US3069759A

US3069759A - Production of dispersion strengthened metals

Info

Publication number: US3069759A
Application number: US24971A
Authority: US
Inventors: Nicholas J Grant; Klaus M Zwilsky
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-04-27
Filing date: 1960-04-27
Publication date: 1962-12-25
Anticipated expiration: 1979-12-25
Also published as: SE317517B; GB935667A

Description

Dec. 25, 1962 N. J. GRANT ETAL 2 Sheets-Sheet 2 Filed April 27, 1960 YIELD STRENGTH RUPTURE LIFE 450 C 100 HR. L

Cu-AI O SYSTEM\ VOL. AlzOz,

NE-AIZO3SYSTEM 2 x w .w i 6.60m. MEDEE mzo. mo. wmwEw INVENTORS' NICHOLAS J. GRANT -KLAUS M. ZWILSKY AGENT 3,069,759 PRODUCTION on DIsPERsIoN STRENGTHENED METALS The present invention relates to dispersion strengthened metals and metal products, and in particular to wrought structural elements of copper group metals characterized by improved yield strength and improved resistance to creep combined with substantially high electrical and thermal conductivities.

This application is a continuation-impart of our U.S. application Serial No. 763,943, filed September 29, 1958, and now abandoned.

Certain pure metals such as pure copper have certain valuable properties which make them attractive for many engineering applications. The properties of major signiticance with respect to copper are electrical conductivity, thermal conductivity, resistance to corrosion, malleability and formability.

The greatest single field of use for copper as wrought structural elements results from its high electrical conductivity, for example electrically conductive elements. Another important field of use, for example, structural elements in heat exchangers, results from its high thermal conductivity. When certain of the basic properties such as resistance to creep, yield strength and other strength properties are improved by the addition of alloying ingredients, as a general rule electrical and thermal conductivity properties are greatly adversely affected.

For example, the addition of 1.5% silicon to substantially pure copper as a solid solution strengthener markedly reduces the thermal conductivity by about 85% and also reduces the electrical conductivity as referred to standard copper by about 88%, While increasing yield strength from about 8,000 p.s.i. to 15,000 p.s.i. (for a 1" round). Similarly, an addition of 3% Si also greatly reduces electrical conductivity by 93% and thermal con-' ductivity by about 90% while-increasing yield strength in the annealed condition for a one inch round to about 22,000 p.s.i.

Adding 5% aluminum to copper likewise adversely affects the conductivity properties by reducing electrical conductivity by about 82.5% and thermal conductivity by about 80%, while increasing yield strength in the annealed condition to about 20,000 to 25,000 p.s.i.

- A further disadvantage of these copper alloys is their lack of high temperature stability at temperatures up to the melting point whereby their strength properties are adversely affected after prolonged heating. a

It would be desirable to provide awrought copper composition having improved resistance to creep, improved yield strength, and improved high temperature stability up to below the meltingpoint in combination with sub-,

in heat exchangers in the form of tubing, fiat stock and, other shapes and as a material of construction for missiles where high strength copper of high thermal conductivity would be desirable as heat sinks in controlling the tem-.

perature of nosecones.

- We pointed out in that case that when producing dis- .ceeding about 8 microhms-centimeter.

Furthermore, it would be additionally desirable to provide dispersion strengthned metals or alloys with improved high temperature properties including resistance to softening at elevated temperatures.

I It is, therefore, the object of the present invention to provide a dispersion strengthened structural metal element, for example of copper characterized by improved strength properties such as resistance to creep at room,

and elevated temperatures, improved yield strength, etc, in combination with substantially high electrical and thermal conductivity.

Another object is to provide a wrought copper composition for use in the production of dispersion strengthened electrical or thermal conductive structural elements having improved strength properties.

A still further object is to provide a method for producing a copper composition or a structural element of copper characterized by the aforementioned improved properties.

It is also the object to provide a method for the production of dispersion strengthened metals characterized by improved physical properties and stability at elevated temperatures.

