Phase-field simulations of partial pseudoelastic stress-strain behavior and microstructure evolution of Ni-Mn-Ga

The partial pseudoelastic stress-strain behavior and the underlying microstructure evolution of Ni-Mn-Ga ferromagnetic shape memory alloy under different values of constant (assisted) magnetic field H and demagnetization factor N are studied by phase-field simulations. The results show that both H and Nfield (component of N parallel to H) have significant influence on the partial strain recovery in the compressive stress loading-unloading cycle, while Nstress (component of N parallel to the stress) only affects the formation of magnetic domains in the stress-preferred variant and has no influence on the strain recovery behavior. The recovered strain can be increased by raising H or reducing Nfield. Moreover, the range of H for the partial strain recovery increases with Nfield. It is shown that Ni-Mn-Ga exhibits the partial pseudoelasticity at moderate/high H under a large Nfield rather than just at low H as observed in existing experiments, demonstrating the significant influence of Nfield on the strain recovery behavior. The work reveals that both H and Nfield affect the strain recovery behavior through the effective magnetic field *Hfield (component of the internal magnetic field parallel to H) during the stress cycle. *Hfield decreases with the twin boundary motion during the reverse martensite reorientation and eventually becomes insufficient to trigger the twin boundary motion, which is responsible for the partial strain recovery.