materials Article Two-Step Laser Post-Processing for the Surface Functionalization of Additively Manufactured Ti-6Al-4V Parts Juliana S. Solheid 1, *, Torsten Wunsch 2 , Vanessa Trouillet 3,4 , Simone Weigel 5 , Tim Scharnweber 5 , Hans Jürgen Seifert 1 and Wilhelm Pfleging 1,4 1 Institute for Applied Materials-Applied Materials Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany; hans.seifert@kit.edu (H.J.S.); wilhelm.pfleging@kit.edu (W.P.) 2 Institute for Micro Process Engineering, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany; torsten.wunsch@kit.edu 3 Institute for Applied Materials-Energy Storage Systems, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany; vanessa.trouillet@kit.edu 4 Karlsruhe Nano Micro Facility, H.-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany 5 Institute for Biological Interfaces, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany; simone.weigel@kit.edu (S.W.); tim.scharnweber@kit.edu (T.S.) * Correspondence: juliana.solheid@kit.edu; Tel.: +49-721-608-22872 Received: 2 October 2020; Accepted: 28 October 2020; Published: 30 October 2020   Abstract: Laser powder bed fusion (LPBF) is one of the additive manufacturing methods used to build metallic parts. To achieve the design requirements, the LPBF process chain can become long and complex. This work aimed to use different laser techniques as alternatives to traditional post-processes, in order to add value and new perspectives on applications, while also simplifying the process chain. Laser polishing (LP) with a continuous wave laser was used for improving the surface quality of the parts, and an ultrashort pulse laser was applied to functionalize it. Each technique, individually and combined, was performed following distinct stages of the process chain. In addition to removing asperities, the samples after LP had contact angles within the hydrophilic range. In contrast, all functionalized surfaces presented hydrophobicity. Oxides were predominant on these samples, while prior to the second laser processing step, the presence of TiN and TiC was also observed. The cell growth viability study indicated that any post-process applied did not negatively affect the biocompatibility of the parts. The presented approach was considered a suitable post-process option for achieving different functionalities in localized areas of the parts, for replacing certain steps of the process chain, or a combination of both. Keywords: laser powder bed fusion (LPBF); post-processing; laser polishing; ultrafast laser; surface functionalization 1. Introduction Over the past few years, the manufacturing industry has been directly affected by the increased environmental awareness. Aspects such as resource consumption, waste management, and pollution control have been the focus of studies concerning the environmental impact of the additive manufacturing process (AM). These investigations led to the conclusion that it is possible to create a sustainable future for the AM industry [1]. Other characteristics, i.e., reduced production lead-times and the possibility of creating complex geometries and internal features, make the AM a preferable alternative to conventional processes for specific niche areas. The mentioned benefits can be associated with the possibility for the customization and personalization of fabricated components with little Materials 2020, 13, 4872; doi:10.3390/ma13214872 www.mdpi.com/journal/materials