超声辅助对激光熔化沉积高温钛合金组织性能的影响机制研究

激光熔化沉积(LMD)成形钛合金构件中的冶金缺陷、较大的残余应力和粗大的显微组织是影响构件质量的关键问题，超声辅助LMD技术是优化其成形构件质量的重要方法。目前，针对超声辅助如何影响LMD成形合金构件中冶金缺陷、残余应力和显微组织尚缺乏深入研究。本项目拟以超声辅助LMD成形的Ti60合金作为研究对象，通过CCD、红外相机和同步辐射X射线衍射技术获得不同工艺条件下激光熔池的瞬时形貌、温度分布和熔体流动状态，研究超声诱发的空化和声流效应对激光熔池热力学和动力学行为的影响机制。采用Micro-CT、XRD、TEM、APT、拉伸和原位拉伸等实验系统研究不同工艺参数对超声辅助LMD成形合金中冶金缺陷、残余应力、显微组织和力学性能的影响，结合激光的熔池行为和其凝固特征，揭示超声辅助抑制合金冶金缺陷、弱化合金残余应力、细化合金显微组织的机理，从而为超声辅助LMD成形合金构件质量的优化提供理论依据。

Laser Melt Deposition (LMD), which deposits powder feedstock through a nozzle and melts it with a laser, is one of highly versatile and flexible Additive Manufacturing technologies, enabling layer-by-layer fabrication of complex near-net-shape components. However, rapid solidification during the LMD process causes several technical challenges including the creation of defects, residual stress and coarse epitaxial grains, which act as a barrier to widespread implementation of LMD technique in safety-critical components. To overcome these limitations, a high-energy ultrasonic vibration-assisted (UV-A) process is added in the LMD. Previous studies have shown that the introduction of a high-energy ultrasonic vibration into the melt can result in two nonlinear effects of acoustic streaming and acoustic cavitation, enabling a significant effect on defects and microstructural features of LMD-produced parts. At present, the mechanism of UV-A method in LMD process is still not well understood. Ti60 alloy is a near-α titanium alloy designed for use as high pressure compressors due to its excellent comprehensive performance at elevated temperatures. In this study, Ti60 alloy is fabricated by UV-A LMD under different process conditions. The transient morphology, temperature field and melt flow behavior of the laser molten pool under different process conditions are obtained by CCD, infrared camera and synchronous X-ray diffraction technique, thereby understanding the influence mechanisms of acoustic streaming and acoustic cavitation on the thermodynamic and kinetic behaviors of the laser molten pool. Several experiments, including Micro-CT, XRD, EBSD, TEM, APT, tensile and in-situ tensile etc., are employed to investigate the characteristics of defects, residual stress, microstructure and mechanical properties of the alloy built by UV-A LMD under different process conditions, so that building the relationship between the process parameters and these characteristics. Based on the laser molten pool behaviors and its solidification characteristics, the mechanisms of refining the grain, mitigating the porosity and residual stress via UV-A method in the LMD process are discussed and unraveled, which can provide a theoretical basis for improving mechanical properties of UV-A LDM-produced components, and promote practical application of UV-A LDM-produced titanium alloys.