Martensitic transformation mechanism of Mg-Sc lightweight shape memory alloys

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