Sintering features of tungsten carbide-cobalt processed from fine powders

process were reported to have higher hardness and fracture toughness. This was attributed to the fine WC grain size and flattened Co grain shape. It was shown that there was no need to use VC to attain the improved properties. INFLUENCE OF TRACE ELEMENTS ON PROPERTIES OF HARDMETALS H.Ortner. (Technical University, Darmstadt, Germany.) Occurrence and effects of trace impurities in hardmetals were reviewed with reference to influences on processing and final properties. Effects of Al, Ca, P, S and 0, on production steps and properties of conventional WC-Co, were investigated. From experience and the investigation it was concluded that heterogeneously distributed impurities are more detrimental to properties than rather more homogeneously distributed elements, both in binder and hard phase. Sources of impurity were discussed. MODELLING HARDNESS VARIATIONS IN WC-COBALT WITH A WIDE GRAIN SIZE VARIATION B.Roebuck et al. (National Physical Laboratory, Tedding-ton, UK.) From modelling studies of properties of hardmetals, it was noted that it is important to have measures of grain size distribution. Models have predicted that materials with a narrow size distribution might be harder or softer than materials with a conventional range of sizes. Different results may be obtained when the number of grains of a given size is used rather than the size fraction of grains of a given size. The latter predicts a reduction in hardness. WC-6%Co hardmetals were produced with a wide grain size distribution and characterized by the linear intercept method. Hardness was measured and compared with conventional WC-Co. It was deduced that the use of size fraction is the more appropriate method. INFLUENCE OF pH ON SLIDING WEAR OF TUNGSTEN CARBIDE BASED MATERIALS N.Axen et al. (Uppsala University, Sweden.) Wear and corrosion of WC with various binders and a binderless WC was investigated with a water based lubricant of pH from 1 to 14 using self-mated pin-on-disc tests to determine the effects of pH on friction and wear. There was a strong relationship between pH and wear rate particularly in the case of the

binderless carbide which was low in acid and high at high pH. SYNTHESIS AND APPLICATION OF CUBIC TITANIUM OXY-CARBIDE PHASES L.M.Berger et al. (Fraunhofer Inst. Ceramics and Sintered Materials, Dresden, Germany.) A carbothermal process for making cubic Ti(C,O,N) materials, for use in A&,0,-Ti(C,O,N) composites and ‘as cutting tools was described. The mechanism was outlined and involved CO-CO, mass transfer and three reaction stages. The final material is Ti(C,O), which in combination with Al,O,, is said to be advantageous in cutting hardened steel at intermediate speeds. USE OF PRESSURE SWING GRANULATION FOR TUNGSTEN CARBIDE-COBALT MIXTURES T.van Doorslaer. (Fitzpatrick Co Europe NV, St. Niklaas, Belgium.) Use of a pressure swing granulator to produce WC-Co granules, from waxed powder mixtures, was described. It was reported that there had been difficulties in producing good granules with a conventional spray-drying technique. EFFECT OF BINDER COMPOSITION ON DIRECT MEASUREMENT OF INTERGRANULAR FRICTION M.Anders, L.Bergstrom. (Inst. for Surface Chemistry, Stockholm, Sweden.) It was noted that there are difficulties in distinguishing between internal and external friction during dry powder compaction. It was reported that atomic force microscopy can do this by sliding a granule against any substrate and recording changes in friction forces. The technique was used to measure friction between two S&N, granules and between one granule and a polished substrate, for which stainless steel and a hardmetal were used. Applied load, binder composition and sliding velocity were varied. The coefficient of friction was lower between granule and substrate than between granule and granule. ANALYSIS OF THE INJECTION STAGE IN POWDER INJECTION MOIJLDING T.Barriere. (Lmarc, Besancon, France.) The injection stage in powder injection moulding was analysed experimentally and by modelling. A multicavity mould was used. Injection temperature and pressure were measured and controlled. A numerical approach was developed for analysis of flow of mixed feedstock. Temperature

effects were taken into account in the experiments and the model. Good agreement between simulation and experiment was reported. Parts, after debinding and sintering, were shown to be of good quality SINTERING FEATURES OF TUNGSTEN CARBIDE-COBALT PROCESSED FROM FINE POWDERS C.H.Allibert. (LPTCM/ENSEEG, St. Martin d’HQr&s, France.) The trend to manufacture WC-Co from increasingly fine powders was noted together with differences in densification behaviour and structural evolution during liquid phase sintering of materials made from pm and sub-pm sizes. It is shown that in the case of sub,um powders there is a greater contribution from solid state sintering and there is abnormal grain growth. Questions still outstanding in the use of ultrafine powders are described. MODELLING THE COMPACTION OF TUNGSTEN CARBIDE-COBALT CHARACTERIZATION AND SIMULATION O.Alvain et al. (CERMeP, Grenoble, France. ) The need to anticipate density gradients and cracks in powder compacts was noted. Theoretical and experimental studies were described. The model treated the powder as a continuous medium, described by classical elasto-plastic theory and simulated by finite element methods. WC-Co was compacted to investigate hardening and elastic parameters. Friction and tensile tests were also carried out. Cam-Clay and Cap models were used. The numerical simulation of compaction of a drawing die was presented with density gradients and forces determined. Simulated and experimental results were compared. MODELLING OF SINTERING OF HARDMETALS G.Leitner et al. (Fraunhofer Inst., Dresden, Germany.) Shrinkage of hardmetals during sintering was discussed with reference to mechanisms. The compositions of particle surfaces in WC-Co were considered to be important in sintering since these may contain oxides. Origins of oxides were reviewed with consideration of methods of quantifying their reduction, using thermobalance and mass spectroscopy. For WC(grain size 0.6 to 28 pm&(8 to 28)%Co it was shown that particle surfaces must be freshly reduced and clean before shrinkage can start. A model was used for interpretation of

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