US3382051A - Dispersion-strengthened iron-group metal alloyed with a small amount of zirconium, hafnium or magnesium and process of making - Google Patents

Description

United States Patent 3,382,051 DISPERSION STRENGTHENED IRON-GROUP METAL ALLOYED WITH A SMALL AMOUNT OF ZIRCONIUM, HAFNIUM OR MAGNESI- UM AND PROCESS OF MAKING William J. Barnett, Wilmington, Del., assignor, by mesne assignments, to Fansteel Metallurgical Corporation, a corporation of New York No Drawing. Filed Sept. 25, 1964, Ser. No. 399,363

7 Claims. (Cl. 29182.5)

ABSTRACT OF THE DISCLOSURE Dispersion-strengthened metals, having a matrix of iron, cobalt or nickel or their alloys with each other or with up to 30% of chromium, molybdenum or tungsten, and having uniform grain size and improved resistance to cracking under extreme stress, are produced by incorporation therein of 0.005 to 0.3 atomic percent of zirconium, hafnium, or magnesium, or a mixture of these metals. The dispersion-strengthening agent is 0.01 to 5.0 volume percent of a particulate, uniformly dispersed metal oxide having a free energy of formation (negative), measured at 1000 C., of greater than 98 kilocalories per gram atom of oxygen and an average particle size of 2 to 250 millimicrons. The zirconium, hafnium or magnesium addition metal is incorporated by blending (a) a powder of the addition metal, its hydride, its alloys with the matrix metal, or hydrides of such alloys with (b) a powder of the dispersion-modified matrix metal, and heating and consolidating the powder blend.

This invention relates to processes for the preparation of ductile, dispersion-modified wrought metals and the products so produced, and is more particularly directed to the steps in such processes comprising (1) preparing a metal-metal oxide powder (A) comprising two components mechanically inseparable from each other, the first of said components consisting essentially of a metallic material selected from the group consisting of (a) a metal of atomic number 26 through 28, and (b) a metal of atomic number 26 through 28 in combination with a Group VI metal selected from the group consisting of chromium, molybdenum and tungsten, the amount of said Group VI metal being up to 30% by weight and the total amount of molybdenum and tungsten not exceeding 30% by weight of said combination, and the second of said components consisting essentially of a refractory metal oxide having a free energy of formation, measured at 1000 C., greater than 98 kcal. per gram atom of oxygen, said oxide being in the form of discrete particles having an average particle size of from 5 to 250 millimicrons, the volume loading of said second component present being 0.01 to 5.0%, (2) uniformly blending (A) with a powder addition material (B) selected from the group consisting of zirconium, hafnium, and magnesium, their hydrides, their master alloys with the matrix metal of (A), and hydrides of said master alloys, said addition material having an average particle size smaller than 20 microns, the refractory oxide component of (A) and addition material (B) being so selected that said refractory oxide has a free energy of formation at least as large as that of any oxide of the metal of the addition material, the mixture of (A) and (B) containing no more than 0.3% by weight of reactive oxygen, and the amount of addition metal of the group consisting of zirconium, hafnium, and magnesium in (B) exceeding that which can combine with said reactive oxygen by 0.005 to 0.3 atomic percent, based on said mixture, (3) heating said mixture (A) and (B) in a non-reactive environment to slightly below the lowest melting point ice of the system A+B and then slowly to from 0.5 to 0.9 of the absolute melting point of A but always below incipient melting, and (4) consolidating the product of the process to at least 99.5% of theoretical density in a non-reactive environment. The invention is further particularly directed to such powder-metallurgy, dispersionmodified, ductile, wrought metal products which can be produced by the described process and have a density of at least 99.5% of theoretical density and a substantially uniform metal grain size, said products being compositions consisting essentially of a matrix metal selected from the group consisting of (a) a metal of atomic number 26 through 28, and (b) a metal of atomic number 26 through 28 in combination with a Group VI metal selected from the group consisting of chromium, molybdenum and tungsten, the amount of said Group VI metal being up to 30% by weight and the total amount of molybdenum and tungsten not exceeding 30% by weight of said combination, said matrix metal having substantially uniformly dispersed therein about from 0.01 to 5.0% by volume of a refractory metal oxide having a free energy of formation, measured at 1000 C., greater than 98 kcal. per gram atom of oxygen, said oxide dispersoid being in the form of discrete particles having an average size of from 5 to 250 millimicrons, and there being alloyed with said dispersoid-containing matrix metal about from 0.005 to 0.3 atomic percent, based on the final product, of an addition metal selected from the group consisting of zirconium, hafnium, and magnesium, the uniformity of distribution of said addition metal in the matrix metal being such as to appear homogeneous under a 1.3 mm. X-ray probe, the dispersoid oxide and addition metal being so selected that the free energy of formation of the dispersoid is at least as large as that of any oxide of the addition metal and the dispersoid in the composition being present in the metal grains as well as at the grain boundaries and the amount of metal oxide other than the dispersoid not exceeding 2 weight percent of said product.

