Pressureless liquid-phase sintered TiC x -NiTi/Ni cermets

Abstract

Abstract TiC 0.7 -NiTi and TiC 0.95 -Ni cermets with 10, 20 and 30 vol% binder content were prepared by pressureless liquid-phase sintering. The shrinkage behavior and liquid forming temperature of TiC 0.7 -NiTi powder compacts were investigated to determine the optimum sintering temperature (1380 °C) and dwell time (60 min). The microstructure of the sintered cermets was characterized and correlated to the measured mechanical properties (hardness, fracture toughness, strength and E-modulus). The TiC x stoichiometry of the TiC 0.7 -NiTi cermets was modified by the addition of TiH 2 powder to the TiC 0.95 +Ni 49.4 Ti 50.6 starting powder mixture, and a pure austenite NiTi binder phase was obtained. The carbide and binder phase displayed a homogeneous elemental distribution in the TiC 0.7 -NiTi and TiC 0.95 -Ni cermets. The differences in grain size, contiguity and binder mean free path length of the TiC 0.7 -NiTi and TiC 0.95 -Ni cermets were correlated to the measured wetting angle between binder and carbide phases at 1380 °C. The Ni binder showed a brittle fracture, whereas the NiTi binder fractured in a ductile way. The hardness and E-modulus of the TiC 0.7 -NiTi cermets were lower than for the corresponding TiC 0.95 -Ni equivalent, whereas the fracture toughness and bending strength were significantly higher.