Definition of an optimal solutioning treatment for a Ni-based superalloy processed by Additive Manufacturing

The current work aims at defining an optimal recipe for the solution annealing (SA) of a high-fraction gamma' Ni-based superalloy manufactured with Laser Powder Bed Fusion process (PBF-LB/M). The studied alloy is designed for the aeronautical or energy sectors to perform above 800 degrees C. The microstructure obtained from PBF-LB/M process (asbuilt state) is extremely fine with grains aligned along the building direction, due to the thermal flow during the process. Moreover, due to the fast cooling, the main reinforcing phase (gamma', a Ni3(Al,Ti) ordered L1(2) precipitate) cannot precipitate. SA temperatures of 1230 degrees C, 1245 degrees C and 1260 degrees C were investigated to obtain the best microstructure in terms of reinforcing precipitates' size, shape and fraction and grain size, keeping the soaking time constant (2 hours). Then, a first aging (FA) was also applied at 1095 degrees C for 4 hours. The test plan was configured to account for industrial furnaces thermal uncertainty, introducing also higher temperatures to verify the presence of any thermal induced porosities (TIPs) or incipient melting traces. The morphology, size and volume fraction of gamma' phase were assessed and quantified using scanning electron microscopy (SEM). Light optical microscopy (LOM) was used to evaluate the grains aspect ratio and growth during SA.