Alexander et al. United States Patent 3,087,234 describes dispersing particulate refractory oxides in such metals as iron, cobalt and nickel to give novel metal compositions having greatly improved properties such as high tensile strength at elevated temperatures. Alexander et al. United States application Ser. No. 857,726 filed Dec. 7, 1959, and issued Sept. 29, 1964, as United States Patent 3,150,443, describes blending such dispersion-modified metals in powder form with powders of non-modified metals to obtain novel metal products having not only improved high temperature properties but also improved fabricability. The latter products are characterized by having a duplex grain structure, the dispersion-modified metal volumes being fine-grained and the non-modified metal volumes being relatively coarse-grained.

For uses in which the environmental conditions are extremely rigorous, as in gas turbine applications, improvement in high ternpeIature tensile strength is important but is not enough. There must be improvement in other properties as well, since the high temperature properties of the material are interrelated. A retardation of the onset of fracture by inhibition of the initiation and propagation of cracks at low stresses in the metal is, for example, extremely important in order to obtain improved workability as well as to attain strength in service applications. It is necessary, as well, to have substantially uniform grain size in the product for optimum performance of the metal product under rigorous conditions. To maintain and improve the effectiveness of strengthening of a metal by means of a dispersed refractory oxide it is therefore essential to recognize both of these criteria,

i.e., retardation of crack formation and uniformity of grain size.

Now according to the present invention it has been found that by incorporating very small amounts of zirconium, hafnium, or magnesium into certain dispersionmoditied metals and alloys in a particular manner, metal products having substantially uniform grain size and improved resistance to cracking under extreme stress can be produced.

In a process of this invention, one first prepares a metal-metal-oxide powder (A). In this powder the metal and metal oxide are mechanically inseparable; they can, however, be separated by chemical means. The metallic component of this powder, which will hereinafter sometimes be referred to as the matrix metal, is a metal of atomic number 26 through 28, i.e. iron, cobalt or nickel, including their alloys with each other, or a said metal in combination with chromium, molybdenum or tungsten or mixtures of them, the amount of chromium, molybdenum or tungsten being up to 30% by weight and the total amount of molybdenum plus tungsten not exceeding 30% by weight of said combination. The particulate refractory oxide which is a component of powder (A) is a metal oxide having a free energy of formation as measured at 1000 C. which is greater than 98 kcal. per gram atom of oxygen in the oxide. As used herein reference to the free energy of formation means, of course, the negative free energy, as will be understood in the art. Refractory oxides in this category and their free energies of formation (AF) at 1000" C. include: zirconia (100), alumina (104), ceria (105), hafnia (105), urania (105), magnesia (112), thoria (119), beryllia (120), lanthana (121), calcium oxide (122), and yttria (125).

The refractory oxide, herein sometimes referred to as the filler or dispersoid, must be in the form of discrete particles in the siZe range of about to 250 millimicrons. When average particle size is referred to, the size of particle as observed in electron micrographs or as calculated from surface area measurements by gas adsorption methods is meant. This is the volume average particle size, using the average dimension of the particles in length, width, and depth, as more fully explained by Irani and Callis, Particle Size Measurement, Interpretation, and Application, John Wiley, New York, N.Y., 1963.

