Basic research of the influence of real structure on magnetic field induced strain (MFIS) in NiMnGa alloys - Magnetic field induced strain (MFIS) in textured polycrystalline ferromagnetic martensitic NiMnGa alloys

报道了NiMnGa单晶由于孪晶边界运动(TBM)而产生的磁场感应应变(MFIS)。这种行为是在低温马氏体相中发现的，它是在冷却时由约750°C有序的立方L21相形成的。MFI的先决条件是单轴磁各向异性和高度可移动的孪晶边界。这两个特征不仅与成分有关，而且与组织和显微组织有关。本项目的目标是建立在多晶NiMnGa中实现TBM微细离子注入的条件。所得结果将用于通过有效的制备路线来制备改进的磁力驱动执行器。随后，这项研究的结果将应用于新型合金系统，以进一步改进铁磁形状记忆元件。首先，将发展这种组合物的高织构大颗粒多晶样品的制备，据报道，这些样品可以通过TBM在单晶中显示微荧光。研究了定向凝固和变形后再结晶两种制备方法。然后，将建立处理这种多晶体以实现微FI的规则。根据初步研究，预计将有必要进行多步骤热机械和/或热磁处理(培训)。最后，确定了组织中的元素，这些元素分别促进了显微组织的形成。通过全面禁止核试验防止小额金融感染。这一步骤需要在优先计划SPP1239内进行更广泛的合作，这意味着将提供该项目的明确样本，以进行详细的结构表征。

Single crystals of NiMnGa are reported to show magnetic field induced strain (MFIS) due to twin boundary motion (TBM). This behavior is found in a low temperature martensitic phase, which forms from a cubic L21 phase ordering around 750 °C upon cooling. Prerequisites for MFIS are a uniaxial magnetic anisotropy and highly mobile twin boundaries. Both features depend not only on composition but also on structure and microstructure. The goal of the present project is to establish the conditions under which MFIS by TBM can be achieved in polycrystalline NiMnGa. The results will be used to prepare improved magnetically driven actuators by efficient preparation routes. Later, the results of this study will be applied to novel alloy systems to further improve ferromagnetic shape memory elements. At the beginning, the preparation of highly textured large grained polycrystalline samples of such compositions will be developed, which are reported to show MFIS by TBM in single crystals. Two routes of preparation will be studied, directional solidification and recrystallization after deformation. Then the rules to treat such polycrystals to achieve MFIS will be established. From preliminary studies it is expected that multi-step thermo-mechanical and/or thermo-magnetic treatments (training) will be necessary. Finally, the elements of the microstructure shall be identified, which promote resp. prevent MFIS by TBM. This step requires extended cooperation within the priority program SPP1239, which means that well defined samples of this project will be provided for elaborated structural characterization.