Mean-field modelling of γ' precipitation in additively manufactured IN738LC Ni-based superalloy

The gamma' precipitate coarsening kinetics in additively manufactured Ni-based superalloys needs to be investigated to predict the microstructure stability at high temperature. Therefore, we investigate the gamma' precipitate coarsening kinetics in a laser powder bed fusion IN738LC Ni-based superalloy at 900 degrees C. We find that the initial bimodal gamma' precipitate size distribution at 24 h of ageing time changes to unimodal distribution at 168 h of ageing time at 900 degrees C. We perform the mean-field modelling to understand the transition physics using gamma-gamma' composition and gamma' volume fraction obtained using atom probe tomography and find that the modelling results are consistent with the experimental observation. Based on the modelling, we found that the gamma' volume fraction is an important parameter in the mean-field modelling, which is slightly higher than the equilibrium value due to the non- equilibrium composition of gamma-gamma' phases in the additively manufactured superalloy. Furthermore, the gamma/gamma' interfacial energy is predicted to increase from bimodal to unimodal distribution due to an increase in Ti/Al ratio in gamma' precipitate, which increases the gamma' precipitate coarsening kinetics. It is also found that the gamma/gamma' interfacial energy and z factor have more influence on the gamma' precipitate coarsening kinetics than the mobility parameter in additively manufactured IN738LC. In conclusion, the gamma' precipitate coarsening kinetics in additively manufactured Ni-based superalloy is predicted to be slightly faster than the alloy with equilibrium composition of phases.