内应力对Mn_2NiGa铁磁形状记忆合金的结构、相变和磁性能的影响

Effect of internal stress on sructure,martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Mn_2NiGa

通过施加压应力的方法,在铁磁形状记忆合金Mn_2NiGa中引入残留内应力,研究了内应力对Mn_2NiGa材料的结构、相变和磁性能的影响.研究发现,加压过程使材料发生了塑性形变,在材料内部引入了大量的位错缺陷.卸载后保留的位错缺陷在材料中造成了残留的内应力,导致了马氏体相变温度大幅度提高,使原本室温下的母相转变成了马氏体相.测量到导致样品转变成马氏体的阈值压应力为1.0GPa.加压形成的马氏体中的残留内应力将矫顽力从低于50 Oe提高到350 Oe.残留内应力在730 K的热处理中由于位错缺陷的消失而得以消除,样品实现了马氏体逆相变.如此高的逆相变温度使得Mn_2NiGa马氏体的居里温度测量成为可能,获得了530K的数值.

The structures,the martensitic transformations and the magnetic properties of ferromagnetic shape memory alloy Mn_2NiGa with the loading and the unloading of the external compressive stress are investigated.The plastic deformation occurring during the stressing causes a high level of dislocation defects existing in the sample.The residual internal stress results in a significant increase of the reversed transformation temperature.The threshold value of compressive pressure for causing the completely martensitic transformation at room temperature is identified to be 1.0 GPa based on the experimental measurements of XRD and magnetic coercivity. The coercivity of the martensitic phase increases from 50 Oe to 350 Oe due to the application of the external stress up to 2.0 GPa.It is also observed that the reversed martensitic transformation occurrs,when the sample is treated by heating up to about 730 K.This is attributed to the elimination of the dislocation by the annealing effect.Such a high reverse martensitic transformation temperature allows the measurement of the Curie temperature of martensitic phase and the obtained value is 530 K.