US3139682A - Strength recovery of dispersion hardened alloys - Google Patents

Description

N. J. GRAN-r 3,139,682

y July?, 1964v s'mfamcm RECOVERY oFfnIsPEvsIon HARDENED ALLYs Filed June 24. l1960 l IN1/Enron.

4009/0045 n! @e4/V2" f United States Patent O 3,139,682 STRENGTH-RECOVERY F DISPERSION f y HARDENED ALLOYS Nicholas J. Grant, 10 Leslie Road, Winchester, Mass. 1 Filed June 24, 1960, Ser. No."38,521

1 Claim. (Cl. 29552.2)l

This invention'relates to a method for the recovery of high`^temperature properties of certain lwrought metal compositions of the class based-` on the metal-metal oxide system in which a matrix metal or alloy 'has distributed fractory oxide phase.

In particular the invention is directed to 4the treatment of the aforementioned class of wrought metals which have been subjected to the deleterious effects of elevated temperatures wherein the-physical and other properties of said metalshave been substantially impaired. My inventionis applicable tothe recovery of those metals of the aforementioned class which have been impaired by heating to very high temperaturcsup to below the melting point `of the matrix` metal wherein recovery and softening has occurred; to those metals which have been subjected to brazing or solid state welding in which the properties at the braze or weld have been deleteriously affected; to those metals which have been heated to above the transformation temperaturevduring fabric-ation o r other treatments in which there has been a' dissipation of stored energy with a consequent loss in strength; and to other situations in which prevailing high temperatures have had an adverse effect upon lthe physical properties of the metal.

Mechanical working, such as cold working, is`A known to increase the hardness and strength of yconventional metals and 'alloys and it is. not uncommon to provide commercially metals having varying-degrees of strain hardening depending upon the ultimate use to which the metals are to be put.` Generally, strain hardened metals, particularly metalsincapable of being heat treated to higher hardnesses, are limited to room temperature applications or totemperatures not too far above room temperature 'for the reason that metals which have been -strain `hardened by cold working are not stable, but tend to revert to the strain freestate when heated to temperatures which produce a softening effect on metals. 't

When ametal is subjected to cold working and therea'fter heated to successively higher? temperatures until-` softening sets in,rthe,temperature at which this occurs is referred to as the temperature of reerystallization. The temperature of softening is related to the degree of strain hardening, that is the higher the amount of cold working, the lower is the temperature of softening or recrystallization. `For example, a copper composition `cold worked 3% (i.e. reduction by cold rolling) may exhibit a temperature of softening in the neighborhood of about 450` i C. while the same`compostion cold rolled to a reduction of y20% may have a lower temperature of softening of about 400 C. `At 50% coldpwork, the softening temper.-

rature maybe about 3,5,0.1. whil e .at 95%' cold work, the

temperature may vfall belojkyl BOQCL f t Because of the foregoing-*limitations it has not been possible to` utilize effectively mechanical working as a t A means of recovering physical or other properties of metals -or alloys which have been impaired through overheating.

However, I have found that as to `certain metal compositions, I can employ mechanical working, i.e. strain f hardening, not only to recover properties lost through overheating, but in many instances to improve upon the properties then existing inthe metal. By mechanical working, I include cold working as well as any working at temperatures above room temperature at which deformationalenergy is stored in the worked metal.

Ihave'ound, `for example, that if the metal was origtherethrougha tine dispersion of `a hard particle or re- Patented 'July 7, 1964 lost through aggravated heating ata very high temperature, wellabove the normal recrystallization temperature of the4 base metal or because of overheating due to 5 welding or b razing, l can bring the metal back to its opti-v mum condition by strain hardening without themetal tending to revert back to the strain free state at elevated temperatures when the recrystallization temperature of the unsupported matrix is exceeded. l'n other words, the

strain hardened metal of my invention retains its high strength properties on heating to relatively high tempera'- ture levels with little dissipation of the stored energy. even above temperatures at which comparable metals or alloys generally recrystallize and soften. Moreover, whereas in conventional metals, e.g. cold worked copper, the temperature of recrystallization decreases substantially with increase in cold work, the compositions with which I work do not appear to be so affected and are relatively stable at elevated temperatures over a range of applied cold work. j v

It is the objectof the invention to provide a method of providing wrought metal articles in which applied cold' work is utilized to recover the strength properties of the metal without affecting the stability of the metal in resisting t recrystallization at elevated temperatures.

