Microstructure and oxidation behavior of Ti(C,N)-based cermets with in situ synthesized Ni3Al phase

Ni3Al phase was synthesized by in-situ reaction of Ni binder and AlN addition during liquid phase sintering. The microstructure and properties of the Ni3Al-containing Ti(C,N)-based cermets were investigated. The hardness of the cermet increased after addition of 2.5 wt%AlN due to the solid-solution strengthening effect of Ni3Al, and further addition of AlN yielded coarser core-rim grains and decrease of hardness. The transverse rupture strength declined rapidly after addition of 5 wt% AlN, which was attributed to the increase of porosity. After static oxidation at 900 °C, the mass gain of the cermet without AlN addition increased rapidly with oxidation time and followed a quasi-parabolic law. After addition of 2.5 wt%AlN, both mass gain and oxidation rate declined obviously, and the oxidation kinetics curve still presented a quasi-parabolic law. The mass gain increased slightly after addition of 5.0 wt% AlN, and larger addition of AlN up to 7.5 wt% resulted in the changing of oxidation kinetics to a linear law. At 900 °C, the Ti(C,N)-based hard phase and Ni binder phase in the cermet all suffered serious oxidation. The Ti(C,N)-based hard phase was mainly oxidized to TiO2, and Ni binder transformed to complex oxides such as Ni3TiO7 and NiTiO3. As for the cermet with 2.5 wt% AlN addition, the oxidation behavior showed much difference. Though Ni3Al- containing binder was oxidized to Ni3TiO7 and NiAl2O4, both the intermediate oxidation product of Ti(C,N) hard phase, i.e. Ti(O0.19,C0.53,N0.32) and Ni3Al remained stable after dwelling for 4 h. The oxide layer on the cermet with 2.5 wt% AlN addition appeared to be dense and protective, which inhibited the diffusion of oxygen into the cermet and improved the oxidation resistance of the cermets.