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Densification and dilation of sintered tungsten-copper alloys
7Ungsten SELECTIVE BURBLE DEFORMATION DURING PROCESSING OF DOPED TUNGSTEN
O.Horacsek et al. (Hungarian Academy of Sciences, Budapest, Hungary.) ht. J. Refractory Metals Hard Mater., Vol 16, No 1, 1998,51-57. Evolution of bubble structures of KAl-S1 doped W was investigated. Examination of bubble dispersion in early stages of processing showed that bubbles containing K deformed less than predicted. This is attributed to greater resistance to deformation of the smaller bubbles. Bubble geometry is analysed and it is suggested that the W/K interface has a lower surface energy than clean W. The consequences of size dependence of bubble deformation and formation of very large bubbles are discussed. CREEP PROPERTIES OF NON-SAG TUNGSTEN RECRYSTALLIZED IN STAGNANT ARGON-OXYGEN
G.Zilberstein. (Osram Sylvania Products Inc, Beverly, USA.) Znt. J. Refractory Metals Hard Mater., Vol 16, No 1, 1998, 71-75. It is noted that contamination of non-sag W with 0 results in impaired service life. An investigation to discover the mechanisms for this is described. Strain-time curves for 0 contaminated W showed a two-slope creep curve. Only a single slope is observed for un-contaminated material. The two slopes were, first, a short-time - high-strain region and secondly a long-time - low-strain zone. Growth of bubbles was observed in O-contaminated materials. Results are discussed in terms of bubble growth. POTASSIUM BUBBLE GROWTH IN
DOPED TUNGSTEN P.Schade. (Osram GmbH, Schwabmunthen, Germany.) Znt. J. Refractory Metals Hard Muter., Vol 16, No 1,1998,77-87. K filled bubbles and pores in K-Al-S1 doped W are discussed with reference to the effects they have on properties and mechanisms of bubble growth. It is shown that a possible mechanism for growth, up to a certain critical size, is controlled by diffusion of K, given the presence of diffusion paths, such as grain boundaries and dislocations. A new model for formation of voids in doped W is proposed which gives a basis for service failure of halogen lamps. DENSLFICATION AND DILATION OF SINTERED TUNGSTEN-COPPER ALLOYS
A.Upadhyaya, R.M.German. (Pennsylvania State University, Pennsylvania, 36
MPR January 1999
USA.) Znt. J. Powder Metall., Vol 34, NO 2,1998,43-55. A comparative study of mixing of elemental W-Cu powders and co-milling of the powders is described. Densification was enhanced by co-milling. Compacts made from mixed powders expanded on heating between 450 and 600°C which is detrimental to shape retention and densitication and is attributed to 0 in the Cu powders. Swelling can be avoided by use of Cu powder with a low 0 content, low pressing pressure and sintering in an inert atmosphere. Co-milling W-Cu powder effectively avoids compact expansion.
Composite materials EFFECTS OF PROCESS PARAMETERS, PARTICLE PROPERTIES AND METAL COATINGS ON COPPER-ALUMINA
Y.Z.Wan et al. (Tianjin University, Tianjin, China.) Powder Metall., Vol 41, No 1, 1998, 59-63. It is reported that PM methods had been used to prepare Cu alloy-Al,O, composites. Mechanical properties were measured to assess the effects of process and material parameters. Some specimens were made from A&O, powders coated with Cu or Ni which gave higher values of mechanical properties. A double press-double sinter route gave superior properties to single press-single sinter. Sintering temperature was an important factor. POWDER PROCESSING OF NIOBIUMTITANIUM DIOXIDE MATERIALS
H.R.Z.Sandim, A.F.Padiha. (University of Sao Paulo, Sao Paulo, Brazil.) Znt. J. Powder Metall., Vol34, No 2,1998,34-44. A study of sintering of Nb-(0.5 to l.O)%TiO, materials is described. Compaction and sintering tests were used to evaluate structural evolution. It was found that there is dissolution of TiO, and volatilization of Nb oxides during vacuum sintering. TiO, is shown to slightly enhance sintering up to 1400°C. An explanation of the role of TiO, is suggested. IMPROVEMENTS IN LEAD-TIN SOLDER BY PARTICLE REINFORCEMENT H.Mavoon, S.Jin. (Bell Laboratories, USA.) Appl. Physics Lett., Vol 73, 1998, 2290. It is reported that the creep properties of Pb-Sn solders had been improved, by a factor of three, by incorporation of nano-sized particulate reinforcements. This is needed to prevent movement of components, in electronic applications, in service. It is suggested that the shock resistance is also increased.