Another object is to provide a method whereby certain metal compositions which have been softened by brazing or welding, such as spot, seam, butt or flash welding, or other forms of overheating can be recovered by mechanical working, whereby the metal thereafter will resist recrystallization at exceedingly high temperatures and substantially retain its stored energy.

These and other objects will more clearly appear from the disclosure and the appended drawings, wherein:` FIG. l depicts graphicallyA the improved rupture life obtained for a coldworked alloy comprising copper and silica;and 4 l `FIG. 2'is similar to FIG. -1 but exhibits the improved rupture life obtained for a cold worked alloy comprising copper and alumina.

`I-have found thatV a metal containing av substantially uniform dispersion of inely divided substantially insoluble refractory material, e.`g. refractory oxide, and whose properties have been impaired by substantial overheating, can be physically processed toconfer improved high temperature properties, e.g.` resistance to creep, by mechanicallyworking said metal. Unlike lthe mechanical `working of conventional metals and alloys, I tind that the mechanical working of my material does not affect 5d adversely the recrystallization temperature but that, on

the contrary, the material so processed resists recrystalliza-v tion at elevated temperatures well above the-normal recrystallization temperature of the matrix metal and appreaching the melting point in the valloys dispersion 5'5 strengthenedtoanfoptimu'rm t.

1 ,IA meta 'regains Phenomenon has been Iz-pointed out hereine worked condifofilnd,that when F Ni lener `is obtained in several wa'ysgfor example', either-by mechanically mixing a substantially inert oxide, eig. A1205', SiOg, T1102, ZrO, and the like, with matrix metal powder followed by consolidation of the mixture into a wroughtl shape,. or by internal oxidation. e

In producing the material by internal oxidation, a refractory oxide-forming metal, e.g.,aluminum, is alloyed asa dilute solution with a matrix metal, such as copper, and the alloy in particulate form, e.g; minus 44 microns, subjected to an oxidation treatment adapted to selectively oxdzealuminum t'o a dispersion of A1203 fol- .lowedby consolidation lof the' particles to a wrought temperatures shown in Table I.

Table I Wt. Voi. Percent Oxidation Oxide Iar- Alloy No. Percent Oxide Temp., ticle Element fC. Radius. A.

powders involved the surface oxidation of4 the powders to form a surface coating rich in Cu3O (and also containing some solute oxide) by heating a given amount of powder in arneasured amount of oxygen at about 450 C. The oxygen from the surface oxide was then diifus'ed into the sample by heating at the desired temperature, e.g. 650 C., under substantially inert-conditions. This method was found vadequate for obtaining up to about 12% by volume of solute oxide within `the matrix metal.

As an--example of one method employed in effecting the internal oxidation of the alloy powder, the surface oxidized powder, for example 450 grams, is sealed in a 1.5 inch diameter tube by iiattening'of the ends. The tube is placed in a large `mutlie furnace held at the desired temperature, e.g. 650 C. or 750 C. for a time, determined by pilot tests, suicient yto obtain a uniform dispersion of 'solutefmetal oxide in each of the matrix metal particles. i t l The internally oxidized matrix metal powder is thereafter hydrogen reduced at an elevated temperature,e.g.

450 C. for'one hour.' to rid the surface of each particle of` copper oxide and then packed by vibration in a copper container of about 1.4 inch I.D. by 4.5 inch long to achieve a pack density of about 50%. Thecontainer is evacuated trusion.

f'course, it will be appreciated that the foregoing met od is by way of illustration and that many variations of accomplishing the same result may be substituted. For example, the internal oxidation could also be achieved by treating the alloy powder at a low partial pressure of oxygen (e.g. subatmospheric pressure) at which copper and sealed and made I'ready for direct ex'- does not readily oxidize and the solutev metal oxidized by diffusion `of the oxygen into'the matrix metal powder', However, I prefer in carrying out my invention to utilize mentioned` at 760 CZ- iising a speed`of about 55 inches minute tof'giv'e an extrusion ratio of about 28 to l. Rods of approximately 0.25 inch diameter by four feet in lengthwere obtained from the alloys.

