Control of martensite variants by magnetic field and giant magnetic field-induced strain in Fe-Pd ferromagnetic shape memory alloys

Fe-Pd 铁磁形状记忆合金中磁场和巨磁场诱导应变对马氏体变体的控制

基本信息

批准号：
15560608
负责人：
FUKUDA Takashi
金额：
$ 2.37万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

Recently, ferromagnetic shape memory alloys have attracted considerable attention because some of them show a giant magnetic field-induced strain of several percent in association with rearrangement of martensite variants. Until now, we have reported that Fe-31.2(at%)Pd alloy exhibits a giant strain of about 3% by the application of magnetic field. Since the giant field-induced strain can be obtained only in the FCT martensite state, it is very important to raise the martensitic transformation temperature. In this study, we first investigated the effect of third elements on the FCT martensitic transformation temperature. As a result, we found that when the FCT transformation temperature is increased, the BCT transformation temperature also increases. The BCT martensite is not suitable for the magnetic field-induced strain and the transformation should be avoided for obtaining good properties. Then, we investigated the most suitable composition at which the FCT transformation temperatur … More e is highest in the Fe-Pd binary system. As a result we found that when Pd content is lower than 30at%, BCT martensite appear in addition to FCT martensite, and the single FCT phase condition is obtained for alloys with Pd content of 30at% and more. We tried to grow a single crystal of Fe-30at% Pd alloy, and found that the composition of specimen varies largely because of a large difference between solidus and liquidus lines at this composition. In order to reduce the segregation introduced during the growing process, we kept the specimen at a temperature just below the melting point for several days, and we succeeded to obtain a homogeneous single crystal whose FCT transformation temperature is close to the room temperature. By using this single crystal, we confirmed that the rearrangement of martensite variants occurs by the application of magnetic field. Furthermore, we measured magnetocrystalline anisotropy constant and twinning stress of an Fe-31.2Pd alloy in a wide temperature range. Using these results, we explained the mechanism of magnetic field-induced strain in ferromagnetic shape memory alloys. Less

最近，铁磁形状记忆合金引起了相当大的关注，因为其中一些铁磁形状记忆合金表现出与马氏体变体重排相关的几个百分点的巨大磁场感应应变。到目前为止，我们报道了 Fe-31.2(at%)Pd 合金表现出这种现象。由于只有在FCT马氏体状态下才能获得约3%的巨应变，因此提高马氏体转变温度非常重要。研究中，我们首先研究了第三种元素对FCT马氏体相变温度的影响，结果发现，当FCT相变温度升高时，BCT马氏体相变温度也会升高。为了获得良好的性能，应避免诱发应变和转变。然后，我们研究了 Fe-Pd 二元体系中 FCT 转变温度最高的最合适的组成。结果我们发现，当 Pd 含量为低于30at%时，除FCT马氏体外，还出现了BCT马氏体，并且对于Pd含量为30at%及以上的合金，获得了单FCT相条件。我们尝试生长Fe-30at%Pd合金的单晶，发现：由于该成分的固相线和液相线之间存在较大差异，因此样本的成分变化很大。为了减少生长过程中引入的偏析，我们将样本在略低于熔点的温度下保存了几天。我们成功地获得了FCT转变温度接近室温的均质单晶，通过使用该单晶，我们证实了通过施加磁场会发生马氏体变体的重排。利用这些结果，我们解释了铁磁形状记忆合金中磁场诱导应变的机制。