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High purity tungsten powder from scheelite by self propagating high temperature synthesis
increased temperature as a result avoidance of cooling by convection.
Ceramic
of
materials
MICROSTRUCTURE AND SUPERPLASTICITY IN ALUMINA-ZIRCONIA MATERIALS
S.Yakka et al. (National Research Inst. for Metals, Tsukuba, Japan. 1J Jpn Sot. Powder Powder Metal., Vol 45, No 12, 1998, 1186-1195. (In Japanese.) High temperature superplasticity in ceramic materials was discussed with regard to the requirement of fine grain size and the ability of ZrO, to supress grain growth in A&O,. Al,O,-ZrO, composites were produced by a colloidal technique, shaped by slip casting and cold isostatic pressing, and sintered at 1400°C. The materials had a small pore size, narrow pore size distribution and a fine grain structure. Tensile elongation over 550% was attained. RESINTERING OF ALUMINA COMPACT W.B.Du et al. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metal., Vol 46, No 2, 1999, 125130. (In English.) Resintering characteristics of Al,O,, after working, were investigated. Resintering is shown to allow densities, up to 99%, to be attained after processing at 1300°C for 1 hour, with little grain growth.
Coatings PERFORMANCE OF CEMENTED CARBIDE TOOLS WITH PHYSICAL VAPOUR DEPOSITED COATINGS
P.C.Jindal et al. (Kennametal, Inc, Latrobe, USA.) Int. J Refractory Metals Hard Mater., Vol 17, No l-3, 1999, 163170. TIN, Ti(CN) and TiAlN were deposited on WC-Gwt%Co by physical methods. Coatings and substrates were characterized for structure, properties and cutting performance, assessed by turning Incone 1718, medium C steel and ductile iron at low and high speeds. Cutting performance was ranked in order TiAlN (best), Ti(CN) and TIN. The superior performance of TiAlN is attributed to high resistance to abrasive and crater wear due to high hot hardness and oxidation resistance at operating temperature at the tool tip. ELECTRO-CHEMICAL-THERMAL GUN FOR DEPOSITION OF HARD COATINGS
S.Wald et al. (Nuclear Research Centre, Yavne, Israel.) Int. J. Refractory Metals Hard Mater., Vo117, No l-3,1999,171-177. It is reported that a new technique, using an electro-chemical-thermal gun,
had been developed for deposition of hard material coatings. Powder of the coating material is sprayed by conventional fuel supported by a pulsed plasma jet that ignites the fuel and accelerates the powder particles to over 1000 m.s-l, which are then energetically deposited. Process parameters are outlined. The method was used to deposit, e.g., sintered carbides onto stainless steel. MECHANICAL BEHAVIOUR CAL-CHEMICAL HARD COATINGS
OF PHYSIVAPOUR DEPOSITED
PSchlund et al. (University of ErlangenNurnberg, Erlangen, Germany.) Int. J. Refractory Metals Hard Mater., Vol 17, No l-3, 1999, 179-185. It is noted that use of chemical vapour deposition may result in deterioration of properties. It is reported that combination of chemical and physical vapour deposition processes may avoid this and may improve properties. Coatings of TiAlN, applied by PVD, and TiN-Ti(C,N)-TiN, applied by CVD, were applied to cemented carbides and mechanical characteristics investigated. Fracture of coatings was studied by electron microscopy. TiAlN had good resistance to sub-critical crack propagation. PVD/CVD gave extended tool lifetimes compared with CVD coated tools. MECHANICAL AND TRIBOLOGICAL CHARACTERISTICS OF WEAR RESISTANT COATINGS W.Fruth et al. (University of ErlangenNurnberg, Erlangen, Germany.) Znt. J. Ref?actory Metals Hard Mater., Vol 17, No l-3, 1999,201-208. Mechanical and tribological characteristics of carbide coatings on steel and polymer substrates were investigated. The coatings, WC or Cr,C!,, which were deposited by physical vapour deposition or combined physical/chemical vapour deposition methods, are shown to have potential for low friction applications. Experiments were also carried out on ball joints with steel plastic couples. PM’98. The following