These and other objects will more clearly appear from the following disclosure taken together with the accompanyin-g drawing wherein:

' FIG. 1 depicts hardness curves of several copper compositions within and outside the invention showing the elfect of annealing temperatures on the wrought mate. rial; FIG. 2 shows graphically the effect of the ratio of matrix metal particle size to disperse phase particle size on the room temperature yield strength and the hour rupture life at 450 C. of the final wrought metal pro-' duced from CuAl O compositions containing 5 and,

10 vol. percent A1 0 FlG. 3 is a plot showing the affect of amount of dis perse phase on the room temperature yield strength and;

100 hour rupture life at 450 C. of copper; and

FIG. 4 is similar to FIG. 3 but differs in that it shows: the effect of the amount of disperse phase on the rupture stress of nickel.

We have discovered copper compositions of CuSiO, and CuAlO and other metal compositions which do' nothave the property limitations of the solid solution 211-. loys discussed hereinbefore. For example, we have found that by using silicon and aluminum in the form of re characterized by improved stability propertywise after prolonged heating at temperatures up to below the melt-Z ing point.

We have also discovered that the invention is applicable to the other copper group elements gold and silver, as well as to ductile metals generally, particularly those' metals having heat conductivities of atleast 0.2,based on.

the c.g.s. system and having electrical resistivities not exhave found that other refractory hardening and strengthening agents may be employed provided they are substantially.insoluble in the metal matrix.

As pointed out in our patent application Serial No.

part, in carrying our invention into practice we prefer for optimum results that the particle size of the matrix metal powder be correlated to that of the refractory hard phase or oxide in producing the desired com-position.

persion strengthened copper or other metals, the particle- Patented Dec. 25, 1962 In addition, we

size of the disperse hard phase, e.g. A1 0 should be smaller than the average particle size of the matrix metalto effect desired improvements in the final product by Working over .a ratio of size ranges in which the average size of the hard phase particles is 30 to 150 times smaller than that of the average' size of matrix metal powder and even as much as 30 to 250 times smaller.

'We find that the foregoing concept may be applied to ductile matrix metal powders of average size ranging up to 20 microns, preferably not exceeding about 10 microns and more preferably not exceeding about microns. The correlation employed on particle sizes of matrix metal of up to about 2 microns and ranging from about /2 to 1 micron is particularly effective in optimizing the high temperature strength properties.

Inworkingover the aforementionedranges -we prefer, as pointed out in our parent application, that the amount of hard phase particles employed to achieve optimum results ranges from about 3% to by volume, although improved results are obtainable over the range of about 3' to volume percent and even over the broader range of about 1 to 15% by volume. The particle size of the disperse phase generally should not exceed 0.3 micron and more preferably should fall Within the range of about 0.01 to 0.1 micron, e.g. 0.01 to 0.05 micron.

The foregoing ranges as to the particle size of the matrix metal, the particle size of the disperse phase, the ratio between the particle size of the matrix metal powder and the disperse phase, the amount of disperse phase,

etc., may be employed in any combination desired. For

example, the broad range -as tothe ratio of average particle size of the matrix m'etalpowder to the disperse phase powder (30 t0 250) may be used with the broad or narrow ranges of the disperse phase composition, for example with either" l to 15volu1ne percent, 3 to l5 volume percent or 3 to 10 volume percent, etc. Similarly, the

narrow range of one can hecombined with the narrow or broad or any other specified range of the other.

In assaying the product provided by the invention,

various test programs were conducted with different sizes.

of copper powder with varioussizes of alumina. powder as .a disperse phase, to wit, using copp'er'powder of minus 7 4 microns, of about 5 microns and of ab out; one micron, and alumina powder of about 0.3 micron, of about.0 .033', volume per-.

micron and about 0.018 micro n,at various centages ranging up to about 10%.

