Evolution of ordering in TiV-M (M = Cr, Nb, Mo, Ta) medium entropy alloys: A combinational study of cluster expansion and Monte Carlo simulations

Combined with density functional theory, cluster expansion, and Monte Carlo simulation, the ordering evolution, phase stability, microscopic structures, and mechanical properties of body-centered cubic TiV-M (M = Cr, Nb, Mo, Ta) medium entropy alloys are investigated. The disorder-order transition temperatures and phase transitions induced by the evolution of atomic chemical ordering for these alloys are determined. The observed phase segregation or random solid solutions in these alloys are consistent with some available theoretical and experimental reports. The localized chemical concentration fluctuations caused by segregation substantially enhance the yield strength. Notably, the pronounced enhancement of yield strength of TiVCr in local chemical ordered structure over random solid solution may be attributed to the large atomic size mismatch and the localized B2-phase formation. This work provides a temperature-dependent atomic structural landscape for TiV-M MEAs, and would provide insights for designing medium and high entropy alloys.