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Showing papers on "Powder metallurgy published in 1990"



Journal ArticleDOI
TL;DR: In this paper, the powder metallurgy of titanium alloys is reviewed for both the blended elemental (BE) and prealloyed (PA) approaches, and the BE technique allows low cost processing with mechanical behaviour at ing...
Abstract: The powder metallurgy of titanium alloys is reviewed for both the blended elemental (BE) and prealloyed (PA) approaches. The BE technique allows low cost processing with mechanical behaviour at ing...

260 citations


Patent
28 Aug 1990
TL;DR: In this paper, a layer of matching powder, modified to incorporate melting point depressants such as boron and silicon, is added to the surface of the sintered region.
Abstract: To repair or join sections of a metal article, matching metal powder is sintered in the solid state to form a porous structure in the joint. A layer of matching powder, modified to incorporate melting point depressants such as boron and silicon is subsequently added to the surface of the sintered region. The joint is processed at a temperature where the modified layer melts while the sintered layer and base metal remain solid. The modified material flows into the sintered layer by capillary action and promotes liquid phase sintering, resulting in a dense joint with properties approaching those of the base metal.

117 citations


Journal Article
TL;DR: In this paper, a self-lubricating powder metallurgy composite, PM212, was developed and evaluated for use as seal inserts, bushings, small inside diameter parts and other applications where plasma-sprayed coatings are impractical or too costly.
Abstract: This paper describes a research program to develop and evaluate a new high temperature, self-lubricating powder metallurgy composite, PM212. PM212 has the same composition as the plasma-sprayed coating, PS212, which contains 70 wt percent metal-bonded chromium carbide, 15 wt percent silver and 15 wt percent barium fluoride/calcium fluoride eutectic. The carbide acts as a wear resistant matrix and the silver and fluorides act as low and high temperature lubricants, respectively. The material is prepared by sequential cold press, cold isostatic pressing and sintering techniques. In this study, hemispherically tipped wear pins of PM212 were prepared and slid against superalloy disks at temperatures from 25 to 850 C in air in a pin-on-disk tribometer. Friction coefficients range from 0.29 to 0.38 and the wear of both the composite pins and superalloy disks was moderate to low in the 10(exp -5) to 10(exp -6) cubic mm/N-m range. Preliminary tests indicate that the material has a compressive strength of at least 130 MPa over the entire temperature range of 25 to 900 C. This material has promise for use as seal inserts, bushings, small inside diameter parts and other applications where plasma-sprayed coatings are impractical or too costly.

98 citations



Journal Article
TL;DR: In supersolidus liquid phase sintering, prealloyed powders are densified by heating to a temperature where a liquid phase nucleates within each particle as discussed by the authors.
Abstract: In supersolidus liquid phase sintering prealloyed powders are densified by heating to a temperature where a liquid phase nucleates within each particle. The approach is attractive because a high degree of densification can be attained using coarse particles sizes. Thus, there is less need for the small particles typical to liquid phase sintering. This review explores the densification mechanism and the effects of various parameters such as particle size, particle shape, heating rate, and hold time on densification and microstructural development

86 citations


Journal ArticleDOI
17 Apr 1990
TL;DR: The characteristics of the high energy product NdFeB permanent magnets obtained by the powder metallurgy route have been improved by appropriate vanadium additions as discussed by the authors, which lead to an intrinsic coercive force of about 1350 kA/m (17 kOe) in Dy-free magnets, without any large decrease of remanence.
Abstract: The characteristics of the high energy product NdFeB magnets obtained by the powder metallurgy route have been improved by appropriate vanadium additions. Specific combinations of V and Co lead to an intrinsic coercive force of about 1350 kA/m (17 kOe) in Dy-free magnets, without any large decrease of remanence. If 1.5-at.% Dy is added, load line down to -B/ mu H=0.5 can be achieved at 180 degrees C without irreversible losses. Corrosion resistance is improved by blocking the selective oxidation of the Nd-rich phase. As a consequence, organic-coated magnets are able to withstand 15 days at 115 degrees C-1.75 bars in a H/sub 2/O saturated atmosphere without any degradation. It is concluded that this set of new properties will enlarge the application fields of Nd-F-B permanent magnets. >

71 citations


Patent
Prabhat Kumar1
12 Dec 1990
TL;DR: A powder of tantalum, niobium, or an alloy thereof, having an oxygen content less than about 300 ppm, and the production thereof without exposure to a temperature greater than about 0.7 T H as discussed by the authors.
Abstract: A powder of tantalum, niobium, or an alloy thereof, having an oxygen content less than about 300 ppm, and the production thereof without exposure to a temperature greater than about 0.7 T H . A powder metallurgy formed product of tantalum, niobium, or an alloy thereof, having an oxygen content less than about 300 ppm, and the production thereof without exposure to a temperature greater than about 0.7 T H .

