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Isotropic and kinematic hardening in dispersion strengthened aluminium alloy
Powder production ROTATING DISC COATINGS FOR CENTRIFUGAL ATOMIZER RAngers et al. (Lava1 University, Quebec, Canada.) Canadian Metal. Q., Vol 35, No 3, 1996, 291-297. An investigation of plasma sprayed ceramic coatings on atomizer discs is described. A graded coating of three layers, a metal bond coat, a compliant layer and a ceramic top coating, was developed to protect 304 stainless steel discs and was assessed by Al and Mg atomization. Tests up to 70 000 rpm are reported to give satisfactory results. FLUID KINETICS AND ATOMIZER DESIGN CRITERIA S.Chen et al. (Central South University of Technology, Changsha, Hunan, China.) Trans. Non-Ferrous Metals Sot. China, Vo16, No 3, 1996, 108-112. The working principle of the vertical loop slot jet nozzle, for atomization, was investigated with reference to fluid dynamics. It is shown that the fluid medium does not focus but forms a hollow double cone. To avoid blockage the leak pipe should be located such that the negative pressure zone of the gas cone is closed.
Fundamentals THERMODYNAMIC ASSESSMENT OF NIOBIUM-TUNGSTEN-CARBON SYSTEM W.Huang, M.Selleby. (Royal Inst. of Technology, Stockholm, Sweden.) 2. Metallkunde, Vol88, No 1, 1997, 55-62. Phase equilibria and thermodynamics of Nb-W-C are reviewed with regard to Gibb’s free energy of the phases. The assessment is based on recent evaluations of the binary systems. Model parameters were obtained by means of a computer program. Consistent parameters were obtained which described the experimental data. MECHANICAL PROPERTIES OF ISOTROPIC POROUS MATERIALS M.S.Kovaltchenko. Poroskouaya Metall., No 9110, 1996, 75-83. (In Russian.) A new approximation for mechanical property/relative density relationships is described. Long scale correlations 34
MPR March 1998
in powder aggregates, mesostructural defects and changes in Poisson’s ratio with porosity are considered. Relationships between yield point and strain hardening with density are developed. A PLASTICITY MODEL FOR SIMULATION OF INDUSTRIAL POWDER COMPACTION J.C.Cante et al. (Polytechnic University of Catalonia, Spain.) Int. J. Solids Structures, Vo133, No 20-22, 1996,3161-3178. A model for simulation of powder compaction, based on large strain plasticity, is presented. Elastic response is described in terms of a hyperelastic model and plastic response by a two-parameter yield surface with regard to density. Two flow rules were tested by experiment. Application to simulation of real compaction is shown. BULK DENSITY MODELLING MICROSTRUCTURE AND FLOW CHARACTERISTICS OF COHESIVE POWDERS M.S.Mohammadi, N.Harnby.(University of Bradford, Yorkshire, UK.) Powder TechnoZ.,Vol92, No 1, 1997, 1-8. Methods of measuring loose and tapped bulk density, and densification during tapping, of powders were refined and used to study various cohesive zeolite powders. Modelling of tap density provided information in agreement with findings from scanning electron microscopy. Development of a technique for prediction of microstructure is reported. DETECTING POWDER MIXTURE INHOMOGENEITY FOR MEASUREMENT ERRORS J.J.Walker, D.K.Rollins. (Iowa State University, Ames, Iowa, USA.) Powder TechnoZ.,Vol92, No 1, 1997, 9-15. A study of methods of describing inhomogeneities in powder mixtures is described. The method of mixing indices is considered and an analysis of variance technique was used to overcome limitations in the mixing indices technique. The paper examines the robustness of the analysis of variance technique. DIRECT MEASUREMENT OF POWDER COHESION BY A TORSIONAL DEVICE J.L.R.Orband, D.Geldart. (University of Yorkshire, UK) Powder Bradford, Techrwl.,Vol92, No 1, 1997, 25-33.