Composition batches containing 1, 2.5, 3 5, 7.5 .and 10 volume percent of alumina were prepared by mixing a specified amount of a particular size copper powder with varying amounts of a particular size alumina powder. We prefer dry mixing in a :ball millor a high speed Waring Blendor over Wet mixing; although satisfactory results are] obtained bythe latter. We have found that dry ball m'ill ing for 24 hours gave very good results. Particularly good results were obtained, however, with a Waring Blendor operating at 15,000 rpm. for about 12, or 15 minutes and it was this latter method that was used in producing the various mixtures. As a certain amount'of surface oxidation occurs during mixing, the blendingwas vgenerally followed by a hydrogen reduction treatmentat atemperature in the neighborhood of 260 C. or 300 C.

The thus-produced batches were then consolidated into aslugof about 1 /2 inchesin diameter by about or Where such correlation prevailed,

3 /2 inches long under a pressure of about 25 tons per square inch. A preferred method comprised hydrostatically compacting the powder mixture by placing it in a rubber sleeve held in a perforated steel canister, the sleeve being closed at both ends Air was evacuated from the assembly. prior to pressing in order to prevent gas entrapment inside the compact. By conducting the hydrostatic pressing at about 35,000 p.s.i. (17.5 t.s.i.), a compact of considerable green strength was assured which enables the handling of the slug under ordinary operating conditions. 7 i

The slug was then removed from the bag and sintered under substantially non-oxidizing conditions, for example in'a reducing atmosphere of substantially pure hydrogen for about 1 hour at 500 C. followed by a further heating of 2 hours at about 950 C. Sintering may be avoided when the slug has high green strength but it is preferred the slug be sintered from 900 C. to 1000 C. As a result of the sintering, the slug had a shrinkage ranging from about 2% to 4% and yielded a sintered product having a -density of about of theoretical density.

The sintered product was enveloped in a sheath of copper, the space between the compact and the inner wall of the sheath being filled-with a spacing material, such as fine A1 0 The purpose of thersheath was to minimize oxidation during hot working, although subsequent tests indicated the sheath to be unnecessary where the sintered slug had a high. density. The sheath was welded shut and thereafter hot extruded at a temperature of 760 C. to a final diameter ranging from about 0.3 to 0.375 inch, using an extrusion ratio of 21:1 in some instances and 29:1 in others. Extrusionratios for the sintered product may range fromabout 14 to about 29 to l, a ratio of 15 to 1 being a preferred minimum. Sound extrusions were obtained in all instances. Maximum densities were obtained on all extrusions. The densities of almost all the extruded products within the invention were close to 98% and up compared to the theoretical density. Several of the products outside the invention resulting from the use of minus 74 micron copper powder with 10% A1 0 (0.3 micron) had' slightly lower densities of the order of about 96% to 98%. a

The compositions employed in the test programs are given in Table 1 as, follows:

Table 1 Alloy N 0. Powder Mlcrons Vol. persize cu, p A1203 cent A1203 Recrystallization hardness curves were determined for some of the compositions bycutting three-eighth inch samples from theextruded rods and cold swaging these to 50% reduction inarea. Each specimen was annealed for one hour at various temperatures and Rockwell F hardness determined after each annealing treatment.

The results-of the tests are shown in FIG. 1 which compares the hardness of Cu Al O wrought alloys produced from minus 74 micron copper powder with alloys produced from one micron powder both of the alloys having the same .sizealumina powder, that is 0.018 mi-. cron, at 5% and 7.5% by volume, respectively.

It will be noted from FIG. 1, that alloys 5A and 6A (produced from minus 74 micron Cu) have. a lower base level of hardness than alloys 13 2rd 15 produced from one micron copper in accordance with the invention. Although the final alloys are the same compositionwise, nevertheless they exhibited different hardness levels, thus illustrating the importance of using finer copper particles having the correct size ratio to the alumina particles. It will be noted that both of the alloys within the invention (No. 13 and No. 15), and 7.5 volume percent Al O exhibited retained hardnesses after annealing at various temperatures of up to about 800 C. of close to 100 R and above as compared to the alloys outside the invention (5A and 6A) which exhibited hardnesses below 90 R and even below 80 R For comparison purposes, pure copper also cold worked 50 percent was similarly subjected to annealing at the same temperatures and fully recrystallized after one hour at about 300 C. as compared to alloy Nos. 13 and which resisted softening up to about 1000 C.

