Phase-Field Modeling of γ′ and γ″ Precipitate Size Evolution During Heat Treatment of Ni-Based Superalloys

Abstract

The goal of an aging heat treatment in Ni-based superalloys is to control the volume fraction and size of the strengthening precipitates. We predict the precipitate size evolution of primary L12 and D022 precipitates in the industrially relevant alloys CMSX-4, René80, and IN718 using a one-dimensional phase-field model with an artificial Gibbs–Thomson driving force considering the shape of non-spherical precipitates. In comparison with the classical theory of precipitate ripening, the presented phase-field model considers all alloying elements, non-isothermal cooling, and heating stages and off-equilibrium volume fraction. We implicitly consider elastic effects between precipitate and fcc solid solution matrix by adjusting the mobility parameters and considering size dependent non-spherical D022 precipitate shapes. Literature data reveals the strong predictive potential of this multi-scale method for integrated computational materials engineering. We identify individual aging stages during which precipitate growth is dominated by either ripening or precipitation from the supersaturated matrix phase.