shown to depend on process conditions. Different morphologies may arise from differing reaction routes.
Self-propagating high temperature synthesis of nickel aluminide-titanium carbide composites
C.Curfs et al. (European Synchrotron Radiation Facility, Grenoble, France.) TiC-NiAI composites were made from elemental powders by self propagating high temperature synthesis. Reactions were investigated by time resolved X-ray diffraction. For TiC-50mol%NiA1 an intermediate phase, A1NizTi, which had a short lifetime, was detected. The final product consisted of rounded TiC particles in a continuous NiA1 matrix. A structural model was suggested.
Debinding and presintering of hardmetals in a plasma reactor
J.A.Escobar et aL (Federal University of St. Catarina, Florianopolis, Brazil.) A plasma technique for delubricating and presintering hardmetals was described. WC-Co-2%paraffin wax lubricant were milled and die compacted. Lubricant was removed either by heating in H at 500°C or by chemical reaction in a plasma reactor using glow discharge in Ar-30%H. Effects of process conditions were studied. The need to maintain stoichiometry of WC, to avoid formation of the h phase, was emphasised. A carburising gas was used to for this purpose.
investigated as a function of pH, by potentiodynamic polarisation. H2SO4, Na2SO 4 and NaOH were used at ambient temperature. Decrease in pH moved free corrosion potential to more noble values. Passivity was detected with NaOH. TaC and TiC had little effect. The active peak was suppressed by Cr2C3 due to a passivalion effect.
Combined control of phase composition and cutting properties of cemented carbides
E.V.Dudkin. (Voigograd State Technical University, Volgograd, Russia.) It was suggested that phase composition and cutting properties of cemented carbide cutting tool inserts could be controlled. To evaluate this the effects of %C were investigated. Magnetic and thermoelectric measurements were the basis of the study. The magnetic property used was coercive force. A thermocoupie was used to measure the rise in temperature during a short period of cutting steel. It was shown that the method has reliability.
Durability of compression sintered hardmetals
H.Klassen, I.Ktibarsepp. (Tallinn Technical University, Tallinn, Estonia.)
Advanced migration sintering of hardmetals
The effects of compression sintering, sinter/HIP, on durability, wear resistance and mechanical properties of sintered hardmetals, used in metal forming, were investigated. It was reported that sinter/HIP is beneficial to those properties relevant to metal forming, toughness and adhesive wear resistance.
P.T.V.Kumar et aL (Widia (India) Ltd., Kamataka, India.)
Compositionally graded hardmetals were discussed with regard to benefits arising from g depleted and binder enriched surface layers and in particular N gradients. Studies of activated migration sintering were described with process conditions considered in respect of migration of Ti and Ta. Increased service life was outlined.
Influence of chromium, titanium and tantalum carbides on corrosion resistance of cemented carbides
A.Lackner et aL (Plansee Tizit GmbH, Reutte, Austria.) Corrosion resistance of WC-Co, with additions of Cr2C3, TiC or TaC, was
Fatigue properties of sintered steels - a review
A.Lawley et al. (Drexel University, Philadelphia, USA.) Material factors affecting the microstruclure of sintered steels were identified. Interaction between materials parameters and process conditions were reviewed in relation to microstructural features and attendant fatigue properties. The structural entities were examined in relation to aspects of fatigue such as high and low cycle fatigue, cracks, notch sensitivity and fatigue ratio. Guidelines for optimisation of material and process parameters were established in relation to fatigue life of PM steels.
Effects of cobalt, niobium and titanium on PM high-speed steels
J.Dagmar et aL (Siovak Academy of Sciences, Ko ice, Slovak Republic.) It was reported that M2 high speed steels, with additions of Co, Nb or Ti, had been produced by atomisation in N, to add N to the steel. Consolidation was by HIP followed by hardening and tempering. Microstructures and mechanical properties were characterised, in particular size and distribution of carbide phases. Co conferred the best properties from the elements added.
Use of microaUoying to increase mechanical properties of sintered structural steels
M.Orban, A.Palfalvi. (University of ClujNapoca, Cluj-Napoca, Romania.) It was noted that microalloying is of interest in production of sintered high-strength, low-alloy steels and that some difficulties may be encountered. The paper reviewed technological aspects of microalloying and proposed some possible PM processing routes.
Dimensional changes during sintering of a steel with additions of boron and carbon
T.Pieczonka et aL (University of Mining and Metallurgy, Krakow, Poland.) The widespread use of AstaloyCrM prealloyed powder for making steel components was noted. For precision parts accurate control and uniformity of dimensions is essential. A study of dimensional changes during processing was described. B and C were added to the steel powder either as elements or as B4C. Dimensional changes were studied by dilatometry. The results were presented and discussed.
Dimensional changes in steels with additions of manganese, molybdenum and carbon
S.C.Mitcheit et al. (University of Bradford, Bradford, UK.) Two types of Fe powders, in proportions 3:1, 1:1 and 1:3 were used to prepare steels with 0, 0.85 or 1.5wt%Mo, 3%Mn and 0.6%C. Sintering, in H-25vol%N, was investigated, by dilatometry, at 1150°C and 1280°C. Cooling was at rates up to 30degC.min-1 to control sinter hardening effects. Dimensional changes depended on Fe powder mixture and on the alloy additions. Mixtures for the