US 3776704 A
Directed to a dispersion-strengthened, nickel-base superalloy produced from mechanically alloyed powder of special composition and characterized, in the consolidated, grain-coarsened condition by coarse elongated grains and by high strength over a wide range of temperatures.
Description (OCR text may contain errors)
United States Patent 11 1 1111 3,776,704
Benjamin Dec. 4, 1973 DlSPERSlON-STRENGTHENED 3,556,769 1/1971 Lambert et 31.. 29 1825 x SUPERALLQYS 3,454,431 7 1969 Fraser et al..... 75 206 x 3,446,679 5/1969 Marsh 75 206 x  Inven or: John S an BonJamln, ffe 3,440,042 4 1969 Kaufman 75/206 N.Y. 3,425,822 2/1969 Lambert et al. 75/206 X 3,386,814 6/1968 Alexander et al. 75/206 X  Assgnee' The lntemamna' N'ckel Cmnpany, 3,382,051 5/1968 Barnett 75/206 x New Ymk, 3,180,727 4 1965 Alexander et 8.1.. 75 206 x 22 Filed: May 17 1971 3,159,908 12/1964 Anders 75/206 X 3,024,] 10 3/ 1962 Funkhouser 75/206  Appl. No.: 143,765 2,823,988 2/1958 Grant 75 206 x Related [1.8. Application Data  Continuation-impart of Ser. Nos. 852,861, Aug. 25, 'r' Exam" wr Cafl Quarfonh 1969, and Ser. NO. 849,133, Aug. 11, 1969, 148mm"! Bummer-R Schafer abandoned, Continuation-impart f S AttorneyMaurice L. Pine] and Ewan C. MacQueen 709,700, March 1, 1968, Pat. NO. 3,591,362.
52 us. Cl. 29/1825, 75/0.5 BB, 75/05 BC,  ABSTRACT  Int CL 82523632 Directed to a dispersion-strengthened, nickel-base su-  Field of 0 5 BB peralloy produced from mechanically alloyed powder 75/0 of special composition and characterized, in the consolidated, grain-coarsened condition by coarse elon- 56] References Cited gated grains and by high strength over a wide range of UNITED STATES PATENTS temperatures 3,591,362 7/1971 Benjamin 75/211 X 5 Claims, 1 Drawing Figure 1 DISPERSION-STRENGTHENED SUPERALLOYS The present application is a continuation-in-part of U.S. application Ser. No. 852,861, filed Aug. 25, 1969, and U.S. application Ser. No. 849,133, filed Aug. 11, 1969, now abandoned, which applications are, in turn, continuations-in-part of U.S. application Ser. No. 709,700 filed Mar. 1, 1968 now U.S. Pat. No. 3,591,362, all applications being in the name of the present inventor.
With the advent of the mechanical alloying process on the metallurgical scene, a new metallurgical tool was afforded which made possible, among other innovations, the production of new superalloys characterized by dispersion-strengthening and also characterized by gamma-prime precipitation hardening. It was known from prior dispersion-strenthened materials, e.g., T.D. Nickel, that incorporation of a small amount of an inert dispersoid such as thoria, having a particle size in the range of about to about 1,000 Angstroms and welldistributed through a metal matrix, e.g., nickel, would contribute greatly enhanced stress-rupture properties to the resulting alloy at high temperatures, e.g., 1,900F. Relatively simple materials such as T.D. Nickel possess properties at room temperature and at intermediate temperatures, e.g., 1,400F., which are not substantially higher than those of, the matrix metal. It would appear that the introduction into a nickelchromium matrix of gamma-prime forming elements such as aluminum and titanium together with a dispersoid, would offer the possibility of providing a superalloy which would have very high strength at room temperature and at intermediate temperatures as well as retaining for the alloy exceptional stress-rupture properties at the higher temperature such as 1,900F. However, it was speedily found that the provision of a dispersion-strengthened superalloy which would have the desired properties over a wide range of temperatures including room temperatue, intermediate temperatures and elevated temperatures, was not merely a matter of providing a known superalloy with a dispersoidstrengthening mechanism imposed thereon. Instead, special problems and unforeseen difficulties were encountered. lt is to the solution of these problems and diffucilties that the present invention is directed.
One of the problems to be solved was that of meeting a recognized criterion in relation to aircraft gas turbine blades that the resulting superalloy should possess at an intermediate temperature such as 1,400F. a 100 hour rupture strength of at least 60,000 psi while providing at 1,900F. a 100 hour rupture strength on the order of 17,000 psi or greater.