The refractory oxide dispersoid is present at a volume loading of about from 0.01 to 5.0%, preferably from 0.5 to 3%, in the powder (A). The fineness of powder (A) is such that it can readily be blended uniformly with powder (B). This condition is met when all of powder (A) will pass through a 60-mesh sieve and at least 50% by weight will pass through a 270-mesh sieve (U.S. Standard), and even finer powders,-e.'g. 90% through a 270- mesh sieve and 100% through a 100-mesh sieve are preferred.

The mechanically-inseparable union of components which comprises powder (A) can be prepared by various methods. The components can be ball milled together for an extended period, such as upwards of 30 hours, if necessary followed by a treatment with hydrogen at elevated temperature to reduce any oxide formed during the ball milling. It can be formed by internal oxidation methods which are already known in the art as, for example, by preferential oxidation of one of the metals in an alloy matrix. In a particularly preferred aspect of the invention, powder (A) can be formed by chemical precipitation methods such as disclosed in the above-mentioned Alexander et al. U.S. Patent 3,087,234, especially Example 2 of that patent.

Powder (A), prepared as above described, is blended with powder (B). Powder (B) can be a metal of the group zirconium, hafnium and magnesium, one or more hydrides of said metals, a master alloy composition of a said metal or metals with a metal of powder (A), or a hydride of such master alloy.

The average particle size of powder (B) should be less than about 20 microns, preferably less than about 5 microns. Powders of the addition metals in this particle size range, particularly zirconium, may be pyrophoric when exposed to the atmosphere; hence hydrides may be used to inhibit the pyrophoric tendency, or, when a master alloy is used, the proportion of the addition metal should not be so high as to create problems of pyrophoricity, or, in the alternative, the blending should be effected in a protective atmosphere.

Powders (A) and (B) should be so selected that the free energy of formation of the refractory oxide dispersoid in (A) is at least as large as that of the oxide of any metal used in powders (A) or (B). This means, of course, that the numerical value is equal or greater, without regard to the fact that the value is a negative quantity.

The proportion of powder (B) to use is quite small. The effect of so small a quantity of Zirconium, hafnium or magnesium is quite out of proportion to what might be expected, but according to the present invention it has been found that if the reactive oxygen content of the blend is severely restricted as hereinafter described, this small proportion of these metals is sufiicient to give the desired effect.

It is most desirable that the blend of powders (A) and (B) contain a minimum, and in no event more than about 0.3% by weight, of reactive oxygen. By reactive is meant oxygen other than that combined in the dispersoid in powder (A) or present in an easily removable form, such as surface oxygen which can be removed by hydrogen treatment of temperatures below 450 C.; such oxygen can react with the metal of component (B), for instance, according to the equation: Zr+O ZrO This reaction can be minimized in either of two ways. One may start with oxygen-free raw materials and work in a protective atmosphere, or one may reduce a large portion of the oxygen that gets into the powder blend before it reacts with the addition metal, by such means as slowly heating the blend in hydrogen or other reducing atmosphere up to 450 C.

Generally, only a minimum amount of (B) will be converted to oxide during the blending operation and if the reactive oxygen thereafter approaches zero the remaining amount of (B) being between 0.005 and 0.3 atomic percent, is available to alloy with the matrix alloy (A). On the other hand, if the reactive oxygen is substantially greater than zero, a portion of the metal in component (B) is irreversibly converted to its oxide on further heating and is not susceptible to reconversion even by treatment with hydrogen at elevated temperatures. Any such oxide so formed not only fails to contribute desirable properties but may even be detrimental in that it may lead to stringering of such oxide in the ultimate product. Oxygen combined with the zirconium, hafnium or magnesium of powder (B) is to be avoided, as above pointed out.

In certain alloys, however, reactive oxygen cannot always be totally avoided. In those cases the amount of (B) to be blended with (A) must be adjusted to provide an amount of addition metal which is chemically equivalent to the amount of reactive oxygen in addition to the amount required for alloying with (A). Those skilled in the art can readily calculate the additional amount of (B) required to scavenge the reactive oxygen remaining in the blend in the event that a substantially reactive oxygen free mixture cannot be prepared.

