Simulation and experimental analysis of nanoscale precipitation during ageing treatment of laser powder-bed fusion fabricated IN718 Ni-based superalloy

Temporal evolution of the nanoscale disc-shaped γ′′ (Ni3Nb) and spherical γ′ (Ni3(Al,Ti)) strengthening precipitates during double-stage ageing treatment of the laser powder-bed fusion (LPBF) fabricated IN718 Ni-based superalloy is studied by thermodynamic-based modeling, electron microscopy, and small-angle neutron scattering (SANS). The precipitation kinetics of both γ′′ and γ′ particles in the multi-component/multi-phase IN718 alloy system was successfully predicted by the Langer–Schwartz–Kampmann–Wagner approach. The simulated particle size and volume fraction during ageing was validated against electron microscopy and SANS results, respectively. The size and volume fraction of the γ′′ phase was monotonically increased during the first ageing stage up to about 100 nm and 14%, respectively, but interestingly unchanged during the second stage. On the other hand, the volume fraction of γ′ phase was sharply increased to about 15% after about 100 s and kept constant until the end of the first ageing stage, where it then decreased to about 7%. The γ′ particle size monotonically increased up to about 20 nm. According to the determined temporal evolution of the nanoscale precipitates, a shorter ageing treatment of the LPBF IN718 superalloy compared to the conventionally manufactured alloy could be suggested.