Alloy No. l'was partially recrystallized n the asextruded condition, that is 'part of the grains making up the copper matrix metal were equiaxed, indicating that some softening had occurred during hot working by extrusion. After subjecting thisalloy to aggravated heating at just below the melting point of copper, 10-hoursv at l050 C., the. matrix metal was 100% recrystallized. The metal was thencold worked 25% and subjected to a rupture life creep test comprising heating the alloy at various stresses at 450 C. until rupture occurs. The results of the test indicated that the alloy in the cold worked condition was markedly superior at 450 C. to

crystalliz'ed condition and maintained these properties for prolonged periods of time at 450 C. without further recrystallization occurring. It will be noted from FIG. 2 that the material cold worked 10% exhibited marked improvement at 'high temperatures over the partially recrystallized material. Similar trends were noted with respect to alloy Nos. 2, 3 and 4. It is thus apparent that strain hardening in this class of alloys does not lower the temperature of recrystallization as in the conventional alloys but. that, onthe contrary, the stored energy is retained at elevated temperatures.

Likewise, similar results 'were obtained on dispersion hardened material produced by the mechanical mixing of powders. In producing alloys by mechanical mixing as disclosed in copending application Serial No. 24,971, tiled April 27, 1960,matrix copper powder about 1 micron in size is mixed separately with speciiiedamounts ot finely divided SiO, or A1203, preferably of particle' size ranging from about 30 to- 150 times smaller than the matrix metal powder, e.g. 0.02 micron. Dry mixing is used by utilizing i a Waring Blendor at a speed of about 15,000 revolutions per minute. Thel mixing is carried out for about 15 minutes and thenfurther mixed by spatulationv on a sheet of clean paper for s few minutes, the procedure with the Blender andthe subsequent spatulation being'repeated about four times. t

The blended powder mixture is thereafter subjected to a reducing treatment in dry hydrogen fora minimum of tive hours at a temperature of about 430 C. to insure clean particle surfaces for subsequence consolidation of the mixture into wrought shapes. Each batch of the mixed powders is introduced into a rubber tube supported withina perforated steel canister about two inches in diameter, one end of the rubber tube being rubber stoppered at the start. `After the powder is introduced, a second rubber stopper havingtin communication therewith a hypodermic needle is inserted, avacuum connection being made through the needle to remove the air from within powder mass. After completion of evacuation, the needle is removed and the canister assembly subjected to hydrostatic pressure hat about 30,000 p.s .i. to yield compacts 1.4 inches'lin diameter and 2.5`inches long.

rnpacts; areQthensjubiected to sintering in dry hydro for a minimum of 10 hours at 830 C. After that; they are each canned by insertion in a pure'copper container and welding vacuum tight followed by extrusion the first method described as I find that this ymethod.leiid itself tocase of control andreadily reproduceabl iat an elevated temperature. The extrusion ratio used is about 16 to 1,'although the ratio could have ranged from' 12|to 1 to V30 to 1.

Shapes produced by the foregoing manner, in which at least some of thegrans of the matrix metal re equiaxed,

lplatinur'n, etc.

at elevated temperatures for prolonged periods of 'time without recrystallization or without substantially losing product exhibited a '100 hour rupture strength at 1100 F. of about 11,000 p.s.i. However,.after cold working the same composition about 25 the 100 hour rupture stress at 1100" F. was raised from 11,000 p.s.i. to 14,000 p.s.i., anincrease of over 27%, the alloy, as cold worked, ex-v hibiting particularresistance to creep at elevated temperatures while resisting recrystallization. A A It is' apparent that the invention is applicable to wide variety of dispersionstrengthened ductile matrixmetals, be they based on alloy matrices or pure metals capable o'f being deformed into a variety of shapes. The lower melting metals Mg, Zn, Cd, Al,l In, Pb, Sn and their alloys containing oxide dispersoids may be so treated. The higher melting metals comprising the copper group metalsV (Cu, Ag, Au) and their alloys, the platinum group metals (Pt, Pd, Ru, Rh, Ir, etc.) and their alloys, the iron group metals (Fe, Ni, Co) and their alloys may also be treated and so zinc; 90% copper and 10% zinc; 60% copper and 40% zinc; 71% copper, 28% zinc and 1% tin; 65% copper, 17% zinc and 18% nickel; 90% silver and 10% copper; up to nickel and the balance silver; 70% gold and the balance palladium; 69% gold, 25% silver and 6% Examples of'iron group alloys include: certain steels; 64% iron and 36% nickel; 31% nickel, 4 to 6% cobalt,