One advantageous manner of insuring a suitably low reactive oxygen content is to compact the powder blend of (A) and (B) to 50 to 85% of theoretical density and then heat the compact in hydrogen at 200 to 450 C., controlling the rate and extent of heating by the dew point of the excess hydrogen. When this dew point has fallen to about F. under a low hydrogen flow rate, the reactive oxygen content will be found to be within the prescribed limit. Preferably, this compact must not be exposed to air because it will be reoxidized.

The blending of powders (A) and (B) may be effected by any means adapted to give intimate mixingthat is, uniform blending, of the powders. The art is well aware of such means. Thus, the powders can be blended in a cone blender, a ball mill or any other device capable of giving intimate mixing.

The mixture of dispersoid-containing metal (A) and addition metal (B), prepared as above described is heated in a non-reactive environment and is consolidated to at least 99.5% of theoretical density. These steps can be carried out in either order or simultaneouslythat is, the powders can be consolidated to a dense product and th1s product subjected to the heating step or the heating may occur in the powder blend and thereafter the powders can be consolidated.

The temperature to which initial heating is effected 1S slightly below the lowest melting point of the system (A+B). Thereafter the temperature is slowly raised to from 0.5 to 0.9 of the absolute melting point of (A), but always below incipient melting. If the matrix metal in A) is an alloy, for example, the latter heating should be to 0.5 to 0.9 of the melting point of the alloy, lIl degrees Kelvin. The heating should be effected in a nonreactive environmentthat is, in an inert gas such as helium, argon or hydrogen, or in vacuum. It will be observed that hydrogen is considered an inert gas at this stage of the process since hydrogen-reducible oxides have been substantially removed prior to such heating.

This heating step effects homogenization of the metal phase. If powder (B) was a hydride, it is decomposed by this heating to the corresponding metal or alloy and hydrogen. Even if the product has already been completely densified, the hydrogen will be evolved, since it diffuses through the metal readily.

The consolidating of the product to at least 99.5% of theoretical density is effected under conditions to prevent oxidation-that is, in a non-reactive environment. The method used may be one with which the art is already familiar, such as rolling, extrusion, forging, swaging, or any similar means for removing voids from the product. A combination of such methods may be employed and the densification and/or homogenization can be effected in a plurality of stages. It is noted, however, that by reason of the presence of the zirconium, hafnium or magnesium the latitude of permissible conditions, such as the total amount of hot reduction, the range of working temperatures, and the degree of thickness reduction at a single pass, is extended as compared with products not containing such added metal.

It will be understood that the order of conducting the individual steps of a process of this invention can be varied as above discussed.

A novel product of this invention is a powder-metallurgy, dispersion-modified, ductile, wrought metal product having at least 99.5% of theoretical density. The metal grain size is substantially uniform. By substantially uniform is meant that the frequency distribution of matrix grain size is essentially normal as contrasted to a bimodal distribution or duplex grain size.

The compositions consist essentially of a matrix metal which is iron, cobalt or nickel metal or an alloy of two or all three of these metals, or .an alloy of a said metal or metals with up to 30% by Weight of chromium, mlybdenum or tungsten or of two or .all three of these metals, the total amount of molybdenum and tungsten not exceeding 30% by weight of said combination, and said matrix metal having substantially uniformly dispersed therein about from 0.01 to 5.0% by volume of a refractory metal oxide having a free energy of formation, measured at 1000 C., greater than 98 kcal. per gram atom of oxygen, said oxide dispersoid being in the form of discrete particles having an average size of from 5 to 250 millirnicrons, and there being alloyed with said dispersoid-contatining matrix metal from about 0.005 to 0.3 atomic percent, based on the final product, of an addition metal selected from the group consisting of zirconium, hafnium, .and magnesium. The uniformity of distribution of the addition metal is such that it appears homogeneous under a 1.3 mm. X-ray probe. Se'e Heinrich, K.F.J., X-ray Probe with Collimation of the Secondary Beam, Advances in X-ray Analysis, vol. 5 (1962), 7-1. Plenum Press, New York, NY. The dispersoid and the addition metal are so selected that the free energy of formation of the dispersoid is at least as large as that of any oxide of the addition metal. The dispersoid in the composition is present in the metal grains and at the grain boundaries.

