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High performance materials
%B below 5%. Structure, hardness and wear resistance were controlled by varying gas flow during CVD. B in the coating increased hardness but reduced adhesion of coating to substrate. A CoWB phase was detected at the interface. Cutting tests showed that the coating had good abrasive wear resistance. The main wear mechanism was cratering.
Deposition and properties of vanadium carbide coatings A.Borisova et al. (E.O.Paton Electric Welding Inst., Kiev, Ukraine.)
Deposition of VC coatings, on C and alloy steels, by diffusion saturation from a borate melt, was described. Coating thickness was 5mm to 15mm and Vicker's microhardness was 20 to 28GPa. Wear resistance against WC2%Co was 15 to 20 times greater than for boride coatings. VC coatings were stable up to 400°C, improve fatigue properties of steel and corrosion resistance. Cutting tool life was increased by up to 30 times.
High performance materials Advances in PM tantalum P.Kumar, H.Uhlenhut. (H.C.Starck Inc., Newton USA.)
Requirements of Ta powder for part production were outlined. It was reported that a process to make 99.99%Ta powder, with less than 150ppm O, had been developed. Quality of parts manufactured from the powder was discussed in terms of purity, structure, texture developed by thermo-mechanical processing and applications.
Alloying of tungsten and development of manufacturing technology for tungsten alloys K.Povarova, P.Makarov. (Leco lnstrumente GmbH, Moscow, Russia.)
It was noted that W and its alloys can be used under severe conditions of temperature, loading and environment but that there are problems such as cold brittleness. Methods of strengthening W are outlined, including solid solution strengthening, and strengthening by fine particles of refractory phases. Enhancement of low temperature plasticity and workability was investigated by removal of impurities and binding of O and C to oxide and carbide-forming elements. Processing methods were considered. It was shown that it is possible to prepare carbide precipitation hardening W alloys by addition of Mo or Re.
Thermo-mechanical processing of molybdenum-lanthanum A.J Mueller et al. (Bechtel Industries Inc., West Mifflin, USA.)
It was shown that variations in oxide species and processing method influenced
38
MPR December 2002
the mechanical properties of oxide-dispersion strengthened Mo materials. Mechanical behaviour of Mo-2vol%La203, in various forms, was investigated at -150°C to 1800°C. Tensile properties were less affected by cold working than the creep properties, which were sensitive to initial microstructure. Stress relieved material had better creep properties than recrystallised alloys at 1200°C. The opposite effect was found at 1500°C. It is emphasised that processing needs to be matched to the specific application.
Microstructure and mechanical properties of molybdenum-zirconium carbide composites T.guzuki et al. (Tohoku University, Sendal Japan.)
It was reported that Mo-(16 and 40)vol%ZrC had been prepared by arc melting blended Mo and ZrC powders and structures and mechanical properties investigated. Mo40%ZrC, annealed at 1600°C for 70 hours, contained primary ZrC particles larger than 10mm and eutectic ZrC particles less than lmm in a Mo matrix with grain size of 3ram. In the Mo-16%ZrC the ZrC particles were 600nm. Materials had good creep strength and fracture toughness
Ductile chromium through oxide dispersion M.P.Brady et aI. (Oak Ridge National Laboratory, Oak Ridge, USA.)
It was noted that it had been shown that sintered and extruded Cr-MgO could yield 20% tensile ductility. This had been attributed to formation of MgCr204 spinel which gathered N from the Cr rendering it ductile. It was reported that this finding had been duplicated and it was suggested that the mechanism was more complex than the earlier explanation as some of the recent samples contained nitride precipitates. Possible mechanisms were proposed and discussed taking into account studies structure and propeties of Cr-6%MgO-(0 to 2.2)wt%Ti.
Characteristics of the interface between molybdenum and vitreous silica B.Retter et al. (Plansee AG, Reutte, Austria.)