`and the balance iron; 54% iron and 46% nickel; 99%` nickel and the balance cobalt; 68% nickel and 32% copper, etc.,

Examples of platinum group alloys are as follows: patinum-rhodium alloys containing up to 50% rhodium; platinum-iridium alloys containing up to 30% iridium; platinum-nickelA containing 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 to8% ruthenium; 60% palladium and 40% silver, etc. t 4

Examples of refractory oxides which maybe used in producing dispersion hardened alloys in accordance with the` invention are SiOg, A1203, MgO, BeO, Zr03, T102, ThO, and oxides of the rare earth metal group,.such as oxides of cerium, lanthanum, neodymium, etc. Such refractory oxides are characterized as having a melting point above the melting point of the matrix metal and generally above 1500 C. In addition, these oxides are characterized by a negative free energy of formation at about C.

. ple, dispersion hardened iron containing about 8% by volume of A1203 was produced by extruding in the austeniticV temperature range, e.g. about 1900? C. The extruded l from about 0.01 to 0.1. Where the dispersion strengthened metal is produced by powder mixing, the metal pow'- der should be larger than 'the oxide and preferably to 150 times larger..

The amount of working applied to dispersion hardened material will depend upon the relative softness of the alloy and the amount of disperse' phase present. Generally, the amount of working will be inversely related to I the vol.,percent of disperse phasepresent, that is, the higher the amount of disperse phase, the lower will be the amount of cold work required to achieve the desired effect. The amount of .cold work in terms of reduction in cross sectional area may range up to about 30% and generally from about 10 to 25%. 'llhe working may be achievedby cold drawing, cold rolling,I cold swaging, shot ing, ,or other forms of working in which a metal is Led beyond itsl elastic limit at room or aboveroom temperature at whcli recrystallization does not normally perature of the matrix. Thus, it is possible to overcomeV any weakness developed in a structural element due to localized overheating merely by peening the affected area.

A 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 Y without departing from the spirit and scope of the invention as those skilled in the art will readily understand, such modifications and variations areconsidered to be within the purview and scope of the invention and the `appended claim. i

What is claimed is:

A method of fabricating a wrought metal product at i elevated temperatures which tend to impair the physical properties of at least a portion of the metal product being fabricated, such as occurs in welding, and at fabrication temperatures in excess of the recovery and recrystallizat tion temperature of the metal product which comprises, providing a metalproduct to be fabricated Vcomprising a metal selected from the group consisting of Fe, Ni, Co, Fe-base, Ni-base and Co-base alloys; Cu, Ag, Au, Cubase, Ag-base `and`Aubase alloys; Pt, Pd, Ru, Rh, Ir

. and Pt-base. Pd-base, Ru-base, Rh-base and Ir-base alloys;

of over 90.000 calories per gram atom of oxygen. For

25 C. of about 96,200, A1203 of about 125,590, MgO of about 136,130, BeO of about 139,000, etc.

i `The amounts of the disperse phase employed may preferably range from about 0.1 to 15 vol. percent, preferably from about 1 to 12 vol. percent, and more preferably from about 3 to 10 vol. percent of the alloy. Where 7 0.1 to 4 vol. percent. I also prefer `that the particle size obtained by internal oxidation range from about to 7 00 A. average diameter.

4 Broadly speaking, the particle size of the disperse phase should not exceed 0.3 micron and preferably should range i i example SiO, has a negative free energy of formation at and` Mg, Zn, Cd, Al, Pb, Snand Mg-base, Zn-ba`se, `Cdbase, Al-base, fPbbase and Sn-base alloys, having dispersed substantially uniformly therethrough about 0.1 to 15 volume percent of a stable insoluble disperse refractory oxide phase characterized by a negative free energy of formation at about25 C. of at least about 90,000 calories per gram atom of oxygen and a particle size not exceeding about 0.3` micron, fabricating` at least a portion of said metal product containing said disperse refractory oxide phase at'an elevated fabrication temperature which tends to impair the physical properties of said portion, and then subjecting said fabricated portion to strain hardening, the amount of strain hardening being inversely related to the volume of the disperse refractory oxide phase present, whereby at least said strain hardened 0 portion is characterized` by improved high temperature strength properties equal to or above the original properties prior to impairment thereof by high temperature heating.

Y (References on followhlg page) lby 30 to Z50-times

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