双电子束耦合缓冷钛合金填丝成形的相控机理和应力缓释效应

Aimed at the difficulties in controlling the phase transformation and the magnitude of the stress existed in formation of TC4 titanium component with wire filling in aerospace, a new technique is proposed to fabricate titanium alloy by using electron beam welding with wire filling based on main-accessory double beams accompanied with slow cooling rate. The cooling section of thermal cycle curve was expanded by introducing an accessory low energy beam. The phase transformation could be controlled and the residual stress of the cladding layers can be released accordingly. Based on transient equilibrium of energy, mass and momentum, as well as the thermal-mechanical relationship during dynamic process of wire filling with liquid bridge transfering by double-beam heat sources, a thermo-dynamics model of the wire filling process with double-beam heat sources are further established. Combining phase transformation characteristic of TC4 titanium alloy in continuous cooling process, the matching relations of the distance D between main and accessory beams, energies of these two beams and their proportions, wire feed rate and welding speed are systematically studied. In addition, the effects of these parameters on the contents and percentage of α/β phases in the α+β region are also investigated. Moreover, the correlations between α/β phase ratio and release of the residual stress, as well as the inhibition mechanism of the formation of α′ martensite phase are clarified. Finally, the effect of the phase transformation control by the supplementary beam on the residual stress relieving is revealed. All of the above researches will help to explore new ideas and provide theoretical guidance for titanium alloy parts fabricated by wire filling.

针对航空航天用TC4钛合金填丝成形中相变及应力较难调控的问题，本项目提出了以主-辅双电子束热源耦合缓冷进行填丝成形的新方法，力图通过引入辅电子束拓展成形过程热循环曲线冷却段来实现相变调控，以实时缓释熔覆层应力。基于主-辅双电子束热源耦合下液桥过渡动态填丝成形的能量、质量、动量的瞬态平衡及热-力关系，建立主-辅双电子束热源耦合的填丝成形热力学动态过程模型，结合TC4合金连续冷却相变特征，系统研究钛合金α+β双相区共存窗口下的主-辅束间距离D、主-辅束能量及分配比例、送丝速度与成形速度匹配关系、以及这些参数对α/β两相含量和比例的影响规律，阐明α/β两相配比与应力缓释的内在联系和α′马氏体相生成的抑制机制，揭示辅束缓冷相变调控对应力缓释的影响规律，为钛合金填丝成形开拓新思路和奠定理论基础。

针对航空航天用TC4钛合金填丝成形中相变及应力较难调控的问题，本项目提出了以主-辅双电子束热源耦合缓冷进行填丝成形的新方法，力图通过引入辅电子束拓展成形过程热循环曲线冷却段来实现相变调控，以实时缓释熔覆层应力。项目基于主-辅双电子束热源耦合下液桥过渡动态填丝成形的能量、质量、动量的瞬态平衡及热-力关系，建立主-辅双电子束热源耦合的填丝成形热力学动态过程模型，通过对模型分析，结合试验验证，表明单一热源成形过程中应力主要集中在每道熔覆层之间以及熔覆层与基板连接位置，其中第一层熔覆层端部由于反复受到热源和后续熔覆层作用应力集中最为严重。总功率相同时（1.5kW），双束热源成形能够降低应力峰值，当主-辅束间距离为4.5mm，主-辅束双热源功率比为7:3时，熔覆层根部应力峰值由单一热源的568MPa降低至505MPa，能够有效释放电子束填丝成形过程的应力。该研究结果揭示了辅束缓冷对应力缓释的影响规律，为钛合金填丝成形开拓新思路和奠定理论基础。