A device for measurement of powder cohesion, the shear strength when no normal stress is applied, is discussed. The instrument is based on an annular shear cell. Variation of cohesion with particle size was determined for two nonmetallic powders. The study enabled a distinction to be made between free flowing powders and to make a qualitative comparison of flowability as a function of particle size.
Aluminium CREEP-FATIGUE OF ALUMINIUM DISPERSION STRENGTHENED WITH ALUMINIUM CARBIDE M.Besterici et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech Republic.) Pokroky Praskove Metal., Vol 34, No 4, 1996, 26-31. (In Czech.) It is reported that creep and creep/fatigue tests had been carried out on Al-8vol%Al,C,. Strain and life to fracture, which were the criteria for creep and creep/fatigue resistance, were measured for a range of loading regimes. Fractures were also examined. MICROSTRUCTURAL CHANGES CAUSED BY DEFORMATION IN ALUMINIUM-ALUMINIUM CARBIDE M.Besterici et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech Republic.) Pokroky Praskove Metal., Vol 34, No 4, 1996,32-38. (In Czech.) Structure/property relationships in AlAl,C, were investigated by tensile tests at various temperatures and strain rates. Dislocation slip was the dominant mechanism up to 300°C irrespective of strain rate. From 300 to 450°C there was also grain boundary slip. Superplasticity was observed at 450°C and lo’l s-l strain rate. ISOTROPIC AND KINEMATIC HARDENING IN DISPERSION STRENGTHENED ALUMINIUM ALLOY A.P.Reynolds, J.S.Lyons. (University of South Carolina, Columbia, USA.) Metall. Mater. Trans. A, Vol26A, No 5,1997, 12051211. The ambient temperature mechanical behaviour of an Al8009 alloy, with a grain size of 0.5 pm and dispersion strengthened with 25~015% of 50 to 100 nm dispersoid, was investigated in tension, compression and reversed loading. Experimental and predicted ideal isotropic hardening and ideal Kl
kinematic hardening are compared. Based on microstructure and fully reversed loading behaviour the deformation is explained. PRODUCTION OF ALUMINIUMCOPPER ALLOY BY TRANSIENT LIQUID PHASE SINTERING
M.Ozawa et al. (Muroran Inst. of Technology, Japan.) J. Jpn Inst. Light MetaZs,Vol46, No 4, 1996, 171-176. (In Japanese.) It is reported that Al-4.5wt%Cu alloys had been prepared by transient liquid phase sintering from elemental powders. Hot pressing above and below the eutectic temperature was used. Structures comprised Al-rich solid solution and CuAl,. CuAl, formed during solidification of the eutectic and could be distinguished from the CuAl, precipitated during the solid-state sintering stage. The alloy that had only been solid-state sintered was harder than the liquid phase sintered material. The alloy that had been liquid phase sintered had the higher strength and elongation, which showed that the transient liquid phase was beneficial. EFFECTS OF ADDITIONS OF IRON AND NICKEL ON STRUCTURE AND PROPERTIES OF ALUMINIUM ALLOY
K.Matsuki et al. (Toyama University, Japan.) J. Jpn Inst. Light Metals, Vol 46, No 4 1996, 189-194. (In Japanese.) The effects of 3%Fe and 0, 3, 5 or lOwt%Ni on structure and mechanical properties of sintered Al2024 alloys were investigated. Air atomized powders, cold isostatic pressing and hot extrusion were used. Ni is shown to improve mechanical properties up to 300°C. Phases present were identified as AlaNi, AlsFeNi, A&Fe, Al,CusFe and an Al rich solid solution, according to composition. Properties are discussed with regard to dislocationldispersoid particle interactions.
