Martensitic Transformation Mechanism of Mg-Sc Lightweight Shape Memory Alloys

Abstract

Mg-Sc alloys are known as novel and promising lightweight shape memory alloys, which have outstanding performance. Yet, a precise understanding of the microscopic picture and interactions governing the martensitic transformation remains elusive. In this study, we systematically investigate the martensitic transformation of Mg-Sc alloys using first-principles methods. The result of G-SSNEB confirms that no energy barrier inhibits the martensitic transformation. We show that the bcc structure of Mg₂₆Sc₆ is dynamical instability at 0 K caused by electron-phonon coupling and Fermi surface nesting. Particularly, high-temperature stability of Mg₂₆Sc₆ was revealed for the first time using the TDEP method. Mg₂₆Sc₆ becomes dynamically stable above 175 K. The softening of the acoustic mode at Γ-R corresponds to two neighboring (1 0 1) planes moving towards each other, and the martensite phase forms. Our calculations provide the complete and atomic-level mechanism for Mg-Sc alloys and shed some light on the design of new LWSMAs.

Keywords: Shape memory alloys, Lightweight shape memory alloy, Martensitic transformation mechanism, Phonon instability, Mg-Sc alloy