EFFECT OF PRESSING TEMPERATURE ON STRUCTURE AND PROPERTIES OF ALUMINIUM ALLOY COMPOSITES
SLee et al. (University of Science and Technology, Pohang, Korea.) Metal Mater Tram A, Vol 28A, No 12, 1997, 26252636. Effects of processing temperature on structure and mechanical properties of 2009 and 2124Al alloys, reinforced with 15%SiC particles, were investigated. Materials were hot pressed at 520, 560, 580 and 600°C followed by extrusion at 450°C. The best properties and structures were attained with 2124Al-Sic pressed at 560°C. This was attributed to refinement of brittle phases containing Mn by the lowest consolidation temperature. HIGH TEMPERATURE DEFORMATION PROPERTIES OF HIP PROCESSED TITANIUM BORIDE-TITANIUM ALUMINIDE S.Ochiai et al. (Teikyo University of Science and Technology, Yamanashi, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 7, 1997, 647-652. (In Japanese.) Mechanical alloying and HIP were used to prepare TiAl-(0, 10, 15 and ZO)vol%TiB, composites from Ti, Al and TiB, powders. Structures and properties were determined. There was partial amorphization during MA. Increase in %TiB, refined the structures. TiAl, T&Al and TiB, were detected in the alloys. Flow stress increased with increase in %TiB,. Strain rate sensitivity exponent was 0.3 at 1100°C in all samples. DENSIFICATION OF IRON-TITANIUM DIBORIDE CERMETS DURING LIQUID PHASE SINTERING
A.Kawasaki et al. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metall., Vol44, No 7, 1997,694699. (In Japanese.) Liquid phase sintering, in Ar, of FeTiB, cermets was investigated with regard to powder properties, sintering conditions and densification. Liquid phase formed at 1240°C. Fine powders were more sinterable than coarse ones. Full density was attained at 1700°C. Use of stainless steel instead of Fe gave better densiflcation than Fe because of increased wettability.
Hec t&al and magnetic materials SYNTHESIS OF COBALT FERRITE PARTICLES T.Sugimoto et al. (Tohoku University, Sendai, Japan.) Powder Technol., Vol96, No 2,1998,85-89.
O.Horacsek et al. (Hungarian Academy of Sciences, Budapest, Hungary.) ht. J. Refractory Metals Hard Mater., Vol 16, No 1, 1998,51-57. Evolution of bubble structures of KAl-S1 doped W was investigated. Examination of bubble dispersion in early stages of processing showed that bubbles containing K deformed less than predicted. This is attributed to greater resistance to deformation of the smaller bubbles. Bubble geometry is analysed and it is suggested that the W/K interface has a lower surface energy than clean W. The consequences of size dependence of bubble deformation and formation of very large bubbles are discussed. CREEP PROPERTIES OF NON-SAG TUNGSTEN RECRYSTALLIZED IN STAGNANT ARGON-OXYGEN
G.Zilberstein. (Osram Sylvania Products Inc, Beverly, USA.) Znt. J. Refractory Metals Hard Mater., Vol 16, No 1, 1998, 71-75. It is noted that contamination of non-sag W with 0 results in impaired service life. An investigation to discover the mechanisms for this is described. Strain-time curves for 0 contaminated W showed a two-slope creep curve. Only a single slope is observed for un-contaminated material. The two slopes were, first, a short-time - high-strain region and secondly a long-time - low-strain zone. Growth of bubbles was observed in O-contaminated materials. Results are discussed in terms of bubble growth. POTASSIUM BUBBLE GROWTH IN
DOPED TUNGSTEN P.Schade. (Osram GmbH, Schwabmunthen, Germany.) Znt. J. Refractory Metals Hard Muter., Vol 16, No 1,1998,77-87. K filled bubbles and pores in K-Al-S1 doped W are discussed with reference to the effects they have on properties and mechanisms of bubble growth. It is shown that a possible mechanism for growth, up to a certain critical size, is controlled by diffusion of K, given the presence of diffusion paths, such as grain boundaries and dislocations. A new model for formation of voids in doped W is proposed which gives a basis for service failure of halogen lamps. DENSLFICATION AND DILATION OF SINTERED TUNGSTEN-COPPER ALLOYS
A.Upadhyaya, R.M.German. (Pennsylvania State University, Pennsylvania, 36
MPR January 1999
USA.) Znt. J. Powder Metall., Vol 34, NO 2,1998,43-55. A comparative study of mixing of elemental W-Cu powders and co-milling of the powders is described. Densification was enhanced by co-milling. Compacts made from mixed powders expanded on heating between 450 and 600°C which is detrimental to shape retention and densitication and is attributed to 0 in the Cu powders. Swelling can be avoided by use of Cu powder with a low 0 content, low pressing pressure and sintering in an inert atmosphere. Co-milling W-Cu powder effectively avoids compact expansion.
