A MODEL OF PHASE TRANSFORMATION KINETICS FOR FERROMAGNETIC SHAPE MEMORY ALLOYS

摘要

As a new kind of magnetic smart material,ferromagnetic shape memory alloys(FSMAs) can be controlled not only by a thermal field and/or a stress field,but alsoby a magnetic field.The strain of FSMAs in the magnetic field is induced for thephase transition or reorientation in material.Based on the energy dissipation ofthermodynamics on the twinned interface of martensite variants,a theoretical modelis suggested in the present paper to describe the behavior of phase transformation ofFSMAs.Considering a specific free Helmholtz energy,a generalized thermodynamicdriving force for martensitic variant reorientation is introduced into the model.Mass-change of martensite is introduced by considering the thermodynamic fluxassociated with the driving force.The thermodynamic equations of phasetransformation are obtained on the assumptions that a threshold function dependingon driving force reaches a certain value when the dissipation reaches a maximum forthe process are employed.Finally,the transformation kinetics model is reduced to theI-D condition and some numerical simulations are carried out.The results of themass fraction of martensitic variant depending on the driving force,stress and strain,as well as magnetic field are obtained.