 1000 F. for 1 /2 hours, then to 1650 F. for 2 hours, the dewpoint of the efiluent hydrogen being below 90 F. after each heating period.

After the reduction was completed hydrogen flow was terminated, and the canned billet was evacuated at temperature. After about 2 hours an ultimate pressure of about 8 microns was attained. The canned billet was cooled to room temperature under vacuum.

The exit and entrance tubes were then forge-welded shut. The canned billet was extruded at 1875 F. to a reduction ratio of 16/1. After extrusion the mild steel can was removed by pickling.

The thoriated nickel-molybdenum alloy bar was then canned in stainless steel tubing of about wall thickness, heated to 1800 F. for 1 hour and swaged from 1800 F. with reheating after each pass, to a reduction of about 47.5 percent in cross-sectional area. After swaging the stainless steel can was removed by pickling. Hardness of the swaged bar was approximately 517 DPH.

The swaged bar was annealed at 2200 F. for 2 hours. Hardness of the annealed bar was 383 Diamond Pyramid Hardness. Metallographic examination of the annealed bar revealed a relatively uniform, tine-grained, recrystallized microstructure.

Stress rupture properties of samples cut from the annealed bar were:

Test Elongation, Reduction Temperature, Stress, p.s.l. Life, hrs. percent of Area, F. percent EXAMPLE 6 The Ni-Mo-ThO powder of Example 5 was used in this example. This powder was cone-blended with zirconium hydride and Darco carbon, and a billet was 7 prepared, canned, and reduced with dry hydrogen, all as described in Example 5, the reduction conditions being as follows:

The billet was heated slowly to about 425 F. under a flow of about 7 cubic feet per hour of said hydrogen. After about 16 hours at temperature the dewpoint of the efiluent hydrogen was less than F. The temperature was then increased to about 670 F. for 2 hours, then to 870 F. for 2 hours, then to 1615 F. for 3 hours, the dewpoint of the eflluent hydrogen being below -90 F. after each heating period.

After the reduction was completed, hydrogen flow was terminated, and the canned billet was evacuated at temperature. After about 1 /2 hours at temperature under vacuum an ultimate pressure of about 5 microns was attained. The canned billet was slowly cooled to room temperature under vacuum.

The exit and entrance tubes were then forge-welded shut. The canned billet was extruded at 1700 F. to a reduction ratio of 8/ 1.

The thoriated nickel-molybdenum alloy extruded bar was canned in stainless steel tubing as in Example 5 and then heated to 1900 F. for 2 hours and swaged from 1900 F. with reheating after each pass, to a reduction of about 51.9 percent in cross-sectional area. Hardness of the swaged bar was approximately 508 DPH.

The swaged bar was annealed at 2200 F. for 16 hours. Hardness of the annealed bar was about 381 Diamond Pyramid Hardness. Metallographic examination of the annealed bar revealed a relatively uniform, fine-grained microstructure.

Stress rupture properties of samples cut from the annealed bar were:

A second piece of the thoriated nickel-molybdenum alloy extruded bar was canned in stainless steel tubing of about wall thickness, heated to 1800 F. for 1 hour and swaged from 1800" F. with reheating after each pass, to a reduction of about 62.9 percent in cross-sectional area. After swaging the stainless steel can was removed by pickling. Hardness of the swaged bar was approximately 517 DPH.

The swaged bar was annealed at 2200 F. for 2 hours. Hardness of the annealed bar was 401 DPH. Metallographic examination of the annealed bar revealed a relatively uniform, fine-grained, recrystallized microstructure.

Stress rupture properties of samples cut from the annealed bar were:

This example was like Example 1 except that 0.3 percent ZrH was added to the Ni-Mo-Th0 starting powder. The billet was sintered for 3 hours at 400 F., 1 hour at 600 F., 2 hours at 875 F. and finally 2 hours at 1650 F. in hydrogen and then evacuated. The billet was extruded at 1700 at 8:1 ratio, swaged 60 percent at 1500 1 1 and heat treated for 2 hours at 1850 F. 1400 F. stress rupture properties were:

40,600 p.s.i. for 16 hours 35,400 psi. for 77 hours 33,000 p.s.i. for 235 hours I claim:

1. A dispersion-modified alloy characterized by having a 1400 F./ 100 hour rupture strength greater than 32,000 psi. and a rupture ductility greater than about 2 percent elongation, the composition consisting essentially of, by weight, about from 12 to (22+8 percent C.) percent of molybdenum, 0.1 to 1.0 percent of zirconium or hafnium, of which greater than 0.02 percent is soluble in bromine-methanol solution, 0.002 to 0.5 percent total carbon, about from 1 to 6 percent by volume of a refractory oxide filler, said oxide having a free energy of formation at 1000 C. greater than 106 kilocalories per gram atom of oxygen, the balance of the composition being nickel or a mixture of nickel with up to 40 percent of cobalt by weight, based on said nickel component, said oxide filler being in the form of particles in the size range of to 250 millimicrons, the average being less than about 100 millimicrons, and said particles being pervasively dispersed in the metal components of the alloy, the

3. A composition of claim 1 in which the average particle size of the dispersed oxide filler is less than about millimicrons.

4. A composition of claim 1 in which the element of the group consisting of zirconium ad hafnium is zirconiurn.

5. A composition of claim 1 in which the molybdenum content is 21 percent, the carbon content is 0.02 to 0.03, and the refractory oxide is thoria and is present in the amount 2.75 percent by weight.

6. A composition of claim 1 in which the total carbon content is about from 0.1 to 0.3 percent by weight.

References Cited UNITED STATES PATENTS 3,067,032 12/1962 Reed et a1. 29182.5

3,074,152 1/1963 Huntress 29-182.5

3,087,234 4/1963 Alexander et a1, 29182.5

3,166,416 l/l965 Worn 29--l82.5

FOREIGN PATENTS 1,213,625 3/1966 Germany.

CARL D. QUARFORTH, Primary Examiner.

R. L. GRUDZIECKI, Assistant Examiner.