FORMATION AND THERMAL STABILITY OF MECHANICALLY ALLOYED COPPER-TITANIUMNICKEL
K.Suzuki et al. (Tohoku University, Sendai. Japan.) J. Alloy. Compd., Vol 238, No 112 1996, 116-127. Formation and thermal stability of nanocrystalline Cu-20at%Ti-lO%Ni powders, after mechanical alloying, were investigated. The milled powder was disordered with a grain size of about 5 nm. There was no grain growth on heat treatment before the nucleation of TiCu, and TiNi phases at about 450°C.
hvn and steel CHARACTERISTICS OF EXPLOSION HAZARDS OF FERRO-ALLOY POWDERS
A.K.Toleshov. (Inst. of Steels and Alloys, Moscow, Russia.) Metallurgy, No 9110, 1995, 19-21. Safety factors in the manufacture of ferro-alloy powders, to avoid self-ignition, are reviewed. Safe conditions are given for ferro-alloys Fe-Mn, Fe-Ti and Fe-Si produced under various milling conditions. It is reported that vibratory milling gave the most dangerously explosive powders. ROBUST SINTERING OF PM IRONPHOSPHORUS STEELS B.J.Bergquist, B.C.Hildenwall. (Vattanfall Utveckling, Alvkarleby, Sweden.) Znt. J. Powder Metall., Vol 33, No 5, 1997, 3344. Robust or parameter design is discussed with regard to the need to avoid product variations caused by disturbances in the process environment. Two experiments using robust design to avoid dimensional variation and to maximize Charpy impact energy are reported. Fluctuations in sintering parameters and variations in green density were investigated. Results show that robust settings are possible but with difficulty in fixing some variables. Guidelines are given.
Molybdenum EFFECTS OF MIXING METHODS ON MOLYBDENUM ALLOYS WITH 3 WT% RHENIUM
L.Sha. (Changsha Technical College, Hunan, China.) Znt. J. Refractory Metals Hard Mater., Vol 15, No 4, 1997, 219222. Mixing of MO compounds, or elemental powder, with Re compounds or elemental powder, in order to make a novel Mo-3wt%Re alloy was investigated. Wet, dry or wet/dry mixing methods were used. It is concluded that wet/dry mixing of elemental powders gave the best results. In the case of mixed compounds there was loss of Re during reduction to metal. FLAKE FORMING BY METAL POWDERS DURING MECHANICAL ALLOYING AND USE IN COMPOSITES
Y.Waku, M.Suzuki. (Ube Industries Ltd, Kogushi, Japan.) J. Jpn Sot. Powder Powo!er Metall., Vol43, No 6,1996,705-711. (In Japanese.) Flake forming behaviour of MO, Ta and Nb during MA of Also,-refractory metal powders, and the strength and structure
of the composite made from the powders, were investigated. Flake formation increased with increase in particle size. It is reported that the flexural strength of the composite is increased by increase in the amount of flake MO. This is attributed to crack blunting at the MO flakes.
Nickel DIFFUSION PROCESSES IN MECHANOACTIVATED SYNTHESIS AMORPHOUS ALLOYS
OF
Y.A.Skakov et al. (Inst. of Steels and Alloys, Moscow, Russia.) Metall. Nouej. Tekhnol., Vol 18, No 2, 1996, 74-79. (In Russian.) X-ray diffraction was used to investigate ball milled Ni and Ni-Ti powders. It is shown that an amorphous phase based on Ni-66at%Ti is formed by reactive diffusion. Deformation favoured formation of contact surfaces and accumulation of point defects providing fast diffusion at low temperatures.
Sihfer SYNTHESIS OF SILVER ALLOY WITH TIN DIOXIDE DISPERSED BY MECHANICAL ALLOYING
G.G.Lee et al. (Mitsubishi Materials Corp, Omiya, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 6, 1996, 795-800. (In Japanese.) It is reported that mechanical alloying had been used to disperse 20vol%SnO, in an Ag powder composite. The milled powders were sintered and extruded. The structure comprised homogeneously distributed nanosized SnO, particles in the Ag matrix.
