Comparative study on the surface integrity of Inconel 718 parts produced by laser powder bed fusion after different finishing techniques

This study evaluates the effectiveness of four surface finishing methods – Glass Bead Blasting (GBB), Ceramic Chip Grinding (CCG), Dry Electropolishing (DEP), and Abrasive Flow Machining (AFM) – on Inconel 718 samples produced via Laser Powder Bed Fusion (PBF-LB). The assessment was conducted based on technical, geometric, and economic criteria tailored for thin-walled aerospace applications. Following heat treatment (comprising stress relieving, hot isostatic pressing, solution annealing, and double aging), the alloy achieved near-theoretical density, a recrystallized microstructure characterized by a 55% fraction of Ʃ3 twin boundaries, and precipitation hardening corresponding to a peak hardness of 428 HV10. At a test temperature of 425 °C, despite variations in surface finishing techniques, the high density of Ʃ3 boundaries combined with high fracture toughness resulted in a satisfactorily high fatigue limit range (at R = 0.05) between 450 and 485 MPa. Apart from GBB, the CCG, DEP, and AFM methods successfully reduced the surface roughness (Ra) to below 2 µm, shifting fatigue crack initiation sites from surface notches to subsurface crystallographic facets. Comparative analysis indicated that the AFM method is the best solution for balancing the established multidimensional criteria. AFM provided high fatigue strength (475 MPa at 425 °C) while exhibiting minimal geometric distortion. Furthermore, this method featured the most favorable ratio of capital expenditure (CAPEX) to operating expenses (OPEX), making it the optimal choice for aerospace components where high-cycle fatigue resistance and cost-effectiveness are paramount.