Grain boundary engineering activated by residual stress during the laser powder bed fusion of Inconel 718 and the electrochemical corrosion performance

Abstract

Conventional grain-boundary engineering (GBE) is not directly compatible with the complicated geometric parts fabricated via laser powder bed fusion (LPBF) owing to the multiple thermomechanical processes involved therein. In this study, GBE was activated by the inherent residual stress of an Inconel 718 superalloy produced via LPBF. The grain boundary character distribution and corresponding electrochemical corrosion behaviors were systematically investigated in a 3.5 wt% NaCl solution. The results indicate that numerous Σ3 boundaries (twin boundary, 64.89%) can be obtained via a simple heat treatment, and a favorable grain size can be maintained owing to the segmentation effect of the twin boundary. The corrosion resistance is closely related to the fraction of low special low-coincidence site lattices because the random boundary networks are broken. In addition, samples fabricated using GBE with the highest fraction of the twin boundary exhibited more compact and stronger passive films. The main components (oxide and metallic states) of thicker passive films provided intrinsic protection for the matrix. This study demonstrates a feasible method for GBE in additive-manufactured superalloys for fabricating complicated geometric parts with unique properties.