Systematical investigation of field controrable shape memory alloys

在体心立方有序结构的Heusler合金中观察到了大的磁场感生应变，并用外加磁场引起的马氏体结构变量的重排解释了这一现象。这些材料作为潜在的磁致动器材料引起了人们的极大关注。我们系统地研究了具有磁性形状记忆效应的智能材料。1.金属间化合物MnCo_1-x&Gt；1-x&Gt；Ge(0.06[小于等于]x[小于等于]0.08)在300K左右发生无扩散热弹性马氏体相变，马氏体相以正交晶系TiNiSi型晶化，随温度升高转变为具有六方Ni2In型晶体结构的母体相。利用朗道热力学势对这些相变进行了热力学分析。2.得到了铁磁形状记忆合金Ni_&lt；50+x&gt；Mn_&lt；12.5&gt；Fe_&lt；12.5&gt；Ga_&lt；25-x&gt；的相图。随着x的增加，居里温度逐渐降低，马氏体相变温度T_M急剧升高，直到x=3.0，然后在x=5.5时达到380K。研究了新型铁磁形状记忆合金Ni_2Mn_&lt；1+x&gt；Z_&lt；1-x&gt；(Z=In和Sn)的磁性和结构性能。在母相中，这些合金表现出铁磁行为。另一方面，马氏体相的自发磁化强度较母相显著下降，表明这些合金在马氏体相中为亚铁磁性或反铁磁性。观察到了Ni2Mnlt；1.44&gt；Sn0.56&gt；的场致马氏体逆转变。

Large magnetic-field-induced strains have been observed in Heusler alloys with a body-centered cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field. These materials have attracted considerable attention as potential magnetic actuator materials. We have investigated systematically the intelligent materials exhibiting magnetic shape memory effect. Research results are as follows :1.Intermetallic compounds MnCo_<1-x>Ge(0.06【less than or equal】x【less than or equal】0.08) exhibit the diffusionless thermoelastic martensitic transformation at about 300 K. The martensitic phase crystallizes in the orthorhombic TiNiSi-type and transforms to the parent one with the hexagonal Ni_2In type crystal structure at T_M with increasing temperature. These phase transformations are analyzed thermodynamically using a Landau-type thermodynamical potential.2.The phase diagram of ferromagnetic shape memory alloys Ni_<50+x>Mn_<12.5>Fe_<12.5>Ga_<25-x> was obtained. The Curie temperature decreases gradually with x. On the other hand, the martensitic transformation temperature T_M increases steeply until x=3.0, after then they reach to the value 380 K at x=5.5. The good ductility was confirmed for the samples with x【greater than or equal】3.0.3.Magnetic and structural properties of new ferromagnetic shape memory alloys Ni_2Mn_<1+x>Z_<1-x>(Z=In and Sn) have been investigated. In the parent phase these alloys exhibit ferromagnetic behavior. On the other hand, the spontaneous magnetization of the martensitic phase drops significantly compared with that of the parent phase, indicating that these alloys are ferrimagnetic or antiferromagnetic in the martensitic phase. We have observed a field-induced reverse martensitic transition for Ni_2Mn_<1.44>Sn_<0.56>.