Phase-field modelling of spinodal decomposition with G-phase precipitation during ageing

The duplex stainless steels (DSSs) are susceptible to thermal ageing embrittlement due to the spinodal decomposition and G-phase precipitation in the ferritic phase. This study presents a ternary (Fe-Cr-Ni) phase-field model for the simulation of spinodal decomposition with concurrent G-phase precipitation. Two Cahn-Hilliard equations and one Ginzburg-Landau equation are used in the model to describe the diffusion of Cr, Ni, and the growth of G-phase, respectively. The model is able to generate a spinodally-interconnected structure with G-phase particles near the α-α′ interfaces, similar to experimental observations. The kinetic synergy between spinodal decomposition and G-phase precipitation is discussed. The simulation results indicate that G-phase can enhance the evolution of spinodal decomposition by occupying the volume where the decomposition could otherwise occur, and that the system’s elastic strain energy is largely contributed by G-phase rather than spinodal decomposition. These results would help in better understanding the states of the materials for plant structural integrity assessment and life management.