It is an object of the present invention to provide, by powder metallurgy, a dispersion-strengthened superalloy possessing high room temperature strength, high stress rupture strength at intermediate temperatures and high stress rupture strength at elevated temperatures.
It is a further object of the present invention to provide, by powder metallurgy, a dispersion-strenthened superalloy having a coarse, elongated grain structure.
Other objects of the invention will become apparent from the following description taken in conjunction with the drawing, which is a reproduction of a photomicrograph taken at 100 diameters depicting the structure of a grain-coarsened alloy provided in accordance with the invention.
Generally speaking, the present invention is directed to a dispersion-strengthened superalloy containing, by weight, about 4 percent to about 5.4 percent or 6 percent aluminum, about 1 percent to about 3 percent titanium, about 10 percent to about 15 percent chromium, about 3 percent to about 15.4 percent cobalt, up to about 6 percent of at least one element from the group consisting of molybdenum and tungsten, about 0.05 percent to about 0.5 percent zirconium, about 0.001 percent to about 0.015 percent boron, about 0 percent to about 0.15 percent carbon, about 0.5 percent to about 2 percent of a fine refractory oxide dispersoid, such as yttria, having a particle size less than about 1,000A and the balance essentially nickel. The alloy may also contain up to about 2 percent tantalum, up to about 2 percent niobium, up to about 1 percent vanadium, up to about 1 percent hafnium, and up to about 0.3 percent iron. The alloy should be low in such impurities as phosphorus, sulfur, lead, tin, bismuth and zinc. Thus, the alloy preferably contains no more than 0.0008 percent lead, no more than 0.0005 percent bismuth and no more than 0.0025 percent tin. Preferably, the alloy contains at least about 3 percent molybdenum.
In order to provide optimum stress-rupture properties the alloy has a coarse elongated grain structure with a grain aspect ratio of at least about 3:1 and with a minimum average transverse grain dimension of at least 30 microns. The alloy is characterized in the grain coarsened condition by a 300 hour rupture life at 1,400F. of at least about 50,000 psi and by a 1,000 hour rupture life at 1,900F. of at least about 14,000 psi. In addition, the alloy is strong at room temperature, affording a room temperature yield strength of at least about 140,000 psi, a tensile strength of at least about 160,000 psi, an elongation of about 1 percent and a reduction in area of about 3 percent.
It is important that the alloy have a melting point of at least about 2,300F. since the germinative grain coarsening anneal is accomplished at a high elevated temperature of at least about 2,250F. A preferred alloy in accordance with the invention contains, by weight, about 5 percent aluminum, about 2 percent titanium, about 12.5 percent chromium, about 6 percent cobalt, about 4.5 percent molybdenum, about 0.1 percent zirconium, about 0.01 percent boron, about 1.1 percent of yttria having a particle size of about 200 to about, 500 Angstroms and the balance essentially nickel. The cargon content is maintained aslow as possible, e.g., the carbon content is usually less than 0.10 Percent about 1 33599919 @119!!! Q-OQBQIQ nt- In preparing, by mechanical alloying and powder metallurgy, the special superalloy provided in accordance with the invention, all processing parameters must be carefully observed in order to achieve a successful result. In general terms, the process employed comprises preparing mechanically alloyed powder to the required composition, the powder is then hot consolidated, e.g., by extrusion, and the consolidated material is subjected to a grain coarsening anneal. The particularly significant processing parameters include the mechanical alloying processing parameters for preparation of the initial powder; the hot consolidation and reduction processing parameters and the germinative grain coarsening anneal parameters. As pointed out in my copending U.S. application Ser. No. 709,700,
the mechanical alloying process contemplates dry milling of metal powder mixtures under high energy conditions to produce a dense, composite powder containing within individual particles thereof material from individual componets of the initial charge united together in finely divided, intimate association. As further explained in my copending US. application Ser. No. 709,700, the mechanical alloying process is a statistical and time dependent process in which a number of operations occur simultaneously. These operations include comminution of original and partially processed particles and cold welding of particles together. It appears that a major site at which welding and structural refinement of the product powder takes place is upon the surfaces of the grinding media employed, e.g., balls. The balls themselves may be metal, e.g., steel, stainless steel, nickel, etc., or may be