The liquid phase sintering mechanisms of Cr-containing Mo2NiB2 base hard alloys were studied for Ni-6mass%B-58.6mass%Mo-(0, 10)mass%Cr compositions. A fine composite microstructure of a M3B2 hard phase and a Ni binder phase was formed from the powders of MoB, Ni, Mo and Cr by a reactive sintering process with a liquid phase. During the solid state sintering stage, there are two reactions of boride formation. First, orthorhombic M3B2 was formed in the compact by a reaction of 2MoB+Ni=Mo2NiB2. Second, orthorhombic M3B2 transformed to tetragonal M3B2 prior to the liquid formation. During the second stage above 1313K, a quasi-eutectic reaction between the M3B2 hard phase and the Ni base binder phase formed a liquid phase, which resulted in considerable densification of the compact.
The microstructures of the hard alloys at various sintering stages were also investigated.
