Surface Shot Peening Post-processing of Inconel 718 Alloy Parts Printed by Laser Powder Bed Fusion Additive Manufacturing

The shot peening (SP) post-processing was applied under different regimes to improve the surface characteristics of the nickel-based Inconel 718 alloy parts printed by a laser powder bed fusion (LPBF) additive manufacturing technique. The effects of SP treatment on surface topography, roughness, waviness, chemical composition, macrohardness, and defects on the surface of the LPBF-printed specimens were estimated in this work. The surface microstructure, phase state, subsurface porosity, microhardness distribution, and stress state in the near-surface layer of the LPBF-built and SP-processed specimens are also addressed to optimize the SP parameters for surface finishing and hardening of the LPBF-built superalloy parts. The experimentation on an industrial SP system and the surface roughness, hardness, and porosity analysis allowed the identification of appropriate peening pressure for surface treatment of the studied LPBF-built alloy. Particular attention is paid to the study of microstructural aspects induced by the severe surface plastic deformation. Results indicated that applied SP treatment leads to a decrease in the Ra roughness parameter providing a new wavy surface microrelief on the surface. The spherical/ellipsoidal balls and partially melted powder particles were successfully removed from the treated surface by the SP treatment, which also reduced a subsurface porosity. As compared to the LPBF-built sample (~370 HV0.025), the SP post-processing leads to work hardening, providing up to 75% increase in the surface microhardness due to the strain-induced grain refinement.