cermet, e.g., tungsten carbide. lnert dispersoid particles, e.g. fine yttria having, for example, a particle size of the order 19 19 1000 Angstroms, present in the initial charge become mixed with the metal powder and/or master alloy powder being milled and become dispersed within the product composite particles being formed at closer and more uniformly distributed interparticle spacings fixed within a composite metal matrix. Dispersoid interparticle spacings of less than one micron or even less than one-half micron may be provided in the product powder. Since cold welding is a feature of the dry milling process, there is evidence that some true alloying of metal constituents present in the charge takes place during the milling operation. The average particle size of the product mechanically alloyed powder will be about 25 to about 250 microns. Preferably, a stirred ball mill of the Szegvari type is employed. A mill of this type is described in the Szegvari U.S. Pat. No. 2,764,359 and in Perrys Chemical Engineers Handbook, Fourth Edition, 1963, at page 8-26. The mill comprises an axially vertical stationary cylinder or tank having a rotatable agitator shaft located coaxially of the mill with spaced agitator arms extending substantially horizontally from the shaft. A cooling jacket preferably is provided about the tank. The mill is operated at a high ball-to-powder ratio which is usually 10:1 or higher. The attritor mill is advantageous in that a major portion of the ball charge can be maintained in a highly activated state of random motion as the agitator arms pass through the charge when the agitator shaft is rotated. The powder charge for the production of the alloy may include carbonyl nickel of high purity containing no more than about 0.1 percent carbon (nickel Type 123 powder having a particle size of approximately four microns), powdered master alloys containing the aluminum, titanium, zirconium and boron, powdered chromium, molybdenum and cobalt. the master alloys should be ground to pass a 200 mesh screen and the other powder constituents should have particle sizes not exceeding 150 microns. If desired, all the alloying constituents appearing in the final alloy except the added dispersoid and some of the nickel may be combined as a master alloy containing about 23 atom percent nickel. Such master alloys are brittle and easy to grind. The master alloy technique has the advantage that all of the alloying elements can be subjected in the molten state to a vacuum boiling treatment to remove volatile impurities and "tramp elements which may accompany certain of the raw materials. Other types of nickel may be employed but since other nickel powders generally are coarser than carbonyl nickel powder, the processing parameters based upon the four micron carbonyl nickel powder will be affected. The powder charge is milled well beyond the point of saturation hardness for the mixture, i.e., the powder charge is milled for a time sufficient to provide composite particles containing material from all of the ingredients of the initial charge united together in intimate admixture to form composite powders of at least about 25 micron average particle size which appear substantially homogeneous when viewed in the optical microscope at 250 diameters. The saturation hardness of the powder will be greater than about 500, e.g., approximately 700, kilograms per square millimeter Vickers pyramid number, and the powder will have a physical integrity in individual particles sufficient to withstand penetration by the diamond pyramid hardness indenter. Preferred pro cessing conditions in a water cooled model 10S Szegvari attritor having a tank capacity of 15 gallons and provided with a coaxial agitator shaft having 6 agitator cross-arms at 1% inch intervals, with the lowest crossarm extending to about 3 ball diameters from the tank bottom and with the cross-arms extending to about 3 ball diameters from the tank sides, include a running time of 20 hours at 182 r.p.m. with a 390 pound charge of 5 inch nickel or steel balls, and a ball-to-powder ratio of about 21:1; i.e., a powder charge weight of about kilograms. A dynamic flowing atmosphere of 250 cubic centimeters of nitrogen per minute and 55 cubic centimeters of air per minute is maintained in the mill during processing. The temperature of the charge during processing is maintained below about 300F. by water cooling of the tank. Processing parameters for applying attritor mills of various sizes to milling of superalloy powders for the invention may be related according to the formula:
l/t KW r R;
wherein t the time in hours; W agitator speed, r.p.m.; r tank radius in centimeters; K a constant for the system involved (usually about 9.5 X 10"" for a nickel-base superalloy); and R ratio of balls-topowder. In milling in larger mills the atmosphere flow should be increased proportionally to the weight of the powder being processed and adjusted further by the ratio of a 20-hour milling time divided by the calculated milling time from the equation.
