Showing papers on "Powder metallurgy published in 1987"

Formation and properties of NdFeB prepared by mechanical alloying and solid‐state reaction

Abstract: Magnetically isotropic Nd15Fe77B8 powder is prepared by mechanical alloying and a solid‐state reaction from the elemental powders. Due to the extremely short reaction time (for example, 10 min at 700 °C) the magnetically isotropic particles have a very fine microstructure comparable to rapidly quenched samples, show a pinning‐type behavior and possess excellent magnetic values such as IHC up to 13 kOe and BHmax up to 12.8 MGOe. Details on the development of the microstructure during milling, the reaction kinetics, and the magnetic properties are reported.

Effect of composition and grain size on slow plastic flow properties of NiAl between 1200 and 1400 K

Abstract: A series of about 15-micron diameter polycrystalline B2 crystal structure NiAl alloys ranging in composition from 43.9 to 52.7 Al (at. pct) have been compression tested at constant velocities in air between 1200 and 1400 K. All materials were fabricated via powder metallurgy techniques with hot extrusion as the densification process. Seven intermediate compositions were produced by blending various amounts of two master heats of prealloyed powder; in addition, a tenth alloy of identical composition, 48.25 Al, as one of the blended materials, was produced from a third master heat. Comparison of the flow stress-strain rate behavior for the two 48.25 Al alloys revealed that their properties were identical. The creep strength of materials for Al/Ni not above 1.03 was essentially equal, and deformation could be described by a single stress exponent and activation energy. Creep at low temperatures and faster strain rates is independent of grain sizes and appears to be controlled by a subgrain mechanism. However, at higher temperatures and slower strain rates, diffusional creep seems to contribute to the overall deformation rate.

Heating of powders in an r.f. inductively coupled plasma under dense loading conditions

Abstract: A study was carried out of the heating of powders in an r.f. inductively coupled plasma under dense loading conditions. The results obtained using a mathematical model taking into account plasma-particle interaction effects reveal an important cooling of the plasma caused by the presence of the particles. This, in turn, gave rise to a corresponding drop of the efficiency of the melting of the particles in the plasma. The effect is shown to depend strongly on the thermodynamic properties of the material of the powder.

Nickel base superalloy articles and method for making

Abstract: A process is described for converting a fine grain superalloy casting into a forging having mechanical properties equivalent to those resulting from powder metallurgy processing. Cast material is extruded and forged. A HIP treatment is employed to close porosity.

Structural development during mechanical alloying of crystalline niobium and tin powders

Abstract: The structural development with milling time during mechanical alloying of niobium and tin powders, of average composition Nb3Sn, was followed by x‐ray diffraction. The elemental powders initially alloy mechanically to form an A15 structure phase. With continued milling, the A15 phase transforms to an amorphous structure. The kinetics of the structure changes are dependent on the milling media and atmosphere. The measured lattice parameter a0 for the A15 phase prepared with tungsten carbide milling media in an argon atmosphere agrees with the literature value of a0 for bulk Nb3Sn. However, milling with steel media introduced significant contamination by iron and an anamolous expansion of the A15 phase lattice. Amorphization of the A15 phase is believed to be due to the creation of a critical defect concentration by the mechanical deformation.

A study of the hot-working behavior of SiC-Al alloy composites and their matrix alloys by hot torsion testing

Abstract: The hot-working behavior of two metal matrix composites (7090+20 vol pct SiC whiskers and 6061+20 vol pct SiC whiskers) and their powder metallurgy matrix alloys (7090 and 6061) was studied by hot torsion testing. Flow stress (σ0) and strain-to-failure (ef) data were generated at deformation temperatures and strain rates corresponding to the potential range for commercially hot-working these alloys. Based on the hot torsion data, hot-working parameters were recommended where (σ0) was low and (ef) was high. Strain rate sensitivities and activation energies of deformation were computed for the alloys.

