AN INVESTIGATION OF THE STRUCTURAL AND MAGNETIC TRANSITIONS IN Ni-Fe-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS
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The phase-field method has been successfully employed during the past ten years to simulate a wide variety of microstructural evolution in materials. Phase-field computational models describe the microstructure of a material by using a set of field variables whose evolution is governed by thermodynamic functionals and kinetic continuum equations. A two dimensional phase-field model that demonstrates the ferromagnetic shape memory effect in Ni2MnGa is presented. Free energy functionals are based on the phase-field microelasticity and micromagnetic theories; they account for energy contributions from martensite variant boundaries, elastic strain, applied stress, magnetocrystalline anisotropy, magnetic domain walls, magnetostatic potential, and applied magnetic fields. The time-dependent Ginzburg-Landau and Landau-Lifshitz kinetic continuum equations are employed to track the microstructural and magnetic responses in ferromagnetic shape memory alloys to applied stress and magnetic fields. The model results show expected microstructural responses to these applied fields and could be potentially utilized to generate quantitative predictions of the ferromagnetic shape memory effect in these alloys.
- Doctoral Dissertations