Analysis of strain-induced precipitates by delta-processing in Inconel 718 superalloy

Delta-Processing (DP) is a suitable heat treatment process aiming at controlling grain growth during hot deformation of the well-known Ni-base superalloy Inconel 718 (IN718). DP is often applied by heating up to 900 degrees C for 24 h in order to promote delta-phase saturation prior to deformation. In addition to the delta-phase, Mo and Cr-rich carbides in the form of M23C6 may also precipitate during the subsequent hot deformation of this alloy in the range of 950-1000 degrees C These carbides are induced by deformation and can affect the static and dynamic recrystallization of the matrix. The objective of the current work is to understand the precipitation of M23C6 carbides when the material has been saturated with delta-phase precipitation, as well as their interaction with recrystallization phenomena. For this purpose, a series of double-strain hot compression test (double-hit) were carried out. Several holding times were applied between the first and the second hit in order to derive the softening/hardening fraction progress with time. Microstructural characterization of the samples was performed through Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) in order to identify the precipitating/dissolving phases under each testing condition.