Ti-Ni-Hf高温记忆合金中准连续网状结构的构建与应变恢复特性研究

Ti-Ni-Hf alloy is one of the most promising high temperature shape memory alloys. However, its shape memory effect is only about 3% due to the low strength of the matrix, which hampers itsapplications at high temperature. In the present proposal, a new method to prepare Ti-Ni-Hf high temperature shape memory alloy is presented. The Ti-Ni-Hf alloy powders and a few ceramic powders (TiB2，SiC or B4C) are mixed and then fabricated by hot press Sintering. The different second phases with quasi-continuous network structure in-situ form around the Ti-Ni-Hf alloy powders by changing the type, size of ceramic powder and the fabrication parameters. We try to get a relatively high martensitic transformation temperature and good mechanical properties in Ti-Ni-Hf alloys containing second phases with a quasi-continuous network structure. Meanwhile, a large completely recoverable strain is expected. The effects of second phases with quasi-continuous network.structure on the martensitic transformation, microstructure and interface structure, the microstructure evolution during phase transformation and deformation, mechanical properties and strain recovery characteristics will be studied systematically. The deformation mechanism of Ti-Ni-Hf alloys containing second phases with a quasi-continuous network structure will be revealed. The principles to get large recoverable strain will be clarified. The present study will provide new ideas and new methods to design and develop new type high temperature shape memory alloy with excellent shape memory effect.

Ti-Ni-Hf合金是最具应用潜力的的高温形状记忆合金之一。体材料基体强度低，形状记忆效应仅为3%是限制其应用的瓶颈。本项目提出将Ti-Ni-Hf合金粉末和微量陶瓷粉末（TiB2，SiC或B4C）混合，采用热压烧结制备高致密度Ti-Ni-Hf合金体材料。调节陶瓷粉末的类型、含量以及制备的工艺参数，使微量的陶瓷粉末与Ti-Ni-Hf合金发生反应，原位自生第二相主要分布于原始Ti-Ni-Hf合金粉末周围，并呈现准连续网状结构。在维持高相变温度和良好机械性能的同时，获得大的完全可恢复应变；查明第二相的准连续网状结构对Ti-Ni-Hf合金马氏体相变、组织与界面结构、相变与形变过程中的组织结构演化、力学性能和应变恢复特性的影响规律；阐明含有准连续网状结构第二相的Ti-Ni-Hf高温记忆合金马氏体变形微观机制，获得具有大可恢复应变的Ti-Ni-Hf合金，为高性能高温形状记忆合金的设计和开发提供新思路。

Ti-Ni-Hf合金是最具应用潜力的的高温形状记忆合金之一。但体材料基体强度低，形状记忆效应仅为3%，针对其应用瓶颈，本项目将 Ti-Ni-Hf 合金粉末与微量陶瓷粉末混合，采用低能球磨和热压烧结相结合的方式制备 Ti-Ni-Hf 高温记忆合金，使其原位自生成的第二相具有准连续网状结构，获得了兼具高相变温度、高强度和大可恢复应变的Ti-Ni-Hf记忆合金复合材料。获得的主要进展包括：(1) 优化球磨工艺与烧结工艺，以含B陶瓷颗粒为原材料，可在Ti-Ni-Hf合金中引入呈准连续网状结构分布的多种陶瓷增强相，制备兼具高强度与大可回复应变的Ti-Ni-Hf基形状记忆复合材料。(2) 查明准连续网状结构第二相对TiB/Ti-Ni-Hf基复合材料马氏体相变行为的影响机制。TiB/Ti-Ni-Hf基复合材料的相变类型均为B2→B19’一步马氏体相变。相变温度随陶瓷相含量的增多而降低。(3) 揭示准连续网状结构第二相对TiB/Ti-Ni-Hf基复合材料组织结构的影响规律。准连续网状分布的第二相周边形成梯度分布的应力场，促进择优取向马氏体生成，且择优取向马氏体范围随陶瓷相体积分数的增加而增加。当增强相数量过多时，转变为连续网状分布，周边区域发生应力集中，引入大量位错。(4) 研究了第二相的准连续网状结构对Ti-Ni-Hf记忆合金力学行为和应变恢复特性的影响规律及作用机理，其力学性能及形状记忆效应均随着网状结构增强相含量的增加而呈现出先升高后降低的趋势。.本项目成功研发制备大块兼备高强度与大可回复应变的Ti-Ni-Hf合金体材料的新原理与新途径，为高性能高温形状记忆合金的设计和应用奠定理论基础。本项目共发表SCI论文27篇，其中JCR Q1区22篇；EI论文30篇。编著教学专著两本。参加国际学术会议6人次，做邀请报告2人次。培养博士研究生5人，已毕业1人；培养硕士研究生6人，已毕业4人。