Promising trends in the development of methods of fabricating structural powder materials (survey)

In the new millennium a trend focused on making improvements in existing technologies of powder metallurgy and on the development of new and promising trends in the creation of powder structural materials is observed. The development of the technology of powder metallurgy is intended to improve methods of warm and injection molding, laser and mechanical alloying, and nitration of high-and lowalloy steels. Considerable attention has been paid to the production of structural materials made of intermetallic compounds, materials, the properties of which exhibit functional gradients. There has also been emphasis on creating nanomaterials fabricated by the sol-gel method, mechanical alloying, and powder spraying. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 92–100, May–June, 2006.     

News from the European powder metallurgy association: Epma marks its tenth anniversary under conditions of increasing globalization of powder metallurgy

EPMA notes increasing shipments of West European powder metallurgy products in 1998 compared with 1988. Growth has been particularly strong in Germany, Switzerland, Austria, and Spain. This is closely connected with the growth of automobile production. Problems of automobile construction, including powder metallurgy, were considered at a special EPMA seminar on 29 May 1999. The powder metallurgy specialists noted that there is a clear tendency towards globalization of automobile producing companies and their suppliers, including powder metallurgy manufacturers. For further development of European powder metallurgy the following are necessary: to be in closer touch with customers; to have a critical mass for research and development in order to promote cutting edge technology, design, and engineering; a global presence and a leading market share, giving financial strength; the capability to design and supply systems; coordination of European demands for automobile parts with those in America; a decrease in the prices of high-quality powders for producing high-strength and dense parts; attainment of more competitiveness of powder metallurgy production technology as in joining and processing technologies. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 123–126, May–June, 2000.     

Sintered copper–graphite powder compacts forindustrial applications

Abstract

Studies were made on copper/graphite based powders and sintered compacts for industrial applications. The dependence of particle shape on friction in the powder mass, compression ratio, and electrical receptivity of powder metallurgy components was studied using near spherical precipitated copper powders and angular or flakelike powders generated by mechanical comminution. Results reveal that powders with particles that are nearly spherical in shape have lower friction, lower compression ratios, and higher electrical resistivities in sintered compacts than powders with acicular or flakelike particles. Also, the effects produced by the small additions of lead and zinc (up to 2·5 wt-%) on the electrical resistivity and hardness of sintered copper–graphite compacts are also presented, and the influence of variation of briguetting pressure is discussed.     

Contemporary powder metallurgy: Achievements and problems

The world’s production and use of powders is discussed. Factors that influence the development of powder metallurgy and measures that will promote wider application of powder products are considered. Estimates for the development of powder metallurgy up to 2011 and some developments that won awards of the Metal Powder International Federation (MPIF) in 2005 are presented. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 122–126, 2007.     

Refractory and ceramic materials

The paper examines the consolidation of 95 mole% ZrO₂-2 mole% CeO₂-3 mole% Y₂O₃ nanocrystalline powder in cold uniaxial double-action pressing, cold isostatic pressing (60 and 120 MPa), and sintering. Five starting powders are produced by processing a suspension after hydrothermal decomposition in different conditions. It is established that a homogeneous microstructure forms only in a material from the powder subjected to two homogenizing grindings. After cold uniaxial pressing and cold isostatic pressing, the sintered samples reach a relative density of 0.96 to 0.94. The bending strength is 600 to 660 MPa. The efficient consolidation of ceramics requires comprehensive processing of starting nanocrystalline powders to modify their morphology. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 45–58, 2007.     

Book Review

Abstract

Currently available compaction-ready aluminium powders enable sintered preforms to be readily produced by the powder metallurgy route. Aluminium bearing materials with good sliding properties can be produced by sintering-in abrasion-resistant particles or by using alloy powders with homogeneously distributed lead additions. Reactively ground and mechanically alloyed granulates with dispersoid particles of oxides, carbides, and inter-metallic compounds provide high-temperature PM materials with improved properties. New techniques for powder production provide aluminium alloy powders with extraordinary metallurgical effects within the particles and controlled properties. The consolidation of rapidly solidified aluminium alloy powders into high-strength PM semiproducts has considerably enlarged the potential of aluminium powder metallurgy. The aims of numerous worldwide development projects in powder metallurgy are to improve conventional aluminium alloys and develop new alloys which cannot be produced by the . traditional melting route. PM/0253     

