Grinding- and robotic hammer peening-induced modifications in the near-surface regions of laser-cladded Inconel 718 coatings

Abstract

Inconel 718 coatings deposited by laser-cladding (LC) on low-alloy steel substrate have been grinded followed by robotic hammer peening (RHP). White layer consisted of nanograins, smaller than 100 nm, has been observed on the surface accompanied with a deformation layer underneath after grinding and RHP. By increasing the RHP intensity (i.e., both the impact energy and the dent overlap), the residual tensile stress measured by X-ray diffraction from the surface of the coating has been monotonically reduced and eventually converted to residual compressive stress with increased in-plane anisotropy, which was accompanied with monotonically increased surface hardening up to 40.5 HRC. Grain deformations have been induced in the white- and deformation-layer, they are dominated by twinning and slipping, respectively. In terms of depth-dependent distributions of low-angle (<15°) grain boundaries and hardening, the effective cold-working thickness induced by the RHP process is over 1000 μm, which is close to the thickness of a single-pass LC deposition. Onset of porosity closures occurred upon the RHP process, especially in the near-surface regions. These findings shed light on integrity enhancement for additive manufacturing of metal alloys by LC-based techniques through introducing interpass RHP process.