Tuning structure, mechanical properties, and oxidation resistance of (Nb, Ta)C1-y solid solution powders via the dissolution-precipitation process

Abstract

The formation of (Nb, Ta)C1-y solid solution powders via annealing NbC, TaC, and Co mixed powders at 1300 °C, 1500 °C, and 1900 °C in inert atmospheres was governed by the dissolution-precipitation mechanism, which was verified by the thermodynamic calculation. Only when the annealing temperature above 1500 °C can lead to the formation of homogeneous (Nb, Ta)C1-y powders and further modify not only the morphology from microcuboids with distinct edges and corners to a rounded shape at 1900 °C but also the carbon vacancy concentration from 0.08 to 0.02. Thermally stable (Nb, Ta)C1-y solid solution particles could achieve good comprehensive performance with the balance between mechanical properties and oxidation resistance by tuning the Nb/Ta ratio. In specific, TaC helped to enhance the oxidation resistance of (Nb, Ta)C1-y even compared with monocarbides, whereas the addition of NbC improved hardness and Young's modulus. Apparently, the presence of carbon vacancy could further increase the hardness.