Phase-field modelling of magnetically induced microstructure evolution in martensitic polycrystals

磁形状记忆(MSM)合金对外加磁场的磁力响应与材料中磁弹性域结构的耦合演化密切相关。因此，磁区演化的动力学路径在决定材料性能方面起着关键作用。基于相场模型的介观模拟可以为理解影响MSM效应的动态过程和主要物理量提供有价值的信息。因此，本项目的目标是开发一种新的相场模型和MSM合金的并行三维模拟器。模型公式包括弹性、磁性和弹磁自由能贡献以及不同的马氏体晶体结构。所考虑的二元Fe-Pd、Fe-PT和三元Ni-Mn-Ga合金的热力学数据和自由能将从SPP 1239的合作基团中交换。该框架应能够描述多晶和多孪晶显微组织的磁场诱导演化，具有不同孪晶界和成分的不连续组织的演化，晶粒长大(粗化)和磁驱动晶界运动的耦合过程，晶界和孪晶界扩散和偏析模式的耦合过程。

The magnetomechanical responses of magnetic shape memory (MSM) alloys to external magnetic fields are correlated with the coupled magneto-elastic domain structure evolutions in these materials. Hence, the kinetic pathways of the domain evolutions play a key role in determining the materials properties. Mesoscopic simulations based on phase-field modelling can provide valuable information to understand the dynamic processes and main quantities affecting the MSM effect. Therefore the aim of this project is to develop both, a new phase-field model and parallel 3D simulator for MSM alloys. The model formulation includes elastic, magnetic and elastomagnetic free energy contributions and different martensitic crystal structures. The thermodynamical data and free energies of the considered binary Fe-Pd and Fe-Pt and ternary Ni-Mn-Ga alloys needed to configurate the phase-field model will be exchanged from cooperating groups of the SPP 1239. The framework should be capable to describe the magnetic-field-induced evolution of polycystalline and polytwinned microstrüctures, of discontinuous structures with different twin boundaries and compositions, of the coupled process of grain growth (coarsening) and magnetically driven grain boundary motion, of grain- and twin-boundary diffusion and segregation patterns.