While efiective increases in hardness were obtained by the invention, electrical and thermal conductivities were maintained at substantially high levels, that is at levels ranging from about 70% to 35% of the standard values for electrolytic copper. This is quite an improvement considering that up to 5% Al metal as an alloy addition of 48,400 p.s.i. exhibited by No. 13. In addition, the

100 hour rupture life of alloy No. 13 at 450 C. was 5,000 p.s.i. higher than 5A. Similarly, alloy No. 7A containing 10 volume percent A1 0 is also markedly inferior to alloy No. 11 of the same composition, the former having been produced from coarse copper powder (minus 74 microns) and the latter from the much finer one micron copper powder. Note that both the yield strength and stress to rupture properties of No. 11 were more than doubled over No. 7A. In addition, the alloys of the invention are markedly superior to pure copper. It is apparent from the foregoing that in order to achieve optimum results, the starting particle size of the matrix metal powder should not be coarse. As stated hereinbefore, the particle size should not exceed 20 microns and more preferably not exceed 5 microns.

However, merely using fine matrix metal powder is not enough as consideration must also be given to the size ratio of matrix metal powder to the dispersoid. As has already been brought out, the size ratio for the purposes of this invention should fall within the broad range of 30 to 250, generally within 30 to 150, and more preferably over the ratio of 50 to 100. The importance of maintaining the correct size ratio will be appreciated reduces the conductivity values of copper to below 15% from Table 3 which follows: of the standard values. Table 3 Concomitant with the improvement in hardness, improved strength properties at room temperature (yield Stress strength) and at elevated temperatures (stress to 100 hour v/o Size of o A1293 Y.S, for 100 rupture at 450 C.) were also obtained as will be ap- Alloy gfg 5mm) PM 3135 parent from Table 2 which compares the inferior results p.s.i. of alloys outside the invention, e.g. 1A to 10A, as well as pure copper, with alloys 11 to 15 provided by the ini8 $88 8% vention. 5 1 313 251000 31000 10 1 30.0 60,500 24,800 Table 2 10 5 150.0 59, 200 20. 000 5 1 55.5 48,400 18,000

v/o Yield 100 rupture 450 C Alloy No. A120; strength, 1iie,str ess, percent Referring to FIG. 2, which illustrates the correlation 91mg 40 between strength properties and the starting matrix metal Pure opper 0 to oxide size ratio at 5 and 10 volume percent of disper- LO 801d, 1t Wlll. be noted that particularly high peak properg 8 ties are obtainable within the size ratio range of 30 to 1 25460 4,000 2 250, particularly within the range of 50 to 100. This pg 38,388 ggg g trend is indicated over the composition range of disperj 281300 121000 1 soid of about 1 to 15% and is indicated for other metal- 18.8 288 88g dispersoid systems, such as systems based on FeAl O 5 251000 81000 2 FeMgO, Cu--SiO Ni-A1 O and others. ig-g ggggg giggg i Broadly speaking, we have observed that when the 1 481400 1 1 2 powder ratio is less than 30:1, for example, 1:1, heavy 33.383 288 short stringers of oxide obtain accompanied by little or no effective strengthening at elevated temperatures. We

1 Nos. 1A to 3A were extruded at a ratio of 29:1 While the remaining compositions were extruded at a ratio of 21:1.

The test bars employed in obtaining the room temperature yield strength and the rupture life data were machined from extruded rods and had a gauge section of 0.160 inch diameter and 1.0 inch long. The threaded sections were either 20 or 34 -24. The machined specimens were polished with emery paper following the machining operation. Where the specimens were used for obtaining rupture life data, each had a thermocouple wired at its center. Rupture life was obtained at various stresses at 450 C. from which the 100 rupture life was determined by interpolation for each alloy.

