A deep insight of re-entrant martensitic transformation mechanism in Co2Cr(Ga,Si) shape memory alloys

Co 2 Cr(Ga,Si) shape memory alloys have a wide application temperature range due to the unique re-entrant martensite phase transformation (RMT) behavior. Nevertheless, the microscopic mechanism of RMT remains elusive and unsystematic. The heart of this investigation lies the comprehensive exploration of phase stability, phase transformation path, and martensite slip direction during RMT from martensite (D0 22 -PM) to austenite (L2 1 -FM). In this work, we systematically investigate the re-entrant martensitic transformation of Co 2 Cr(Ga,Si) SMAs using first-principles methods for the first time. Firstly, the density of states (DOS) calculation indicates that the stability of L2 1 -FM is higher than D0 22 -PM. The charge density calculation further indicates that the bonding strength between Co atoms and Cr (Si) atoms in the L2 1 -FM phase is the highest. In addition, Fermi surface calculation further reveals that phase instability is due to the Fermi surface nesting caused by electron-phonon coupling. Moreover, the minimum energy path was calculated by the G-SSNEB method for the first time, which indicates the RMT can occur. Finally, the calculation of the elastic constants indicates that RMT is caused by the crystal plane slip of the D0 22 -PM phase along the <110> direction. Our calculations provide the electronic-level and thermodynamic mechanism for RMT of Co 2 Cr(Ga,Si) alloy and shed some light on the revelation of the phase transformation mechanism. • The re-entrant martensitic transformation mechanism of Co 2 Cr(Ga,Si) alloy has been studied systematically for the first time. • The Fermi surface of Co 2 Cr(Ga,Si) SMAs was calculated for the first time. • The minimum energy path of Co 2 Cr(Ga,Si) alloy is studied by G-SSNEB method for the first time,