Analysis and evaluation of Mo0.52wt%TiO2-0.55%(Y,Ce) mixed oxide sealing foils against vitreous SiO 2 was reported. This application requires good adhesion between alloy and glass which needs good wettability and chemical and mechanical bonding The investigation used three types of lamps with SiO 2 envelopes. ~IIO2 in the alloy produces a this interface fihn which promotes adhesion and the mixed (Y,Ce)203 oxide, in 1 to 3mm particles, promotes localised bonding. It is concluded that the distribution of metal
oxides is critical for long-term performance of this glass-to-metal seal.
Characterisation of porous tungsten by microhardness J. V. Wood et al. (Uniiversity of Nottingham, Nottingham, UK.)
Use of porous W as a high current dispenser cathode was noted. This is fabricated by impregnation of porous W with an electronemissive material. Controlled and uniform porosity is, thus, a critical parameter. Microhardness was used to study uniformity of pore distribution and homogeneity of microstructure supported by optical and scanning electron microscopy.
Research and development of tungsten electrodes with additions of rare earth oxides ZNie et al. (Beijing Polytechnic University, Beijing, China.)
Studies of W welding electrodes, with additions of La, Ce, Y and Th oxides, singly or in combination, were described. At low and medium currents W-2.2wt% La203 had the best performance. At higher currents the electrode containing Y203 was best. Electrodes with two or more additives were superior to those containing single additives.
General topics Effects of intermittent annealing on mechanical properties of rolled rhenium T.Smith et al. (Loyola Marymount University, Los Angeles, USA.)
Mechanical and other properties of rolled Re were investigated at 0, ° 45 ° and 90 ° to the rolling direction at 10 to 12% reduction and annealed intermittently at 1200°C, 1650°C and 1800°C. Textures were evaluated and correlated with mechanical properties. Microhardness increased with reduction in thickness. At the 45°-mode work hardening rate was lower than in the 0° or 90 ° modes. Twinningbecame more evident as reduction in thickness increased.
Modelling of sintering graded materials M.Gasik, B.Zha~g.(Helsinki University of Technology, Espoo, Finland.)
Graded materials are identified as having gradients of composition, phase distribution, porosity and the related properties. Sintering of graded materials was modelled and simulated by computer, particularly for hardmetals. Heat transfer, sintering by conventional, microwave and hybrid methods and-grain growth were considered using finite element methods. WCCo plate and cone samples were investigated
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Deposition and properties of vanadium carbide coatings A.Borisova et al. (E.O.Paton Electric Welding Inst., Kiev, Ukraine.)
Deposition of VC coatings, on C and alloy steels, by diffusion saturation from a borate melt, was described. Coating thickness was 5mm to 15mm and Vicker's microhardness was 20 to 28GPa. Wear resistance against WC2%Co was 15 to 20 times greater than for boride coatings. VC coatings were stable up to 400°C, improve fatigue properties of steel and corrosion resistance. Cutting tool life was increased by up to 30 times.
High performance materials Advances in PM tantalum P.Kumar, H.Uhlenhut. (H.C.Starck Inc., Newton USA.)
Requirements of Ta powder for part production were outlined. It was reported that a process to make 99.99%Ta powder, with less than 150ppm O, had been developed. Quality of parts manufactured from the powder was discussed in terms of purity, structure, texture developed by thermo-mechanical processing and applications.
Alloying of tungsten and development of manufacturing technology for tungsten alloys K.Povarova, P.Makarov. (Leco lnstrumente GmbH, Moscow, Russia.)
It was noted that W and its alloys can be used under severe conditions of temperature, loading and environment but that there are problems such as cold brittleness. Methods of strengthening W are outlined, including solid solution strengthening, and strengthening by fine particles of refractory phases. Enhancement of low temperature plasticity and workability was investigated by removal of impurities and binding of O and C to oxide and carbide-forming elements. Processing methods were considered. It was shown that it is possible to prepare carbide precipitation hardening W alloys by addition of Mo or Re.
Thermo-mechanical processing of molybdenum-lanthanum A.J Mueller et al. (Bechtel Industries Inc., West Mifflin, USA.)
