Fabrication of Anion-Substituted ZrN_1-xC_x and TaN_1-xC_x Ceramics

Abstract

An attempt was made to fabricate ZrN_1-xC_x and TaN_1-xC_x (0≤x≤1.0) ceramics without additives in order to obtain highly pure and dense polycrystalline anion-substituted materials by high pressure reaction hot-pressing.
Compositional and temperature dependences of Vickers microhardness, fracture toughness and thermal conductivity of ZrN-ZrC and TaN-TaC systems were examined. The compositional dependence of lattice constant of ZrN_1-xC_x obeyed Vegard's law. The full solid solution of TaN_1-xC_x could not be synthesized, but a partial solid solution system with the composition range of 0.3≤x≤1.0 was prepared. The microhardness of ZrN_1-xC_x decreased with increasing nitrogen content, but the microhardness of TaN_1-xC_x increased with nitrogen content. The fracture toughness of ZrN_1-xC_x decreased linearly from 4.6 to 3.3MN/m^3/2 with increasing mole fraction X. Little change in K_Ic of TaN_1-xC_x was observed at the range of 0.3≤x≤1.0 and the value of K_Ic was 4.5MN/m^3/2. The thermal conductivity of ZrN_1-xC_x at room temperature decreased continuously with increasing X. But the thermal conductivity of TaN_1-xC_x decreased rapidly with increasing carbon content and reached the minimum value at TaN_0.5C_0.5, and then increased with increasing amount of carbon.