Giant magnetostriction of ferromagnetic shape memory alloys with the grain boundary controlled by rapidly solidified method

本研究的提出是多功能传感器/驱动器材料的发展方向，对复杂的小型机器人和微型机械有一定的应用价值。铁磁形状记忆合金(FSMA)是一种新型的对磁场响应快的致动器材料，而热弹性形状记忆合金对热的响应较慢。铁磁形状记忆合金是一种新型的致动器材料，它是在外加磁场的作用下马氏体相的重新排列而产生的巨大应变。为了获得具有良好控制织构的FMSA，对Fe-Pd、Fe-Pt、Heusler型Co_2NiGa和Fe-Ga合金采用了快速凝固方法：1)Fe-29.6at%Pd、Fe-23at%Pt合金：虽然单晶和块体样品只在室温下才有马氏体相，但快速凝固薄带的巨磁致伸缩系数分别为1800(Fe-29.6at%Pd)和420(Fe-23at%Pt&Gt)；在~373K，薄带是由强[10 0]取向的柱状组织形成的，其晶粒尺寸为1~3μm，尤其是约1μm的晶粒由30~40 nm厚的细小层状结构组成。这些纳米层平行于柱状组织，为应力诱发马氏体孪晶。纳米级马氏体孪晶使相变温度提高到~373K.2)Co_2NiGa合金：为了发展FSMA，快速凝固Heusler型Co_2NiGa和在低温下表现出巨大磁致伸缩的Ni_2MnGa。在350~400K的温度范围内，带状样品具有较大的磁致伸缩和良好的形状恢复。3)Fe-17at%Ga合金：具有300ppm的大磁致伸缩的单晶是非常脆弱的。快速凝固薄带具有延展性，具有200ppm的大磁致伸缩性能。

The propose of this study as the developments of multi-functional sensor/actuator material, whish is useful as complex, small robots and micro-machines. Ferromagnetic shape memory alloys(FSMA), in which giant strain is caused by re-arrangements of the martensitic variants by applying magnetic field, are new type of actuator material rapidly responded to magnetic field, while, thermo-elastic shape memory alloys respond to heat slowly. In order to obtain the FMSA with good controlled texture, a rapidly solidified method was applied to Fe-Pd,Fe-Pt,Heusler-type Co_2NiGa and Fe-Ga alloys.1)Fe-29.6at%Pd,Fe-23at%Pt alloys : Although a single crystal and bulk samples have martensite phase only under room temperature, rapidly solidified ribbons exhibit giant magnetostnction of 1800(Fe-29.6at%Pd) and 420(Fe-23at%Pt> at〜373 K. The origin is due to that the ribbons are caused by strongly [100] oriented columnar microstructure with the size of grain, 1〜3μm. Especially, the grains of about 1μm size consist of fine layer-structure of 30-40nm thickness. These nano-scale layers are parallel to the columnar structure, which is stress-induced martensite twin. The nano-scale martensite twins make phase-transformation temperature increase to〜373 K.2)Co_2NiGa alloy : Heusler-type Co_2NiGa as well as Ni_2MnGa, which exhibits giant magnetostnction at low temperature, is rapidly solidified in order to develop a FSMA. The ribbon sample exhibits large magnetostnction and good shape recovery at temperature range of 350〜400K.3)Fe-17at%Ga alloy : a single crystal with large magnetostriction of 300ppm is much bnttle. The rapidly solidified ribbon has ductility and exhibits large magnetostnction of 200ppm.