全过渡族合金Mn_(50)Ni_(50-x-y)Fe_(x)Ti_(y)的马氏体相变行为研究

Martensitic transformation behaviors of all-d-metal Heusler Mn_(50)Ni_(50-x-y)Fe_(x)Ti_(y) alloys

本文制备了一系列Mn_(50)Ni_(50-x-y)Fe_(x)Ti_(y)全过渡族(all-d-metal) Heusler合金的甩带样品,并系统研究了Ti, Fe元素替代对其马氏体相变的影响.相同Fe含量时, Ti含量的升高能够稳定B2母相,从而降低马氏体相变温度.此外,Ti8合金中,马氏体相变温度随Fe含量的升高而下降,这表明Fe取代Ni原子也可以稳定B2结构的母相;同时,随着Fe含量的增加, Ti8合金中部分5M马氏体转变为L1_(0)马氏体并降低了热滞,表明L1_(0)马氏体与母相之间的相变驱动力小于5M马氏体与母相之间的相变驱动力.而当y>8时,马氏体相变温度会随着Fe含量的升高而略微上升,这可能是由于Fe原子的无序占位所致.此外, Fe的加入具有铁磁激活的作用,建立了磁有序,使居里温度上升.电阻率测量显示,马氏体相变过程中伴随有显著的电阻变化,其原因是马氏体的显著晶格畸变对电子的散射作用.进一步发现,退火处理可以消除Fe原子无序占位,从而稳定B2母相,使得不同Ti含量的马氏体相变温度均可由高温下降至室温附近.本研究表明, Ti, Fe替代可以在室温附近获得一系列马氏体相变,为进一步的磁热及弹热研究提供了候选材料.

A series of Mn_(50)Ni_(50-x-y)Fe_(x)Ti_(y) all-d-metal Heusler alloys ribbon samples were fabricated, and the effect of dual element Fe-and Ti-doping on the Martensitic transformation(MT) has been studied systemically. For the alloys with same Fe content, the increase of Ti content would stabilize the B2 parent phase and then reduce the MT temperature. In addition,the MT temperature also decreases with the increase of Fe in the Ti8 alloys, suggesting that the substitution of Fe for Ni atoms could stabilize the B2 parent phase. Meanwhile, part of 5 M martensite transforms into L1_(0) martensite with increasing Fe content higher than 2 in the Ti8 alloys, causing the decrease of thermal hysteresis. This result reveals that the driving force of the MT between L1_(0) martensite and parent phase is lower than that between 5 M martensite and parent phase. On the contrary, the MT temperature increases slightly with increasing Fe content for the y>8 alloys, which is due to the possible disordered occupation of Fe atoms. The introduction of Fe has a ferromagnetic activation to establish the weak ferromagnetic ordering and increase the Curie temperature. A large change of resistivity is observed during the MT transition, which is due to the electron scattering effect of the distinct lattice distortion in martensite.Furthermore, proper annealing treatment could eliminate the effect of disordered occupation of Fe atoms and stabilize the B2 parent phase, resulting in the reduction of MT temperature for all Ti-doped samples. The present work suggests that a series of MT transitions could be obtained by dual element Fe-and Ti-doping, and it provides the candidates for future research on magnetocaloric and elastocaloric materials.