Ni-Mn-Ga铁磁合金7M马氏体形核与长大特性研究

Ferromagnetic Ni-Mn-Ga alloys, with the combination of thermoelastic martensitic transformation and magnetic-field shape memory effect, have attracted great attention as a novel class of smart materials. The configuration of martensitic variants represents a decisive factor for these alloys to achieve large strain output through magnetic-field-induced variant reorientation. However, due to the complexity of lattice modulation of Ni-Mn-Ga martensite and the limitations of traditional characterization techniques, there is a lack of the detailed information about local microstructural evolutions associated with the martensitic transformation that decides the final variant configuration. Especially, the intrinsic nature and the transformation route for the nucleation and growth of 7M modulated martensite remain unclear. To gain a deep insight into this key issue, this research proposal is dedicated to the crystallographic study on the nucleation and growth characteristics of 7M martensite in Ni-Mn-Ga alloys. Based on the spatially-resolved electron backscatter diffraction (EBSD) as well as in-situ microstructure observation, the crystallographic and morphologic characters of 7M martensite during nucleation and growth will be analyzed. The underlying mechanisms on the nucleation and growth of 7M martensite, the lattice deformation and the strain accommodation will be further revealed. Moreover, the crystallographic model depicting the martensitic transformation will be developed, which is expected to advance the martensitic transformation crystallography. Based on the above investigations, we will further explore effective methods to realize the modification of inter-variant interface configuration, which may offer guidance for the design and property optimization of novel magnetic field controlled functional materials.

Ni-Mn-Ga铁磁合金是近年来引起广泛关注的一类具备热弹性马氏体转变特征及磁控形状记忆性能的新型智能材料，其马氏体变体组态是磁场诱发马氏体再取向获取大磁致应变的关键因素。由于传统表征方法的局限及长周期调制马氏体超结构的复杂性，对于决定马氏体变体组态的马氏体相变微观组织结构演变过程的关键信息仍十分缺乏，特别是涉及7M马氏体的形核、长大路径及转变机制尚不清楚。本申请项目拟以EBSD取向分析技术为关键手段，结合原位微观组织观察，研究Ni-Mn-Ga铁磁合金7M马氏体形核与长大特性，在解析马氏体相变晶体学与组织形貌学特征的基础上，揭示马氏体的形核与长大机制，阐明马氏体相变的晶格变形及应变协调机理，构建马氏体相变过程晶体学理论模型；基于对7M马氏体变体组态及复合孪晶界面的认识，进一步探索调控马氏体界面分布的有效途径，以期为新型磁控功能材料的设计与性能优化提供支撑。

Ni-Mn-Ga铁磁合金是近年来引起广泛关注的一类具备热弹性马氏体转变特征及磁控形状记忆性能的新型智能材料，其马氏体变体组态是磁场诱发马氏体再取向获取大磁致应变的关键因素。由于传统表征方法的局限及长周期调制马氏体超结构的复杂性，对于决定马氏体变体组态的马氏体相变微观组织结构演变过程的关键信息仍十分缺乏，特别是涉及7M马氏体的形核、长大路径及转变机制尚不清楚。本项目以EBSD取向分析技术为关键手段，结合原位微观组织观察，研究了Ni-Mn-Ga铁磁合金7M马氏体形核与长大特性。在解析马氏体相变晶体学与组织形貌学特征的基础上，揭示了马氏体的形核与两阶段长大机制；提出根据马氏体相变取向关系构造变形矩阵的晶体学分析方法，阐明了马氏体相变的晶格变形、应变协调机理与自协调机制。基于对7M马氏体变体组态的认识，利用准原位EBSD测量，进一步解析了7M马氏体在应力场作用下的变体选择和变形机制。项目实施以来，共发表SCI期刊论文21篇。

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