7lmgsten VAN DER WAALS APPROXIMATION FOR POTASSIUM BUBBLES IN TUNGSTEN
A.Nagy. (GE Lighting Tungsram Rt.. Budapest, Hungary.) Metall. Muter. Trans B, Vol27B, No 6, 1996, 987-992. The role of finely dispersed potassium bubbles in promoting high-temperature sag resistance of W lamp filaments is discussed. It is noted that ideal gas theory is used to describe K bubbles. It is shown that a van der Waals approximation can account for phase changes and describe a two-phase region, and that bubbles in the size range of tenths of a micron can exist in the two-phase state. Some experimental findings are discussed.
MPR March 1998 35
Fundamentals THERMODYNAMIC ASSESSMENT OF NIOBIUM-TUNGSTEN-CARBON SYSTEM W.Huang, M.Selleby. (Royal Inst. of Technology, Stockholm, Sweden.) 2. Metallkunde, Vol88, No 1, 1997, 55-62. Phase equilibria and thermodynamics of Nb-W-C are reviewed with regard to Gibb’s free energy of the phases. The assessment is based on recent evaluations of the binary systems. Model parameters were obtained by means of a computer program. Consistent parameters were obtained which described the experimental data. MECHANICAL PROPERTIES OF ISOTROPIC POROUS MATERIALS M.S.Kovaltchenko. Poroskouaya Metall., No 9110, 1996, 75-83. (In Russian.) A new approximation for mechanical property/relative density relationships is described. Long scale correlations 34
MPR March 1998
in powder aggregates, mesostructural defects and changes in Poisson’s ratio with porosity are considered. Relationships between yield point and strain hardening with density are developed. A PLASTICITY MODEL FOR SIMULATION OF INDUSTRIAL POWDER COMPACTION J.C.Cante et al. (Polytechnic University of Catalonia, Spain.) Int. J. Solids Structures, Vo133, No 20-22, 1996,3161-3178. A model for simulation of powder compaction, based on large strain plasticity, is presented. Elastic response is described in terms of a hyperelastic model and plastic response by a two-parameter yield surface with regard to density. Two flow rules were tested by experiment. Application to simulation of real compaction is shown. BULK DENSITY MODELLING MICROSTRUCTURE AND FLOW CHARACTERISTICS OF COHESIVE POWDERS M.S.Mohammadi, N.Harnby.(University of Bradford, Yorkshire, UK.) Powder TechnoZ.,Vol92, No 1, 1997, 1-8. Methods of measuring loose and tapped bulk density, and densification during tapping, of powders were refined and used to study various cohesive zeolite powders. Modelling of tap density provided information in agreement with findings from scanning electron microscopy. Development of a technique for prediction of microstructure is reported. DETECTING POWDER MIXTURE INHOMOGENEITY FOR MEASUREMENT ERRORS J.J.Walker, D.K.Rollins. (Iowa State University, Ames, Iowa, USA.) Powder TechnoZ.,Vol92, No 1, 1997, 9-15. A study of methods of describing inhomogeneities in powder mixtures is described. The method of mixing indices is considered and an analysis of variance technique was used to overcome limitations in the mixing indices technique. The paper examines the robustness of the analysis of variance technique. DIRECT MEASUREMENT OF POWDER COHESION BY A TORSIONAL DEVICE J.L.R.Orband, D.Geldart. (University of Yorkshire, UK) Powder Bradford, Techrwl.,Vol92, No 1, 1997, 25-33.
A device for measurement of powder cohesion, the shear strength when no normal stress is applied, is discussed. The instrument is based on an annular shear cell. Variation of cohesion with particle size was determined for two nonmetallic powders. The study enabled a distinction to be made between free flowing powders and to make a qualitative comparison of flowability as a function of particle size.