68 citations


Journal ArticleDOI
TL;DR: In this article, the effect of excessive mechanical alloying on glass formation was studied by continuing ball-milling beyond the completion of the glass formation for the powders with the average compositions Ni30Zr70, Ni50Zr50 and Ni70Zr30.
Abstract: Elemental powders of nickel and zirconium were mechanically alloyed over a wide concentration range 10 to 90 at % Zr. The amorphous single phase was formed over the range 20 to 80 at % Zr. The effect of the excessive mechanical alloying on the glass formation was studied by continuing ball-milling beyond the completion of the glass formation for the powders with the average compositions Ni30Zr70, Ni50Zr50 and Ni70Zr30. A partial crystallization took place in all three cases and its initiation was the fastest in Ni30Zr70 and was delayed with decreasing zirconium content. The critical factor for triggering the crystallization was attributed to the oxygen contamination for the zirconium-rich Ni30Zr70 powders and to the reduction in glass-forming ability for the nickel-rich Ni70Zr30 powders. The latter conclusion is drawn from the facts that the impurity concentrations arising from the debris of the stainless steel balls and the vial are gradually accumulated with increasing milling time and that the effective zirconium concentration is reduced below the critical concentration of approximately 20 at % as a result of alloying with the elements iron, chromium and nickel in the stainless steel.

66 citations


Book
31 Dec 1990
TL;DR: In this article, the authors describe powder properties, characterization and mixing compaction sintering post-sintering operations compositions, mechanical properties and testing procedures porous PM components magnetic materials wrought PM products and other specialities.
Abstract: Why make things from powder? powder manufacture powder properties, characterization and mixing compaction sintering post-sintering operations compositions, mechanical properties and testing procedures porous PM components magnetic materials wrought PM products and other specialities.

56 citations


Journal ArticleDOI
01 Mar 1990-JOM
TL;DR: In this article, the use of hydrogen as a temporary alloying element was used to enhance both the fabricability and mechanical behavior of titanium alloys, which significantly enhances both the fabrication and mechanical properties of the alloys.
Abstract: As the performance requirements of structures and devices increase, new and improved materials and processes are required. One such technique is thermochemical processing, which involves the use of hydrogen as a temporary alloying element. Thermochemical processing significantly enhances both the fabricability and mechanical behavior of titanium alloys.

Book ChapterDOI
01 Jan 1990
TL;DR: In this paper, free energy calculations can be made to establish the tendency for reaction to occur, but kinetic studies are usually necessary to establish a processing window, which is particularly a problem in continuous fibre reinforced composites.
Abstract: Metal matrix composites are produced by essentially two routes: molten metal processing and powder metallurgy. The former route is the most severe from the point of view of interfacial reactions because of the kinetics in the liquid state, but some liquid phase is usually present during the consolidation stage of powder metallurgy. Free energy calculations can be made to establish the tendency for reaction to occur, but kinetic studies are usually necessary to establish the processing window. Extensive interface reaction can result in degradation of the reinforcement, which is particularly a problem in continuous fibre reinforced composites, and it can also result in a modification of the matrix metallurgy and properties.


Journal ArticleDOI
TL;DR: In this article, three techniques for processing Bi-Pb-Sr-Ca-Cu-O powders were investigated: dry-mixing, sol-gel formation, and freeze-drying.
Abstract: Three techniques for processing Bi-Pb-Sr-Ca-Cu-O (BPSCCO) powders were investigated: dry-mixing, sol-gel formation, and freeze-drying. It was found that sintering for 120 h at 850°C is required to form nearly single-phase (Bi,Pb)2Sr2Ca2Cu3O10-y by dry-mixing, whereas sintering for 30 h at 840°C was sufficient to form the 110 K (2223) phase when freeze-drying was used. The sol-gel route was found to be intermediate in efficiency between these two techniques. Freeze-drying provided highly reactive, intimately mixed, and carbon-free precursors. The presence of carbonates in the uncalcined powders was the major cause of phase segregation and sluggishness of the 110 K phase formation.

