Sintering and evolution of microstructure in TiC-Ni3Al cermets

TiC-Ni3Al cermets are under development for application in diesel engines b ecause of their attractive physical properties and wear resistance. Powder compacts with intermetallic binder contents from 30-50v/o were fabricated b y pressureless sintering under vacuum followed by low gas pressure isostati c pressing. Increasing the Ni3Al content improved densification when using prealloyed powders, as expected. When the Ni3Al binder phase was formed by in-situ reaction synthesis of Ni and NiAl, densification decreased with hig her binder contents. The final microstructure consisted of a 'core-rim' str ucture with TiC cores surrounded by (Ti,W)C rims. In some cases, Ni and Al were also observed in the peripheral region of the rim structure. Grain siz es of the TiC increased with binder content and temperature. Preferred orie ntation of the Ni3Al binder phase was observed due to its large grain size, on the order of millimeters.