Isothermal Phase Relationships in the Nickel-rich Region of the Nickel-Titanium-Oxygen System

In order to study fundamentally the influences of oxygen on the properties of TiC-base cermets, the phase relationships of the Ni-Ti-O system, which is a part of the four ternary systems constituting the Ni-Ti-C-O quaternary system, were determined at 1000°C (in a solid state) and at about 2000°C (in a liquid state) mainly in the region of less than 50 at % Ti.Even in the molten state at 2000°C or above, the oxide-metal phase separation was observed over a wide composition range, and the mutual solubility scarcely changed with temperature. At 1000°C, a nickel solid solution (γ-phase) was in equilibrium with Ti2O3, Ti3O5, Magneli phases, TiO2, NiTiO3 and NiO in turn as the titanium content decreased. The solubility of oxygen in the γ-phase was minimum at about 4 at% Ti.