Showing papers on "Powder metallurgy published in 1988"

Glass-forming range in mechanically alloyed Ni-Zr and the influence of the milling intensity

Abstract: Amorphous Ni‐Zr powders have been prepared by mechanical alloying from crystalline elemental powders. The glass‐forming range has been determined by x‐ray diffraction, differential scanning calorimetry and saturation magnetization measurements. From 27 to 83 at. % Ni the powders become amorphous. This shows that deep eutectics do not play any role, contrary to amorphization by melt spinning. Crystallization temperatures, crystallization enthalpies, and wave numbers Qp, obtained from x‐ray diffraction investigations, are compared with the data received for rapidly quenched samples. In addition, the effect of the milling intensity on the glass formation has been studied for the first time. If the intensity is too high, crystalline intermetallic phases are formed. On the other hand, the powder needs an extended milling time to become completely amorphous if the milling intensity is too low. Conclusions on the actual temperature of the individual particle during mechanical alloying and on the glass‐forming process are drawn from these results.

Effects of sic whiskers and particles on precipitation in aluminum matrix composites

Abstract: The age-hardening precipitation reactions in aluminum matrix composites reinforced with discontinuous SiC were studied using a calorimetric technique. Composites fabricated with 2124, 2219, 6061, and 7475 alloy matrices were obtained from commercial sources along with unreinforced control materials fabricated in a similar manner. The 7475 materials were made by a casting process while the others were made by powder metallurgy: the SiC reinforcement was in the form of whiskers or particulate. It was found that the overall age-hardening sequence of the alloy was not changed by the addition of SiC, but that the volume fractions of various phases and the precipitation kinetics were substantially modified. Precipitation and dissolution kinetics were generally accelerated. A substantial portion of this acceleration was found to be due to the powder metallurgy process employed to make the composites, but the formation kinetics of some particular precipitate phases were also strongly affected by the presence of SiC. It was observed that the volume fraction of GP zones able to form in the SiC containing materials was significantly reduced. The presence of SiC particles also caused normally quench insensitive materials such as 6061 to become quench sensitive. The microstructural origins of these effects are discussed.

Finite element simulation of hot isostatic pressing of metal powders

Abstract: Description detaillee de la procedure de calcul Presentation de l'application de la methode de simulation a deux cas pratiques

Calorimetry study of the synthesis of amorphous Ni-Ti alloys by mechanical alloying

Abstract: We synthesized amorphous Ni33Ti67 alloy powder by ball milling (a) a mixture of elemental nickel and titanium powders and (b) powders of the crystalline intermetallic NiTi2. We characterized the reaction products as a function of ball-milling time by differential scanning calorimetry and X-ray diffraction. The measurements suggest that in process (a) the amorphous alloy forms by a solid state interdiffusion reaction at the clean Ni Ti interfaces generated by the mechanical attrition. In process (b), the crystalline alloy powder stores energy in the form of chemical disorder and lattice and point defects. The crystal-to-amorphous transformation occurs when the stored energy reaches a critical value. The achievement of the critical stored energy competes with the dynamic recovery of the lattice.

Aerosol flow reactor production of fine Y1Ba2Cu3O7 powder: Fabrication of superconducting ceramics

Abstract: An aerosol flow reactor operating at 900–1000 °C is used to prepare high‐purity Y1Ba2Cu3O7 powders with a uniform chemical composition and a submicron to micron average particle size by thermally decomposing aerosol droplets of a solution consisting of the nitrate salts of Y, Ba, and Cu in a 1:2:3 ratio. The powders were at least 99% reacted based on thermogravimetric analysis, and the x‐ray diffraction pattern is essentially that of Y1Ba2Cu3O7. Magnetic susceptibility measurements showed the powders to be superconducting with a transition at 90 K even for average reactor residence times as short as 20 s. Sintering cold‐pressed pellets between 900 and 1000 °C provides dense, fine grained (average size on the order of 1 μm) superconducting ceramics with sharp 90 K transitions. The grain size and shape of a final sintered part could be varied depending on powder production, processing, and sintering conditions.

