Ni-Mn-Ga合金质子辐照改性与低驱动磁场门槛值关联性研究

The research focuses on the bottleneck of Ni-Mn-Ga magnetically shape memory alloy as an actuiator materials in MEMS - its high critical driving magnetic field. Proton irradiation was proposed as a new method to adjust electronic and atomic local structure of magnetic atoms, improve magnetocrystalline anisotropy and susceptibility and decrease the critacal driveing magnetic field of Ni-Mn-Ga alloy. Based on the study of the interaction between incident protons and lattice atoms, the microstructure evolution of multi-type defects induced by proton irradiation is studied, and the interaction of mult-type defects and twin boundary atoms is clarified. Then the effect of irradiation defects on the twin boundary mobility is discussed. After that, the correlation of the irradiation defects, mangetic fine structure, twin boundary characteristics and its mobility and the critical driving magnetic field is build, which provide a theoretical guidance for the study of magnetic memory alloy with low crtical driving magnetic field.

课题针对Ni-Mn-Ga磁性记忆合金驱动磁场门槛值高这一应用关键瓶颈，提出利用质子辐照调整磁性原子的电子结构及原子局域结构，提高磁晶各向异性和磁化率，降低驱动磁场门槛值的新思路。课题在研究入射质子与晶格原子交互作用基础上，探明以多类型辐照缺陷为主导的微观组织结构演化，阐明多类型辐照缺陷与马氏体孪晶界面原子交互作用，建立缺陷作用下孪晶界面运动规律，结合宏观磁感生应变行为测试，建立辐照缺陷—磁精细结构—孪晶界面及其可动性—驱动磁场门槛值的关联性，为低驱动磁场门槛值磁性记忆合金研究提供理论指导。

Ni-Mn-Ga磁性形状记忆合金可在外磁场作用下产生宏观可逆应变在航天器中具有广阔的应用前景。质子等带电粒子辐照是航天器材料与器件在轨服役期间性能衰减乃至失效的重要诱因。因此本文系统研究了质子辐照对Ni-Mn-Ga薄膜微观组织结构、马氏体相变、磁学特性和磁感生应变的影响规律，揭示了Ni-Mn-Ga合金质子辐照效应的微观机理。.研究发现，Ni-Mn-Ga薄膜经质子辐照后其微观组织结构发生明显变化。7M马氏体Ni-Mn-Ga薄膜经质子辐照后发生中间马氏体相变；继续增大剂量，NM马氏体体积分数增大。马氏体态Ni-Mn-Ga薄膜经3MeV、2×1016p/cm2辐照时，薄膜呈现母相-7M马氏体和7M-NM马氏体两步相变。辐照态薄膜马氏体正逆相变温度随质子剂量增加而升高。正电子湮没实验结果表明，质子辐照在Ni-Mn-Ga薄膜中引入大量空位、位错等晶体缺陷，形成内应力场，诱发母相-7M马氏体和7M-NM马氏体相变。.120keV质子辐照Ni-Mn-Ga薄膜后，马氏体的饱和磁化强度及磁晶各向异性常数先升高后降低。剂量低时，入射质子与晶格原子发生级联碰撞，形成大量Ga空位点缺陷，造成Mn和Ni原子有悬挂电子或未配对电子存在，Mn和Ni原子本征磁矩增大，饱和磁化强度升高；剂量高时，辐照薄膜中形成大量低饱和磁化强度的再取向7M马氏体，两者的竞争作用导致薄膜饱和磁化强度随辐照剂量增加先升高后降低。.NiMnGa合金的磁感生应变随质子辐照剂量的增加先升高后下降，临界磁场先降低后升高。质子辐照影响合金磁感生应变的机制源于两个方面。辐照初期，合金的Ku和Ms均升高，界面移动驱动力升高起主要作用，且合金组织结构为界面可动性良好的7M马氏体，因而合金的磁感生应变显著增大。当辐照剂量进一步升高时，合金的Ms和Ku降低，界面移动驱动力降低，同时合金中形成NM马氏体，7M和NM马氏体相之间的随机弯曲界面运动困难，因此磁感生应变降低。