强磁场下MnNi反铁磁多孔合金的多重记忆效应及相关机制的研究

Antiferromagnetic porous MnNi alloys will be fabricated by using high magnetic field (HMF) sintering. Their multi-memory effects such as single-way, two-way thermal-control shape memory effect（SME）, magnetic field-control SME, volume memory effect and correlation effect between shape and volume will be studied. Phase transition (fcc-fct martensitic transformation and paramagnetic-antiferromagnetic transition) and the multi-preferred orientation (grain alignment, reorientation of martensitic variants, rearrangement of antiferromagnetic domain wall) of microstructures under HMF will be investigated experimentally so as to explore the optimum methods to improve the multi- memory effects. Dynamic model of complex interface (combining martensitic twin interface and antiferromagnetic domain wall) associated with HMF will be build in MnNi alloys based on the in-situ observation. The mechanism of multi-memory effects connected with HMF will be proposed from the analyses of martensitic transformation and magnetic transition as well as micro-structural evolution. The equation of recoverable strain related with HMF will be built in porous alloys. Our project will promote the study of new methods, new phenomena and new theories in material science, especially in the field of ultimate properties of new materials under extreme conditions, and will establish the new research frontier of high-magnetic field functional materials.

本课题采用强磁场烧结制备MnNi反铁磁多孔合金，研究强磁场对多孔合金多重记忆效应(包括单/双程温控、磁控形状记忆效应，体积记忆效应以及形状与体积关联效应)的影响规律；实验研究强磁场对MnNi多孔合金中fcc-fct马氏体相变和顺磁-反铁磁相变的影响以及强磁场下微观组织的多重择优取向(晶粒取向、马氏体变体再取向、反铁磁磁畴再取向)及其机制，探寻提高反铁磁材料记忆效应的有效方法；原位观察相变过程中相界和畴界等多种界面迁移的动态过程，建立与强磁场关联的复合界面(马氏体孪晶界与反铁磁畴耦合界面)迁移的动力学模型；基于强磁场，结合马氏体相变、反铁磁相变、微观组织演化特征，建立强磁场下MnNi多孔合金多重记忆效应的微观机制，并建立与强磁场关联的多孔合金可恢复应变理论计算模型。本课题将促进强磁场下材料科学中新现象、新方法、新理论的探究，特别是新材料在极端条件下极限性能的研究，有利于形成强磁场功能材料学。

实验制备多孔MnNi合金，并对其形貌、结构、成份等进行分析表征，对其力学性能进行分析；建立MnNi合金中的多相界畴(马氏体孪晶畴+反铁磁畴)耦合的界面运动方程，系统研究了单晶和多晶中多物理场(应力场和磁场)对界面迁移的影响规律，并对相关的磁致应变进行了分析；当外加应力有利于铁磁态对应的变体出现时，反铁磁-铁磁转变的临界磁场将有所降低，反之则临界磁场会升高；将相场与有限元结合起来，实现了基于微观组织演化的性能设计，包括记忆效应、超弹性、弹热效应等，并从相变和相界面迁移的角度揭示了其内在机理；对于MnNi合金中的多步相变进行了模拟，发现其第一步相变由热力学驱动，第二步相变则由内应力协助驱动；界面应力决定了微观组织演化的形态；利用Mn基合金中的马氏体相变和反铁磁相变，可对合金的模量进行调控，并提出模量-温度-成份相图，这对于恒弹性合金的设计具有积极的指导作用；根据相平衡，提出求解热力学参数的方法，利用此方法得到Mn基合金的相参数，并系统研究Mn基合金中的单步、多步相变热力学及相关的马氏体/母相界面热力学；结合多晶构造模型，分析了晶界对相变塑性的协调作用机制。