Referring to Table 2, it will be noted that alloys Nos. 1A to 7A produced from coarse copper powder (minus 74 microns) and fine alumina exhibited low yield strength and lowstress to rupture properties as compared to alloy Nos. 11 to 15 produced from copper powder of much. finer particle size not exceeding 20 microns, that is at 5 and 1 microns. Comparing specifically alloy No. 5A with alloy No. 13, both of which contained 5 volume percent of A1 0 5A exhibited the much lower yield strength value of 26,600 p.s.i. as against the higher value have also observed that when the ratio exceeds substantially 250:1, the oxide particles are so fine that they 001- lect extensively in the interstices between the metal particles and behave as a fluid on extrusion, whereby they are squeezed out and result in long stringers in the matrix. Because the particles tend to cluster together in the interstices, poor dispersion results in the extruded product and hence the desired properties are not obtained.

The importance of controlling the dispersoid composh tion over the rangeof 1 to 15 volume percent is illustrated 'by FIG. 3 which shows that optimum properties are assured when working within the aforementioned range,

especially within the range of about 3 to 15 volume per-- cent and, more particularly, within the range of about 3 to 10 volume percent. This-trend is likewise indicated for other metal-dispersoid systems, for example the NiAl O system illustrated in FIG. 4.

The beneficial effects of other hard phases on improving strength properties of copper, such as SiO TiO ZrO were also realized. For example, copper containing 7.5 volume percent SiO produced from 1 micron copper powder and 0.02 micron SiO powder was able to sustain a stress of over 10,000 p.s.i. for hours at 450 C. before rupturing as compared to a composition containing 10 volume percent of coarse SiO (minus 10 microns) which could only sustain a stress; of 4,800 psi at the lower temperature of 350 C. It is apparent that particle size as well as particle size ratio is also important in so far as SiO is concerned when used as the disperse phase. Similar trends were indicated for Ti and ZrO Work conducted with micron nickel powder and alumina powder of about 0.02 micron size indicates that the concepts developed in producing dispersion strengthened copper are also applicable to nickel. Mixtures containing 3.5, 9 and 15 volume percent A1 0 were similarly prepared as in the case of the copper-A1 0 each sintered into acompact and each compact placed in a nickel jacket, welded tight and the whole heated to a temperature of about'2000 F. for one hour and extruded at a ratio of 16:1 to form a rod 0.6 inch in diameter and 24 inches long. Stress-rupture specimens were similarly prepared as the copper'specimens earlier discussed and were subjected to stress rupture tests at 1500 F. and the 100'hour rupturelife determined as follows:

It will be noted from FIG 4 that peak strength properties are indicated for the Ni'Al 0 system in the neighborhood of 8 to 10% and within the broader range of 3 to volume percent of A1 0 for an initial particle size ratio of Ni to A1 0 of about 250 to 1. i

Improved results were also obtained in the dispersion strengthening of iron, starting with 3 micron iron poW- der containing 4, 6, 8 and 10 volume percent, respectively, of A1 0 of about 0.03 micron average diameter (100 to 1 size ratio). After blending the powders, each batch of the mixed powders were introduced into a rubber tube supported within a perforated steel canister about two inches in diameter, one end of the rubber tube being rubber stoppered at the start. After the powder was introduced, a second rubber stopper having in com-' munication therewith a hypo'dermic'needle was inserted, a vacuum connection being made through the needle to remove the air from within powder mass. After completion of evacuation, the needle was removed and the canister assembly subjected to hydrostatic pressure at about 30,000 p.s.i. to yield compacts about 1.4 inches in diameter and 3 inches long.

Using correspondingly larger amounts of powder, compacts have been preparedby'the same te'chniqueup to 3 inches in diameter and 6 inches long. Depending upon the size of presses,'-billets Of u m inches diameter are envisaged. i

The compacts produced as aforementioned were then subjected to sintering in dry hydrogen for a minimum of 10 hours at 1525 F. After that they were each canned by insertion in a mild steel can and welded vacuum tight followed by extrusion at an elevated temperature. The extrusion ratio was about 16to 1'.

The following alloys were produced:

The alloys were then subjected to tensile tests at room and elevated temperatures and to long time stress rup ture testing. at 1200" F. The results of th one tests are as follows:

Table 6 Y.S. Stress for Alloy No. Temp, (p.s.i.) 100 hr.

