外磁场对Ni-Mn-Ga磁性形状记忆合金相变应变及显微组织的影响

Effect of external magnetic field on transformation strain and microstructure of NiMnGa magnetic shape memory alloy

研究了外磁场对Ni52Mn24.6Ga23.4(%,原子分数)单晶马氏体相变及其相变应变的影响,并对磁场增强相变应变的微观机制进行了探讨。研究结果表明无外加磁场时,NiMnGa合金发生马氏体相变时可产生约0.3%的收缩形变,沿单晶[100]方向施加外磁场,其相变应变随磁场的增加而呈近线性增加。当外磁场强度为6.37×105A/m时,应变量达到最大值(3.5%)。磁场作用下冷却形成的马氏体虽然孪晶亚结构不变,但自协作组态消失,并伴随有孪晶板条的增厚。磁场对马氏体相变应变的增强效应来自于磁场作用下的马氏体变体的择优取向。

The effect of external magnetic field on martensitic transformation and transformation strain of Ni52Mn24.6Ga23.4 (at%) single crystal were described, and the mechanism of enhancement of magnetic field on transformation strain was discussed. It was found that transformation strain is up to 0.3% without external field. With the increasing of magnetic field along the [001] direction transformation strain increases linearly. The maximum strain is 3.5% in 6.37×105 A/m field. Upon cooling to Mf temperature in magnetic field, the oriented martensite forms and the martensite bands become broad, while the substructure of martensite twins keeps unchanged. It was shown that the orientation of martensite variants in magnetic field enhances the transformation strain.