ORIGINAL ARTICLE Surface topography investigations on nickel alloy 625 fabricated via laser powder bed fusion Tuğrul Özel 1 & Ayça Altay 1 & Alkan Donmez 2 & Richard Leach 3 Received: 27 April 2017 /Accepted: 28 September 2017 # Springer-Verlag London Ltd. 2017 Abstract Laser powder bed fusion as an additive manufactur- ing process produces complex surface topography at multiple scales through rapid heating, melting, directional cooling, and solidification that are often governed by laser path and layer- to-layer scanning strategies and influenced by process param- eters such as power, scan velocity, hatch distance, and resul- tant energy density. Investigations on manufactured surfaces, as-built and after applying electropolishing, are performed using stylus profilometry, digital optical microscopy, and scanning electron microscopy techniques to reveal the com- plex surface texture of the nickel alloy 625 test cubes that are produced by following an experimental design. Surface tex- ture is further explored using image processing together with machine learning-based algorithms. Measurement uncertainty is also discussed briefly. The results reveal a complex nature of laser powder bed fusion created surface topography and textures as exposed with electropolishing that may further lead to a quantitative understanding of such textures and their for- mations influenced by different scanning strategies and pro- cess parameters. Keywords Powder bed fusion . Surface topography . Surface texture . Nickel alloy 1 Introduction The implementation of powder bed fusion (PBF)-based additive manufacturing processes in various industries for direct fabrica- tion of metal parts with complex geometries is continuously growing [10]. Laser-based powder bed fusion (LPBF) is advan- tageous in obtaining fully dense three-dimensional (3D) struc- tures without a need for post processing. LPBF typically requires high energy levels, lower scan velocities on the order of 1 m/s, and layer-to-layer rotation of scan patterns for fabricating uni- formly dense parts [3, 17]. It is reported in literature that due to the high energy densities applied on the powder material with the laser beam and the related melt pool instabilities [5], material evaporation, and keyhole effects [13], the resultant structure of the fabricated 3D part, irregular microstructure [1], and subsur- face integrity are some of the major concerns among other issues in laser powder bed fusion processes, especially fabricating pow- der nickel alloys 718 (IN718) or 625 (IN625) for mission-critical aerospace applications [4, 18]. In a PBF system, several important steps occur that affect the way the part is manufactured: (i) the part computer-aided design (CAD) geometry is oriented in the build volume and sliced into layers, (ii) the slices are then imported into a build preparation software that allows the user to specify the exact location of these slices on the substrate, (iii) a set of processing parameters (laser scan velocity, laser power, hatch spacing, etc.) are specified in the software, and (iv) laser beam path corresponding to the selected hatch pattern is generated for every layer based on the part location on the build area and the specified processing parameters. Currently, there are no specification standards that explicitly cover measurement and characterization of surface texture for PBF metal additive manufacturing due to the unique challenges caused by the high degree of irregularity and the selection of appropriate scales of interest [16]. Understanding surface * Tuğrul Özel ozel@rutgers.edu 1 Industrial and Systems Engineering, Manufacturing and Automation Research Laboratory, Rutgers University, Piscataway, NJ, USA 2 National Institute of Standards and Technology, Engineering Laboratory, Gaithersburg, MD, USA 3 Manufacturing Metrology Team, Faculty of Engineering, University of Nottingham, Nottingham, UK Int J Adv Manuf Technol https://doi.org/10.1007/s00170-017-1187-z