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

激光粉床融合(简写为LPBF)是一种添加剂制造工艺，在该工艺中，通过逐渐沉积和熔化粉末层来生产近净形状的金属结构部件。这种添加制造的部件显示出独特的表面结构，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，高的近表面孔隙率会由于其引发裂纹的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精加工工艺来抵消。然而，到目前为止，还没有关于喷丸参数(压力、入射角、喷丸介质)对材料特性的影响的详细调查，例如粗糙度或可能的边界层压实。此外，熔化过程中引入的固有应力与通过表面处理引入的压应力之间的相互作用也是一个必须考虑的重要方面。在技术上，除了必须包括在加工策略中的积聚的各向异性之外，对复杂的组件几何形状(空洞、晶格几何形状)进行后处理的可能性构成了另一个重要的挑战。到目前为止，这种工艺-结构-性能关系几乎没有得到系统的研究，因此忽略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改善性能的能力。因此，该项目要实现的目标是通过引入压应力、降低表面粗糙度以及使用喷丸、显微喷丸和超声波喷丸方法压实靠近表面的气孔，从而提高机械承载能力。由于这些材料和表面性能对循环承载能力的影响至关重要，因此将评估传统制造材料的机制和方法的可转换性，并将确定和分析与LPBF过程中的性能(残余应力、微结构、孔隙率和粗糙度)可能存在的相互作用。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，将利用航空航天和医疗技术中对边界层状态已有要求的应用来比较和增强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.