Grain Growth in Ti(C,N)-Based Cermets During Liquid-Phase Sintering.

Growth behavior of Ti-based carbonitride ceramic grains in two high-Mo Ti(C,N)-based cermets with Ni and Ni-20Cr (wt %) binders was investigated during liquid-phase sintering under vacuum at 1410°C, using DSC, XRD, SEM, AEM, and EDS. Grain growth occurred primarily through two-dimensional nucleation and lateral growth. Most significantly, the grain growth kinetics followed the cubic law, which was controlled by the diffusion of dissolved mass through liquid Ni-based binder phase. However, when Ni-20Cr (wt%) was used as metallic binder, the inner rim of ceramic grains with the typical core-rim structure was seldom complete, and there were often some fine Ni-rich and Mo-rich speckles in their core. In Ni-rich and Mo-rich speckles, there were two kinds of microstructure: one consisted of Ni-based superlattice phase, and the other consisted of Ti-based carbonitride ceramic phase and unknown phases. The three-dimensional thermodynamic equilibrium shape of Ti-based carbonitride ceramic grains evolved from a {111}-faceted and round-edged octahedron to a {111}-faceted and sharp-edged octahedron. In addition, the grain growth rate increased, which was mainly attributed to that the decrease of solid/liquid transformation temperature of Ni-based binder phase led to the increase of the diffusion rate of dissolved mass through liquid Ni-based binder phase. [ABSTRACT FROM AUTHOR]