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

本研究的目的在于发展多功能感测/致动材料，应用于复杂、小型机器人及微机械。铁磁形状记忆合金（FSMA）是一种对磁场快速响应的新型驱动器材料，其马氏体变体在外加磁场作用下发生重排而产生巨大的应变，而热弹性形状记忆合金对热响应较慢。为了获得具有良好织构控制的FMSA，对Fe-Pd，Fe-Pt，Heusler型Co_2NiGa和Fe-Ga合金进行了快速凝固处理。虽然单晶和大块样品在室温下只有马氏体相，快凝薄带在373 K时的巨磁致伸缩系数分别为1800（Fe-29.6at%Pd）和420（Fe-23at%Pt）。其原因是带状组织是由晶粒尺寸为1 ~ 3μm的强[100]取向柱状组织形成的。特别是1μm左右的晶粒由30- 40 nm厚的精细层状结构组成。这些纳米尺度的层平行于柱状结构，这是应力诱导马氏体孪晶。（2）Co_2NiGa合金：通过快速凝固，使Heusler型Co_2NiGa和低温下表现出巨磁致伸缩的Ni_2MnGa形成FSMA。在350 ~ 400 K温度范围内，薄带样品具有较大的磁致伸缩和良好的形状回复。3）Fe-17at%Ga合金：具有300 ppm大磁致伸缩的单晶体是非常脆的。快速凝固的薄带具有延展性，并表现出200 ppm的大的磁致伸缩性。

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.