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MM: Fachverband Metall- und Materialphysik
MM 31: Postersitzung II
MM 31.42: Poster
Mittwoch, 16. März 2011, 17:15–18:45, P5
Phase-field Modeling of Twin Boundary Motion in Magnetic Shape Memory Alloys — •Christian Mennerich, Frank Wendler, Marcus Jainta, and Britta Nestler — Karlsruhe University of Applied Sciences, Karlsruhe, Germany
Magnetic shape memory (MSM) alloys have gained high interest in the last decade. As actuators, they provide fast response times and low energy costs in operation. When in the low temperature martensitic state, large recoverable strains (more than 6% in Ni2MnGa-based alloys) can be achieved in these ferromagnetic hard materials by controlling the motion of twin boundaries by applying an external magnetic field.
Using a multi-phase field model of Allen-Cahn type basing on a Helmholtz free energy density formulation, the microstructure rearrangement in Ni2MnGa is described. Order parameters, related to the different eigenstrains of the twin variants, describe their time-spatial evolution, depending on energy contributions for twin interfaces and bulk phase states (including micromagnetic and magneto-elastic energies). Assuming an isothermal setting below the Curie temperature and the martensitic start temperature, we can solve for the elastic displacement field (damped wave equation) and the volume averaged magnetization (Landau-Lifshitz-Gilbert equation using a geometric integration scheme). We show results of simulations of the reversible transformation process in single crystals, and we propose an extension of the model to polycrystalline settings. The coupled evolution of twin variants and magnetic domains is investigated in more detail, and the resulting magnetic domain structure is visualized.