Microstructural and mechanical characterization of a shot peening induced rolled edge on direct aged Inconel 718 alloy

Shot peening of complex geometries can generate rolled edges which mechanical properties, compared to a flat shot peened specimen, are not well known. Electron BackScattered Diffraction (EBSD) analyses and nanoindentation tests were conducted to characterize the microstructural changes and hardening induced in the rolled edge compared to a reference flat part of an Inconel 718 direct aged specimen. Dictionary Indexing was used to improve the indexation quality in zones presenting severe plastic deformations. Geometrically necessary dislocation densities were estimated from the EBSD orientation maps and correlated with the nanoindentation measurements using a Taylor hardening model. The rolled edge zone presented 1 GPa higher hardening values and a steeper hardening gradient as compared with the reference. This was mainly attributed to work hardening, due to higher dislocation densities around the rolled edge. Such differences could result from a pure shear state induced by bending of the surface close to the sample's border during the rolled-edge formation.