Micromechanical modeling of stress–strain behaviors with intermartensitic transformation in NiFeGa alloys

Magnetic shape memory alloys (MSMAs) NiFeGa are reported as good alternatives to Ni2MnGa for their better mechanical behavior. Experimental data show its multistage transformation behavior. In spite of the recent progress in the development of material characteristics, no theoretical model has been developed to calculate the stress–strain behaviors of NiFeGa alloys. A model based on the micromechanical and the thermodynamic theory is presented for such a purpose. In the first plateau stage, the material is modeled as a three-phase composite, and a two-phase system for the second plateau stage. The end of the first plateau stage is considered as the origin of the second one. The kinetic equation is established in terms of the thermodynamic driving force derived from the reduction of Gibbs free energy of MSMA. The nonlinear and hysteretic strain response of NiFeGa is investigated under tensile load. The theoretical results are found to be in good agreement with experimental data.