Upon completion of the milling, the charge is drained from the mill under the milling atmosphere and packed into a can which is then sealed shut as by welding on a cover. The can may be made of mild steel, nickel, stainless steel, etc. The powder is sealed in the can without evacuation. The closed can may then be heated to an extrusion temperature of 1,950F. and extruded with an extrusion ratio of from 12:1 to 20:1. A strain rate equivalent to that obtained inextruding a 3 inch diameter can at a ram speed of at least one inch per second should be employed. In this connection it should be borne in mind that the strain rate is directly proportional to the extrusion ram speed and inversely proportional to the diameter of the billet being extruded. Accordingly, when larger billets comprising canned powders are extruded, a higher ram speed than one inch per second would be required. It is found that the can and its contents extrude very easily even at the relatively low extrusion temperature of 1,950F. This phenomenon apparently is due to the extremely fine grained size of the compacted material at this point in the processing. Thus, an extrusion provided from the alloy of the invention would normally have a grain size not exceeding about 2 microns, a grain size rendering the material amen able to superplastic working. In contrast thereto,-
known superalloys containing approximately the same hardener level can be extruded only with difficulty and higher extrusion temperatures substantially higher than 1,950F., e.g., 2,150F. or higher, would be required. Thus. attempts to extrude cast 3% inch diameter billets made to the alloy composition of the invention but without a dispersoid were unsuccessful. When the foregoing processing parameters are observed, it is found that the extruded bar can be heated to a temperature in excess of 2,250F. for a period of at least about 5 minutes, e.g., about to about 150 minutes, and will demonstrate the capability of growing a substantially uniform coarse grain having an aspect ratio of about 3:1 as a minimum, and having a minimum average transverse grair di m en; sion of at least 30 microns. Preferably, the grain aspect ratio will be at least about 8:1 and the minimum grain dimension will be at least about 50 microns. The grain coarsened material is then aged at a temperature between },300? ang 1,600F. for at least 10 hours, e.g., about 12 to about 30 hours. Aging at a series of successively reduced temperatures within the aforementioned range for about 12 to about 30 hours at each temperature may be employed. Alternatively, a slow cool, e.g., at a rate not exceeding about 100F. per hour, may be employed. An aging treatment comprising 24 hours at 1,550F. is satisfactory. While extrusion has been described as the exemplary means of hot compacting the mechanical alloyed powder contemplated in accordance with the invention, other hot compaction means may be employed. For example, hot rolling of a mass of powder contained in a flat can of rectangular section may be resorted to.
As noted, a small amount of oxygen is maintained in the mill during processing because it minimizes nitrogen pickup and prevents excessive welding of the powder charge to the balls. The product powder will accordingly contain a small amount of oxygen which will usually be in the range of about 0.8 percent to about 1.3 percent including the oxygen added as dispersoid. A further small amount of oxygen will be present in the interstices between powder particles when the powder is canned, since the can is extruded without evacuation. Oxygen from the aforementioned sources is not harmful since it quickly reacts with one of the active metals present on heating to form a further amount of welldispersed oxide which can enhance dispersionstrengthening.
In order to give those skilled in the art a better understanding of the advantages of the invention, the following Example is provided.
EXAMPLE A powder batch weighing 8.5 kilograms was made up consisting of: 1,133 grams of a nickel-31.6 percent aluminum-6.58 percent titanium master alloy passing 200 mesh; 289 grams of a nickel-17.3 percent aluminum-27.1 percent titanium master alloy passing 200 mesh; 93.5 grams of yttrium oxide of approximately 300A particle size; 1,095 grams of chromium powder ground to pass a 100 mesh screen; 204 grams of molybdenum powder of 325 mesh particle size; 995 grams of cobalt powder of approximately 5 microns average particle size; 20.6 grams of a nickel-28 percent zirconium alloy passing 325 mesh; 6.5 grams of a nickel-l 7 percent boron master alloy passing 325 mesh; 76 grams of a nickel-65 percent vanadium master alloy passing 200 mesh; 4.23 grams of 12 mesh graphite flake; and 4,085 grams of carbonyl nickel Type 123 of approximately 4 microns particle size.
The charge was placed in a Model 105 Szegvari attritor with 390 pounds of +14 inch nickel pellets and run for 20 hours at a speed of 182 r.p.m. while maintaining a dynamic atmosphere of 236 cubic centimeters per minute of nitrogen and 46 cubic centimeters per minute of air. At the end of this time, the valve on the bottom of the machine was opened, and the powder was drained into a sealed can under the same atmosphere. Following screening to 45 mesh to remove occasional coarse flakes, 4,000 grams of this powder were packed in a 3 /2 inch diameter steel can with a inch wall thickness and sealed without evacuation. This can was heated to 1,950F. in approximately 2 hours and was extruded through a /4 inch die using both glass and grease lubrication with a 2 inch long hot graphite follower block placed between the billet and the cold steel follower block of the ram. An extrusion ram speed of from 3 in chesto Sjnch e spersecond was measured during this operation. Chemical analysis showed this alloy to contain by weight: 13.2 percent chromium, 2.5 percent molybdenum, 12.0 percent cobalt, 4.7 percent total aluminum, 2.0 percent titanium, 0.58 percent vanadium, 0.07 percent zirconium, 0.086 percent carbon, 0.016 percent boron, 0.95 percent total oxygen, about 1.1 per-' cent yttria dispersoid and the balance essentially ti 3.3L...
