基于第一原理计算研究成分对Ni-Mn-Ga合金中间马氏体相变的影响规律及机理

First-principles calculations will be adopted in this research, to systematically investigate the influence of alloying composition on the thermal stability of austenitic parent phase and three kinds of martensitic phases (5-layer modulated martensite, 7-layer modulated martensite, non-modulated martensite) in the Ni-Mn-Ga alloys; to reveal the variation of the intermartensitic transformation temperatures with the composition adjustment, and to clarify the nature of the difference of the martensitic transformation sequence with the change of the electronic concentration e/a. Furthermore，the variation of the atomic magnetic moments and total magnetic moments in the Ni-Mn-Ga alloys with the change of the composition will be discussed, and the relevant mechanism will be elucidated from the point of view of the electronic density of states. According to the calculation results, optimized composition range with the highest thermal stablity of the modulated martensite (5M or 7M) and magneitc properites can be predicted, which will be validated by experimental results. The research achievements will fill the gap in the theoretical study on the complete sequence of the martensitic transformation in the off-stoichiometric Ni-Mn-Ga alloys; will reveal the variation of the thermal stablity of the parent phase and the three kinds of martensitic phases with composition tuning process; will elucidate the mechanism of the change of the intermartensitic transformation temperature and martensitic transformation sequence with alloying composition; and finally will lay a solid theoretical foundation for the design and performance improvement of Ni-Mn-Ga ferromagnetic shape memory alloys.

申请者拟采用第一原理计算的方法，系统地研究成分对Ni-Mn-Ga合金的奥氏体母相和三种马氏体相（5层调制、7层调制和非调制）的热稳定性的影响；揭示中间马氏体相变温度随合金成分的变化规律，并从形成能的角度阐明Ni-Mn-Ga合金随电子浓度（e/a）不同而马氏体转变序列各异的物理本质；探讨Ni-Mn-Ga合金的原子磁矩和总磁矩随合金成分的变化规律，并从电子态密度的角度阐明磁性能变化的相关机理。根据第一原理计算的结果，确定调制马氏体（5M或7M）稳定性最高以及磁性能最优的合金成分范围，并进行实验验证。 该项目的完成不仅可以填补非化学计量比Ni-Mn-Ga合金的马氏体转变序列的理论研究的空白，揭示奥氏体母相和三种马氏体相的热稳定性随合金成分的变化规律，并阐明中间马氏体相变温度和马氏体转变序列随合金成分变化的机理，同时还可以为新型铁磁形状记忆合金的设计和性能改进奠定坚实的理论基础。

本项目采用第一原理计算的方法，系统地研究成分对Ni-Mn-Ga合金的奥氏体母相和三种马氏体相（5层调制、7层调制和非调制）的相稳定性的影响；揭示了中间马氏体相变温度随合金成分的变化规律，并从形成能的角度阐明Ni-Mn-Ga合金随电子浓度（e/a）不同而马氏体转变序列各异的物理本质；研究结果表明富Ni系列合金（Ni2+xMn1-xGa，0.05≤x≤0.25和Ni2+xMnGa1-x，0.05≤x≤0.10）有利于得到相对稳定的NM马氏体相，而适量的富Mn系列合金（Ni2Mn1+xGa1-x，0.10≤x≤0.20）有利于得到相对稳定的7M马氏体相。因此可以在成分区间宽泛的Ni2Mn1+xGa1-x（0.10≤x≤0.20）合金中获得作为稳定相的7M马氏体，并且高Mn含量合金的马氏体转变温度能够满足实际应用的要求。本项目探讨了Ni-Mn-Ga合金的磁性能随合金成分的变化规律，并从电子态密度的角度阐明磁性能变化的相关机理。此外，本项目还研究了Ni-Mn-Ga合金中添加第四组元Cu对合金晶体结构，相稳定性和磁性能的影响。. 本项目探索了不同成分Ni-Mn-Ga合金中调制马氏体的结构参数，相稳定性和磁性能变化，为实际应用奠定理论基础；揭示了合金磁性能变化的物理本质，并阐明中间马氏体相变温度和马氏体转变序列随合金成分变化的机理，为新型磁致形状记忆合金的成分设计和性能优化提供理论支撑。