Ti-Ni-Nb合金经适当过量变形可获得宽相变滞后，其连接紧固件扩径后可在室温下存储，应用方便，前景广阔。但过量变形恶化了应变恢复特性，已成为航空等领域高性能连接的应用瓶颈。本项目提出采用Co添加改善过量变形马氏体的可逆性，在获得宽相变滞后的前提下提高应变恢复特性的新思路。系统研究Ti-Ni-Nb-Co合金的微观组织结构、马氏体相变与应变恢复特性，重点查明Co添加对相组成、相变行为和力学性能的影响规律和机理，研究Co含量和形变对相变滞后和应变恢复特性的影响规律，获得兼具有宽相变滞后、大恢复率和高恢复力的Co含量及形变量和形变温度。研究形变马氏体的形态、亚结构和界面结构随Co含量和变形条件变化的演变规律及其逆转变特性，揭示Co添加提高形变马氏体可逆性、改善应变恢复特性的微观机制，该研究对丰富马氏体相变理论和开发应变恢复特性优异的宽滞后形状记忆合金具有重要意义。

Wide transformation hysteresis can be obtained through proper excessive deformatioon for Ti-Ni-Nb alloys. The connector and fastener made of Ti-Ni-Nb alloys can be stored at room temperature and applied conveniently, which exhibits bright future in the application. However, the excessive deformation can deteriorate the strain recovery characterisitics. This becomes the obstacle the field of application with the requirement of high performation connection. In this project, the new idea, that Co addition improves the reverse transformtion characteristics of deformed excessively martensite at the prerequisite of wide transformation hysteresis, is put forward. The microstructure, martensitic transformatioon and strain recovery characterisitcs of Ti-Ni-Nb-Co alloys are investigated. The relationship between the Co content and the phase, transformation behavior and mechanical properties of Ti-Ni-Nb-Co alloys is clarified. The effect of Co content and deformation condition on the transformation hysteresis and strain recovery characterisitc is studied to obtain the optimal Co content and deformtion condition with wide transformation hysteresis, large recovery ratio and high recovery stress. The evolution of the morphology, substructure and interface structure in the deformed martensite with the change of Co content and deformation condition is investigated. The corresonding reverse transformtion is also studied. Finally, the mechanism that deformed martensite reversibility and recovery characterisitcs are improved due to Co addition is disclosed. This research is very improtant to enrich martensitic transformtion theory and explore wide hysteresis shape memory alloys with high performance.