First-principles calculation of various phase transition in Al–Sc system

Abstract

Sc as one of the most important microalloying elements in advanced Al alloys has gained tremendous attentions in recent years. The newly identified Sc-rich clusters demonstrate new strengthening effect in Al alloys and thus entail a comprehensive understanding on their phase relationship. In this work, various phase transitions of binary Al–Sc system are systematically investigated by first-principles calculation together with cluster expansion. The results show the phase transition from FCC Al to HCP Sc bypass a BCC structure as a function of Sc concentration. The ordered BCC lattice experiences BCC to FCC, BCC to HCP and BCC to ω phase transitions through the Bain, Burgers and ω phase transition paths, respectively. The possibility of those phase transitions is evaluated from the calculated energy landscape along the transition paths. BCC to FCC and BCC to ω phase transitions are energetically more favorable in Al–Sc system. The bonding electron density and effective cluster interaction suggests the Al–Sc interactions play a key role in individual phase transition at different Sc concentration.