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

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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.