Impact resistant clad composite armor and method for forming such armor

Abstract: Impact resistant clad composite armor and method for forming such armor. The impact resistant clad composite armor includes a ceramic core, and a layer of metal surrounding the ceramic material and bonded to the ceramic core. The metal layer is formed by cold isostatically pressing powder metal surrounding the ceramic core to a high initial density followed by vacuum sintering. The composite armor may be hot isostatically pressed to densify the powder metal to approximately 99% full density.

Sintering of monosized, spherical yttria powders

Abstract: Monosized, spherical Y2O3 was processed from raw commercial Y2O3 by homogeneous precipitation in aqueous solution via urea decomposition. Dry-pressed pellets of the synthesized and raw powders were sintered to 1500°, 1600°, and 1700°C for 7 to 720 min. Microstructural development was followed with scanning electron microscopy. The differences between sintering behavior of the two powders are discussed.

Formation of amorphous Ni-Zr alloy powder by mechanical alloying of intermetallic powder mixtures and mixtures of nickel or zirconium with intermetallics

Abstract: Mechanical alloying was used to synthesize NixZr1−x alloys from mixtures of intermetallic compound powders, and also from mixtures of intermetallic compound powders and pure elemental powders. The mechanically alloyed powders were amorphous in the range 0.24 ⩽ x ⩽ 0.85. This range is larger than amorphous alloys produced by the melt-spinning technique and mechanical alloying of elemental crystalline powders. Two-phase mixtures of the amorphous phase and the corresponding crystalline terminal solid solution were formed in the range 0.10 ⩽ x ⩽ 0.22, and x=0.90. It is found that the morphological development during mechanical alloying of these powders is different from mechanical alloying using only pure ductile crystalline elemental powders. The thermal stability has been investigated. The enthalpy and activation energy of crystallization for Ni-Zr amorphous powders prepared by mechanical alloying are lower than those for melt-spun samples of the same composition. The crystallization temperature of the mechanically alloyed Ni-Zr amorphous powders is higher than that of meltspun samples in the composition range Ni20Zr80 to Ni33Zr67 and Ni40Zr60 to Ni60Zr40. The presence of tiny crystallites as nucleation centres and high oxygen levels in the mechanically alloyed amorphous alloys might be responsible for the differences in crystallization behaviour. A new crystalline metastable phase was observed during crystallization studies of Ni24Zr76 amorphous powder.

Mechanically alloyed isotropic and anisotropic Nd‐Fe‐B magnetic material

Abstract: Starting from elemental powders, hard‐magnetic Nd‐Fe‐B can be produced by mechanical alloying and a solid‐state reaction. Due to the short reaction time at relatively low temperatures (typically 30 min at 700 °C), the magnetically isotropic particles are microcrystalline and show a high coercivity. These powders can be compacted to dense isotropic magnets by hot uniaxial pressing. An additional deformation at elevated temperatures is used to form magnetically anisotropic samples. With regard to microstructure, magnetic properties, compaction, and formation of anisotropy, the magnetically alloyed material is comparable with the rapidly quenched Nd‐Fe‐B. The formation characteristics and the magnetic properties of resin‐bonded powder, hot compacted isotropic material, and hot deformed anisotropic samples are described.

Manufacture of a novel porous metal

Abstract: Description d'une methode de metallurgie des poudres permettant la realisation d'un nouveau produit poreux a partir de poudre d'alliage Ti-6Al-4V. Caracteristiques mecaniques et formabilite des materiaux produits par cette technique

Method for electroless plating of ultrafine or colloidal particles and products produced thereby

Abstract: The present invention provides a process for the electroless plating of easily reducible metals onto ultrafine, usually inert, particles. Such plating is achieved through careful and accurate control of such parameters as the feed rates of the various solutions, the control of pH of the solution, the temperature, pressure and the rate of agitation of the solution in which the plating is taking place. The plated ultrafine composite particles and the powders made from the particles produced by the process are also a part of the invention. There is also provided a metal article of manufacture consisting of a metla such as copper, silver, gold, ruthenium, rhodium, palladium, osmium and platinum with a plurality of shperical shaped ultrafine particles with a diameter of less than about 10 microns dispersed substantially evenly through the metal article. The articles are fabricated using the plated ultrafine composite powders by methods involving, such as for example, casting, powder metallurgy and mechanical compression. The ultrafine particle is most generally of an inert material. There is also provided a process for making cast articles and recastable mixtures using the plated composite ultrafine powder. The cast articles have the inert ultrafine particles dispersed evenly throughout the cast article.

