钛合金管材流体压力热剪切弯曲成形极限和微观组织演变规律

A novel tube hot shear hydro-bending method of titanium alloys is proposed to satisfy the requirement of ultra-small bending radius tubes for aero engine, unmanned aircraft and high-speed aerospace vehicles. The method breaks through the limitation of the bending radius of titanium alloys of the conventional tensile-compressive bending method and solves the cracking problem at room temperature of the shear bending method. Based on the theory of plasticity, the thermo mechanical model and material constitutive model and the three-dimensional forming limit diagram and fracture criterion are established considering the normal internal high pressure. The plastic deformation behavior of titanium alloy tube under the shear deformation is studied systematically. The effects of microstructure evolution, slip and twinning, dislocation and grain boundaries on the microstructure of titanium alloy are studied by molecular dynamics and phase field method. The mechanism of grain refinement and the microstructure evolution under the coupling of temperature field and stress field are revealed. On this basis, the combination of temperature field and three-dimension stress is used to improve the forming limit and adjust the microstructure and properties. The objective is to explore an integrated control method of process and microstructure properties of the titanium alloy tube bending. This project will promote the technological progress of titanium alloy tube bending in China.

针对航空发动机、无人机及高速飞行器对钛合金极小弯曲半径管的需求，提出钛合金管材流体压力热剪切弯曲成形新方法，突破传统拉压变形弯曲方法对钛合金管材极限弯曲半径的限制，解决室温开裂的难题。以塑性理论为基础，建立热力耦合的本构模型和考虑法向流体压力的三维成形极限和断裂准则，系统研究复杂应力场和温度场耦合作用下的钛合金剪切塑性变形行为。利用分子动力学和相场法数值模拟研究钛合金微观组织演变及滑移和孪生，位错与晶界的影响等机制，揭示剪切弯曲细化晶粒的机制和温度场和应力场耦合作用下的微观组织演变规律。在此基础上，通过温度场和三向应力的组合控制，来提高成形极限，调整组织和性能，探索出一种工艺和组织性能一体化控制的钛合金管材弯曲成形方法。

针对航空发动机、无人机及高速飞行器对钛合金极小弯曲半径管的需求，提出了钛合金管材流体压力热剪切弯曲成形新方法。建立了管材三维应力热变形的热力耦合模型和三维成形极限，揭示了温度场和应力场耦合作用下的塑性变形行为和缺陷形成机制。开展了微观组织特征和微观结构演化机制研究，揭示了管材组织与性能的内在联系，解决了管材室温充液剪切弯曲成形困难，易开裂等难题，从而提高钛合金剪切弯曲成形极限和壁厚均匀性，突破钛合金管材极限弯曲半径的限制，为钛合金管件在航空、航天和汽车等领域的应用奠定理论基础。