窄滞后NiCoMnSn记忆合金薄膜及其低磁场驱动马氏体相变及磁感生应变研究

The high critical magnetic field for driving the martensitic transformation and magnetic-field-induced strain is the crucial problem limiting the development of magnetic field-induced phase transformation shape memory alloy thin film. In this project, the new idea for decreasing the critical magnetic field is proposed in NiCoMnSn thin film by narrowing its thermal hysteresis width of martensitic transformation. The thermal hysteresis behavior of NiCoMnSn thin film is systematically investigated. The internal relationships between composition, heat treatment process and thermal hysteresis of martensitic transformation are revealed. The optimal principle for composition and heat treatment process to achieve narrow hysteresis martensitic transformation is determined. Then the narrow hysteresis NiCoMnSn thin film is fabricated. Moreover, the internal relationships among narrow hysteresis, the interface structure between parent phase and martensite as well as its motion characteristics, microstructure of martensite, and crystal defects are founded. The mechanism of narrow hysteresis of martensitic transformation is clarified. The internal law of the low magnetic field-induced martensitic transformation is researched. The thermal model of martensitic transformation under application of magnetic field is founded. In addition, the characteristics of low magnetic field-induced strain and its mechanism are investigated. The internal relationships between the critical magnetic field, motion characteristics of parent phase-martensite interface and narrow hysteresis of martensitic transformation are revealed. Furthermore, the principle for design of NiCoMnSn thin film which exhibits low critical magnetic field, high output stress and large strain is presented. The researches mentioned above provide theoretical guidance for developing novel magnetic shape memory alloy thin film.

磁驱相变记忆合金薄膜中驱动马氏体相变及磁感生应变的临界磁场高是限制其发展的关键问题。本项目提出在NiCoMnSn磁驱相变记忆合金薄膜中，通过减小马氏体相变热滞后，降低临界磁场的新思路。项目拟从研究NiCoMnSn薄膜的马氏体相变热滞后行为入手，揭示薄膜成分、热处理工艺与相变热滞后之间的内在联系，确定获得窄相变滞后的合金成分及热处理工艺优化准则，制备窄滞后NiCoMnSn薄膜；建立相变窄滞后与母相-马氏体界面结构及其可动性、马氏体组织结构和晶体缺陷的内在联系，揭示马氏体相变窄滞后机制；研究低磁场驱动窄滞后马氏体相变的内在规律，建立磁场作用下的马氏体相变热力学模型；研究低磁场驱动磁感生应变的规律及机制，揭示临界磁场与母相-马氏体界面可动性及相变窄滞后之间的内在联系，确定获得低临界磁场、高恢复力和大应变NiCoMnSn磁性形状记忆合金薄膜的设计准则，为新型磁性形状记忆合金薄膜的发展奠定基础。

本项目围绕窄滞后NiCoMnSn磁驱相变记忆合金薄膜的制备、马氏体相变及磁感生应变开展研究，以期开发低临界磁场、高恢复力和大应变的新型磁性记忆合金薄膜。项目系统研究了NiCoMnSn薄膜的制备工艺，查明了制备工艺对薄膜化学成分、膜厚及表面形貌的影响规律，阐明了薄膜的生长动力学。首次系统揭示了NiCoMnSn薄膜的晶化行为，计算出薄膜的晶化激活能，揭示了晶化过程中形核与长大机制，研究结果对于制备高质量的NiCoMnSn薄膜及器件有重要指导价值。在此基础上，揭示了薄膜成分、热处理工艺与马氏体相变热滞后之间的内在联系，确定了获得窄相变滞后的合金成分及热处理工艺优化准则，成功制备出窄滞后NiCoMnSn薄膜，其热滞后大小仅为3-4K。进一步建立了相变窄滞后与母相-马氏体界面结构及其可动性、马氏体组织结构和晶体缺陷的内在联系，从热力学角度揭示了马氏体相变窄滞后的微观机制。深入研究了低磁场驱动窄滞后NiCoMnSn薄膜马氏体相变的内在规律，采用第一性原理计算从电子层次首次揭示了NiCoMnSn薄膜独特的磁驱马氏体相变的微观机制，研究结果对于高性能磁性记忆合金材料设计有理论指导意义。探索了制备高质量无约束NiCoMnSn薄膜的有效途径，有力促进其在微机电系统中的应用。研究了NiCoMnSn薄膜的基本磁性质，重点探讨了低磁场驱动磁感生应变的规律及机制，阐明了NiCoMnSn薄膜磁感生应变的影响因素，揭示了临界磁场与相变窄滞后之间的内在联系，确定获得低临界磁场、高恢复力和大应变NiCoMnSn磁性形状记忆合金薄膜的设计准则，为新型磁性形状记忆合金薄膜的发展奠定基础。