Iron base powder mixture and method

Abstract: An iron base powder mixture for powder metallurgy, comprising an iron based powder and an alloying powder and/or a powder for improving machinability, wherein the alloying powder and/or the powder for improving machinability are adhered to the surface of the ferrous powder by means of a melted-­together binder composed of an oil and a metal soap or wax.

Elevated temperature tensile properties of powder metallurgy Ni3Al alloyed with chromium and zirconium

Abstract: The tensile properties of hot extruded powders of Ni-24.1Al, Ni-19.1Al-8.5Cr, and Ni-17.4Al-7.9Cr-0.5Zr have been evaluated from room temperature to 1000° C. These powder metallurgy materials have a fine grain size that results in relatively little increase in yield stress with increasing temperature compared to coarse-grained or single-crystal materials. The alloy containing chromium and zirconium shows greatly reduced dynamic embrittlement in the temperature range 600 to 800° C where the unalloyed aluminide exhibits brittle behaviour. The Cr- and Cr + Zr-containing alloys deform superplastically above 900° C. The mechanism of superplastic deformation appears to be predominantly grain-boundary sliding.

Elevated temperature aluminum-titanium alloy by powder metallurgy process

Abstract: An aluminum-titanium alloy and a process of making it, the alloy consistingssentially of aluminum, 4-6 wt. % titanium, 1-2 wt. % carbon, and 0.1-0.2 wt % oxygen. The alloy is an aluminum matrix supersaturated with titanium, and having throughout a fine, homogeneous dispersion of Al 3 Ti particles. It is fine grained and has grain boundary dispersoids of carbides and oxides, predominantly of aluminum. An aluminum-titanium melt is rapidly solidified and then mechanically alloyed in the presence of a carbon-bearing agent. The resulting powder is degassed and hot consolidated to form articles which exhibit high strength, ductility, and creep resistance at temperatures greater than 200° C.

High density tungsten-nickel-iron-cobalt alloys having improved hardness, and method for making them

Abstract: A tungsten-nickel-iron-cobalt high density alloy having unexpected improved strength and hardness properties and the method of making such alloy are disclosed. The alloy has from about 85-98% by weight tungsten with the remainder being a nickel-iron-cobalt binder in which the cobalt is present in amounts of from at least about 5% up to 47.5% by weight of the binder and the amount of cobalt being equal to or less than the amount of nickel. After the powders of the elements in the indicated amounts are homogeneously blended, compacted into a shape and sintered, the sintered shape is subjected to a heat treatment in a flowing argon atmosphere for a period of time and at a temperature at least sufficiently high to solubilize the intermetallic or μ phase, Co 7 W 6 , formed at the matrix to tungsten interface during cooling from the sintering temperature, and to diffuse into the gamma austenitic phase, thus leaving the alpha tungsten/gamma austenite boundaries substantially or essentially free of such intermetallic or μ phase. The alloy is subsequently subjected to a swaging step resulting in a reduction in area of from 5 to 40% and then may be aged for about an hour within the range of about 300°-600° C.

Properties of Nd‐Fe‐B anisotropic powder prepared from rapidly solidified materials

Abstract: Anisotropic Nd‐Fe‐B permanent magnets can be prepared by consolidation and hot forming of melt‐spun ribbon material; energy products to 45 MGOe have been obtained by this method. One feature of this type of magnet is that they can be converted into stable powders for subsequent processing into anisotropic resin‐bonded magnets. The stability of this powder contrasts markedly with that prepared by grinding conventional ‘‘sintered’’ magnets, a factor attributed to the much smaller crystallite size of the rapidly solidified materials. In this work the properties of the anisotropic powder are presented along with preliminary properties of bonded magnets; energy products of 15–17 MGOe have been achieved by compression molding techniques and energy product as high as 20 MGOe are believed to be readily achievable.

