Simulation of co-precipitation kinetics of γ' and γ" in superalloy 718

Abstract

In this paper, we will study the co-precipitation kinetics of phases in Superalloy 718 using the simulation tool we have developed using the CALPHAD approach. This tool considers concurrent nucleation, growth and coarsening of these precipitates. Furthermore, it is directly integrated with thermodynamic calculation engine to obtain instant update of phase information, such as the composition of the matrix and the nucleation driving force for each precipitate. In addition to the average particle size, the more advanced KWN (Kampmann and Wagner Numerical) model was implemented to allow for predication of the full evolution of the particle size distribution (PSD). In this paper, we will perform virtual experiments using this tool to simulate the co-precipitation of the γ′ and γ″ phases under different heat treatment conditions. Simulation results, such as temporal evolution of volume fraction, number density, and mean size of the precipitates, as well as the final particle size distribution will be presented and discussed. The impact of δ precipitate and the initial microstructure will also be briefly discussed. These virtual experimental results can be used to understand the microstructural features of Superalloy 718 and serve as guidance for further optimization of heat treatment schedule.