Journal ArticleDOI
TL;DR: In this paper, the authors examined combustion associated with the reduction of metal oxides during mechanical alloying, and showed the effect of the reaction enthalpy on powder morphology and powder temperatures.
Abstract: This letter examines combustion associated with the reduction examines combustion associated with the reduction of metal oxides during mechanical alloying, and shows the effect of the reaction enthalpy on powder morphology and powder temperatures


Journal ArticleDOI
TL;DR: In this article, the authors describe the fabrication of disk shaped functionally gradient material with an optimum distribution of composition for thermal stress reduction in a specific material combination of PSZ/Stainless Steel.
Abstract: The fabrication of disk shaped functionally gradient material with an optimum distribution of composition for thermal stress reduction in a specific material combination of PSZ/Stainless Steel is described. The thermal stress generated during cooling from sintering temperature was analized by finite element method as a function of conpositional distribution and sample size.According to the optimum compositional gradient, the sintered compact of the PSZ /SUS304 functionally gradient material was successfully fabricated.

Journal ArticleDOI
TL;DR: The basic unit processes for making thin strip by the powder metallurgy (PM) route based on roll compaction are reviewed in this paper, where various powder and plant parameters that affect the quality of the gree...
Abstract: The basic unit processes for making thin strip by the powder metallurgy (PM) route based on roll compaction are reviewed. The various powder and plant parameters that affect the quality of the gree...

Journal ArticleDOI
01 Aug 1990-JOM
TL;DR: In this article, the shape memory transition temperatures can be tailored over a wide temperature range (from −78 to 460°C) by substituting a third element such as palladium or iron for nickel.
Abstract: Combustion synthesis is a new and promising method of producing Ni-Ti series shape memory alloys. It has the advantage of both time and energy savings compared with the conventional melting or powder metallurgy approaches. The value of the ratio ΔH∘ƒ,298/ Cp,298 plays a key role in this method, especially if a liquid product is required. Solidified products made by the combustion synthesis process were hot rolled into plates exhibiting the shape memory effect. It was discovered that shape memory transition temperatures can be tailored over a wide temperature range (from −78 to 460°C) by substituting a third element, such as palladium or iron, for nickel. This approach should greatly extend the application of such alloys.

Journal ArticleDOI
TL;DR: In this article, the Osprey Process has been applied satisfactorily to mill rolls and the results indicate that a fine grain size is obtained by controlling operational parameters; the as-sprayed preform exhibits higher mechanical properties compared with conventional cast rolls.
Abstract: Rapid solidification processing generally results in fine grained and macrosegregation free microstructures and improves hot-workability of highly-alloyed metals (e.g., superalloys and high alloy steels).The Osprey Process is a technology capable of producing rapidly solidified materials in thick sections. The Process also provides a means of producing dense preforms in one step directly from liquid metal by an integrated atomisation/deposition operation. Consequently, the Process retains most of advantages of powder metallurgy methods while eliminating the major disadvantages resulting from multi-stage processing (i.e., powder production, sizing, compaction and sintering) which often leads to high cost and oxide contamination in the final product.In the present investigation, the Osprey Process has been applied satisfactorily to mill rolls.The results indicate that:(1) A fine grain size is obtained by controlling operational parameters;(2) The as-sprayed preform exhibits higher mechanical properties compared with conventional cast rolls;(3) In experimental tests the amount of wear of Osprey products is 1/2 to 1/6 of conventional cast material; and(4) The life of Osprey rolls under service in a wire-rod mill exceeded that of conventional ones by two to three times.