Composite materials EFFECTS OF PROCESS PARAMETERS, PARTICLE PROPERTIES AND METAL COATINGS ON COPPER-ALUMINA
Y.Z.Wan et al. (Tianjin University, Tianjin, China.) Powder Metall., Vol 41, No 1, 1998, 59-63. It is reported that PM methods had been used to prepare Cu alloy-Al,O, composites. Mechanical properties were measured to assess the effects of process and material parameters. Some specimens were made from A&O, powders coated with Cu or Ni which gave higher values of mechanical properties. A double press-double sinter route gave superior properties to single press-single sinter. Sintering temperature was an important factor. POWDER PROCESSING OF NIOBIUMTITANIUM DIOXIDE MATERIALS
H.R.Z.Sandim, A.F.Padiha. (University of Sao Paulo, Sao Paulo, Brazil.) Znt. J. Powder Metall., Vol34, No 2,1998,34-44. A study of sintering of Nb-(0.5 to l.O)%TiO, materials is described. Compaction and sintering tests were used to evaluate structural evolution. It was found that there is dissolution of TiO, and volatilization of Nb oxides during vacuum sintering. TiO, is shown to slightly enhance sintering up to 1400°C. An explanation of the role of TiO, is suggested. IMPROVEMENTS IN LEAD-TIN SOLDER BY PARTICLE REINFORCEMENT H.Mavoon, S.Jin. (Bell Laboratories, USA.) Appl. Physics Lett., Vol 73, 1998, 2290. It is reported that the creep properties of Pb-Sn solders had been improved, by a factor of three, by incorporation of nano-sized particulate reinforcements. This is needed to prevent movement of components, in electronic applications, in service. It is suggested that the shock resistance is also increased.
EFFECT OF PRESSING TEMPERATURE ON STRUCTURE AND PROPERTIES OF ALUMINIUM ALLOY COMPOSITES
SLee et al. (University of Science and Technology, Pohang, Korea.) Metal Mater Tram A, Vol 28A, No 12, 1997, 26252636. Effects of processing temperature on structure and mechanical properties of 2009 and 2124Al alloys, reinforced with 15%SiC particles, were investigated. Materials were hot pressed at 520, 560, 580 and 600°C followed by extrusion at 450°C. The best properties and structures were attained with 2124Al-Sic pressed at 560°C. This was attributed to refinement of brittle phases containing Mn by the lowest consolidation temperature. HIGH TEMPERATURE DEFORMATION PROPERTIES OF HIP PROCESSED TITANIUM BORIDE-TITANIUM ALUMINIDE S.Ochiai et al. (Teikyo University of Science and Technology, Yamanashi, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 44, No 7, 1997, 647-652. (In Japanese.) Mechanical alloying and HIP were used to prepare TiAl-(0, 10, 15 and ZO)vol%TiB, composites from Ti, Al and TiB, powders. Structures and properties were determined. There was partial amorphization during MA. Increase in %TiB, refined the structures. TiAl, T&Al and TiB, were detected in the alloys. Flow stress increased with increase in %TiB,. Strain rate sensitivity exponent was 0.3 at 1100°C in all samples. DENSIFICATION OF IRON-TITANIUM DIBORIDE CERMETS DURING LIQUID PHASE SINTERING
A.Kawasaki et al. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metall., Vol44, No 7, 1997,694699. (In Japanese.) Liquid phase sintering, in Ar, of FeTiB, cermets was investigated with regard to powder properties, sintering conditions and densification. Liquid phase formed at 1240°C. Fine powders were more sinterable than coarse ones. Full density was attained at 1700°C. Use of stainless steel instead of Fe gave better densiflcation than Fe because of increased wettability.
Hec t&al and magnetic materials SYNTHESIS OF COBALT FERRITE PARTICLES T.Sugimoto et al. (Tohoku University, Sendai, Japan.) Powder Technol., Vol96, No 2,1998,85-89.