I 2% rupture,

otlset) p.s.i.

R.T. (i6, 200 1, 200 13, 70 11,000 R.T. 68,

S300

1, 200 16, 200 13, 800 ILT. 60, 900 l, 200 21, 300 18, 000 R.T. 104, 300 1, 200 26, 800 24, 000

extruded condition, a yield strength at roomtemperature of about 25,000 p.s.i., and at 1000 F. of about 6,600 p.s.i. While exhibiting a 100 hour rupture life (at 1200 F.) under a stress of 2,600 p.s.i. (12% elongation).

The results indicate that the properties of iron are markedly improved by the presence of A1 0 as a dispersion strengthener. The improvement is particularly noticeable with respect to strength properties at elevated temperatures. In this connection, reference is made-to the 100 hour rupture properties which show an increase in rupture life stress over similarly prepared pure iron of about 4 to 9 times for alumina contents ranging from 4 to 10 v./o'.

Tests in which Mg'O was used as the dispersion strengthener-for iron were also conducted. Using the same particle size iron powder (3 microns) and MgO with its particle size ranging from about 0.05 to 0.1 micron, room temperature yield strengths of 84,500; 102,000 and 129,000 p.s.i. were obtained for iron'alloys containing 4, 6 and 10 v./o., respectively, ranging from over 3 to over 5 times the value of that obtained for pure iron. Likewise, yield strength values at 1000 F. were obtained ranging from about 22,800 to 30,600 p.s.i., as against 6,600 p.s.i. for pure iron similarlyprepared. As. for 100 hour rupture life at 1200 F., stresses ranging from about one and a half to two and a half times that of pure iron were obtained.

It is apparent from the data for nickel andiron, that what has been said for copper is also applicable to other ductile metals and alloys.

With respect to copper, the types of copper that can be employed in carrying out the invention include com-- mercial electrolytic, deoxidized copper (e.g. OFHC, oxygen free high conductivity copper), etc. The invention is applicable to copper compositions of electrical and heat conductivities of at least 50% of the standard values for pure copper and preferably applicable to copper of at least 99.5% purity.

In addition, the. invention is applicable to the other copper group metals gold and silver and alloys based on Examples of such alloys are: 90% copper and 10% nickel, copper and 20% nickel; 70% copper and 30% nickel; 70% copper and- 30% gold; 65% copper, 30% gold and 5% nickel;

copper group metals.

Heat resisting alloys based on one or more of the iron,

group metals nickel, iron and cobalt may also be dispersion strengthened.

With respect to platinum group alloys, the following are examples: platinum-rhodium alloys containing up to 50% rhodium; platinum-iridium alloys containing up to 30% iridium; platinum-nickel containng up to 6 or 10% nickel; platinum-palladium-ruthenium containing 77% to 10% platinum, 13% to 88% palladium, and 10% to 2% ruthenium; alloys of palladium-ruthenium containing up to 8% ruthenium; 60% palladium and 40% silver, and others.

While alumina is preferred as the dispersoid, other types of refractory compound materials may be employed provided they are stable and insoluble in the ductile matrix metal, such as copper group metals (Cu, Ag, Au) or other metals, so as not to greatly adversely affect the electrical and thermal conductivities. Such materials should have melting points above 1500 C. and should not decompose during processing when mixed with copper or are not reduced by copper or wetted by copper oxide. Examples of such refractory materials in addition to Al O and SiO are ThO ZrO BeO, MgO, CeO TiO and carbides, borides, silicides and nitrides of certain of the refractory metals of groups IV, V and VI of the periodic table. These materials may be employed over the same composition range indicated for A1203 and SiO With respect to the aforementioned type refractory oxides these may be defined for the purposes of this invention as those oxides having a melting point above 1500 C. and a negative free energy of formation at about 25 C. of at least about 90,000 calories per gram atom of oxygen and preferably at least about 110,000 calories per gram atom. For example, SiO has a negative free energy of formation at 25 C. of about 96,200, A1 of about 125,590, MgO of about 136,130, BeO of about 139,000, etc.

