Mapping of three-dimensional residual stresses by neutron diffraction in nickel-based superalloy discs prepared under different quenching conditions

Abstract

Large interior residual stresses, generated during various thermomechanical treatments, could greatly affect not only the machining dimension precision during subsequent machining processes but also the structural stability under service in superalloy components. In this paper, neutron diffraction measurements have been carried out to characterize the three-dimensional residual stress distributions in IN718 superalloy discs quenched with different media, including water, oil, air and insulation. Three-dimensional residual stress maps have been derived in these specimens. It was found that, in the water-quenched, oil-quenched and air-cooled specimens, the residual stresses are compressive near the surface balanced by tension within the interior, with the peak magnitude stresses of 560 MPa, 480 MPa and 120 MPa, respectively. It was evidenced that there is no obvious residual stress in the insulation-cooled specimen. The corresponding Vickers hardness maps show a larger hardness at the core and smaller hardness near the surface in the water-quenched, oil-quenched and air-cooled specimens, whereas there is a larger hardness near the cylindrical surface and smaller hardness at the central axis in the insulation-cooled specimen, achieved by the differential cooling rate control. Our investigations show that the coordinated regulation of residual stress and microstructure and properties can be realized by reasonably selecting cooling media.