Journal ArticleDOI
TL;DR: In this article, the deoxidation limit for Ti powders under Ca-CaO co-existence was found to be 500 ppm at 1 273 K. This was attributed to CaO which were confined inside the sintered Ti particles and could not be exposed to the rinsing solution.
Abstract: Synopsis : According to the measurements of equilibrium oxygen concentration in Ti under Ca-CaO co-existence, the deoxidation limit is 500 ppm at 1 273 K. On the basis of these data, preparation of Ti powders have been carried out by reduction of TiO2 using saturated Ca vapors, liquid Ca and CaH2 powders at 1 273 K and subsequent rinsing of CaO in the aqueous solution of HCl, CH3COOH or NH4Cl. The oxygen and calcium levels in the Ti powders reduced by the saturated Ca vapors and the liquid Ca were not below 2 000 and 1 000 ppm, respectively. This was attributed to the CaO which were confined inside the sintered Ti particles and could not be exposed to the rinsing solution. Reduction of the TiO2-CaO mixtures has led to the residual oxygen with the range of 1 000-2 000 ppm, thus the presence of CaO in the starting oxide was effective to control the sintering between reduced Ti powders. The particle size of the reduced Ti was 1-10 Reduction of TiO2 by mixing with excess amount of CaH2 powders could eliminate oxygen below 700 ppm which is close to the deoxidation limit for Ti by Ca of activity of unity.

Journal ArticleDOI
TL;DR: In this article, a thermocouple with 1.9 cm 2 cross section and 1.3 cm length was produced by sintering, and the cold junction was subsequently formed using a lead-silver solder.

Patent
08 Jun 1990
TL;DR: In this paper, a preform is made from a powder alloy by compacting the powder into a pre-form, sintering the preform, preheating the sintered preform in a highly-reducing atmosphere, such as an inert gas-based atmosphere containing hydrogen or pure hydrogen, to a temperature of at least 1000°C.
Abstract: High strength steel parts or articles are made from a powder alloy by compacting the powder into a preform, sintering the preform in a sintering furnace or the like under a highly-reducing atmosphere and at a temperature of at least 1150° C., cooling the preform, preheating the sintered preform in a highly-reducing atmosphere, such as an inert gas-based atmosphere containing hydrogen or pure hydrogen, to a temperature of at least 1000° C. and transferring the preheated preform to an impact forging device and impacting the preform at a peak averaging forging pressure of at least about 1000 MPa to obtain a forged part or article. The time period between removal of the preheated preform from the preheater and the first forging impact is no more than about 8 seconds. The sintering and preheating steps can be combined with the sintered preform being cooled to the preheating temperature in the sintering furnace and transferred directly from the sintering furnace to the impact forging device.

Journal ArticleDOI
TL;DR: In this paper, high textured specimens of Bi2Sr2CaCu2O8 were obtained by shock compaction of powder at 30-140 kbar and by sintering.
Abstract: Highly textured specimens of Bi2Sr2CaCu2O8 were obtained by shock compaction of powder at 30–140 kbar and by sintering. The compacts were characterized by x‐ray diffraction, magnetic susceptibility, electrical resistance, optical microscopy, and scanning electron microscopy data. Preferential orientation with the a‐b plane in the plane of the disk‐shaped compacts was achieved by tapping platelet‐shaped powder with a controlled size distribution, followed by shock compaction or by sintering. The shocked compacts were annealed to induce metallic resistance while maintaining preferential crystallographic orientation. The electrical and magnetic data demonstrate that shock compaction heterogeneously heats and bonds grain boundaries.

Journal ArticleDOI
TL;DR: In this article, methods of preparing non-agglomerated powders for three systems (yttria, titania, and yttria-stabilized zirconia) are reviewed.
Abstract: Methods of preparing non-agglomerated powders for three systems -- yttria, titania, and yttria-stabilized zirconia -- are reviewed. The non-agglomerated nature of these powders should make it possible to sinter them into dense ceramic bodies with nanocrystalline grain sizes. Experiments with yttria-stabilized zirconia have shown that this is indeed the case, with mean linear intercept grain sizes of 60 nm resulting from original powder particle diameters of 13 nm. This ultrafine-grained zirconia is shown, in turn, to have superplastic forming rates 34 times faster than a 0.3 {mu}m-grained commercial zirconia of the same composition. 7 refs., 9 figs.

