铁磁形状记忆合金Ni-Mn-Ga单晶的马氏体孪晶再取向应力应变行为

MARTENSITIC TWINS REORIENTATION AND STRESSSTRAIN BEHAVIOR OF FERROMAGNETIC SHAPE MEMORY ALLOYS Ni-Mn-Ga SINGLE CRYSTALS

采用定向凝固区熔法制备了铁磁形状记忆合金Ni53Mn23.5Ga23.5,Ni54Mn23Ga23和Ni50Mn27Ga23晶体.用线切割切取5 mm×5 mm×6 mm的长方体单晶,X射线极图法测定单晶体的生长方向与[100]方向相差小于5°.沿单晶试样的3个边分别进行压缩实验,研究马氏体孪晶再取向应力应变行为.结果表明,沿单晶生长方向为孪晶再取向最有利方向,孪晶再取向应力最小,仅为3-7 MPa.压缩能有效地提高马氏体变体的有序化和择优化,形成近单变体状态.

Ferromagnetic shape memory alloys Ni53Mn23.5Ga23.5, Ni54Mn23Ga23 and Ni50Mn27Ga23 single crystals were prepared by zone-melting unidirectional solidification. The orientations of the cut single crystals were determined by X-ray diffraction method. The Ni-Mn-Ga crystal growth direction is along [100] with the deviation less than 5degrees. The martensitic twins reorientation process was detected by the stress-strain curves. The compression experiments along different directions were performed, respectively. The results show that the compression improves the texture of favorable martensitic variants and turns them into a single martensitic variant by martensite reorientation.