Following a germinative grain growth treatment of 2 hours at 2,350F. and an aging treatment of 24 hours at 1,550F., it was found that this material exhibited a coarse grain structure elongated in the direction of extrusion. The attached figure illustrates the coarse elongated grain achieved in the alloy of the invention. The results of stress rupture tests performed on this bar at both 1,900F. where predominant strengthening is due to dispersion strengthening effects and at 1,400F. where the predominant strengthening is due to gamma prime precipitation hardening are shown in Table 1. It can be seen that the stress rupture properties at 1,400F., a stress for a -hour life of approximately 70,000 psi, exceeds that value required for use in rotats J engine 11 1%:
TABLE 1 ADDITIONAL STRESS RUPTURE AND CREEP PROP- ERTlES OF ALLOY 1N EXAMPLE Minimum Test temp. Stress Life Percent Percent creep rate "F. psi hours E1. RA (percent/hour) 1900 20,000 34.4 3.0 3.9 2.06X 10- 1900 17,000 194.3 3.0 3.1 3.26 X 10- 1900 16,000 362.9 3.0 4.7 1.26 10'-" 1750 35,000 2.6 5.0 9.3 2.5 10- 1750 23,000 439.2 4.0 4.3 1.67 X 10-" 1600 52,000 7.8 3.0 5.1 9.89 X 10- 1600 37,000 307.6 3.0 3.9 1.05 X 10 1400 85.000 10.2 4.0 6.3 2.66 X 10' 1400 70,000 188.3 1.0 3.5 4.2 X10 1200 140,000 6.7 4.0 7.0 1200 120,000 50.7 4.0 6.3 5.0 X 10- 1200 95,000 1543.2 3.0 6.6 9.6 X10"" By comparison of the data of Table 1 with standard published data for known superalloys, for example, the publication entitled Nickel Base Alloys, 2nd Edition, published in 1968 by The International Nickel Company, lnc., it will be seen that the strength properties provided in accordance with the invention are very high. Thus, of the known superalloys, it is possible to provide comparable properties only in cast alloys, with attendant disadvantages in consistency of properties and other limitations which accompany the casting process. At temperatures of 1,700F. and above, the alloy of the invention is clearly superior in rupture strength to standard cast nickel-base superalloys such as 713C and IN 100.
The grain structure of the germinatively grain coarsened material should be substantially uniform, i.e., should not comprise a mixture of fine and coarse grains. to provide consistently high stress-rupture properties thereto.
While the metallurgical phenomena underlying the present invention are not fully understood, it has been demonstrated experimentally that grain coarsened material having consistently high stress-rupture properties is provided when the compositional and processing parameters set forth hereinbefore are observed. In processing the initial powder charge of controlled composition to produce mechanically alloyed powder, the powder is processed up to and substantially beyond the point of saturation hardness, i.e., the substantially equilibrium hardness level which is not substantially increased by further dry milling. Shorter milling times open the possibility of creating undesirable segregation in the product and longer milling times result in reduced properties in the final consolidated and graincoarsened annealed product. As an example of the foregoing, material of the same composition as that of the example was similarly milled for 40 hours, was similarly canned and was extruded at 1,850F. to Vs inch bar diameter. The extruded bar was heat treated two hours at 2,350F. and aged 24 hours at 1,550F. At l,900F. and 17,000 psi, a stress-rupture life of only 11.9 hours was obtained and at 1,400F. and 65,000 psi, a stress-rupture life of only 45.9 hours was obtained.
In another example an alloy having the composition 18 percent chromium, 4 percent molybdenum, 18.5 percent cobalt, 3.3 percent aluminum, 2.9 percent titanium, 0.05 percent zirconium, 0.006 percent boron, 0.08 percent carbon, 1.33 percent yttria and the balance essentially nickel, was produced by the procedure described in the example. It was found that the longitudinal grain dimension and grain aspect ratio of grains in the material after the grain-coarsening anneal were less than those found in the material of the example, although grain-coarsening had occurred. At l,900F. and 17,000 psi, a stress-rupture life of 2.1 hours was ob tained, while at 1,400F. and 65,000 psi a stressrupture life of 74.9 hours was obtained. These results indicate that the compositional requirements set forth herein contribute importantly to the production of high stress-rupture properties.
