A first-principles-calculation exploration of ternary borides as potential alternatives to WC-Co

Abstract

To find high-performance ternary borides as the hard phase of the cermets, first-principles calculation was applied to systematically investigate the structure, mechanical, electronic and thermal properties of 26 ternary borides MⅠxMⅡBx (x = 1 or 2). The phase stability and mechanical properties were evaluated by formation enthalpy and elastic constants. Debye temperatures were calculated to study the thermal conductivity, and the hardnesses of the candidates were predicted via the overlap populations calculation and hardness model. The results show that all the candidates possess thermodynamic and mechanical stability. Most of the MⅠxMⅡBx (x = 1 or 2) exhibit a better ductility than WC, except Ta2FeB2, Mo2MnB2, Nb2CrB2, Nb2FeB2 and Ti2ReB2. Moreover, sorted from high to low, Nb2CrB2, Mo2CoB2, W2MnB2, Mo2FeB2, Ti2ReB2, NbFeB, MoCoB, Mo2NiB2, Nb2FeB2, and Mo2NbB2 have a larger Debye temperature than WC. All the candidate ternary borides exhibit a lower hardness than WC, with the maximum hardness of 26.3 GPa for MoCoB. The analysis of electronic properties indicates that all the MⅠxMⅡBx (x = 1 or 2) exhibit metallic, ionic and covalent hybrid properties. The calculated results are expected to provide guideline for developing ternary boride-based cermets or coating materials that may replace WC-Co cermet.