Abstracts .are from papers presented at the 1998 Powder Metallurgy World Congress which was held in Granada, Spain, in
Powder production PRODUCTION OF HOLLOW COPPER PARTICLES FOR PRODUCTION OF CELLULAR STRUCTURES
H.Danninger et aZ. (Technical University of Vienna, Vienna, Austria.) It was reported that hollow Cu pax-ticles had been made by cementation of Cu
on to spherical Fe powders followed by leaching the Fe with HCl. The Cu particles were fragile and had rough surfaces. By coating with Sn and heat treatment there was increased strength and improved smoothness. By gravity sintering, without compaction, material with good strength:weight ratio was made. MAKING OF SCANDIUM POWDER A.Antonov et al. (Technoatom, Moscow, Russia.) SC powder was produced by H reduction of oxides, below lOOO”C, to obtain fine grained materials. Differential thermal analysis and thermogravimetric analysis were used to characterize the powder and the results were compared with results for Sm powder, reduced from oxide. The suitability of the powder for PM processing was evaluated. The studies were used to establish the technology of rare earth powder production. PRODUCTION OF EXTRAFINE ZINC POWDER
I.Avram et al. (Inst. for Technology of Mineral Raw Materials, Yugoslavia.) Production of Zn powder by evaporation/condensation was described. Zn is melted at 900°C. The Zn vapour was condensed in a drum rotating at 0.5 to 10 rpm and at 25 to 250°C. Powders were spherical. HIGH PURITY TUNGSTEN POWDER FROM SCHEELITE BY SELF PROPAGATING HIGH TEMPERATURE SYNTHESIS R.Curcic et al. (Inst. for Technology of Mineral Raw Materials, Yugoslavia.) Rapid production of W powder from Scheelite, CaO+WO,, by self propagating high temperature reaction with Mg, was reported. MgO and CaO are leached with HCl. Very high temperatures are attained and impurities are evaporated leaving high purity W. CRYSTAL STRUCTURE OF RAPIDLY COOLED ALUMINIUM POWDERS G.Arghir, E.Abrudan. (University of Cluj-Napoca, Cluj-Napoca, Romania.) Crystal structures of spherical, rapidly cooled, face-centred cubic Al powders were investigated. Relationships between particle size, cooling rate and lattice parameters were established. By extrapolation to zero particle size and infinite cooling rate the lattice parameter is shown to be 406.53 pm. COMPUTER MODELS IN DESIGN OF CENTRIFUGAL ATOMIZATION SYSTEMS S.Sheikhaliev, J.J.Dunkley. (Atomising Systems Ltd, Sheffield, UK.)
MPR May 2000 47
Ceramic
of
materials
MICROSTRUCTURE AND SUPERPLASTICITY IN ALUMINA-ZIRCONIA MATERIALS
S.Yakka et al. (National Research Inst. for Metals, Tsukuba, Japan. 1J Jpn Sot. Powder Powder Metal., Vol 45, No 12, 1998, 1186-1195. (In Japanese.) High temperature superplasticity in ceramic materials was discussed with regard to the requirement of fine grain size and the ability of ZrO, to supress grain growth in A&O,. Al,O,-ZrO, composites were produced by a colloidal technique, shaped by slip casting and cold isostatic pressing, and sintered at 1400°C. The materials had a small pore size, narrow pore size distribution and a fine grain structure. Tensile elongation over 550% was attained. RESINTERING OF ALUMINA COMPACT W.B.Du et al. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metal., Vol 46, No 2, 1999, 125130. (In English.) Resintering characteristics of Al,O,, after working, were investigated. Resintering is shown to allow densities, up to 99%, to be attained after processing at 1300°C for 1 hour, with little grain growth.
