Surface finishing of Ti6Al4V implants produced by laser powder bed fusion

Abstract

The surface roughness of samples produced by laser powder bed fusion (L-PBF) heattreated Ti6Al4V ELI for medical implants is described in this study taking into account the samples' location on the build plate. Three different shapes of samples were used, namely horizontal, vertical, and semisphere samples. The surface roughness of the samples in an as-built state, after they were polished by dry electropolishing only and after the combination of dry electropolishing and chemical polishing in HF-HNO3 solutions, were analyzed. Scanning electron microscopy and a profilometer were used to examine the surface roughness of horizontal, vertical, and semisphere samples. The morphological features of the surfaces are displayed both before and after surface finishing. Top surfaces are formed by overlapped tracks and stripes since single layers are manufactured in a track-by-track manner in stripes, while 3D objects as a whole are made layer-by-layer in L-PBF, and side surfaces are defined by layers. It was demonstrated that while the top and side surfaces of the vertical and horizontal samples had different origins, their roughness values measured by the profilometer were generally similar because the measured roughness was primarily determined by the powder particles sticking to both the samples' upper and side surfaces. The samples with the highest surface roughness were those located farthest from the argon (Ar) input and recoater starting line. The roughness of the semisphere samples is generally similar in all the zones since their roughness is linked to the staircases, powder material sticking, and ripples. After the analysis of the as-built samples, it was concluded that Ti6Al4V medical implant samples produced by L-PBF require postprocessing to meet the surface finish expected for medical implants. The 60, 90, and 120 minutes of dry electropolishing made L-PBF surfaces smoother but did not meet international standards for medical implants. A longer time of dry electropolishing and chemical polishing in HF-HNO3 solution allows the achievement of surface roughness (Ra) of less than 5 μm, but the weight loss increases, which can influence the L-PBF implant dimensions and shape.