Patent
19 Jul 1990
TL;DR: In this article, a method for the production of a metallic powder molding material is disclosed which comprises a step of imparting mechanical energy due to at least one of such physical actions as vibration, pulverization, attrition, rolling, shocks, agitation, and mixing a metallic particles in a vessel whose interior is held under vacuumized atmosphere or an atmosphere of inert gas.
Abstract: A method for the production of a metallic powder molding material is disclosed which comprises a step of imparting mechanical energy due to at least one of such physical actions as vibration, pulverization, attrition, rolling, shocks, agitation, and mixing a metallic particles in a vessel whose interior is held under vacuumized atmosphere or an atmosphere of inert gas thereby enabling the metallic particles to contact each other and acquire improvement in surface quality and a step of hot molding the metallic particles thereby producing a molding material.

Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to develop a quantitative approach to the swelling during isothermal liquid phase sintering of Fe-Cu compacts by measuring anisotropic changes in dimensions using photography and micrometry.
Abstract: An attempt has been made to develop a quantitative approach to the swelling during isothermal liquid phase sintering of Fe–Cu compacts The time dependent expansion was followed during sintering at 1150°C by measuring anisotropic changes in dimensions using photography and micrometry Cylindrical compacts containing up to 20%Cu, pressed at 200, 250, and 300 MPa, were examined Differences were observed in the extent of swelling, sintering behaviour, and sintered structure between compacts containing ≤5%Cu and ≥10%Cu; these differences can be reasonably attributed to differences in the quantity of the fused melt The extent of swelling can be assessed satisfactorily on the basis of the bulk density of green compacts, which reflects both powder characteristics and compaction conditions Such an assessment enables quantitative comparison of results obtained under different sintering conditions PM/0501

Journal ArticleDOI
TL;DR: In this article, the effect of powder characteristics on the microstructures and dielectric properties of (Ba,Nb)-doped TiO{sub 2} ceramics was investigated.
Abstract: The effect of powder characteristics on the microstructures and dielectric properties of (Ba,Nb)-doped TiO{sub 2} ceramics was investigated. Two powders were prepared: one by coprecipitation and the other from mixing of reagent oxides. The powder characteristics were determined by TEM, x-ray powder diffraction, SEM, and centrifugal particle analysis. Extensive abnormal grain growth is observed in samples sintered from coprecipitated powder, while it is not found in samples sintered from reagent oxide powder. The effects of crystallite size, agglomerate distribution, and chemical homogeneity on abnormal grain growth are discussed. A mechanism of abnormal grain growth is given, and chemical homogeneity is determined to be the main factor which caused abnormal grain growth. The effect of powder characteristics on dielectric properties is also described.

Journal ArticleDOI
TL;DR: In this paper, abnormal grain growth was found in sintered Nd•Fe•B magnets which are made from powder milled after hydrogen decrepitation, and the abnormal grain size in the magnets sintering at 1000 °C for 1.5 h was as large as 400 μm.
Abstract: Abnormal grain growth was found in sintered Nd‐Fe‐B magnets which are made from powder milled after hydrogen decrepitation. The abnormal grain size in the magnets sintered at 1000 °C for 1.5 h was as large as 400 μm. The formation of abnormally large grains reduced the magnetic properties. As sintering temperature increased, the number of large grains increased and coercivity reduced. However, abnormal grain growth was rarely found when the magnets were fabricated without hydrogen decrepitation. A grain growth mechanism is discussed in relation to the effect of hydrogenation and sintering process.

Journal ArticleDOI
TL;DR: In this paper, the effect of interfacial structure on the mechanical properties of aluminum-ceramic composite materials fabricated by liquid phase sintering was studied and the composites were based on two matrix alloys (powder metallurgy alloys 201 and 601) reinforced with either Al2O3 or SiC particulate.
Abstract: The effect of interfacial structure on the mechanical properties of aluminum-ceramic composite materials fabricated by liquid phase sintering was studied. The composites were based on two matrix alloys (powder metallurgy alloys 201 and 601) reinforced with either Al2O3 or SiC particulate. Characterization of the interfacial regions demonstrated that the SiC-matrix interfaces were faceted whereas the Al2O3-matrix interfaces had an incomplete layer of a silicon-rich amorphous phase. Preferential attack of the particles during sintering is believed to cause the crystallographic facets to form on SiC. Locally high silicon concentrations near Al2O3 particles led to the formation of a glassy phase from the reduction of Al2O3. The difference in interfacial structure resulted in a higher particle-matrix bond strength and therefore improved composite mechanical properties in the SiC-reinforced materials compared with the Al2O3-reinforced materials.