Coatings PERFORMANCE OF CEMENTED CARBIDE TOOLS WITH PHYSICAL VAPOUR DEPOSITED COATINGS
P.C.Jindal et al. (Kennametal, Inc, Latrobe, USA.) Int. J Refractory Metals Hard Mater., Vol 17, No l-3, 1999, 163170. TIN, Ti(CN) and TiAlN were deposited on WC-Gwt%Co by physical methods. Coatings and substrates were characterized for structure, properties and cutting performance, assessed by turning Incone 1718, medium C steel and ductile iron at low and high speeds. Cutting performance was ranked in order TiAlN (best), Ti(CN) and TIN. The superior performance of TiAlN is attributed to high resistance to abrasive and crater wear due to high hot hardness and oxidation resistance at operating temperature at the tool tip. ELECTRO-CHEMICAL-THERMAL GUN FOR DEPOSITION OF HARD COATINGS
S.Wald et al. (Nuclear Research Centre, Yavne, Israel.) Int. J. Refractory Metals Hard Mater., Vo117, No l-3,1999,171-177. It is reported that a new technique, using an electro-chemical-thermal gun,
had been developed for deposition of hard material coatings. Powder of the coating material is sprayed by conventional fuel supported by a pulsed plasma jet that ignites the fuel and accelerates the powder particles to over 1000 m.s-l, which are then energetically deposited. Process parameters are outlined. The method was used to deposit, e.g., sintered carbides onto stainless steel. MECHANICAL BEHAVIOUR CAL-CHEMICAL HARD COATINGS
OF PHYSIVAPOUR DEPOSITED
PSchlund et al. (University of ErlangenNurnberg, Erlangen, Germany.) Int. J. Refractory Metals Hard Mater., Vol 17, No l-3, 1999, 179-185. It is noted that use of chemical vapour deposition may result in deterioration of properties. It is reported that combination of chemical and physical vapour deposition processes may avoid this and may improve properties. Coatings of TiAlN, applied by PVD, and TiN-Ti(C,N)-TiN, applied by CVD, were applied to cemented carbides and mechanical characteristics investigated. Fracture of coatings was studied by electron microscopy. TiAlN had good resistance to sub-critical crack propagation. PVD/CVD gave extended tool lifetimes compared with CVD coated tools. MECHANICAL AND TRIBOLOGICAL CHARACTERISTICS OF WEAR RESISTANT COATINGS W.Fruth et al. (University of ErlangenNurnberg, Erlangen, Germany.) Znt. J. Ref?actory Metals Hard Mater., Vol 17, No l-3, 1999,201-208. Mechanical and tribological characteristics of carbide coatings on steel and polymer substrates were investigated. The coatings, WC or Cr,C!,, which were deposited by physical vapour deposition or combined physical/chemical vapour deposition methods, are shown to have potential for low friction applications. Experiments were also carried out on ball joints with steel plastic couples. PM’98. The following
Abstracts .are from papers presented at the 1998 Powder Metallurgy World Congress which was held in Granada, Spain, in
Powder production PRODUCTION OF HOLLOW COPPER PARTICLES FOR PRODUCTION OF CELLULAR STRUCTURES
H.Danninger et aZ. (Technical University of Vienna, Vienna, Austria.) It was reported that hollow Cu pax-ticles had been made by cementation of Cu
on to spherical Fe powders followed by leaching the Fe with HCl. The Cu particles were fragile and had rough surfaces. By coating with Sn and heat treatment there was increased strength and improved smoothness. By gravity sintering, without compaction, material with good strength:weight ratio was made. MAKING OF SCANDIUM POWDER A.Antonov et al. (Technoatom, Moscow, Russia.) SC powder was produced by H reduction of oxides, below lOOO”C, to obtain fine grained materials. Differential thermal analysis and thermogravimetric analysis were used to characterize the powder and the results were compared with results for Sm powder, reduced from oxide. The suitability of the powder for PM processing was evaluated. The studies were used to establish the technology of rare earth powder production. PRODUCTION OF EXTRAFINE ZINC POWDER
I.Avram et al. (Inst. for Technology of Mineral Raw Materials, Yugoslavia.) Production of Zn powder by evaporation/condensation was described. Zn is melted at 900°C. The Zn vapour was condensed in a drum rotating at 0.5 to 10 rpm and at 25 to 250°C. Powders were spherical. HIGH PURITY TUNGSTEN POWDER FROM SCHEELITE BY SELF PROPAGATING HIGH TEMPERATURE SYNTHESIS R.Curcic et al. (Inst. for Technology of Mineral Raw Materials, Yugoslavia.) Rapid production of W powder from Scheelite, CaO+WO,, by self propagating high temperature reaction with Mg, was reported. MgO and CaO are leached with HCl. Very high temperatures are attained and impurities are evaporated leaving high purity W. CRYSTAL STRUCTURE OF RAPIDLY COOLED ALUMINIUM POWDERS G.Arghir, E.Abrudan. (University of Cluj-Napoca, Cluj-Napoca, Romania.) Crystal structures of spherical, rapidly cooled, face-centred cubic Al powders were investigated. Relationships between particle size, cooling rate and lattice parameters were established. By extrapolation to zero particle size and infinite cooling rate the lattice parameter is shown to be 406.53 pm. COMPUTER MODELS IN DESIGN OF CENTRIFUGAL ATOMIZATION SYSTEMS S.Sheikhaliev, J.J.Dunkley. (Atomising Systems Ltd, Sheffield, UK.)
MPR May 2000 47