细晶Ni-Mn-Ga-Gd合金薄膜马氏体相变的尺寸效应与高温形状记忆特性

Ni-Mn-Ga alloy is a kind of promising high temperature shape memory alloy (SMA) due to its excellent thermo-stability and high transformation temperature. It should be noted that the Ms is up to 400 C by adjusting the composition. However, its instinctive brittleness seriously prohibits its further development and applications. In the present project, a high-plasticity Ni-Mn-Ga-Gd SMA thin film with fine grain is obtained by Gd doping and rapid annealing of amorphous films. The influence and mechanism of Gd doping on the crystallization behavior and crystallizaiton kinetics of Ni-Mn-Ga-Gd SMA thin films is studied to accurately adjust and control the grain size. The influence of grain size on martensitic transformation, tensile deformation, shape memory effect and its thermo-stability is investigated to reveal the corresponding mechanisms. The critical grain size for martensitic transformation is determined by both experiments and calculation. The evolution of martensite substructure, variants characteristics and self-accommodation morphology with the decrease of grain size is investigated to disclose the mechanism of size effects of martensitic transfomation. The relationship among grain size, plasticity, martensitic transformation and reversible strain is bulit up. The high-temperature SMA thin film with high plasticity and high thermo-stability is developed. This enriches the theory of martensitic and shape memory effect and provides the guidance to develop new type high temperature SMAs.

Ni-Mn-Ga合金具有高的热稳定性，通过调节成分，Ms温度可达400℃以上，是一种极具发展潜力的高温记忆合金。但该合金脆性大，已成为制约其发展和应用亟待解决的瓶颈。本项目拟采用Gd掺杂和非晶薄膜快速加热退火细化晶粒，制备高塑性Ni-Mn-Ga-Gd高温记忆合金薄膜。研究Gd掺杂对非晶薄膜晶化行为和晶化动力学的影响规律和机制，精确调控晶粒尺寸；研究晶粒尺寸对马氏体相变、拉伸变形行为及其机制、形状记忆效应及其热稳定性的影响规律和物理本质，确定发生马氏体相变临界晶粒尺寸；阐明马氏体亚结构、变体特征及其自协作形态随晶粒尺寸减小的演化规律，揭示马氏体相变尺寸效应的微观机制；建立晶粒尺寸-塑性-相变温度-可逆应变定量关系，研制出高塑性、高热稳定性高温记忆合金薄膜。这些研究对于发展微纳米尺度下马氏体相变和形状记忆效应理论及新型高温记忆材料具有重要意义。

Ni-Mn-Ga合金具有高的热稳定性，通过调节成分，Ms温度可达400℃以上，是一种极具发展潜力的高温记忆合金。但该合金脆性大，已成为制约其发展和应用亟待解决的瓶颈。本项目采用了Gd掺杂和非晶薄膜快速加热退火细化晶粒，制备了高塑性Ni-Mn-Ga-Gd高温记忆合金薄膜。研究了Ni-Mn-Ga-Gd合金薄膜的制备，总结了磁控溅射功率和溅射气压对薄膜表面粗糙度、成分、致密度和内应力的影响规律；研究了薄膜晶化行为，确定了晶化温度和晶化激活能；通过控制晶化温度，获得了不同晶粒尺寸的Ni-Mn-Ga-Gd薄膜；研究了晶粒尺寸对马氏体相变、拉伸变形行为及其机制、形状记忆效应及其热稳定性的影响规律和物理本质，发现随着晶粒尺寸的减小，马氏体相变温度降低，当晶粒尺寸小于20nm时，相变被抑制，拉伸断裂应变随着晶粒尺寸的减小先升高再降低，形状记忆效应随着晶粒尺寸的减小而降低，另外试验结果表明Ni-Mn-Ga-Gd薄膜具有比块材更优秀的热稳定性；研究了马氏体亚结构、变体特征及其自协作形态随晶粒尺寸减小的演化规律，揭示了马氏体相变尺寸效应的微观机制，发现随着晶粒尺寸减小，晶粒内马氏体板条逐渐减小，亚结构消失，晶粒内马氏体的自协作组态由不同方向的马氏体板条转变成一对平行排列的板条，变体之间保持（202）Ι型孪晶关系；研究了薄膜在拉伸变形过程中的组织结构演化规律，揭示微观变形机制，发现当变形量为3%时，薄膜马氏体板条内7个原子层微孪晶被破坏，部分转变成5个原子层微孪晶，形成5M马氏体，另一部分变成无规律的微孪晶，变成T马氏体，当变形量提高到6%时，薄膜发生了有利取向马氏体板条再取向现象；建立晶粒尺寸—塑性—相变温度—可逆应变定量关系，研制出高塑性、高热稳定性高温记忆合金薄膜。这些研究对于发展微纳米尺度下马氏体相变和形状记忆效应理论及新型高温记忆材料具有重要意义。共发表SCI论文16篇，其中影响因子大于3的论文7篇，申请国家发明专利两项。项目组成员中2位同学通过博士论文答辩，2位同学通过硕士论文答辩。