Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S75/00—Specialized metallurgical processes, compositions for use therein, consolidated metal powder compositions, and loose metal particulate mixtures
  • Y10S75/95—Consolidated metal powder compositions of >95% theoretical density, e.g. wrought
  • Y10S75/951—Oxide containing, e.g. dispersion strengthened

Definitions

• This invention relates to a method of processing dispersion strengthened or hardened metals and, in particular to a method of hot working said metals while inhibiting the dissipation of stored energy arising from the strain deformation of such metals.
• Dispersion strengthening of alloys consists of dispersing a finely divided non-metallic phase throughout a metal matrix and then storing energy of deformation in the structure.
• Several techniques have been employed to obtain the desired dispersion and among these, mechanical mixing and internal oxidation have thus far shown the most promise.
• Mechanical mixing is the fastest and least expensive way to obtain dispersion strengthened materials.
• Internal oxidation by comparison, is a more expensive and time consuming process to operate on a larger scale and involves the use of fine alloy powders not readily available. tory oxide-forming metal, e.g.
• aluminum is alloyed with a matrix metal, such as copper, and the alloy in particulate form subjected to an oxidation treatment to oxidize selectively aluminum to a dispersion of A1 followed by consolidation of the particles to a wrought shape.
• a matrix metal such as copper
• the latter technique is usually capable of providing wrought shapes exhibiting markedly improved results for smaller amounts of the non-metallic phase than wrought shapes produced from mechanically mixed powder.
• dispersion strengthened alloys stress rupture data have shown that such alloys are generally characterized by extreme flatness of slope on a log stress versus log rupture life plot. Because of this characteristic, the superiority of such alloys over conventional materials becomes markedly effective as time and/or temperature are increased. This is due to the fact that conventional materials, such as age hardenable alloys, are subject to over aging or solution of a second phase as affected by time and temperature, whereby a rapid drop-off in properties occurs.
• oxide dispersion strengthened materials have been known to be generally stable up to below the melting point of the base or matrix material.
• Strengthening in these alloys has been postulated to arise from two sources.
• One is the effect of the dispersion, which imparts strength to the matrix metal even in the annealed condition.
• the other efiFect arises from the introduction of the strain energy during the working process, tag. the extrusion process, with the consequent retention of this energy by the alloy by virtue of the presence of the dispersed phase.
• Another object is to provide a method of processing dispersion strengthened iron and iron alloys with the aim of producingmaterial of enhanced strength properties, such as improved resistance to creep.
• An additional object is to provide a method of processing a matrix metal, such as iron or an iron-base alloy, having dispersed therethrough fine particles of a refractory oxide wherein the processing temperature is determined according to the temperature of phase transformation of the matrix metal and the temperature of crystallographic transformation of the refractory oxide.
• a matrix metal such as iron or an iron-base alloy
• finely divided iron is mixed with up to about 15 W0 (volume percent) of a refractory oxide, such as A1 0 the particle size of the iron being preferably below 20 microns and generally below 10 microns.
• a refractory oxide such as A1 0 the particle size of the iron being preferably below 20 microns and generally below 10 microns.
• the refractory oxide have a particle size less than that of the matrix metal, for example from about 30 to 250 times smaller, preferably from about 30 to times smaller, so as to obtain adequate distribution of the oxide and control the interparticle spacing between the oxide particles.
• the metal powder is mixed with the refractory oxide preferably in the dry state by means of a high speed dry blender, or a ball mill, for a suitable time to effect uniform mixing, e.g. ranging from about 15 to 60 minutes in the blendor and 1 to 24 hours for the ball mill.
• a reduction treatment with hydrogen to reduce any iron oxide present at an adequate reducing temperature, e.g. from 700 to 900 F., and then hydrostatically pressed to the desired iron-base shape, followed by sintering in hydrogen to form a compact capable of being handled.