In particularly preferred embodiments of the invention, the matrix metal is nickel, an alloy of nickel and molybdenum, an alloy of nickel and chromium, or an alloy of nickel, chromium and molybdenum, the dispersoid is thoria, and the addition metal is zirconium. Such compositions are preferably made by precipitating thoria with an oxide of the matrix metal and reducing the matrix metal oxide with hydrogen or a carbonaceous material and blending this powder (A) with zirconium hydride powder (B), and thereafter heating and consolidating to theoretical density.

The products of the invention have outstanding utility for the manufacture of structural parts which must withstand high temperatures without cracking or substantial loss of strength, for example, in gas turbines. The products have particular utility where fabrication conditions are so severe as to present cracking problems in the absence of the active addition metal.

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

Example 1 A nickle powder having uniformly dispersed therein 2% by volume of particles of thoria having an average particle size of about 40 millimicrons, was prepared by the method disclosed in Example 2 of US. Patent 3,087,- 234. The resultant powder had a screen analysis such that 54% of the powder would pass a 270 mesh screen. One tenth percent by weight of zirconium hydride, the average particle size of which was less than ten microns, was cone blended with this nickle powder for two hours in a twin shell blender.

A billet was prepared by hydrostatically compacting the resulting powder blend at 60,000 psi. The billet was slowly heated to 900 F. in flowing hydrogen until the dew point of the efiiuent hydrogen was less than F. and then to a maximum temperature of approximately 2200 F. until the dew point of the efiluent hydrogen was less than 90 F. The billet was cooled to room temperature, machined, canned in mild steel, evacuated, reheated to 1700 F., and extruded into a rod with an extrusion ratio of 10/1.

The rod so obtained was swaged at room temperature, after removal of the mild steel can, until a reduction of 62% in cross-sectional area had been effected.

The ultimate tensile strength of this rod was 18,300 psi. at 1800 F. The ductility, measured by reduction in cross-sectional area, was 43.5 In stress rupture testing a specimen machined from the swaging lasted 45.6 hours at 9.000 p.s.i., 2000 F. Chemical analysis of the rod showed the zirconium to be uniformly distributed throughout the bar. By digesting the rod in brominemethanol solution, it was found that over 60% of the zironium added remained as zirconium alloyed in the nickel matrix. The remaining approximately 40% (approximately 0.05 weight percent of product) was in the form of ZrO or similar compounds insoluble in brominemethanol.

Metallographic examination of the rod revealed a uniform, fine-grained microstructure. The only evidence of zirconium in the microstructure was the occurrence of an occasional large (about 0.5 micron) inclusion in the electron micrograph, believed to be ZrO The thoria as observed in the electron micrograph was evenly distributed throughout the sample, and there were no areas larger than 5.0 square micron which were free of thoria.

Samples of the extruded bar were machined to a right circular cylinder 0.6" in diameter by 1 long. This cylinder was upset forged to a 75% reduction in height. When upset forged at 1800 F., 2000 F, and 2200 F. very little or no cracking occurred in the barrel section of the forging. Comparable samples which did not contain zirconium exhibited gross longitudinal surface cracking in the barrel section when similarly forged at 1800, 2000, or 2200 F.

Example 2 A thoriated nickel powder was prepared by ball milling Mond D nickel powder with thorium oxide powder for 32 hours. One hundred percent of the resultant powder would pass a 270 mesh screen. One tenth zirconium hydride was cone blended with this thoriated nickel powder for /2 hour.

A billet was formed 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 can containing entrance and exit tubes for passing hydrogen over the billet. The billet was heated slowly to 840 F. under a flow of dry hydrogen. After one hour at 840 F. the dew point of the exit hydrogen was less than -90 F. The temperature was then increased to 1650 F. The canned billet was then cooled and evacuated. The exit and entrance tubes were pressure-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 and the thoriated nickel rod was then swaged to a reduction of 66% in cross-sectional area.

A sample of the rod was tested in tension at 1800 F. The ultimate tensile strength was 28,000 p.s.i. and the ductility was 28.6% reduction in area. A stress rupture sample of the swaging lasted for 14.5 hours at 12,000 p.s.i. and 2000 F. It was possible to detect a zirconiumrich metallic phase by metallographic examination.