Glass formation in mechanically alloyed transition-metal-Zr alloys

Abstract: A large number of TM-Zr alloys (where TM is a transition metal) have been produced by mechanical alloying from crystalline powders of the elements. The first milled products showed a layered microstructure of the powder particles, which became finer with increasing milling time. Longer milling led to amorphous powder. The formation of amorphous TM-Zr (TM ═ Cu, Ni, Co, Fe, Mn) was monitored by X-ray diffraction and differential thermal analysis. Amorphous V-Zr or Cr-Zr could not be produced. The experimental results are compared with the glass-forming ability predicted by free-enthalpy diagrams calculated from the Miedema model. The amorphization is found to depend strongly on a large negative heat of mixing.

Abrasive material, especially for turbine blade tips

Abstract: An abrasive material comprised of a metal matrix and evenly distributed ceramic particulates, is made by mixing powder metal with the ceramic powder and heating to a temperature sufficient to melt most, but not all of the powder. In this way the ceramic does not float to the top of the material, yet a dense material is obtained. A nickel superalloy matrix will have at least some remnants of the original powder metal structure, typically some equiaxed grains, along with a fine dendritic structure, thereby imparting desirable high temperature strength when the abrasive material is applied to the tips of blades of gas turbine engines. Preferred matrices have a relatively wide liquidus-solidus temperature range, contain a melting point depressant, and a reactive metal to promote adhesion to the ceramic.

Shock-compression fabrication of high-temperature superconductor/metal composite monoliths

Abstract: In spite of the recent spectacular achievements in developing high-temperature (transition temperature Tc ≥ 77 K) superconductivity in systems generically represented by ABa2Cu3O7–x (where A = Y, La, Nd, Sm, Eu, Gd, Ho, Er, Lu)1,2, it has been difficult to prepare large powder sample batches (≥0.5 kg). More importantly, efforts to consolidate or sinter superconducting powder samples or to place powders (such as Y–Ba–Cu–O) in useful environments or monolithic structures which are not brittle and friable, and the fabrication of high-temperature superconducting products have been frustrating at best3. Based on the process integration of several fundamental principles involving shock-compression science4,5, we have successfully fabricated composite/laminate monoliths containing shock-compacted, consolidated and bonded Y–Ba–Cu–O superconducting powder channels (with Tc≥90K) in a solid copper matrix6. Using ammonium-nitrate-based explosives (with detonation velocities, VD, adjusted to be ∼1,800 m s–1), we have progressed from shock-consolidated, superconducting YBa2Cu3O7 powder-channel rings with mean diameters of 4.4cm and 4mm2 cross-sections in explosively (implosive shock-wave) clad solid copper matrices, to monoliths from which copper matrix rings have been cut containing shock-consolidated, superconducting YBa2Cu3O7 powder channels with mean diameters of 24 cm (with 2.5 cm width) and cross-sections of 1.85cm2.

Permanent magnet having good thermal stability and method for manufacturing same

Abstract: A thermally stable permanent magnet with reduced irreversible loss of flux and improved intrinsic coercivity iHc of 15KOe or more having the following composition: (Nd.sub.1-α Dy.sub.α)(Fe.sub.1-x-y-z Co.sub.x B.sub.y M z ) a wherein M represents at least one element selected from the group consisting of Nb, Mo, Al, Si, P, Zr, Cu, V, W, Ti, Ni, Cr, Hf, Mn, Bi, Sn, Sb and Ge, 0.01≦x≦0.4, 0.04≦y≦0.20, 0≦z≦0.03, 4≦a≦7.5 and 0.03≦α≦0.40. This can be manufactured by (a) sintering an alloy having the above composition by a powder metallurgy method, (b) heating the sintered body at 750°-1000° C. for 0.2-5 hours, (c) slowly cooling it at a cooling rate of 0.3°-5° C./min to temperatures between room temperature and 600° C., (d) heating it at 540°-640° C. for 0.2-3 hours, and (e) rapidly cooling it at a cooling rate of 20°-400° C./min.

