Laser Powder Bed Fusion (PBF-LB/M) processed Ti6Al4V parts are widely used in high-performance applications, such as in aerospace. To fully utilize the lightweight potential of additively manufactured parts, structural adhesive bonding can be applied as a viable alternative to conventional joining methods. However, reliable adhesive bonding requires an in-depth understanding of the adherends surface morphology influences on bond performance. In the case of PBF-LB-Ti6Al4V surfaces, the bonding capabilities and limitations have to be investigated by considering the effects of their inherent surface roughness. Moreover, it is crucial to determine a suitable surface pretreatment process, potentially leveraging the inherent roughness, ensuring adhesive bonds with high strength, fatigue resistance and environmental durability. This work presents advancements in structural adhesive bonding of PBF-LB-Ti6Al4V parts, with a primary focus on the influences of surface morphology on bond performance. The PBFLB-surfaces were characterized in as-built and pretreated conditions, considering different build orientations. Subsequently, the surface-related effects on the bond performance were assessed for quasi-static, fatigue and environmental loading cases. Comprehensive fracture surface analysis assisted in analyzing the surface morphology influences and interactions between the surface features. The main adhesion-promoting surface features on the as-built surfaces were found to be the partially melted particles from the powder bed, which proved to be highly effective in causing mechanical interlocking in the adhesive. The number of particles correlated with the strengths and fatigue lifetimes of the adhesive bonds. However, in areas with no or few attached particles, the as-built surfaces exhibited substantial adhesive failure and poor bond durability. To enhance bond performance, the pretreatment processes grit blasting and laser treatment were investigated. A particular focus was placed on laser treatment, which is a key novel contribution of this work for bond preparation of PBF-LB-Ti6Al4V parts. Different laser fluences were assessed and optimized to generate a distinct nanoporous oxide layer with uniform thickness on the surface. This resulted in a hierarchical surface morphology, consisting of the inherent surface roughness of the as-built surfaces superimposed with the laser-induced uniform nanoporous oxide layer. With this surface morphology, a significant improvement in bond performance was achieved compared to the as-built condition. An almost complete cohesive failure in the adhesive was reached across all applied loading cases. Digital image correlation measurements further revealed that laser treatment substantially slowed down crack growth in the adhesive bond during cyclic fatigue loading. As an application, co-cured hybrid joints with pin-reinforcements between PBF-LB-Ti6Al4V and CFRP were examined, using as-built, release-agent-coated, and laser-treated titanium surfaces to evaluate the role of surface morphologies in hybrid joints. A highly similar mechanical performance was found for the hybrid joints with as-built and release-agent-coated surfaces. In contrast, laser treatment significantly enhanced the joint stiffness, limit load, and energy absorption, while the ultimate tensile shear strength increased moderately.     «

Laser Powder Bed Fusion (PBF-LB/M) processed Ti6Al4V parts are widely used in high-performance applications, such as in aerospace. To fully utilize the lightweight potential of additively manufactured parts, structural adhesive bonding can be applied as a viable alternative to conventional joining methods. However, reliable adhesive bonding requires an in-depth understanding of the adherends surface morphology influences on bond performance. In the case of PBF-LB-Ti6Al4V surfaces, the bonding ca...     »