Warm shock consolidation of IN 718 powder

Abstract: Explosive consolidation of the rapidly-solidified nickel-base super-alloy powder IN 718 was successfully accomplished. The effects of explosive type, explosive-to-powder mass ratio, powder container material and thickness, type of confinement, shielding material, and preheating temperature were investigated. Conditions for satisfactory consolidation, with good mechanical properties and low microcrack density, were established. The best consolidation was achieved by using a double-tube design in which a flyer tube was explosively accelerated, impacting the (cylindrical) powder container. The powder was pre-heated at 525° C and the initial consolidation pressure was calculated to be 18 GPa, resulting in approximately 20% apparent interparticle melting (white-etching regions between particles). The quality of the consolidates was evaluated by optical and electron microscopy, and by tensile testing.[/p]

Niobium-alloyed high speed steel by powder metallurgy

Abstract: A philosophy for the use of strong carbide formers like niobium in high speed steels is described It follows the concept of independently optimizing the compositions of the matrix (for maximum secondary hardening potential) and the volume fraction of the blocky carbides (for protection against abrasive wear) Normally, the two are interdependent through the action of the solidification equilibria, but separate control becomes possible when the blocky carbides are formed by a strong carbide former such as niobium During normal ingot solidification, such strong carbide formers would produce very large primary carbides This can be avoided by atomization and powder metallurgical processing In this way, a steel has been produced whose matrix composition is similar to that of AISI M2, and whose primary carbides are all of NbC type Its composition is 13C, 2W, 3Mo, 16V, 32Nb (wt pct) Because of its high stability, NbC is a much more effective obstacle to grain growth than the normal high speed steel carbides, and this allows substantially higher austenitization temperatures to be used Despite its leaner composition, the Nb-alloyed steel matches the cutting performance of AISI M2, and its secondary hardening seems to be more persistent at high temperatures

Fabrication of high performance powder-metallurgy aluminum matrix composites

Abstract: Recent years have seen the development of a wide range of high-performance discontinuously reinforced aluminum powder metallurgy composites. These materials have combined both standard wrought, e.g., 6061 and 2124, and specialty matrix compositions, e.g., Al-Cu-Mg-Li and Al-Fe-Ce, with a wide variety of discontinuous reinforcements, e.g., Al2O3, B4C, SiCp and SiCw. This paper discusses the manufacturing procedures utilized to fabricate these light-weight powder-metallurgy composites. Emphasis is given to developing a generalized framework for understanding the interrelationship existing between thermo-mechanical treatment and the mechanical behavior of these composite systems.

Glass-forming ranges of mechanically alloyed powders

Abstract: The glass-forming ranges in mechanically alloyed TM-Zr alloys (where TM is a transition metal) have been determined by means of magnetization and crystallization experiments, by Mossbauer spectroscopy, and by investigating the superconducting properties. Glass formation by mechanical alloying is possible in the central composition range, i.e. from 30–78 at.% iron, 27–85 at.% nickel and 27–92 at.% cobalt. For TM-rich or zirconiumrich compositions, two-phase regions exist between the primary phases and the amorphous phase. It is shown that the measurement of the physical properties allows a more accurate determination of this than does X-ray diffraction.

Composite alloy steel powder and sintered alloy steel.

Abstract: High-strength and high-toughness sintered alloy steel and composite alloy steel powder for use in production of the steel are disclosed. The steel contains as final product alloy components Ni, Mo and/or W and, if necessary, C with the content of Ni being 0.50 to 3.50 wt %, the content of Mo+1/2W being 0.65 to 3.50 wt % and, if necessary, the content of C being 0.3 to 0.8 wt %, and the balance being Fe and unavoidable impurities, and has a density of at least 7.0 g/cm3 and a tensile strength of at least 130 kgf/mm2. The content of each of Ni and Mo+1/2W in the alloy steel powder of a particle size of 45 mum or less are 2.0 to 4.2 times as much as the average content of the whole powder. This composition gives high-strength and high-toughness sintered alloy steel by powder metallurgy using a comparatively low alloy formulation and heat-treated sintered steel satisfying requirements for automobile parts, etc.

Method of preparing iron base powder mixture for pm

Abstract: An iron base powder mixture for powder metallurgy, comprising an iron based powder and an alloying powder and/or a powder for improving machinability, wherein the alloying powder and/or the powder for improving machinability are adhered to the surface of the ferrous powder by means of a melted-together binder composed of an oil and a metal soap or wax.

