激光熔化沉积钛合金成形过程的残余应力演变研究

The deformation of metal components by laser melting deposition has seriously hindered the wide application of this technology, which is also a bottleneck in the development of laser additive manufacturing technology for metal materials. It is very important to reveal the evolution and function of residual stress in the forming process, because it is directly related to the size stability and performance of components, and to the popularization and application of the technology in the fields of aerospace, machinery manufacturing, energy transportation and so on, and to the rapid promotion of the traditional manufacturing industry and the coming into being of intelligent manufacturing. In this project, the titanium alloy with a large number of applications in the field of aerospace is selected as the research object, and the laser ultrasonic nondestructive testing technology is used as a research method. The mission is to establish the mechanical model for the characterization of residual stress in complex stress state based on the acoustoelastic theory. The titanium alloy sample is manufactured by laser melting deposition and the residual stress distribution is measured synchronously. The residual stress field in spatial stress state can be reconstructed and inversed by means of multi-modal ultrasonic wave combined method. The evolution of residual stress, microstructure and properties of titanium alloy during the complex forming process is conducted in order to realize the reasonable restraint for the residual stress of the titanium alloy component with laser melting deposition. The aim is to reveal the evolution and distribution of residual stress in the process of laser melting deposition. The results will provide an important scientific basis in term of materials science for the wide application of laser melting deposition technology.

激光熔化沉积金属构件成形过程中的变形严重妨碍该技术取得广泛的应用，也是金属增材制造技术发展遇到的一个瓶颈。厘清成形过程的残余应力的演变与作用至关重要，直接关系到高性能构件的成形尺寸稳定性和使用性能，也关系到增材制造技术能否迅速推动我国传统制造业升级换代和发展智能制造新业态。本课题以航空航天领域大量应用的钛合金作为研究对象，以激光超声无损检测技术为手段，基于声弹性理论建立复杂应力状态下残余应力表征的力学模型，研究激光熔化沉积钛合金成形过程并同步测量宏观残余应力分布规律，通过多模态超声波相结合的方法实现空间应力状态残余应力场的反演与构建；研究激光熔化沉积钛合金成形过程中残余应力的演变，实现钛合金增材制造构件残余应力的合理抑制。旨在明确激光熔化沉积钛合金成形过程中残余应力的演变与分布规律，为激光熔化沉积技术的广泛应用提供科学依据，为钛合金材料成形技术的选用提供材料学依据。

针对金属增材制造过程残余应力的调控需求，解决了激光熔化沉积钛合金成形过程的残余应力演变与作用的科学问题，建立了激光熔化沉积成形钛合金的粉体制备、成形过程温度场和应力场数值模拟、激光超声无损检测、成形工艺对残余应力及组织性能的调控等一体化技术，阐明了激光熔化沉积钛合金过程控制与微观组织结构的调控机理，发展了激光超声无损检测残余应力新方法。.研究了钛合金球形粉末VIGA气雾化制备工艺对粉末特性的影响，获得了适合激光熔化沉积技术的专用钛合金粉末。数值模拟研究了激光熔化沉积TC4合金的温度场与应力场，为激光熔化沉积成形工艺优化提供参考。采用有限元数值模拟分析了激光诱导超声的物理过程，明确了激光诱导超声的机理以及各种模态超声波在待测构件中的传播规律。提出了等效载荷法对声弹性常数的测定过程进行数值模拟，为激光超声技术在材料力学性能的高精度无损检测提供了依据。研究了激光熔化沉积工艺对TC4钛合金的复杂残余应力状态的影响，获得了平面应力状态下残余应力的大小与分布。研究了扫描策略对激光熔化沉积TC4钛合金组织和力学性能以及残余应力的分布规律，为调控激光熔化沉积成形合金的残余应力提供指导。对于激光熔化沉积增材制造钛合金在航空航天领域的应用具有重要的科学意义和应用价值。发表国内外学术期刊论文11篇，其中，SCI收录8篇，EI收录3篇。获得授权发明专利3项，申请发明专利1项。