Heat treatment behaviour of IN718 superalloy fabricated by laser-powder bed fusion

IN718 Ni-superalloy samples were produced by Laser Powder Bed Fusion (LPBF). The phase transformations that occur during different heat treatments, the microstructure evolution and static mechanical properties were investigated. Two-steps artificial ageing (AA), solution annealing followed by artificial ageing (SA + AA) and homogenization annealing followed by solution annealing and artificial ageing (HA + SA + AA) were performed and the relevant phase transformations were investigated through dilatometric analysis. The precipitation temperature of γI (525 ◦C), γII (725 ◦C) and δ (935 ◦C) were determined. The activation energy of γI precipitation was estimated by means of Kissinger-like method to be about 248 ± 21 kJ/mol. It was demonstrated that the strengthening effect after AA is attributed to γII precipitation. Besides, SA and HA are responsible of the chemical homogenization and anisotropy removal. SA itself is not able to completely recover the solidification structure, so HA is necessary for a full recrystallization.