Corrective capabilities of different rescanning strategies to restore microstructure and density of initially porous 316L laser powder bed fusion

Abstract

Abstract. Mechanical properties of Laser Power Bed Fusion (LPBF) parts, and particularly fatigue properties, are heavily affected by defects including surface roughness or porosity. To mitigate the occurrence of these defects, in-situ and on-line corrective measures can be implemented to the fabrication process, among them, rescanning, which consists in remelting an already solidified layer. Initially porous LPBF samples were created and then rescanned using different scanning parameters and strategies. Results show that it is possible to regain part’s health, compared to a standardly processed one, in terms of density, hardness and even improved roughness. This remelting process is known to refine microstructure of fabricated materials as well as reduce surface roughness and porosity without requiring further post-processing steps. Therefore, employing rescanning as a corrective technique appears to be a promising approach for rectifying detected defects during the fabrication process. The objective of this study is to assess the corrective capabilities of different rescanning strategies to restore the microstructure of an initially porous 316L LPBF simulating a defected part. This study shows that various rescanning strategies allow for densification of initially porous material from 98.83 ± 0.20 % to 99.75 ± 0.09 %, as well as lateral surface roughness reduction from Ra 20.2 ± 5.2 µm to Ra 12.7 ± 0.1 µm and microhardness increase from 243 ± 5 HV0.5 to 253 ± 3 HV0.5.