Diffusion controlled early-stage L1₂-D0₂₃ transitions within Al₃Zr

Antiphase boundary (APB) in Al₃Zr was regarded to play an important role in the L1₂-D0₂₃ phase transition, the formation of which has long been explained through the shearing/slipping mechanism. Herein, the detailed atomic structures of conservative {100} APBs within L1₂-Al₃Zr particles forming at the early-stage of L1₂-D0₂₃ transition in an Al-Zr alloy were systematically studied by high angle annual dark-field scanning transmission electron microscope (HAADF-STEM). As a strong evidence of diffusion-limited phase transformation process, significant de-ordering of atoms in APBs and the neighboring atomic planes have been found. By analyzing the two possible pathways, it is suggested that L1₂-D0₂₃ phase transition has been achieved through a diffusion mechanism, instead of shearing mechanism while the formation of APB is an intermediate stage of the phase transition process. First principles density functional theory (DFT) reveals that the formation of APBs and subsequent phase transition are energetically favorable, which provide the driving force for diffusion.