Crystallographic insights into diamond-shaped 7M martensite in Ni-Mn-Ga ferromagnetic shape-memory alloys
Crystallographic insights into diamond-shaped 7M martensite in Ni-Mn-Ga ferromagnetic shape-memory alloys
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Ni-Mn-Ga 铁磁形状记忆合金中金刚石形 7M 马氏体的晶体学见解
DOI：
10.1107/s2052252519010819
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发表时间：
2019
期刊：
影响因子：
3.9
通讯作者：
Zuo Liang
中科院分区：
文献类型：
--
作者：
Li Zong Bin;Yang Bo;Zhang Yu Dong;Esling Claude;Zhao Xiang;Zuo Liang
对于heusler型Ni-Mn-Ga铁磁形状记忆合金，马氏体变体的结构是通过场致变体重定向获得较大磁性形状记忆效应的决定性因素。基于空间分辨电子背散射衍射技术，研究了多晶Ni53Mn22Ga25合金由奥氏体向七层调制（7M）马氏体转变的显微组织演变过程。结果表明，晶粒内部形核导致在母体奥氏体基体内形成菱形7M马氏体。这种金刚石微观结构通过四个侧习惯面协调向外移动的各向同性扩展进一步生长，随后是i型孪晶对向前扩展的各向异性延伸。提出了一种两步生长模型来描述7M马氏体的具体形貌和结晶学。此外，习惯面具有台阶结构，{10 1}a平面为阶地，{10 1}a平面为台阶。从最小相变总应变的角度分析了马氏体相变的特征组合和自调节机制，并根据实验确定的两相取向关系构建了变形梯度矩阵。本研究结果可加深对铁磁形状记忆合金马氏体相变过程中特殊马氏体组织的认识。
For Heusler-type Ni–Mn–Ga ferromagnetic shape-memory alloys, the configuration of the martensite variants is a decisive factor in achieving a large magnetic shape-memory effect through field-induced variant reorientation. Based upon the spatially resolved electron backscatter diffraction technique, the microstructural evolution associated with the martensitic transformation from austenite to seven-layered modulated (7M) martensite was investigated on a polycrystalline Ni53Mn22Ga25 alloy. It was clearly shown that grain interior nucleation led to the formation of diamond-shaped 7M martensite within the parent austenite matrix. This diamond microstructure underwent further growth through an isotropic expansion with the coordinated outward movement of four side habit planes, followed by an anisotropic elongation with the forward extension of a type-I twin pair. A two-step growth model is proposed to describe the specific morphology and crystallography of 7M martensite. In addition, the habit planes were revealed to possess a stepped structure, with the {1 0 1}A plane as the terrace and the {0 1 0}A plane as the step. The characteristic combination of martensite variants and the underlying mechanism of self-accommodation in the martensitic transformation have been analysed in terms of the minimum total transformation strain, where the deformation gradient matrix was constructed according to the experimentally determined orientation relationship between the two phases. The present results may deepen the understanding of special martensite microstructures during the martensitic transformation in ferromagnetic shape-memory alloys.