• the sintering temperature should preferably not exceed the transformation temperature of the matrix metal.
• the sintering temperature be maintained in the alpha iron region, for example at 1525 F.
• This temperature is also important where gamma alumina is used as the dispersoid as it is below the gamma to alpha transformation temperature.
• severe agglomeration of the powders is substantially avoided.
• the sintered compact is thereafter vacuum packed in a can and the whole extruded at an elevated temperature at an extrusion ratio sufficient to achieve maximum density, e-.g. ranging from about 10 to 1 to 28 to l.
• dispersion strengthened iron or iron-base alloys produced by the foregoing powder metallurgy or similar technique generally exhibit markedly improved strength properties, provided that the deformation employed in producing a dispersion strengthened metal shape of maximum density is carried out while the material is in the ferritic or alpha condition.
• the consolidation of the mixture should be conducted at an elevated temperature below the temperature at which phase transformation occurs inorder to insure optimum strength properties.
• the stored energy is dissipated as the worked material cools down through the, phase transformation range of the material and converts from one crystallographic structure to another; for example, as in iron from austenite to ferrite.
• Iron powder of about 3 microns average particle size was mixed with varying amounts of up to about 10 v/o of alumina having an average particle size of about 0.027 micron, the ratio of particle size of iron to aluminum being a little more than .100 to l.
• the alloys were prepared by dry mixing the iron matrix metal'powder and the aluminum oxide in lots of about 500 grams, the mixing being conducted in a high speed blendor, e.g. a Waring Blendor, at a speed of about 15,- 000' revolutions per minute; The mixing of each lot was carried out for about 5 minutes and then further mixed by spatulation on a sheet of clean paper for a few minutes, the procedure including the blendor and subsequent spatulation being repeated about 4 times.
• a high speed blendor e.g. a Waring Blendor
• the blended powder batches were thereafter subjected to a reducing treatment in dry hydrogen for a minimum of five hours at a temperature of about 800 F. to insure clean particle surfaces for subsequent consolidation of the mixture into wrought shapes.
• Each batch of the mixed powders was 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.
• a second rubber stopper having in communication therewith a hypodermic needle was inserted, a vacuum connection being made through the needle to remove the air from within powder mass.
• 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.
• compacts have been prepared by the same technique up to 3 inches in diameter and 6 inches long.
• billets of up to 20 inches diameter are envisaged.
• the compacts produced as aforementioned were then subjected to sintering in dry hydrogen for a minimum of -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 16 to 1.
• Table I V01. V01. Extru- Al loy No. percent percent 2 sion F81 A1203 te m? 1 3 micron iron powder. 2 0.027 micron A1203 powder.
• the alloys were then subjected to tensile tests at room worked No. 4.
• No. 3 was extruded at 1550 F., i.e. in the ferritic region of the matrix metal.
• Table II it will be noted that No. 3 exhibited a yield strength at 1200 F. of 21,300 p.s.i. as compared to the value of 10,800 p.s.i. (about half) obtained for No. 4 which was subjected to austenitic extrusion.
• No. 3 exhibited a yield strength of 13,900 p.s.i. as against the much lower value of 6,200 p.s.i. for the austenitically V The same trendwas indicated with respect to the 100 hour rupture'life at. 1200" F.
• a dispersoid which crystallographically transforms at an'elevated temperature, that the temperature of consolidation of the alloy be also maintained below this transformation temperature as well as below the phase transformation of the matrix metal.
• iron-base matrix alloys such as carbon steels, certain of the ferritic stainless steels subject to gamma or other transformation, certain of the iron-base alloy steels and the like.
• iron-base alloys would be those single phase binary alloys which have a second metal which does not oxidize readily such as binary alloys of Fe-Cr (up to 20% Cr), FeW (up to 4% W), FeMo (up to 4%), FeNi (up to 10% Ni), FeSi (up to Si), etc. It will be appreciated that some of these alloys may have an alpha or gamma phase stable up to very high temperature in which case they may not present any problems.
