Pressureless Sintering of MoSi2 Materials

Various powder mixtures were prepared by a modified mechanical alloying technique. Starting from elemental Mo-, Si- and C-powders the influence of milling conditions on phase formation during the milling process and the subsequent heat treatment was investigated. Phase formation during sintering and sintering kinetics of activated starting mixtures were studied by differential scanning calorimetry (DSC), thermal graphimetry (TG), X-ray diffraction (XRD) and dilatometry. The results show that phase formation during milling or sintering strongly depends on milling conditions. Optimized powder mixtures of single phase and reinforced molybdenum silicides show high densities up to 98,5 % TD by pressureless sintering in various atmospheres. Full density is possible by post-HIP because the samples show only closed porosity. The microstructure was studied in dependence of sintering parameters. The level of impurities, i.e. C, O2 was determined. Hardness, fracture toughness and bending strength were measured for single phase and particle reinforced materials.