It was shown that variations in oxide species and processing method influenced
38
MPR December 2002
the mechanical properties of oxide-dispersion strengthened Mo materials. Mechanical behaviour of Mo-2vol%La203, in various forms, was investigated at -150°C to 1800°C. Tensile properties were less affected by cold working than the creep properties, which were sensitive to initial microstructure. Stress relieved material had better creep properties than recrystallised alloys at 1200°C. The opposite effect was found at 1500°C. It is emphasised that processing needs to be matched to the specific application.
Microstructure and mechanical properties of molybdenum-zirconium carbide composites T.guzuki et al. (Tohoku University, Sendal Japan.)
It was reported that Mo-(16 and 40)vol%ZrC had been prepared by arc melting blended Mo and ZrC powders and structures and mechanical properties investigated. Mo40%ZrC, annealed at 1600°C for 70 hours, contained primary ZrC particles larger than 10mm and eutectic ZrC particles less than lmm in a Mo matrix with grain size of 3ram. In the Mo-16%ZrC the ZrC particles were 600nm. Materials had good creep strength and fracture toughness
Ductile chromium through oxide dispersion M.P.Brady et aI. (Oak Ridge National Laboratory, Oak Ridge, USA.)
It was noted that it had been shown that sintered and extruded Cr-MgO could yield 20% tensile ductility. This had been attributed to formation of MgCr204 spinel which gathered N from the Cr rendering it ductile. It was reported that this finding had been duplicated and it was suggested that the mechanism was more complex than the earlier explanation as some of the recent samples contained nitride precipitates. Possible mechanisms were proposed and discussed taking into account studies structure and propeties of Cr-6%MgO-(0 to 2.2)wt%Ti.
Characteristics of the interface between molybdenum and vitreous silica B.Retter et al. (Plansee AG, Reutte, Austria.)
Analysis and evaluation of Mo0.52wt%TiO2-0.55%(Y,Ce) mixed oxide sealing foils against vitreous SiO 2 was reported. This application requires good adhesion between alloy and glass which needs good wettability and chemical and mechanical bonding The investigation used three types of lamps with SiO 2 envelopes. ~IIO2 in the alloy produces a this interface fihn which promotes adhesion and the mixed (Y,Ce)203 oxide, in 1 to 3mm particles, promotes localised bonding. It is concluded that the distribution of metal
oxides is critical for long-term performance of this glass-to-metal seal.
Characterisation of porous tungsten by microhardness J. V. Wood et al. (Uniiversity of Nottingham, Nottingham, UK.)
Use of porous W as a high current dispenser cathode was noted. This is fabricated by impregnation of porous W with an electronemissive material. Controlled and uniform porosity is, thus, a critical parameter. Microhardness was used to study uniformity of pore distribution and homogeneity of microstructure supported by optical and scanning electron microscopy.
Research and development of tungsten electrodes with additions of rare earth oxides ZNie et al. (Beijing Polytechnic University, Beijing, China.)
Studies of W welding electrodes, with additions of La, Ce, Y and Th oxides, singly or in combination, were described. At low and medium currents W-2.2wt% La203 had the best performance. At higher currents the electrode containing Y203 was best. Electrodes with two or more additives were superior to those containing single additives.
General topics Effects of intermittent annealing on mechanical properties of rolled rhenium T.Smith et al. (Loyola Marymount University, Los Angeles, USA.)
Mechanical and other properties of rolled Re were investigated at 0, ° 45 ° and 90 ° to the rolling direction at 10 to 12% reduction and annealed intermittently at 1200°C, 1650°C and 1800°C. Textures were evaluated and correlated with mechanical properties. Microhardness increased with reduction in thickness. At the 45°-mode work hardening rate was lower than in the 0° or 90 ° modes. Twinningbecame more evident as reduction in thickness increased.
Modelling of sintering graded materials M.Gasik, B.Zha~g.(Helsinki University of Technology, Espoo, Finland.)
Graded materials are identified as having gradients of composition, phase distribution, porosity and the related properties. Sintering of graded materials was modelled and simulated by computer, particularly for hardmetals. Heat transfer, sintering by conventional, microwave and hybrid methods and-grain growth were considered using finite element methods. WCCo plate and cone samples were investigated
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