Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/14—Treatment of metallic powder
  • B22F1/142—Thermal or thermo-mechanical treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0408—Light metal alloys
  • C22C1/0416—Aluminium-based alloys

Definitions

• a method of treating a metallurgical object containing metastable featureless regions adversely affecting fracture toughness comprising heating the object for transforming the regions at least sufficiently out of their metastable state to improve fracture toughness; and, a method of treating metal particles containing metastable featureless regions which adversely affect fracture toughness when the particles are bonded together to form a metallurgical object, comprising heating the particles for transferring the regions at least sufficiently out of their metastable state to improve fracture toughness in metallurgical objects formed by bonding the particles together.
• Figure 1 composed of Figures 1a to 1d, are photomicrographs of a powder used in the invention.
• Figures 2 to 4 are plots of data.
• Featureless Regions The present invention concerns a treatment of metallurgical objects containing certain metastable, featureless regions. The treatment improves fracture toughness.
• zone A regions is synonymous to "featureless regions", as can be observed, for instance, in the references antedating Jones, as cited in the preceding paragraph), such indicating that discussion is of crystalline material.
• the featureless regions result from rapid cooling.
• Figure 1 illustrates the phenomenon of featureless regions.
• Figure 1a taken using optical microscopy, the featureless regions appear white as compared to the other regions which have a texture that appears to be black specks on a gray background. Note that the smaller particles tend to be completely featureless, an effect of the higher cooling rate experienced by the smaller particles.
• Figures 1b-1d further illustrate the featureless regions, which appear uniformly gray as compared to the remaining, dendritically textured regions.
• Figures 1b and 1d show again the smaller, completely featureless regions.
• Figure 1c shows in particularly good detail that the particle has a featureless half-moon region on its lower side. This is an aspect which also shows in Figures 1a and 1b, namely that higher cooling rates in some parts of a particle versus slower cooling rates in other parts can lead to a situation where the particle will be featureless in the rapidly cooled parts and textured in the slower cooled parts.
• alloys In general, any alloy containing featureless regions can be treated according to the invention.
• a preferred Al alloy consists essentially of 4 to 12% Fe, 2 to 14% Ce, remainder Al. Fe combines with Al to form intermetallic dispersoids and precipitates providing strength at room temperature and elevated temperature. Ce combines with Fe and Al to form intermetallic dispersoids which provide strength, thermal stability and corrosion resistance. Further information concerning this alloy is contained in U.S. Patent Nos. 4,379,719 and 4,464,199.
• the featureless particles are stabilized and they become deformable.
• Deformation after the uniformizing treatment for instance deformation in the form of compaction, extrusion or rolling, will provide a more uniform microstructure, with improved bonding between powder particles. Improved interparticle powder bonding further increases toughness and resistance to crack propagation.
• Table A illustrates results achieved by procedure according to the present invention (with heat treatment, i.e. 1 to 3 minutes at 900°F followed by cooling to 725°F extrusion temperature) compared to results without heat treatment (i.e. the billet was heated directly to the 725 °F extrusion temperature and then extruded). Processing in going from extruded bar to sheet was the same in both instances.
• the invention improves toughness and thermal stability in metallurgical objects based on rapid solidification processes. It is expected that creep behavior will also be improved. Further illustrative of the invention are the following examples.
• a pot of such composition was alloyed by adding high purity alloying elements to high purity aluminum. The melt was passed through a filter and atomized using high temperature flue gas to minimize the oxidation of the alloying elements. During atomization, the powder was continuously passed through a cyclone to separate the particles from the high velocity air stream. The majority of powder particles had diameters between 5 and 40 micrometers. Powder was screened to retain only less than 74 micrometers size powder and fed directly into a drum.
• the powder had the following percentages of impurities: Si 0.14, Cu 0.02, Mn 0.04, Cr 0.01, Ni 0.02, Zn 0.02, Ti 0.01.
• the powder was found to have featureless regions in about the same quantity and distribution as shown in Figure 1.
• the particle size distribution of the powder was 4.4% in the range 44 to 74 micrometers and 95.4% smaller than 44 micrometers.
• Average particle diameter was 15.5 microns as determined on a Fisher Subsieve Sizer.
• Billet was made from this powder by cold isostatic pressing to approximately 75% of theoretical density.
• Each 66 kg (145 1b) cold isostatic compact was encapsulated in an aluminum container with an evacuation tube on one end.
• the canned compacts were placed in a 658 K (725°F) furnace and continuously degassed for six hours, attaining a vacuum level below 40 microns. Degassed and sealed compacts were then hot pressed at 725°F to 100 percent density using an average pressure of 469.2 MPa (68 ksi).
• a cylindrical extrusion charge measuring 15 cm (6.125 in.) diameter x 30.5 cm (12 in.) length was machined from the billet and subjected to a uniformizing treatments of 1 minute at 850°F and 1 minute at 900°F. Heating was done using an induction furnace operating at 60 H z . Temperature was measured by a thermocouple placed at an axial location about 1.2 cm (0.5 in.) from the end.
• Example II Extruded bar of Example I was rolled at 600 °F to sheet of final thickness equalling 1.60 mm (0.063 inch). Prior to rolling, the extrusion was sawed to approximately 25 cm (10 in.) lengths. Surface roughness, caused by pickup of aluminum on the extrusion dies, was eliminated by machining the extrusions to the thicknesses listed in Table III. Also listed are process parameters used to roll the Al-Fe-Ce 1.60 mm (0.063 in.) sheet. Each piece was cross rolled until the desired width, greater than 41 cm (16 inches) was obtained, followed by straight rolling to the desired thickness, 1.60 mm (0.063 inch).
• Figure 3 shows the graphic representation of the strength/fracture toughness, K c , relationships for representative samples of Table II, while Figure 4 provides a corresponding presentation from Table II in the form of toughness indicator, or unit propagation energy, against yield strength.
• the superiority of sheet treated according to the present invention compared to the ingot metallurgy representatives is apparent. It is to be noted that for a given alloy, the tradeoff between strength loss and toughness improvement is a function of time and temperature during the uniformizing treatment. TABLE II Room Temperature Tensile and 1 Fracture Toughness 1.60mm (0.063 In.) Sheet

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• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
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• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)

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• 1986
  • 1986-05-15 EP EP86903818A patent/EP0222002B1/de not_active Expired - Lifetime
  • 1986-05-15 WO PCT/US1986/001050 patent/WO1986006748A1/en active IP Right Grant

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