Predicting Coherency Loss of γ^″ Precipitates in IN718 Superalloy

Precipitate hardening through coherent particles is an important strengthening mechanism in Ni-based IN718 superalloy. The change of coherency state, e.g., loss of coherency, can affect the precipitation kinetics and the efficacy of precipitate hardening. In this work, we predict the critical size of γ^″-Ni₃Nb precipitates in IN718 to trigger coherency loss using the phase-field approach with available materials parameters from first-principles calculations and from the literature. The predicted critical size lies within the range of experimentally reported values. The effect of coherency loss on precipitate morphology and kinetics, as well as the aging time to reach this critical size during heat treatment, is also predicted and discussed. These predictions provide guidance in controlling the size of γ^″ precipitates and optimizing the strength of IN718 alloys.