Pressure Induced Disorder-Order Phase Transitions in the Al4Cr Phases

Abstract

An ordered ω-Al4Cr phase synthesized recently by a high-pressure sintering (HPS) approach was calculated to be stable by density function theory (DFT), implying that high pressure can accelerate the disorder-order phase transitions. The structural building units of the ω-Al4Cr phase as well as the non-stoichiometric disordered ε-Al4Cr and μ-Al4Cr phases have been analyzed by the topological “nanocluster” method in order to explore the structural relations among these phases. Both the ε-and μ-Al4Cr phases contain the typical Macky or pseudo-Macky cluster, and their centered positions were all occupied by Cr atoms, which all occupy the high-symmetry Wyckoff positions. The mechanism of the pressure-induced disorder-order phase transitions from the ε-/μ-Al4Cr to the ω-Al4Cr phase has been analyzed. and the related peritectic and eutectoid reactions have been re-evaluated. All results suggest that the stable ω-Al4Cr phase are transformed from the μ-Al4Cr phase by the eutectoid reaction that is accelerated by high-pressure conditions, whereas the ε-Al4Cr phase should form by the peritectic reaction.