SINTERING OF M3/2 HIGH-SPEED STEEL MODIFIED BY ADDITIONS OF COPPER PHOSPHIDE AND TITANIUM-BASED CERAMIC COMPOUNDS

Composite materials were produced by adding TIC, TiN, or TiO2 particles to a base mixture of AISI M3/2 high speed steel powder containing 7 wt-% Cu3P powder and 0.5 wt-% graphite. The composites were sintered in the temperature range 1140-1170 degrees C, by an activated sintering mechanism that involved an iron phosphide rich liquid phase. Sinterability increased in the order TiO2 < TiN < TiC for the composites, which was identical to the wettability of the ceramic particles by the liquid phase formed during the sintering process. Ceramic particles were well bonded to the matrix in the sintered microstructures, with a precipitation of MC type carbides from the liquid phase along the ceramic/matrix interfaces. The composites containing TiO2, however, were very porous and the hardness of the particles decreased significantly due to their interaction with the matrix, making these additions unsuitable.