It is preferred for optimum results that the refractory oxides be used in that form which is crystallographically stable at elevated temperatures, and, if not, to use process ing temperatures at which transformation does not occur. For example, because gamma alumina tends to transform to the alpha at temperatures above 850 C., where large amounts of fine alumina is present, e.g. 10 volume percent of 0.02 micron size, agglomeration is apt to occur with a consequent falling off in physical properties. This can be avoided by using a larger particle size, e.g. 0.05 micron, and lower amounts of alumina, e.g. 5 to by volume. Or straight alpha alumina can be used from the start.

Broadly speaking, in producing the novel product provided by the invention, a given amount of the matrix metal powder and the dispersoid is blended uniformly together and the mixture then compacted at pressures of about 10 t.s.i. to t.s.i. (e.g. hydrostatically) to produce a slug of adequate green strength of density at least about 60% to 80% of true density. The slug is sintered (depending upon the green strength the slug may or may not be sintered) under substantially non-oxidizing conditions (e.g. a reducing atmosphere of dry hydrogen, or in a vacuum, or in an inert atmosphere) at an elevated temperature below the melting point of the matrix metal, for example, in the case of copper at a temperature of at least about 500 C. and more preferably from about 700 C. to about 900 C. The sintering time and temperature should be sufficient to produce a sintered product of density at least 90%, for example 2 to 4 hours at 900 to 1000 C. for copper and higher temperatures for matrix metals of still higher melting points.

The sintered product is then subjected to hot working, preferably extrusion, by encasing the product in a ductile metal sheath such as copper where the matrix metal is copper, and the whole reduced in size sufficient to remove substantially all of the voids. Where the sintered product prior to extrusion has a high density, e.g. about it) it may not be necessary to encase it in a sheath and may be extruded directly. The extrusion ratio should be at least 15 to 1 and preferably should range from about 20 to 1 to 25 to 1 with extrusion pressures ranging from about 50 tons/sq. inch to tons/ sq. inch.

Depending upon the product being produced, the initial hot working may comprise the forming of wire bar sizes from which wire of various sizes can thereafter be produced by other conventional working methods. Or tube stock can be produced by extrusion for subsequent reduction to tube sizes for specific purposes such as heat exchanger elements, hollow cable stock, etc. Or various other structural shapes may be extruded, such as angles, flats, square bar stock, and the like. In any event, the product of the invention lends itself to any conventional means of production in common use for copper group metals.

Examples of other types of structural elements contemplated by the invention include such heat conductive elements as de-icers for air craft for use under conditions where resistance to creep at relatively high temperatures is important; supporting elements in electronic devices where good heat conductivity coupled with high temperature strength is an essential requirement and as electrical contacts where hardness and resistance to wear coupled with high electrical conductivity is important. In this connection, the invention is particularly applicable to the production of hard silver contacts and other wear resistant contact members.

One of the advantages of the invention is that the oxidation of pure matrix metals, such as copper, is improved. The reason for this is that the fine oxide particles in the matrix metal appear to act as anchor points to hold the metal oxide on the surface and thereby prevent flaking which normally occurs on such metals as pure copper.

As has been stated with respect to copper, the invention is particularly applicable to the strengthening of metals in which it is desirable to maintain good or adequate heat and electrical conductivity, for example to such metals as those having thermal conductivities of at least 20% that of copper and resistivities not exceeding about 8 microhm-cm.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations 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.

What is claimed is:

1. A method of producing a dispersion strengthened wrought metal product characterized by improved physical properties at room and elevated temperatures which comprises mixing a ductile matrix metal powder of average particle size ranging up to about 20 microns with about 1 to 15 volume percent of a refractory oxide powder whose negative free energy of the oxide at about 25 C. is at least about 90,000 calories per grame atom of oxygen and whose average particle size does not exceed about 0.3 micron and ranges from about 30 to 250 times smaller than the average particle size of said matrix metal powder, and fabricating said mixture into a dense wrought metal structure.

