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Synthesis and processing of nanocrystalline tungsten carbide-cobalt powders
A study of structure and properties of ordered and disordered VC was described. It was shown that ordered VC is harder than disordered VC. The order/disorder transition was investigated. Ordered domains could be revealed in microstructures and it was demonstrated that ordering is nucleated at grain boundaries. STUDY OF RARE EARTII PHASE IN CEMENTED CARBIDE Y.Yi et al. (University of Science and Technology, Beijing, China.) Distribution and effects of rare earths in cemented carbides were investigated. It was shown that the rare earths segregate to grain boundaries and interfaces, are spherical in shape and below 0.5 pm in size. Solubility of W in the Co binder and service life are increased by rare earths. STRUCTURE AND PROPERTIES OF GRADED CEMENTED CARBIDES SINTER-BONDED ONTO STEEL
reference to use of metals at the interface to improve adhesion. Development combined plasma based of a chemical/physical vapour deposition process to apply the metal interlayer and the C coating was reported. An adherent diamond-like C coating was deposited on the metal underlayer. The C coating was either amorphous or had a dense columnar structure. TOOL LIVES OF IIIGII SPEED STEEL INDEXABLE INSERTS WITH TITANIUM BASED COATINGS M.Ciskal et al. (Inst. of Metal Cutting, Cracow, Poland.) A study of cutting properties of TiN, Ti(C,N) and (Ti,Al)N coatings on T15 high speed steel tools was described. Physical and chemical vapour deposition processes were used for deposition. Cutting tests were on annealed steel and continued to failure to determine tool life. Results were described. Best results were given by PVD (Ti,Al)N.
A.Ikegaya et ~2. (Sumitomo Electric Industries Ltd, Itami, Japan.) It was noted that some coatings on steel such as stellite or cemented carbide may not adhere well to the substrate owing to thermal stresses. An investigation of compositionally graded WC-Co coatings, sinter-bonded onto steel by pressure and pulsed resistance heating, was described. Crack-free, wellbonded coatings, with high surface hardness and good service performance, were reported.
Atomization
SYNTHESIS AND PROCESSING OF NANOCRYSTALLINE TUNGSTEN CARBIDE-COBALT POWDERS
EFFECT OF ATOMIZER GEOMETRY ON GAS FLOW FIELD IN GAS ATOMIZATION
A.Rosen et al. (Technion, Haifa, Israel.) Sintering and structure of nanocrystalline WC-15wt%Co-l%VC cermets were investigated. Powders were made by MA or spray conversion processing. Sintering was in vacuum or in a dilatometer. Milled powder compacts staked to shrink at a lower temperature than sprayed powder compacts and differences in microstructure were detected. The milled powder sintered compacts had a layered structure. The sprayed powder compacts contained equiaxed and elongated grains.
H.Liu, R.Dax. (Concurrent Technologies Corp, USA.) Gas atomization was reviewed with regard to equipment, process conditions and powder characteristics. A numerical simulation of gas flow field close to the nozzle was described for free fall and close-coupled atomizers under sub- and supersonic conditions. Gas flow patterns were modelled and the effect of atomization pressure on gas flow field was quantified. Good agreement with experiment was reported.
AMORPHOUS DIAMOND-LIKE CARBON COATINGS WITH GRADED METAL INTERFACES H.Bolt et al. (Forschungszentrum Jiilich GmbH, Jtilich, Germany.) Poor adhesion of diamond-like C coatings, as a result of thermal stresses and weak bonding, was discussed with 40
MPR May 1998
PM2TEC’97. The following Abstracts are of papers presented at the 1997 International Conference on Powder Metallurgy and Particulate Materials which was held in Chicago, USA, in June 1997.
OPTIMIZING MELT TIP GEOMETRY FOR HIGH-PRESSURE GAS ATOMIZATION J.Ting et al. (Ames Laboratory, USA.) The importance of controlled aspiration at the melt tip in high-pressure gas atomization was emphasized. It was shown how melt tip design can be optimized.
GAS DYNAMICS OF ANNULAR SLIT CONVERGENT-DIVERGENT IIIGIIPRESSURE GAS ATOMIZATION J.Ting et al. (Ames Laboratory, USA.) It was reported that a gas atomizer with a convergent-divergent nozzle showed promise for production of high yields of fine alloy powders. The results of a gas-only fluid dynamics study were described. Navier-Stokes equations were solved for an annular slit. Variations in operating pressure and melt tip geometry were examined. The results show the existence of a recirculation region. It was suggested that the results will improve the design of convergent-divergent annular slits for atomization of liquid metals. ROTATING ELECTRODE ATOMIZATION FOR PRODUCTION OF FINE POWDERS OF REACTIVE METALS S.Miller, N.F.Levoy. (Nuclear Metals Inc, USA.) It was reported that gas atomization and rotating electrode processing had been combined for production of fine Ti and Fe powders. The rotating electrode serves as a means of delivering the melt to the atomization gas flow. Powder yields were shown to be increased and contamination was avoided. Equipment design and test results, and powder were morphology structure and described. POWDER PRODUCTION BY IMPACTCENTRIFUGAL ATOMIZATION OF A MELT Y.M.Lytvyneko, O.N.Grigoriev. (Inst. for Problems of Materials Science, Kiev, Ukraine.) A novel technique for powder production, impact-centrifugal atomization, was described. The method produced tine powders solidified at up to 106”C.s1. Use for hard and soft magnetic materials and corrosion-resistant alloys was reported. The raw alloy is melted, directed onto impeller blades, atomized and impacted on a rotating screen. Technological perspectives and subsequent compaction were discussed. ALLOYING AND DEVELOPMENT OF NOVEL MICROSTRUCTLJRES BY ATOMIZATION D.Apelian. (Worcester Polytechnic Inst., USA.) Atomization was discussed with reference to surface areas of powders and heat and mass transfer. The possibility of alloying by reaction with a reactive atomization gas was considered. Theory for in situ alloying was outlined in terms of energetics. Some experimental examples were given.
