Improvement of the surface state of additively manufactured TiAl6V4 load-bearing structures from laser powder bed fusion processes

激光粉末床熔融（简称LPBF）是一种增材制造工艺，通过粉末层的增量沉积和熔化来生产近网状金属结构部件。这种增材制造的部件具有明显的表面结构，具有高粗糙度，因此具有很强的缺口效应。这些通常是材料或部件过早失效的原因，特别是在循环加载的情况下。此外，根据制造策略的不同，高近表面孔隙率由于其裂纹引发特性而导致寿命缩短。在工艺链中，这些缺点可以通过使用抛光或喷丸方法的定制表面处理过程来抵消。然而，到目前为止，还没有对喷丸参数（压力、入射角、喷丸介质）对材料特性（如粗糙度或可能的边界层压实）的影响进行详细的调查。此外，熔化过程中引入的固有应力与表面处理引入的压应力的相互作用也是必须考虑的一个重要方面。从技术上来说，对复杂部件几何形状（空腔、晶格几何形状）进行后处理的可能性提出了另一个重要的挑战，除了必须包含在处理策略中的堆积的各向异性特性。迄今为止，这种工艺-结构-性能关系几乎没有得到系统的研究，因此忽视了具有最佳表面和残余应力状态的LPBF组件的潜力以及它们在循环机械应力下提高性能的能力。因此，在这个项目中要实现的目标是增加机械承载能力，因为引入了压应力，减少了表面粗糙度，以及使用射击，微观和超声波强化方法对靠近表面的孔隙进行压实。由于这些材料和地形特性对循环承载能力的影响是至关重要的，因此将评估常规制造材料的机制和方法的可转移性，并将识别和分析LPBF工艺特性（残余应力，微观结构，孔隙率和粗糙度）的可能相互作用。钛合金Ti-Al6-V4在LPBF工艺中的可加工性已经得到了广泛的研究，将作为本研究的材料。作为本研究中表面工程步骤的参考，应用于对边界层状态有既定要求的航空航天和医疗技术，将用于比较和提高喷丸部件的机械承载能力。

Laser Powder Bed Fusion (Abbr. LPBF) is an additive manufacturing process in which near-net-shaped metallic structural components are produced by an incremental deposition and melting of powder layers. Such additively manufactured components show a distinct surface structure with high roughness and therefore strong notch effects. These are often reason for a premature material or component failure, especially in the case of cyclic loading. Furthermore, depending on the manufacturing strategy, high near-surface porosities lead to a reduction in lifetime due to their crack-initiating properties. Within the process chain, these disadvantages can be counteracted by a tailored surface finishing process using polishing or peening methods. Todate, however, no detailed investigation of the effects of peening parameters (pressure, angle of incidence, peening media) has been carried out regarding material characteristics, such as roughness or possible boundary layer compaction. In addition, the interaction of the inherent stresses introduced during the melting process with the compressive stresses introduced via surface treatment also represents an important aspect, which must be considered.Technologically, the possibility to post-process complex component geometries (cavities, lattice geometries) poses another important challenge, in addition to the anisotropic properties from the build-up which have to be included in the processing strategy. Such process-structure-property relations have so far hardly been systematically investigated and thus neglect the potential of LPBF components with an optimal surface and residual stress state and their capability to improve the performance under cyclic mechanical stresses. Theobjective to be accomplished in this project is therefore an increase in the mechanical load-bearing capacity due to the introduction of compressive stresses, the reduction of surface roughness as well as the compaction of pores close to the surface using shot-, micro- and ultrasonic peening methods. Since the influence of these material and topography properties on cyclic load-bearing capacity is of paramount importance, the transferability of the mechanisms and methods for conventionally manufactured materials will be evaluated and possible interactions with the properties from the LPBF process (residual stresses, microstructure, porosity and roughness) will be identifiedand analyzed. The titanium alloy Ti-Al6-V4, which has already been extensively investigated for its processability in the LPBF process, is to be used as material in this investigation. As reference for the surface engineering steps in this investigation applications in aerospace and medical technology with established requirements on the boundary layer state will be used to compare and augment the mechanical loadbearing capacity of peened components.