"准同型相界"在铁磁性形状记忆合金中的研究和应用

This research project concerns with the exploitation on new class of ferromagnetic shape memory alloys (FSMAs) with high magnetic responses by introducing the newly proposed phenonmenon of general "morphortropic phase boundary" (MPB) in ferroic materials. As FSMAs combine the properties of ferromagnetism with those of a thermoelastic martensitic transformation, it is desirable to establish the coupling between the martensite MPB and magnetic MPB in the newly designed alloys. Under the influences of various external fields (thermal, stress and/or magnetic field), the evolution of the crystal structure, strain domain and magnetic domain due to the thermal unstability at MPB will be studied. By understnding the relationship between the various microstructure units and the general properties, this project aims to achieve the optimization of magnetostrain and magnetomechanical performances of the alloys. By utilizing MPB in FSMAs, it is expected to search for novel ferromagnetic shape memory alloys with high magnetic response, low magnetic field requirement and narrow transformation hysteresis.

本项目拟以新近提出的"准同型相界"(MPB)在铁性材料中的适普性为理论指导,探索铁磁性形状记忆合金中的MPB,并期待在MPB处开发出具有高磁响应的新型合金。铁磁性形状记忆合金是具备马氏体相变的铁磁性材料,合金的MPB既是马氏体的MPB也是磁结构的MPB，通过探索热、应力以及磁场等多场作用下合金MPB由于热力学失稳所带来的晶体结构、应变畴及磁畴的演变规律，认识晶格和各种微结构单元与材料宏观性能的相互关联性。期待在MPB处开发出具有高磁响应、低场要求以及窄滞后的新型磁性形状记忆合金。

本项目以"准同型相界"(MPB)在铁性材料中的适普性为理论指导，探索铁磁性形状记忆合金中的 MPB，利用热力学失稳这一特性，构建出在 MPB 处的具有较高高磁响应的新型合金。在著名的NIMnIn/Ga体系中，MPB的相界通过超声共振和磁学测量表征出来，并在MPB成分点上的合金表现出优于其他成分的磁学性能。铁磁性形状记忆合计的MPB新型成分中同时出现应变玻璃这一物理现象，在这种该体系中也是首次提出并被证实。