Aluminium CREEP-FATIGUE OF ALUMINIUM DISPERSION STRENGTHENED WITH ALUMINIUM CARBIDE M.Besterici et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech Republic.) Pokroky Praskove Metal., Vol 34, No 4, 1996, 26-31. (In Czech.) It is reported that creep and creep/fatigue tests had been carried out on Al-8vol%Al,C,. Strain and life to fracture, which were the criteria for creep and creep/fatigue resistance, were measured for a range of loading regimes. Fractures were also examined. MICROSTRUCTURAL CHANGES CAUSED BY DEFORMATION IN ALUMINIUM-ALUMINIUM CARBIDE M.Besterici et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech Republic.) Pokroky Praskove Metal., Vol 34, No 4, 1996,32-38. (In Czech.) Structure/property relationships in AlAl,C, were investigated by tensile tests at various temperatures and strain rates. Dislocation slip was the dominant mechanism up to 300°C irrespective of strain rate. From 300 to 450°C there was also grain boundary slip. Superplasticity was observed at 450°C and lo’l s-l strain rate. ISOTROPIC AND KINEMATIC HARDENING IN DISPERSION STRENGTHENED ALUMINIUM ALLOY A.P.Reynolds, J.S.Lyons. (University of South Carolina, Columbia, USA.) Metall. Mater. Trans. A, Vol26A, No 5,1997, 12051211. The ambient temperature mechanical behaviour of an Al8009 alloy, with a grain size of 0.5 pm and dispersion strengthened with 25~015% of 50 to 100 nm dispersoid, was investigated in tension, compression and reversed loading. Experimental and predicted ideal isotropic hardening and ideal Kl
kinematic hardening are compared. Based on microstructure and fully reversed loading behaviour the deformation is explained. PRODUCTION OF ALUMINIUMCOPPER ALLOY BY TRANSIENT LIQUID PHASE SINTERING
M.Ozawa et al. (Muroran Inst. of Technology, Japan.) J. Jpn Inst. Light MetaZs,Vol46, No 4, 1996, 171-176. (In Japanese.) It is reported that Al-4.5wt%Cu alloys had been prepared by transient liquid phase sintering from elemental powders. Hot pressing above and below the eutectic temperature was used. Structures comprised Al-rich solid solution and CuAl,. CuAl, formed during solidification of the eutectic and could be distinguished from the CuAl, precipitated during the solid-state sintering stage. The alloy that had only been solid-state sintered was harder than the liquid phase sintered material. The alloy that had been liquid phase sintered had the higher strength and elongation, which showed that the transient liquid phase was beneficial. EFFECTS OF ADDITIONS OF IRON AND NICKEL ON STRUCTURE AND PROPERTIES OF ALUMINIUM ALLOY
K.Matsuki et al. (Toyama University, Japan.) J. Jpn Inst. Light Metals, Vol 46, No 4 1996, 189-194. (In Japanese.) The effects of 3%Fe and 0, 3, 5 or lOwt%Ni on structure and mechanical properties of sintered Al2024 alloys were investigated. Air atomized powders, cold isostatic pressing and hot extrusion were used. Ni is shown to improve mechanical properties up to 300°C. Phases present were identified as AlaNi, AlsFeNi, A&Fe, Al,CusFe and an Al rich solid solution, according to composition. Properties are discussed with regard to dislocationldispersoid particle interactions.
FORMATION AND THERMAL STABILITY OF MECHANICALLY ALLOYED COPPER-TITANIUMNICKEL
K.Suzuki et al. (Tohoku University, Sendai. Japan.) J. Alloy. Compd., Vol 238, No 112 1996, 116-127. Formation and thermal stability of nanocrystalline Cu-20at%Ti-lO%Ni powders, after mechanical alloying, were investigated. The milled powder was disordered with a grain size of about 5 nm. There was no grain growth on heat treatment before the nucleation of TiCu, and TiNi phases at about 450°C.