Ferrous mixed powder for powder metallurgy having excellent machinability and mechanical property after sintering

Abstract: PURPOSE: To manufacture ferrous mixed powder for powder metallurgy having excellent machinability and mechanical property after sintering by blending MgO-SiO 2 series compound oxide powder specifying compositing component ratio and average particle size with the ferrous raw material powder at the specific ratio. CONSTITUTION: The powder having 3W20μm average particle size and composing of MgO-SiO 2 series compound oxide in the range of 1.0W3.0 the value of MgO/ SiO 2 in mol ratio, is blended with the ferrous raw material powder at the ratio of 0.1W1.5wt.% to prepare the ferrous mixed powder for powder metallurgy. By using ferrous mixed powder, the sintered machinery part having excellent machinability is obtd. as holding to the same degrees of dimensional variation and mechanical property after sintering as the conventional iron powder without any damaging to brick in a sintering furnace and exothermic body. COPYRIGHT: (C)1989,JPO&Japio

Preparation of ductile NbAl powders for the fabrication of Nb3Al superconductors

Abstract: The influence of rapid quenching and hydrogenation on the structure and phase composition of niobium-rich NbAl alloys was investigated. Starting ingots were prepared by conventional arc melting of compacted powder mixtures. The phase diagram for NbAl, presented by Jorda et al., was confirmed in the examined concentration range up to about 30 at.% aluminium. Specimens were quenched with cooling rates not less than 104 K s−1, both from the solid and liquid state. A metastable extension of the niobium solid solution up to 27 at.% aluminium was obtained after quenching small droplets from temperatures T ⩾ 2200 °C. Contrary to previous publications, it is shown that rapid quenching of solids (19–24 at.% aluminium) from 1750 °C in a eutectic GaIn bath does not lead to the formation of metastable states in the region of the Nb3Al phase. Ductile Nb-Al powders of an average composition “Nb3Al” were prepared with a combined hydridingdehydriding process. The retransformation of the metastable powders was determined to occur in the temperature range between 710 and 860 °C depending on the aluminium concentration. Based on these findings, a new perspective results for the powder metallurgical fabrication of Nb3Al superconductors.

Nb3Al formation in sputter-deposited Nb/Al multilayer samples

Abstract: The critical current density of powder metallurgy processed (PM) wires is determined in part by the extent of the A15 phase formation in the vicinity of the Nb/Al interface. A series of multilayered samples was made to simulate the reactions in the PM wires. Transmission electron microscopy was used to study the reactions between the multilayers. The results indicate that the reactions at the Nb/Al interface depend strongly on the niobium and aluminum layer thickness and distribution. No evidence of the metastable Nb(Al) solid solution formation was found. It is concluded that the Nb 2 Al and the residual niobium present in the reacted PM wires can be avoided if the niobium and aluminum layers are sufficiently thin and uniformly distributed with the proper stoichiometry.

Boron nitride ceramics: problems and development perspectives

Abstract: The heat resistance, high thermal shock resistance, chemical inertness, structure, and lubricating ability of boron nitride ceramics are discussed along with its uses in high temperature and abrasive applications. Problems are reviewed in sintering, hardening, and impurity control procedures. The most effective strengthening agents for boron nitride ceramics were determined to be organosilicon compounds. A method using molecular thermal cross-linking to incorporate these agents into the ceramic is outlined. The method consists of applying thin layers to powder particles, performing heat treatment until these layers break down and impregnate the pore structure and then cross-link with active pyrolysis products. Comparative data are tabulated for pyrolytic, hot pressed, and sintered boron nitrides with several strengthening agents.

Alloyed steel powder for powder metallurgy

Abstract: An alloyed steel powder for powder metallurgy is provided with a water-atomized alloyed steel powder wherein an alloy component, an oxide of which is difficult to be reduced with hydrogen in the production of the powder, has been prealloyed in a composition range not exerting a bad influence upon compressibility of the steel powder, and an alloy component or components easier to be reduced with hydrogen than the above alloy component, the said easily reducible alloy component or components being partially diffused and adhered in a powdered form to the particle surfaces of the water-atomized alloyed steel powder.