Mold powder technology for continuous casting of low-carbon aluminum-killed steel

Abstract: Etude de la viscosite et de la temperature de fusion des poudres metalliques. Caracterisation de la vitesse de vitrification de la poudre et l'epaisseur de la poudre liquide fondue dans le moule

Process for producing tungsten heavy alloy sheet

Abstract: A process is disclosed for producing a sheet of tungsten heavy alloy which involves uniformly blending elemental powder components of the alloy by forming a slurry of the powder components in a liquid medium, removing the liquid medium from the powders and forming a planar cake of the powders, drying the cake, sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.

Pitting Corrosion of Powder Metallurgy AlZnMg Alloys

Abstract: Pitting susceptibility in 3.5% NaCl was compared for three AlZnMg alloys containing 2.5% Mg and 8.8, 9.0, and 12.5% Zn. Pit nucleation potentials were determined using electrochemical tech...

Method of forming a metal article from powdered metal

Abstract: A container for holding powdered metal is formed by electroplating a layer of metal over a pattern having a configuration which corresponds to the configuration of an article to be formed. A rigid core is surrounded by the pattern material and the layer of metal. The pattern material is removed from the layer of metal to form a container in which the core is disposed. The core and container may be held against relative movement by gripping the core with the layer of metal or by pin elements extending between the core and layer of metal. The container is filled with metal powder. The metal powder is cold compacted to plastically deform the particles of metal powder without significant bonding between the particles of metal powder. The metal powder is cold compacted by exposing the container to fluid at a relatively low temperature and high pressure. Metal powder particles are pressed against each other and against the core by the fluid pressure applied against the container to plastically deform the metal powder particles. After being cold compacted, the metal powder is hot compacted to bond the particles of metal powder together and form a unitary body which surrounds the core. The core is subsequently removed from the unitary body to form a recess in the body.

K2O · 6TiO2 whisker-reinforced aluminium composite by a powder metallurgical method

Abstract: Amelioration de la resistance du materiau composite par une methode de metallurgie des poudres. Etude de la relation entre la resistance a la traction et la fraction volumique de barbes dans le materiau

Method for producing very fine microstructures in titanium alloy powder compacts

Abstract: A process for producing titanium alloy articles by Hot Isostatic Pressing of a rapidly-solidified titanium alloy powder is provided wherein such pressing is carried out at a pressure greater than 30 ksi, and a temperature of about 60 to 80 percent of the beta-transus temperature of the alloy, in degrees C. Hot Isostatic Pressing under these conditions allows retention of the fine microstructure of the rapidly-solidified powder. The compacted article may be subjected to heat treatment to alter its microstructure.

Oxide-dispersed titanium alloys Ti-Y prepared with the rotating electrode process

Abstract: This work deals with an evaluation of the range of cooling rates during solidification necessary to obtain rare earth oxide-dispersed titanium alloys, which constitute a potentially interesting alloy system for high temperature use, due to the thermodynamic stability of rare earth oxides in titanium. The results of the microstructural studies on binary Ti-Y alloy powders prepared by the rotating electrode process show that it is possible to obtain e fine and homogeneous dispersion of yttrium oxide Y2O3 in a titanium maul with relatively moderate cooling rates (≈ 104 K sec−1). The results also indicate that the stability of the dispersion is excellent during hot consolidation but only in theα phase temperature region (< 882.5° C). The preliminary mechanical teas performed on consolidated products show u substantial increase in 0.2% Woof stress (about 100 M Pa) up to 55O° C with respect to unalloyed titanium of commercial purity. Above 550° Q this strength increment becomes negligible or disappears. These results imply that the oxide dispersion loses its hardening effect at high temperatures, probably due to the increasing importance of grain-boundary sliding.

