Synthesis of (Ti, W, Mo, Ta, Cr)(C, N) solid solution powders by carbothermal reduction-nitridation in an open system

Abstract

The single-phase (Ti, W, Mo, Ta, Cr)(C, N) solid solution powders were successfully synthesized from oxides by carbothermal reduction-nitridation (CRN) in an open system. It was investigated in this paper that the effects of synthesizing temperature and isothermal time on the C/N ratio, free carbon content, oxygen content, as well as the morphology of the synthesized powders. Powder X-ray diffraction results show the single-phase solid solution could be prepared with the minimum temperature at 1600 °C for 4 h. The phase transformations of titanium compound from raw material to final products during the whole process were as follows: Anatase-TiO2 → Rutile-TiO2 → Ti4O7 → Ti3O5 → Ti(C, N). The morphological and microstructural investigations indicate that Ti, W, Mo, Ta and Cr were homogeneously distributed in the solid solution powders. Ultimately, the homogeneously distributed single-phase (Ti, W, Mo, Ta, Cr)(C, N) powders with an average size of ∼2 μm were obtained by heating the reaction system at 1800 °C for 4 h. The chemical composition of the solid solution with the optimal process could be drawn as (Ti0.882, W0.068, Mo0.030, Ta0.015, Cr0.005)(C0.72, N0.28), in which the C/N ratio is close to 7/3, and the oxygen and free carbon contents are both less than 0.3 wt.%. In addition, the obtained multi-solid solution powders were also used in the preparation of (Ti, M)(C, N)-based cermets to show its high potential in future applications.