Chemical analysis revealed the zirconium to be relatively uniformly distributed. It had apparently been homogenized during the sintering and extrusion cycle. The electron micrograph did show an occasional large (0.5 micron) non-metallic inclusion believed to be zirconium oxide. Digestion of the sample in bromine-methanol solution revealed that about 50% of the zirconium was alloyed in the nickel matrix.

Right circular cylinders similar to those prepared in Example 1 were machined and forged at 1000 and 2000 F. to a reduction of 75% in height. Only minor cracking occurred on the barrel section of these forgings, and the cracking was significantly minimized as compared to a sample which did not contain zirconium. Forging to 50% upset produced a crack-free sample.

Example 3 A thoriated nickel powder was prepared by drying an aqueous solution of thorium nitrate and nickel nitrate and then hydrogen-reducing the combined oxides. The resultant powder was ground so that at least 50% passed a 270 mesh screen. The powder was processed with 0.1% zirconium hydride in a manner similar to Example 2. Tests at 1800 F. showed the tensile strength of the product to be 29,000 p.s.i. and the reduction in crosssectional area to be 29%. Stress rupture testing at 2000 F. gave 0.4 of an hour life at 15,000 p.s.i. Metallographic and forging observations were similar to Example 2.

Example 4 A thoriated nickel-9% molybdenum powder was ball milled for two hours and then blended with 0.15% zirconium hydride. The powder was compacted into a billet by the hydrostatic compaction technique. The billet was canned as in Example 2. The canned billet was heated slowly to 900 F. for four hours under llowing dry hydrogen. The temperature was then raised to 1650 F. for two hours and subsequently to about 2000 F. After sintering, the billet was evacuated and the tubes pressure welded shut. The billet was extruded at 1700 F. to a reduction ratio of 10/1. The mild steel can was removed from the rod by pickling. Subsequently, the rod was swaged 62% reduction in area at room temperature.

The tensile properties of the resultant swaging, as measured at 2000 F., showed an ultimate tensile strength of about 22,000 p.s.i. and a reduction in area of about 18% in duplicate tests. Another sample was subjected to stress rupture testing at 2000 F. After approximately 123 hours at 11,000 p.s.i., the stress on the sample was increased to 12,000 p.s.i. for approximately 28 hours and subsequently to 13,000 p.s.i. for 11.6 hours whereupon the sample failed.

Another sample of the extrusion was swaged to 76% reduction in area. It had a reduction in area of 28.5% and lasted 162 hours in stress rupture at 13,000 p.s.i. and 2000 F. A sample of the extruded rod was digested in bromine-methanol. About 55.5% of the zirconium was found to be soluble in bromine-methanol, that is, alloyed with the components of the nickel-molybdenum matrix. The remaining 44.5% was probably in the form of ZrO Metallographic examination using the electron microscope again revealed an occasional large particle believed to be ZrO The stress rupture sample of this alloy was examined metallographically and was found to be characterized by a uniform equi-axial grain structure. The size of the grains was 10 to 20 microns and many grains were heavily twinned, indicating recrystallization. The thoria was distributed evenly throughout the structure. X-ray microprobe examination of the metallographic sample showed the Zirconium had diffused generally throughout the structure. The zirconium concentration as measured by a one millimeter X-ray probe was uniform. No thoriafree areas were observed that were larger than 10 square microns.

I claim:

1. In a process for the preparation of a ductile, dispersion-modified wrought metal, the steps comprising (1) preparing a metal-metal oxide powder (A) comprising two components mechanically inseparable from each other, the first of said components consisting essentially of a metallic material selected from the group consisting of (a) a metal of atomic number 26 through 28, and b) a metal of atomic number 26 through 28 in combination with a Group VI metal selected from the group consisting of chromium, molybdenum and tungsten, the amount of said Group VI metal being up to 30% by weight and the total amount of molybdenum and tungsten not exceeding 30% by weight of said combination, and the second of said components consisting essentially of a refractory metal oxide having a free energy of formation, measured at 1000 C., greater than 98 kcal. per gram atom of oxygen, said oxide being in the form of discrete particles having an average particle size of from 5 to 250 inillirnicrons, the volume loading of said second component present being 0.01 to 5.0%, (2) uniformly blending (A) with a powder addition material (B) selected from the group consisting of zirconium, hafnium and magnesium, their hydrides, their master alloys with the matrix metal of (A), and hydrides of said master alloys, said addition material having an average particle size smaller than 20 microns, the refractory oxide component of (A) and addition material (B) being so selected that said refractory oxide has a free energy of formation at least as large as that of any oxide of the metal of the addition material, the mixture of (A) and (B) containing no more than 0.3% by weight of reactive oxygen, and the amount of addition metal of the group consisting of zirconium, hafnium, and magnesium in (B exceeding that which can combine with said reactive oxygen by from 0.005 to 0.3 atomic percent, based on said mixture, (3) heating said mixture of (A) and (B), in an environment selected from inert gas and vacuum, to an elevated temperature below the lowest melting point of the system A+B and then slowly to from 0.5 to 0.9 of the absolute melting point of (A) but always below incipient melting until the metal present is homogenized and any addition metal hydride present is decomposed to hydrogen and the corresponding metal or alloy, and (4) consolidating the product of the process to at least 99.5% of theoretical density in a nonreactive environment.

2. In a process for the preparation of a ductile, dispersion-strengthened wrought metal, the steps comprising (1) preparing a metal-metal oxide powder (A) consisting essentially of thoria dispersed in nickel, said thoria being in the form of discrete particles, 95% of which have a particle diameter less than about 180 millimicrons and the mean particle diameter of which is less than 60 millimicrons, and the volume loading of the thoria in the nickel being from 0.5 to 2.0%, said metal-metal oxide powder being fine enough to pass a US. Standard 270- mesh sieve, (2) uniformly blending (A) with an addition material (B) consisting of zirconium hydride in the form of a powder having an ave-rage Fisher sub-sieve partic le size smaller than 3 microns said blend of (A) and (B) having a reactive oxygen content less than 0.3 by weight, the amount of zirconium added as said hydride exceeding that which can combine with said reactive oxygen by from 0.005 to 0.3 atomic percent, based on said mixture, (3) compacting said powder blend to greater than 50% but less than 85% of theoretical density, (4) heating said compact in hydrogen, first at 200 to 450 C. until oxygen other than that present in the refractory metal oxide of (A) is combined with the hydrogen and thus removed, and then at from 588 to 1200 C. until the metal present is homogenized and the zirconium hydride is decomposed to hydrogen and zirconium metal, and (5) consolidating said heat-treated compact to at least 99.5% of theoretical density by mechanically working it in a nonreactive environment.

3. A powder metallurgy, dispersion-modified, ductile, wrought-metal product having a density at least 99.5 of theoretical density and a substantially uniform metal grain size, the composition consisting essentially of a matrix metal selected from the group consisting of (a) a metal of atomic number 26 through 28, and (b) a metal of atomic number 26 through 28 in combination with a Group VI metal selected from the group consisting of chromium, molybdenum and tungsten, the amount of said Group VI metal being up to 30% by weight and the total amount of molybdenum and tungsten not exceeding 30% by weight of said combination, said matrix metal having substantially uniformly dispersed therein about from 0.01 to 5.0% by volume of a refractory metal oxide having a free energy of formation, measured at 1000 C., greater than 98 kcal. per gram atom of oxygen, said oxide dispersoid being in the form of discrete particles having an average size of from 5 to 250 millimicrons, and there being alloyed with said dispersoid-containing matrix metal about from 0.005 to 0.3 atomic percent, based on the final product, of an addition metal selected from the grou consisting of zirconium, hafnium, and magnesium, the uniformity of distribution of said addition metal in the matrix metal being such as to appear homogeneous under a 1.3 mm. X-ray probe, the dispersoid oxide and addition metal being so selected that the free energy of formation of the dispersoid is at least as large as that of any of the addition metal, and the dispersoid in the composition being present in the metal oxides grains as well as at the grain boundaries and there being no more than 2 weight percent metal oxide other than the dispersoid based on final alloy composition.