Microstructures and mechanical properties of boride-dispersed precipitation-hardening stainless steels produced by RST

Abstract: Two commercial precipitation-hardening (PH) stainless steels were modified with 2.64 to 2.86 wt% Ti and 1.2 to 1.3 wt% B via rapid solidification technology (RST) and powder metallurgy (PM). The resulting alloys exhibited improved tensile and yield strengths over their commercial PH stainless steel counterparts at room and elevated temperatures. Ductility improvements at elevated temperatures were also observed. The improved mechanical properties were due to extremely fine microstructures stabilized by a fine dispersion of boride phases.

Production of water atomized powder metallurgy products

Abstract: A method for utilizing a powder metallurgy ("P/M") slurry by employing water atomized metallic powders and subsequently reducing the oxide levels therein to acceptable levels. The slurry comprises a carbon containing binder. The slurry is consolidated and sintered under controlled conditions to reduce the oxide levels.

Two-step infiltration in a single furnace run

Abstract: There is provided a process for infiltrating a compacted ferrous powder metal body with copper or a copper alloy which process is characterized by presintering the ferrous metal body at a temperature of from about 1875° F. to a temperature below the melting point of the infiltrant, and then in the same furnace, raising the temperature above the melting point of the copper or copper alloy infiltrant for a period sufficient to infiltrate the powder metal body. This process is more economical than the prior double run infiltration processes and provides excellent impact strengths and tensile strengths.

Billet conditioning technique for manufacturing powder metallurgy preforms

Abstract: A process for manufacturing powder metallurgy (P/M) preforms which are conditioned for optimum intrinsic workability is described which comprises steps of heating a quantity of P/M material in a can to a first preselected temperature under vacuum to degas the material, compacting the canned material at a second preselected temperature under pressure to provide a compact of the material; or cold compacting the powder to about 75% density and degassing it at suitable temperature and then vacuum hot pressing the powder at about 0.75 melting point; generating flow stress data as a function of strain rate and temperature on samples of the compact at predetermined strain within predetermined ranges of temperature and strain rate and determining powder dissipation efficiency of the compact and entropy rate ratio within those ranges of temperature and strain rate; selecting values of strain rate and extrusion temperature at which dynamic recrystallization is the dominant metallurgical mechanism characterizing the compact: and extruding the compact in an extrusion can at the selected extrusion temperature and at an extrusion rate corresponding to the selected strain rate using a streamlined die. An improved processing map for preselecting optimum processing parameters for the material is described.

Sintering of magnesium partially stabilized zirconia – behaviour of an impurity silicate phase

Abstract: The formation and evolution of the grain boundary silicate phase in a commercially available 8 mol.-%Mg partially stabilized zirconia powder during the early stages of sintering has been studied using analytical transmission electron microscopy. The results show that forsterite is the first formed silicate phase in the range 1350–1450°C. Between 1550 and 1600°C, forsterite melts incongruently to a silica-rich composition which wets tetragonal zirconia, pulling the individual grains into clusters. However, below 1700°C, the silicate does not wet the cubic zirconia grain boundaries significantly. The consequences of this behaviour on the sintering of the ceramic are discussed.MST/559

Heat-resistant al alloy for powder metallurgy

Abstract: PURPOSE: To obtain a heat-resisting Al alloy for powder metallurgy excellent in strength at high temp. and hot workability by incorporating specific amounts of Cr or further Zr and/or Mn to Al and also adding and incorporating specific alloying elements. CONSTITUTION: A molten Al alloy having a composition containing, by weight, 3W20% Cr and ≤10% of one or ≥2 elements selected from the group consisting of Fe, Ti, Co, Ni, V, Ce, Mo, La, Nb, Y and Hf or further containing either or both of Zr and Mn by ≤7% is cooled rapidly at 10 2 W10 6 °C/sec cooling rate, by which an Al alloy powder formed of the above composition and having a structure in which reapective grain sizes of the crystallized grain and the precipitated grain of in intermetallic compound are regulated to ≤10μm is prepared. This Al alloy powder is subjected to hot extrusion in a nonoxidizing atmosphere at ≥450°C, by which the heat-resisting Al alloy for powder metallurgy used for connecting rod for internal combustion engine, etc., and excellent in high temp. strength and hot workability can be obtained. COPYRIGHT: (C)1989,JPO&Japio