hvn and steel CHARACTERISTICS OF EXPLOSION HAZARDS OF FERRO-ALLOY POWDERS
A.K.Toleshov. (Inst. of Steels and Alloys, Moscow, Russia.) Metallurgy, No 9110, 1995, 19-21. Safety factors in the manufacture of ferro-alloy powders, to avoid self-ignition, are reviewed. Safe conditions are given for ferro-alloys Fe-Mn, Fe-Ti and Fe-Si produced under various milling conditions. It is reported that vibratory milling gave the most dangerously explosive powders. ROBUST SINTERING OF PM IRONPHOSPHORUS STEELS B.J.Bergquist, B.C.Hildenwall. (Vattanfall Utveckling, Alvkarleby, Sweden.) Znt. J. Powder Metall., Vol 33, No 5, 1997, 3344. Robust or parameter design is discussed with regard to the need to avoid product variations caused by disturbances in the process environment. Two experiments using robust design to avoid dimensional variation and to maximize Charpy impact energy are reported. Fluctuations in sintering parameters and variations in green density were investigated. Results show that robust settings are possible but with difficulty in fixing some variables. Guidelines are given.
Molybdenum EFFECTS OF MIXING METHODS ON MOLYBDENUM ALLOYS WITH 3 WT% RHENIUM
L.Sha. (Changsha Technical College, Hunan, China.) Znt. J. Refractory Metals Hard Mater., Vol 15, No 4, 1997, 219222. Mixing of MO compounds, or elemental powder, with Re compounds or elemental powder, in order to make a novel Mo-3wt%Re alloy was investigated. Wet, dry or wet/dry mixing methods were used. It is concluded that wet/dry mixing of elemental powders gave the best results. In the case of mixed compounds there was loss of Re during reduction to metal. FLAKE FORMING BY METAL POWDERS DURING MECHANICAL ALLOYING AND USE IN COMPOSITES
Y.Waku, M.Suzuki. (Ube Industries Ltd, Kogushi, Japan.) J. Jpn Sot. Powder Powo!er Metall., Vol43, No 6,1996,705-711. (In Japanese.) Flake forming behaviour of MO, Ta and Nb during MA of Also,-refractory metal powders, and the strength and structure
of the composite made from the powders, were investigated. Flake formation increased with increase in particle size. It is reported that the flexural strength of the composite is increased by increase in the amount of flake MO. This is attributed to crack blunting at the MO flakes.
Nickel DIFFUSION PROCESSES IN MECHANOACTIVATED SYNTHESIS AMORPHOUS ALLOYS
OF
Y.A.Skakov et al. (Inst. of Steels and Alloys, Moscow, Russia.) Metall. Nouej. Tekhnol., Vol 18, No 2, 1996, 74-79. (In Russian.) X-ray diffraction was used to investigate ball milled Ni and Ni-Ti powders. It is shown that an amorphous phase based on Ni-66at%Ti is formed by reactive diffusion. Deformation favoured formation of contact surfaces and accumulation of point defects providing fast diffusion at low temperatures.
Sihfer SYNTHESIS OF SILVER ALLOY WITH TIN DIOXIDE DISPERSED BY MECHANICAL ALLOYING
G.G.Lee et al. (Mitsubishi Materials Corp, Omiya, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 6, 1996, 795-800. (In Japanese.) It is reported that mechanical alloying had been used to disperse 20vol%SnO, in an Ag powder composite. The milled powders were sintered and extruded. The structure comprised homogeneously distributed nanosized SnO, particles in the Ag matrix.
7lmgsten VAN DER WAALS APPROXIMATION FOR POTASSIUM BUBBLES IN TUNGSTEN
A.Nagy. (GE Lighting Tungsram Rt.. Budapest, Hungary.) Metall. Muter. Trans B, Vol27B, No 6, 1996, 987-992. The role of finely dispersed potassium bubbles in promoting high-temperature sag resistance of W lamp filaments is discussed. It is noted that ideal gas theory is used to describe K bubbles. It is shown that a van der Waals approximation can account for phase changes and describe a two-phase region, and that bubbles in the size range of tenths of a micron can exist in the two-phase state. Some experimental findings are discussed.
MPR March 1998 35