Production and properties of brass-base P/M constructional materials. A review

Conclusions The best processing properties are exhibited by brass powders manufactured by the diffusional impregnation technique, using a zinc powder, brass swarf, or a copper-zinc master alloy as a point source. However, as this is a very labor-intensive process, normally preference should be given to melt atomization as a method of manufacture of brass powders. Brass P/M parts produced by the conventional method consisting of pressing a powder and sintering the resultant compacts have porosities of not less than 7–10%, and consequently this method is not widely used for the production of constructional brass parts. The sintering of compacts from copper and copper-zinc master alloy powders gives more stable zinc contents compared with the sintering of compacts from copper and zinc powders; the greatest stability of chemical composition is exhibited by sintered compacts from a homogenized brass powder. The formation of diffusional porosity accompanying the evaporation of zinc may be prevented by performing sintering in the presence of a liquid phase (which appears in the presence of a phosphorus or lead addition), saturating the sintering atmosphere with zinc vapor, and adding carbonates or halides of alkali and rare-earth metals to starting powders. The mechanical properties of materials can be markedly improved by eliminating their porosity. This may be achieved by subjecting porous preforms to hot forging, which enables brass P/M parts to be obtained whose mechanical properties are comparable to those of cast parts.Translated from Eoroshkovaya Metallurgiya, No. 3(255), pp. 56–64, March, 1984.     

A lubricant for pressing aluminum powder

Studies have been made on the effects of some organic compounds produced in the CIS countries on the technological behavior of aluminum powders with various grain sizes. The purpose has been to establish the best lubricant for pressing them. The effects of the lubricants have been examined on the density, fluidity, and shaping capacity of the powders, as well as the pressing forces needed. The organic compound edamid PS has been found to be in no way inferior to acrawax in its technological characteristics, the latter being the compound used in aluminum powder metallurgy in the USA. Siberian Technical Physics Institute, Institute for Strength Physics and Materials Science, Siberian Division, Russian Academy of Sciences, Tomsk, and Yakutsk State University, Russia. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 78–85, January–February, 1999.     

Effects of pressing temperature on the consolidation of titanium nickelide powders

The plastic aftereffect and the shape memory effect hinder the manufacture of high-density materials based on titanium nickelide by traditional powder metallurgy methods. Studies have been made on the effects of temperature and pressing pressure for powders containing titanium nickelide on the elastic aftereffect, crystal growth during the initial stage of sintering, and density of the sintered material. If the pressing is at a temperature exceeding the temperature for the start of the martensite transformation, one can increase the density of the material substantially by comparison with pressing at room temperature. For that purpose, the pressing temperature needs to be raised only to 200°C.Tomsk Polytechnical Institute. Translated from Poroshkovaya Metallurgiya, No.3 (363), pp. 19–22, March, 1993.     

Effect of chemistry and particle size of cryochemical powders on the properties of humidity sensors

A comparative analysis of various sintered materials based on cryochemical powders was carried out. The electrical resistance of compacts of pure aluminum oxide and its mixtures with CoO, MgO, ZrO₂, and Y₂O₃ were compared with data on the specific surface area, phase composition, and pore size distribution in the sintered ceramics. Conclusions were drawn about the suitability of the materials as humidity sensors. Highest sensitivity was found in sensors based on aluminum—cobalt spinel, and aluminum—magnesium spinel mixed with zirconium oxide. Deceased. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(400), pp. 39–43, March–April, 1998.     

Ceramic humidity sensors based on magnesium aluminate spinel. II. Relation between the parameters of water adsorption kinetics and the service characteristics of ceramic humidity sensors in the MgAl2O4 system

he parameters of water vapor adsorption on the surfaces of powders and compacted powders (compacts) are compared with data on the variation of the electrical resistance of the same compacts in media with various water vapor contents. A study of the kinetic features of water vapor adsorption from the air indicated that powders with small specific surfaces adsorb water vapor and are saturated more rapidly than do powders with large specific surfaces, while their absolute moisture content is lower. The amount of water vapor adsorbed on the surface varies in the same way. The data are consistent with the results from porous structure studies. The rate of water vapor adsorption and the amount adsorbed increase for smaller pores, in which the water vapor condenses more quickly. Data on the specific surface of compacted and sintered materials, their porous structure and their adsorptivity of water vapor provide a basis for making a prior choice of technological parameters of the ceramic treatment so as to enhance the quality of humidity meters. Deceased. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos 7–8(402), pp. 46–50, July–August, 1998.     

60 years of powder metallurgy at the I. P. Bardin Central Research Institute of Ferrous Metallurgy

This article is devoted to the history of the development of powder metallurgy at the Central Research Institute of Ferrous Metallurgy over a 60-year period. It also looks at the history of the Powder Metallurgy Laboratory, which was established in 1946. Information is presented on technologies that have been developed to obtain iron and alloy powders, and their uses are discussed along with the methods employed to make semifinished products and parts composed of powder metals and alloys. __________ Translated from Metallurg, No. 4, pp. 54–58, April, 2006.     

Powder metallurgy in North America continues to grow

The current state of the production of metal powders and articles made from metal powders in North America is considered. New technologies that yield an increase in the density and an improvements in the mechanical properties of powder materials are considered. Technological developments and products that were awarded prizes by the North American Federation of Powder Metallurgical Enterprises in 2005 are presented. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), 122–128, July–August, 2006.     