2. The method of claim 1, wherein the average size of matrix metal powder ranges up to about 10 microns, and wherein the amount of refractory oxide powder ranges from about 3 to 15 volume percent and has an average particle size which ranges from about 30 to times smaller than the average particle size of the matrix metal powder.

3. The method of claim 2 wherein the average size of the matrix metal powder ranges up to about 5 microns and wherein the amount of refractory oxide ranges from about 3 to 10 volume percent and has an average parti-. cle size ranging from about 0.01 to 0.1 micron.

4. The method of claim 1', wherein the. matrix metal is selected from the group consisting ofcopper, silver, gold and copper-base, silver-base and gold-base alloys.

5. The method of claim 4, wherein the average particle. of the matrix metal ranges up to about microns, and wherein the amount of refractory oxide powder ranges from about 3 to 15 volume percent and has an average particle size 30 to 150 times smaller than the average particle size of the matrix metalpowder.

6. The method of claim 5, wherein the matrix metal is comprised substantially of copper.

7. The method of claim 1, wherein the matrix metal is selected from the group consisting of iron, nickel, cobalt and iron-base, nickel-base and cobalt-base alloys.

8. The method of claim 7, wherein the average particle size of the matrix metal ranges up to about 5 microns, and wherein the amount of refractory oxide powder ranges from about 3 to 15 volume percent and has an average particle size 30 to 150 times smaller than the average particle size of the matrix metal powder.

9. The method of claim 1, wherein the matrix metal is selected from the group consisting of Pt, Ir, Os, Pd, Rh and Ru and alloys based on these metals.

10. The method of claim 9, wherein the average particle size of the matrix metal ranges up to about microns, and wherein the amount of refractory oxide powder ranges from about 3 to volume percent and has an average size 30to 150 timessmaller than the average particle size of the matrix metal powder.

11. A metallurgical powder composition mixture for use in the powder metallurgical production of dispersion strengthened metals by the fabrication of said composition into a dense wrought structure comprising separate particles of" aductile matrix metal powder of average I particle size ranging up to about 'micronsha'ving substantially uniformly 'mixed'j therewith separateparticles of about 1 toi1'5 volumepercent'of a refractory oxide'pow der whose ne'gative'free' energy of the oxid'e'at' about C. is at least about 90,000 calories per gram atom of oxygen. and whose average particle size does not exceed about 0.3 micronsand ranges from about to 250 times smaller than the average particle size of said matrix metal powder.

12. The metallurgical powder composition of claim 11, wherein the matrix metal powder has an average particle size ranging up, to about 10 microns and wherein the refractory oxide mixed therewith ranges from about 3 to 15 volume percent and has an average particle size ranging from about 30 to times smaller than the average'particle size of said matrix metal powder.

13. The metallurgical'powder composition of claim 12', wherein the matrix metal powder has an average particle size ranging up to about Smicrons and wherein the refractory oxide mixed therewith ranges from about 3 to 10 volume percent and has. an average particle size of about 0.01 to 0.1 micron, said average particle size being about 30 to. 150 times smaller than the average particle size of said .matrix metal powder.

References Cited in the file of this'patent UNITEDI STATES PATENTS Alexander et a1. Jan; 30, 1962

Claims

11. A METALLURGICAL POWDER COMPOSITION MIXTURE FOR USE IN THE POWDER METALLURGICAL PRODUCTION OF DISPERSION STRENGTHENED METALS BY THE FABRICATION OF SAID COMPOSITION INTO A DENSE WROUGHT STRUCTURE COMPRISING SEPARATE PARTICLES OF A DUCTILE MATRIX METAL POWDER OF AVERAGE PARTICLE SIZE RANGING UP TO ABOUT 20 MICRONS HAVING SUBSTANTIALLY UNIFORMLY MIXED THEREWITH SEPARATE PARTICLES OF ABOUT 1 TO 15 VOLUME PERCENT OF A REFRACTORY OXIDE POWDER WHOSE NEGATIVE FREE ENERGY OF THE OXIDE AT ABOUT 25*