reference to use of metals at the interface to improve adhesion. Development combined plasma based of a chemical/physical vapour deposition process to apply the metal interlayer and the C coating was reported. An adherent diamond-like C coating was deposited on the metal underlayer. The C coating was either amorphous or had a dense columnar structure. TOOL LIVES OF IIIGII SPEED STEEL INDEXABLE INSERTS WITH TITANIUM BASED COATINGS M.Ciskal et al. (Inst. of Metal Cutting, Cracow, Poland.) A study of cutting properties of TiN, Ti(C,N) and (Ti,Al)N coatings on T15 high speed steel tools was described. Physical and chemical vapour deposition processes were used for deposition. Cutting tests were on annealed steel and continued to failure to determine tool life. Results were described. Best results were given by PVD (Ti,Al)N.
A.Ikegaya et ~2. (Sumitomo Electric Industries Ltd, Itami, Japan.) It was noted that some coatings on steel such as stellite or cemented carbide may not adhere well to the substrate owing to thermal stresses. An investigation of compositionally graded WC-Co coatings, sinter-bonded onto steel by pressure and pulsed resistance heating, was described. Crack-free, wellbonded coatings, with high surface hardness and good service performance, were reported.
Atomization
SYNTHESIS AND PROCESSING OF NANOCRYSTALLINE TUNGSTEN CARBIDE-COBALT POWDERS
EFFECT OF ATOMIZER GEOMETRY ON GAS FLOW FIELD IN GAS ATOMIZATION
A.Rosen et al. (Technion, Haifa, Israel.) Sintering and structure of nanocrystalline WC-15wt%Co-l%VC cermets were investigated. Powders were made by MA or spray conversion processing. Sintering was in vacuum or in a dilatometer. Milled powder compacts staked to shrink at a lower temperature than sprayed powder compacts and differences in microstructure were detected. The milled powder sintered compacts had a layered structure. The sprayed powder compacts contained equiaxed and elongated grains.
H.Liu, R.Dax. (Concurrent Technologies Corp, USA.) Gas atomization was reviewed with regard to equipment, process conditions and powder characteristics. A numerical simulation of gas flow field close to the nozzle was described for free fall and close-coupled atomizers under sub- and supersonic conditions. Gas flow patterns were modelled and the effect of atomization pressure on gas flow field was quantified. Good agreement with experiment was reported.
AMORPHOUS DIAMOND-LIKE CARBON COATINGS WITH GRADED METAL INTERFACES H.Bolt et al. (Forschungszentrum Jiilich GmbH, Jtilich, Germany.) Poor adhesion of diamond-like C coatings, as a result of thermal stresses and weak bonding, was discussed with 40
MPR May 1998
PM2TEC’97. The following Abstracts are of papers presented at the 1997 International Conference on Powder Metallurgy and Particulate Materials which was held in Chicago, USA, in June 1997.
OPTIMIZING MELT TIP GEOMETRY FOR HIGH-PRESSURE GAS ATOMIZATION J.Ting et al. (Ames Laboratory, USA.) The importance of controlled aspiration at the melt tip in high-pressure gas atomization was emphasized. It was shown how melt tip design can be optimized.
GAS DYNAMICS OF ANNULAR SLIT CONVERGENT-DIVERGENT IIIGIIPRESSURE GAS ATOMIZATION J.Ting et al. (Ames Laboratory, USA.) It was reported that a gas atomizer with a convergent-divergent nozzle showed promise for production of high yields of fine alloy powders. The results of a gas-only fluid dynamics study were described. Navier-Stokes equations were solved for an annular slit. Variations in operating pressure and melt tip geometry were examined. The results show the existence of a recirculation region. It was suggested that the results will improve the design of convergent-divergent annular slits for atomization of liquid metals. ROTATING ELECTRODE ATOMIZATION FOR PRODUCTION OF FINE POWDERS OF REACTIVE METALS S.Miller, N.F.Levoy. (Nuclear Metals Inc, USA.) It was reported that gas atomization and rotating electrode processing had been combined for production of fine Ti and Fe powders. The rotating electrode serves as a means of delivering the melt to the atomization gas flow. Powder yields were shown to be increased and contamination was avoided. Equipment design and test results, and powder were morphology structure and described. POWDER PRODUCTION BY IMPACTCENTRIFUGAL ATOMIZATION OF A MELT Y.M.Lytvyneko, O.N.Grigoriev. (Inst. for Problems of Materials Science, Kiev, Ukraine.) A novel technique for powder production, impact-centrifugal atomization, was described. The method produced tine powders solidified at up to 106”C.s1. Use for hard and soft magnetic materials and corrosion-resistant alloys was reported. The raw alloy is melted, directed onto impeller blades, atomized and impacted on a rotating screen. Technological perspectives and subsequent compaction were discussed. ALLOYING AND DEVELOPMENT OF NOVEL MICROSTRUCTLJRES BY ATOMIZATION D.Apelian. (Worcester Polytechnic Inst., USA.) Atomization was discussed with reference to surface areas of powders and heat and mass transfer. The possibility of alloying by reaction with a reactive atomization gas was considered. Theory for in situ alloying was outlined in terms of energetics. Some experimental examples were given.