含纳米相Ti-Ni-Hf高温记忆合金薄带大完全可恢复应变机理

Ti-Ni-Hf alloy is one of the most promsing shape memory alloy for high temperature applications. However, it only exhibits a ~3% completely recoverable strain. Such a bad shape memory effect is a serious barrier to its development and applicaitons. It has been found that, in our previous studies, Cu addition improve the glass forming ability of Ti-Ni-Hf alloys and does not change the phase transformation temperatures obviously. The amorphous Ti-Ni-Hf alloy ribbons can be prepared by the melt-spinning method. Then a large amount of nanoscale particles precipitate during the proper crystallization process. Thus, the Ti-Ni-Hf alloy ribbons containing nanoscale particles shows a large completely recoverable strain of 6.1%. In the present project, the effects of the nanoscale precipitates (including their types, size and distribution) on the martensitic transformation behaviors, martensite interface structure and its mobility, evolution of micriostructure and interface structure will be revealed. Meanwhile, the mechanisms of deformation in Ti-Ni-Hf alloys containing nanoscale precipitates will be revealed. The interaction relationship between nanoscale precipitates and martensite interface will be studied to clarify the reasons for the change of deformation micromechanisms in Ti-Ni-Hf alloy ribbons. A model on the effect of nanoscale precipitates on the deformaiton mechanisms of Ti-Ni-Hf alloy ribbons will be built up. The mechanisms of large completely recoverable strain obtained in Ti-Ni-Hf alloy ribbons containing nanoscale precipitates will be revealed. These studies will provide the new ideas and methods to get large completely recoverable strain in high temperature shape memory alloys.

Ti-Ni-Hf合金是最具有应用前景的高温形状记忆合金，但其形状记忆效应差，完全可恢复应变低(仅3%)，是其发展和应用的瓶颈。申请者通过前期研究发现，可向Ti-Ni-Hf合金中添加少量的Cu提高合金的非晶形成能力，用甩带法制成非晶薄带，然后通过适当的晶化处理获得纳米析出相，使Ti-Ni-Hf高温记忆合金薄带呈现高达6.1%的完全可恢复应变。本项目拟系统研究Ti-Ni-Hf合金薄带中纳米相的形态、尺寸及分布等对马氏体相变行为、马氏体界面结构及其可动性、变形过程中组织与界面结构演化的影响规律和内在本质；查明纳米相与马氏体界面之间的相互作用关系与机理，揭示含有纳米相的Ti-Ni-Hf合金薄带变形微观机制以及纳米相对变形微观机制的影响机理，并建立相应模型；揭示含有纳米相Ti-Ni-Hf合金薄带获得大完全可恢复应变的物理本质，为大完全可恢复应变高温记忆合金的设计和开发提供新思路和理论指导。

如何使Ti-Ni-Hf合金兼具高相变和大应变恢复特性是长期以来限制其进一步应用的瓶颈与关键。传统的合金化、热机械处理和时效均无法有效解决这一问题，本项目提出一种“非晶+晶化”的方法，采用甩带方法制备非晶态的Ti-Ni-Hf基合金薄带，随后晶化处理在薄带中获得纳米尺度的析出相，调节相变温度，获得大完全可恢复应变。获得的主要进展包括：1. 系统研究了含纳米相的Ti-Ni-Hf合金基合金薄带的组织结构和相变行为，阐明了纳米尺寸析出相对组织和界面结构影响规律。2. Ti-Ni-Hf合金薄带经晶化处理后，析出纳米尺寸的(Ti,Hf)2Ni析出相。纳米尺寸析出相改变基体中的(Ti+Hf)/Ni比，因而导致合金薄带相变温度的变化。3. 揭示了Ti-Ni-Hf合金合金薄带变形过程中的组织演化规律和变形微观机制。引入纳米相的Ti-Ni-Hf合金薄带变形过程中的组织结构演化规律为：弹性变形后发生(001)复合孪晶的再取向和去孪晶过程。这与体材料明显不同，表明纳米相的引入抑制了塑性变形的引入，从而获得了大完全可恢复应变。Ti-Ni-Hf基合金薄带经适当的退火处理后，最大完全可回复应变可达6%，为目前其它Ti-Ni-Hf合金形状记忆性能的2倍。本项目为开发新型高温记忆合金及高性能记忆合金薄带提供了新方法和新思路。本项目发表SCI论文21篇（其中JCR一区17篇）；参加国际会议4次，其中做特邀报告3次。培养博士生5人，已毕业2人；硕士生12人，已毕业10人。