Sintering of Tungsten and Tungsten Heavy Alloys of W–Ni–Fe and W–Ni–Cu: A Review

Tungsten is a refractory metal possessing good mechanical properties of high strength, high yield point, and high resistance to creep. Therefore, tungsten and its alloys are used in many high temperature applications. Due to the high melting point, they are generally processed through powder metallurgy method. The powders are compacted using die pressing or isostatic pressing. The compacts are sintered in a sintering furnace to achieve high density, thereby, making the metal suitable for further processing. This article reviews the recent research findings of consolidating tungsten and its alloys (W–Ni–Fe and W–Ni–Cu), from preparation of powder alloys to sintering of the compact. The advances in sintering are based on the objective of achieving good densification of the metal at lower temperature and at faster rate. The use of microwave sintering and spark plasma sintering techniques resulted in significant reduction in sintering time and producing products of good mechanical properties.     

Powder metallurgy of beryllium: The developments of the national scientific center “Khar’kov physicotechnical institute”

For the first time in the production of construction beryllium an integrated technology for the production of a new generation of high-purity isotropic materials has been developed and mastered. The technology combines processes of vacuum distillation of the metal, gas flow atomization of a melt, specialized processing of the powder prior to densification and hot isostatic pressing. A technology for the production of spherical powders of beryllium and beryllium-based alloys by atomization of a melt is also developed and employed for the first time. A technology is developed and optimal conditions of isostatic pressing of spherical powders are determined. Isotropic beryllium with high physico-mechanical characteristics is obtained. The properties of the materials thus obtained are studied. The strength of the new materials is 20%, and their plasticity two to three times greater, than commercial beryllium. It is shown that the high purity of the initial powder, the cellular structure, uniform distribution, and dispersity of the particles of beryllium oxide and segregations of secondary phases are the principal factors that govern the level of the properties of compact beryllium materials. __________ Translated from Poroshkaya Metallurgiya,Nos. 3–4(448), pp. 118–125, March—April, 2006.     

Finely dispersed Si3N4−SiC powders and materials based on them

The objectives of the present research were to investigate the preparation of homogeneous ultrafine composite Si₃N₄−SiC powders by a plasmochemical process and the properties of ceramics produced from them. The chemical and phase compositions of the powders depended on the particle size of the initial powder, silicon input rate, and ratio of ammonium and hydrocarbon flow rates. The particle size and specific surface area of the compounds depended on the concentration of particles in the gas jet, and the cooling rate of the products. Composite powders containing from a few up to 90 mass % SiC, with specific surface areas of 24–80 m²/g and free silicon and carbon content less than 0.5 mass % were obtained. The main phases present were α-Si₃N₄, β-Si₃N₄, β-SiC, and X-ray amorphous Si₃N₄. Dense materials were prepared both by hot pressing at 1800°C under a load of 30 MPa and gas-pressure sintering at 1600–1900°C under a pressure of 0.5 MPa nitrogen. The plasmochemical composites had smaller pore sizes, were finer grained, and densified more rapidly than materials sintered from commercial powders. Institute of Inorganic Chemistry, Latvian Academy of Sciences, Salaspils. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 7–12, January–February, 1999.     

Experience of Improving Standards and Methods for Studying the Properties of Metal Powders and Sintered Articles

Reasons are considered for improving standards in the following methods for testing powder materials: tensile, transverse bending, gas and liquid permeability, and determination of powder compact dimensions after compaction pressure removal and during sintering. Calculated data for representative specimen dimensions (cross section and thickness) for these and other test methods for sintered articles (materials) prepared from mono- and polyfraction iron powder of different sizes are confirmed by experiment. It is shown that the representative specimen dimensions prepared from monofraction powder are more than an order of magnitude less than for those prepared from polyfraction powder. The reason for this difference is considered to be the special role of individual particles (for monofraction powder) or assemblies of these particles (for polyfraction powder) in forming elementary fragments within the structure of compacts and sintered articles. Data are provided for the improved ISO 4492-1985 standard and a new GOST 29012-91 standard developed on the basis of it for precise determination of changes in the dimensions of powder compacts during pressing and sintering. Use of this method makes it possible to reveal the existence of different structural states within narrow porosity limits for powder materials. It is shown by experiment that the pulsed ultrasonic method for monitoring these structural states based on measuring the propagation rate and (or) the elastic wave damping factor, exhibits high sensitivity, it is rapid, and it may be recommended for extensive introduction and standardization in powder metallurgy.     

Review of trends in European PM production and technology

Details are given of the activities of the European Powder Metallurgy Association EPMA, which was founded seven years ago. Data are given on the production volumes of metal powders and parts made from them in Western Europe in 1991–1996. The structures of these products are described. A survey is presented of powder metallurgy development trends in Europe in the hear future. European Powder Metallugy Association, Shrewsbury, UK. Published in Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 114–120, January–February, 1999.