Yttria is the preferred refractory oxide dispersoid for use in accordance with the invention. Other refractory oxide dispersoids including ceria, lanthana, thoria or the rare earth oxide mixtures didymia or Rare Earth Oxide may be employed. The dispersoid has a particle size in the range of about 100 to about 1,000 Angstroms. Satisfactory refractory oxides have a melting point of at least about 1,200C. and a heat of formation of at least minus kilocalories per gram mol of oxygen at 1,000C., preferably at least minus 200 or even minus 220 kilocalories per gram mol of oxygen at 1,000C.
Although the invention is not to be so limited, observations resulting from experimentation with dispersionstrengthened superalloys containing effective amounts of gamma prime hardeners such as aluminum and titanium has indicated that the capability of the consolidated powder metallurgy alloy to undergo germinative grain growth at temperatures of about 2,250F. to below the melting point is a function of the total energy content of the hot consolidated material. The two primary sources of enhanced energy content would appear to be the mechanical alloying processing which produces extremely high hardness and mechanical straining of a high order in the powder (E and the energy contributed during thermomechanical working to hot consolidate and shape the powder (E in general terms, total energy, E E E It has been observed that certain extruded shapes produced from satisfactory mechanically alloyed superalloy powder but extruded at conditions of insufficient strain rate or excessive temperature for the reduction conditions employed did not undergo germinative grain growth when heated above 2,250F. It was found that such material could be rendered capable of exhibiting germinative grain growth by the imposition of further thermomechanical working, e.g. hot rolling. These experimental findings appear to confirm that a wrought alloy provided in accordance with the invention must be brought to a threshold energy content or level before the material is capable of exhibiting germinative grain growth at temperatures within approximately 200F. of the melting point.
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variation may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.
1. A wrought, dispersion-strengthened alloy characterized by a coarse grain structure having an aspect ratio of at least about 3:1 and a minimum grain dimension of at least 30 microns consisting essentially of, by weight, about 4 percent to about 6 percent aluminum, about 1 percent to about 3 percent titaniu'm, about 10 percent to about 15 percent chromium, about 3 percent to about 15.4 percent cobalt, up to about 6 percent of at least one element from the group consisting of molybdenum and tungsten, less than about 0.15 percent carbon, up to about 2 percent tantalum, up to about 2 percent niobium, up to about 1 percent hafnium, about 0.05 percent to about 0.5 percent zirconium, about 0.001 percent to about 0.015 percent boron, a refractory oxide dispersoid having a particle size less than about 1,000 Angstroms in a volume amount equivalent to about 0.5 percent to about 2 percent, by weight, of yttria and the balance essentially nickel.
2. An alloy in accordance with claim 1 containing, by weight, about 5 percent aluminum, about 2 percent titanium, about 12.5 percent chromium, about 6 percent cobalt, about 4.5 percent molybdenum, about 0.1 percent zirconium and about 0.01 percent boron.
3. An alloy in accordance with claim 1 wherein said dispersoid is a refractory oxide from the group consisting of yttria, ceria, panthana, thoria, or rare earth oxide mixtures.
4. An alloy in accordance with claim 2 wherein the dispersoid is yttria having a particle size of about to about 1,000 Angstroms.
5. Mechanically alloyed metal powder of substantially saturation hardness, said powder having an average particle size of at least about 25 microns ahd having a composition consisting essentially of, by weight, about 4 percent to about 6 percent aluminum, about 1 percent to about 3 percent titanium, about 10 percent to about 15 percent chromium, about 3 percent to about 15.4 percent cobalt, up to about 6 percent of at least one element from the group consisting of molybdenum and tungsten, less than about 0.15 percent carbon, up to about 2 percent tantalum, up to about 2 percent niobium, up to about 1 percent hafnium, about 0.05 percent to about 0.5 percent zirconium, about 0.001 percent to about 0.015 percent boron, of a refractory oxide dispersoid having a particle size less than ut! q nwqmsiaa u nq n untequiva ent to about 0.5 percent to about 2 percent, by weigth, of
yttria and the balance essentially nickel.