4. A powder-metallurgy, dispersion-modified, ductile, wrought metal composition having high strength at from 1200 F. to 95% of its melting point, having a density at least 99.5 of theoretical density, and having a substantially uniform metal grain size, the composition consisting essentially of a matrix metal, nickel, having sub stantially uniformly dispersed therein about from 0.5 to

3.0% by volume of thoria in the form of discrete particles, 95 of which have a particle diameter less than 180 millimicrons and the mean particle diameter of which is less than 60 millimicrons, there being alloyed with said thoria-containing nickel about from 0.005 to 0.3 atomic percent, of zirconium based on the final product, the uniformity of distribution of the zirconium in the nickel being such as to appear homogenous under a 1.3 mm. X-ray probe, the composition containing less than about 0.5% by weight of zirconium oxide, and the thoria being present in the metal grains as well as at the grain boundarms.

5. A powder-metallurgy, dispersion-modified, ductile, Wrought metal composition having high strength at from 1200 F. to 95% of its melting point, having a density at least 99.5 of theoretical density, and having a substantially uniform metal grain size, the composition consisting essentially of a matrix metal consisting of nickel and about from 5 to 22% by weight of molybdenum, the matrix metal having substantially uniformly dispersed therein about from 0.5 to 4.0% by volume of thoria in the form of discrete particles, 95% of which have a particle diameter less than about millimicrons and the mean particle diameter of which is less than 60 millimicrons, there being alloyed with said thoria-containing matrix metal about from 0.005 to 0.3 atomic percent of zirconium, based on the final product, the uniformity of distribution of the zirconium in the matrix metal being such as to appear homogeneous under a 1.3 mm. X-ray probe, the composition containing less than about 1.0% by weight of zirconium oxide, and the thoria being present in the metal grains as well as at the grain boundarms.

6. A powder-metallurgy, dispersion-modified, ductile, wrought metal composition having high strength at from 1200 F. to of its melting point, having a density at least 99.5 of theoretical density, and having a substantially uniform metal grain size, the composition consisting essentially of a matrix metal consisting of nickel and about from 10 to 25% by weight of chromium, the matrix metal having substantially uniformly dispersed therein about from 0.5 to 4.0% by volume of thoria in the form of discrete particles, 95% of which have a particle diameter less than about 250 millimicrons and the mean particle diameter of which is less than 80 millimicrons, there being alloyed with said thoria-containing matrix metal about from 0.005 to 0.3 atomic percent of zirconium, based on the final product, the uniformity of distribution of the zirconium in the matrix metal being such as to appear homogeneous under a 1.3 mm. X-ray probe, the composition containing less than about 2% by weight of metal oxides other than thoria and the thoria being present in the metal grains as well as at the grain boundaries. 1

7. A powder-metallurgy, dispersion-modified, ductile, wrought metal composition having high strength at from 1200" F. to 95 of its melting point, having a density at least 99.5% of theoretical density, and having a substantially uniform metal grain size, the composition consisting essentially of a matrix metal consisting of nickel and about 12 to 25% by weight of chromium and 8 to 15% by weight of molybdenum, the matrix metal having substantially uniformly dispersed therein about 2% by volume of thoria in the form of discrete particles, 95 of which have a particle diameter less than about 250 millimicrons and the mean particle diameter of which is less than 80 millimicrons, there being alloyed with said thoria-containing matrix metal about 0.1 atomic percent of zirconium, based on the final product, the uniformity of distribution of the zirconium in the matrix metal being such as to appear homogeneous under a 1.3 mm. X-ray probe, the composition containing less than about 2% by weight of metal oxides other than thoria, and

the thoria being present in the metal grains as well as at 3,087,234 4/1963 Alexander et a1. 29182.5 the grain boundaries. 3,152,389 10/1964 Alexander et a1 29182.5 3,161,949 12/1964 Dickinson et a! 29--182.5

References Cited I U XR O H P UNITED STATES PATENTS 5 CAR D. Q 1- F RT Hfl'lllly EACZHIZIZEI.

2,362,007 11/1944 Hensel et a1. 75 -201 DEWAYNE RUTLEDGE Emma 2,823,988 2/1958 Grant et a1. 29-4825 R. L. GR-UDZIECKI, Assisfant Examiner.