• iron-base alloys is meant to include solid solution alloys containing at least 50% Fe and, preferably, at least 65% Fe.
• matrix metals and alloys to which the invention is applicable are cobalt (transforms between 800 to 900 F.), and such cobalt alloys as Co-Mo, CoNi-W, CoCrW, CoCrMo, etc., reference being made to available phase diagrams in determining adequate fabrication temperatures free from phase transformations. Still others are titanium (a phase transformation at about 1615 F.), zirconium (a phase transformation at about 1470 F.), uranium (a phase transformation at about 1115 F.) as well as other metals and alloys.
• the matrix metal have a melting point above 1800" F.
• the metal in particulate form is .rnixedwith a refractory oxide powder, shaped and converted into a form capable of being easily handled during deformation working, and the whole but worked at an elevated temperature below the phase transformation temperature of the matrix metal and also preferably beloW the crystallographic transformation temperature of the dispersed refractory oxide.
• refractory oxides which may be used in producing dispersion hardened alloys in accordance with the invention are SiO A1 0 MgO, CaO, BaO, SrO, BeO, ZrO TiO Th0;; 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, for example above 2700 F. and generally above
• these oxides are characterized by a negative free energy of formation at about 25 C. of over 90,000 calories per gram atom of oxygen.
• SiO has .a negative free energy of formation at 25" C.
• the temperature of fabrication of the alloy should not exceed the crystallographic transformation temperature for gamma alumina which falls within range of about 1500 F. to 1920" F., otherwise agglomerations of the alumina particles occurs.
• the temperature of fabrication makes no difference in so far as the alpha alumina is concerned as it is in the stable high temperature form.
• SiO exhibits several transformations, ZrO has a monoclinic form which is stable to about 1830 F.
• oxides of the foregoing types may range from about 1 to 15 We and preferably from about 3 to 12 v/o.
• the particle size of the oxide should be 30 to 250 times smaller than the matrix metal powder, preferably 30 to times smaller, and also preferably range in size from about 0.01 to 0.1 micron for particle size of the matrix metal powder ranging up to about 20 microns or over the range of 1 to 20 microns.
• the invention enables the production of high strength Wrought metal products characterized by structural stability and. by the ability to retain high strength properties at elevated temperatures.
• metal structures are heat exchangers, turbine buckets of iron or iron alloys and other metals for use in steam and gas turbines, furnace structures where resistance to creep at elevated temperatures is an important consideration, boiler tubing for carrying super-heated steam and many other applications too numerous to mention.
• a method of producing a dispersion strengthened wrought metal product from a matrix metal selected from the group consisting of iron, cobalt, iron-base and cobaltbase metals of melting point above 1800 F. characterized by a phase transformation temperature at an elevated hot working temperature and from an insoluble refractory oxide dispersion hardener characterized by a negative free energy of formation at about 25 C. of at least about 90,000 calories per gram atom'of oxygen which comprises, providing a powder mixture comprising said matrix metal and a substantially uniform dispersion of said shape atan'elevated temperature'not exceeding the temperature at which the phase transformation of said matrix metal begins, whereby dissipation of stored energy is greatly inhibited.
• a method of producing a dispersion strengthened wrought metal product from an iron-base matrix metal of melting point above 1800 F. comprised substantially of iron characterized by a ferritic to austenitic transformation temperature at anelevated hot working temperature and'frorn an insoluble refractory oxide dispersion hardener characterized by a negative free energy of formation at about 25 C.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)

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Citations (3)

• 1960
  • 1960-03-15 US US15036A patent/US3070439A/en not_active Expired - Lifetime
• 1961
  • 1961-02-27 BE BE600659A patent/BE600659A/fr unknown
  • 1961-03-01 DK DK89661AA patent/DK107782C/da active
  • 1961-03-02 GB GB7727/61A patent/GB923949A/en not_active Expired
  • 1961-03-10 CH CH291961A patent/CH402572A/fr unknown
  • 1961-03-14 SE SE2697/61A patent/SE303612B/xx unknown

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