Temperature-dependent stable phase domains of Zr-C-N (Zr-ZrC-ZrC0.96-Zr(C1-xNx)-ZrN, x=0.1-0.9) systems from ab initio calculations and experimental results

Despite the importance of ZrC, ZrN, and their intermediate solid solutions, the temperature-dependent phase stability of the Zr-C-N system has not previously been determined precisely. This work reports these phase stabilities determined experimentally and using ab initio calculations within the quasi-harmonic approximation. Special quasi-random structure models and supercell models with random substitution were used to mimic the random atomic distribution of C and N in the sublattice of Zr(C1-xNx) solid solutions. The results indicated that volume and high-temperature entropy changes are important to determine the free energy of the solid solutions and that moderate temperatures (similar to 1500-2000 K) were needed to synthesize Zr(C1-xNx) solid solutions. The calculated stable phase domains were then successfully produced. Our results clarify the synthesis and stable phase prediction of the Zr-C-N system under certain external conditions, and they will help broaden the applicability of ZrC, ZrN, and their solid solution phases. (C) 2016 Elsevier B.V. All rights reserved.