纳米尺度Ni-Ti薄膜相变与变形行为研究

纳米尺度Ni-Ti薄膜性能的可调控性与稳定性是提高MEMS纳米器件制造工艺水平的关键。当薄膜的厚度减小到纳米尺寸时，Ni-Ti薄膜的相变行为表现出与膜厚相关联的奇异特征，如相变温度降低、相变路径改变和相变应力下降等，而现有物理模型在解释这种尺寸效应时遇到了困难。目前，虽然诸多研究从晶界约束、内应力、表面氧化等方面分析了相变行为的影响因素，但对相变奇异行为与微结构演变的关联仍然认识不清。由于马氏体相变具有可逆性，传统研究方法无法表征相变过程的动态微结构特征，原位研究具有不可替代的优势。因此，本项目拟通过原位技术表征马氏体相变与变形过程中的微结构变化，重点研究Ni-Ti薄膜热诱发马氏体相变行为、纳米尺度超弹性和循环变形稳定性，揭示马氏体相变与变形行为的尺寸效应，阐明纳米尺度Ni-Ti薄膜尺寸效应的物理机制，为设计制造高性能、高可靠性的纳米器件提供科学依据。

The modulation and stability of nanoscale Ni-Ti thin film properties are the key to improve the manufacturing process of nanodevices in MEMS. When film thickness is reduced to nanoscale, the phase transformation behaviors of Ni-Ti thin films showed thickness-related abnormal behaviors, such as transformation temperature decline, transformation path variation and transformation stress drop, which can’t be explained by current physical models. Although efforts have been devoted into the interpreting phase transformation behaviors in terms of grain boundary constraint, internal stress and surface oxidation, the correlation between abnormal transformation behaviors and microstructure revolution still isn’t clear yet. Due to the reversibility of martensitic phase transformation, traditional methods are not capable of characterizing dynamic microstructures in phase transformation, while the in situ methods showed their advantages. Therefore, we try to characterize in situ microstructure evolution in phase transformation and deformation process, focusing on the thermal-induced martensitic phase transformation behaviors, nanoscale superelasticity and cyclic deformation stability. We aim to reveal the size effect of phase transformation and deformation in Ni-Ti thin films, as well as their physical mechanism, in order to provide scientific base for fabricating nanodevices with high performance and stability.