Criteria of predicting phase formation for MSi2-Type High-Entropy refractory metal silicides

Abstract

MSi2-type high-entropy refractory metal silicides (HERMS) have excellent oxidation resistance at medium and high temperatures due to high entropy effect, which is a promising ultrahigh temperature structural material. HERMS have two phase structures, C11b and C40, due to allotropic transformation. Compared to C40, C11b has better fracture toughness, but it is now difficult to synthesize single-phase C11b. The first-principle was used to systematically study phase formation ability of HERMS. Formation enthalpy (ΔHf), mixing enthalpy (ΔHmix) and mixing enthalpy difference (δmix) were calculated for 504 MSi2-type HERMS structures. δmix, VEC and ΔHmixC11b were identified to characterize and predict phase stability of MSi2-type HERMS, in which δmix is a decisive factor, and has general applicability and important guiding significance for material systems with allotropic transformation. The generalized criteria of predicting phase formation for MSi2-type HERMS were proposed. C11b phase formation criterion is VEC > 4.58, δmix < −0.05 eV/atom, ΔHmixC11b < −0.02 eV/atom. C40 phase formation criterion is VEC ≤ 4.58 and ΔHmixC11b > 0.09 eV/atom. Its accuracy was verified by experimental data to be 100%. This work is of great significance for composition design of HERMS and the further study of C11b-type HERMS.