High-toughness and high-speed steel by powder metallurgy

Abstract: PURPOSE: To improve the toughness of the subject steel by prepg. the high-speed steel contg. specific ratios of C, Si, Mn, Cr, V, Mo and W and having the specific grain size of its carbide by powder metallurgy. CONSTITUTION: The steel material is formed by using the steel powder contg., as essential components, by weight, 0.7W2.5% C, ≤2.0% Si, ≤1.5% Mn, 3.0W6.0% Cr and 0.8W25.0% V, contg., as selectional components, either or both between 3.0W10.0% Mo and 1.0W20.0% W and consisting of the balance Fe with inevitable impurities by powder metallurgy to prepare the high-speed steel contg. the carbide having, by the equivalent diameter to a circle, ≤1.0μ grain size. By this method, the high-speed steel having excellent hardness and wear resistance and having much more improved toughness is obtd. COPYRIGHT: (C)1989,JPO&Japio

Characteristics of high-Tc oxide wire

Abstract: We have prepared an Y-Ba-Cu-O superconducting wire with silver sheath by a powder metallurgy technique. The crystal structure of the oxide core was orthorhombic and no structural change was found after cold-drawing. The wire showed superconductivity after heat-treatment at 890°C. Diffusion behavior of oxygen atoms through the sheath material is discussed. The highest critical current density of 640 A/cm2 was obtained for the sample heat-treated in oxygen flow.

Improvement of coercive force in Fe-Ce&#183;Didymium-B powder prepared by conventional powder techniques

Abstract: Enhancements of the coercive force (iHc) of Fe- (33-38)wt%(5Ce'Didymium)-1wt%B powders were tried by chemical polishing and the several annealing methods The chemical polishing lowers the coercive force of powders by creating the etch pits on the surfaces of the ground powders The optimum process to prepare the powders with good magnetic properties was: the green compacts with magnetic alignment were annealed at 1050°C, ground into powders, and underwent 2nd- annealing The anisotropic powders resulted in the coercive force of 7-8 kOe Utilizing the presently prepared powders, the anisotropic resin-bonded magnets are formed with (BH)max of nearly 8 MGOe This will be then the first report to demonstrate that the anisotropic bonded magnets can be produced by the conventional powder techniques

Process for making composite bearing material produced thereby

Abstract: A process for making a composite bearing material comprising a steel backed, prealloyed, lead-bronze sintered powder metal matrix whereby the first sinter step includes induction heating the prealloyed powder and steel backing to above 650° C. and thereafter sintering the same at temperatures of about 850° C. in a second sintering furnace. A composite bearing material made by the same process and comprising a lead particle size averaging less than about 8 microns and having no lead islands larger than about 44 microns.

Niobium-Base Superalloys via Powder Metallurgy Technology

Abstract: This paper provides some insight into an area that has been neglected, namely the possibility of developing high-strength, niobium-base alloys by improved oxidation resistance via the consolidation of rapidly solidified powders. Powder metallurgy (PIM) is an attractive processing technique because of its flexibility and versatility, and it may provide the alloys with properties and workability not obtainable via metal casting. A critical review of both U.S. and Russian literature is presented along with suggestions on the most promising compositions and processing techniques available to meet these competing goals. Previous work on many niobium alloys reveals that long term properties are retained well above those obtained on nickel-base superalloys. Cast and wrought alloys extend specific strength beyond 1200°C (2200°F), but lack oxidation resistance. Remarkable oxidation resistance is obtained, however, on miniature castings of certain ternary alloys which are too brittle for any processing. A better understanding of the oxidation mechanism is necessary before the proper PIM (RST) approach is taken on compositions which could provide compatibility between the two competing goals through grain refinement and a homogeneous distribution of the contributory phases. Finally, ways to upscale production ofNb powder are discussed, including thermodynamic feasibility for the direct reduction of NbCl5 in a 1.5 MW plasma reactor.