Phase-Field Simulation of Phase Transformation in Fe-Cu-Mn-Ni Quaternary Alloy

Abstract

The phase decomposition in α(bcc) phase and the subsequent structural phase transformation from α to γ(fcc) phase during isothermal aging of an Fe-Cu-Mn-Ni quaternary alloy, which is a base alloy of the light-water reactor pressure vessel, have been simulated by the phase-field method. At the early stage of spinodal decomposition, Cu-rich α phase is formed, and the Mn and Ni, which are minor components, are partitioned to the Cu-rich phase. As the Cu composition in the precipitate is increased, the Ni atoms inside the precipitates move to the interface region between the precipitate and matrix, but Mn atoms remain inside the Cu particles. When the Cu-rich particles eventually transform to the fcc structure, the Mn atoms also move to the interface region, which results in the shell structure of the fcc Cu precipitates, where each particle is surrounded by a thin layer enriched in Mn and Ni. This microstructural change can be reasonably explained by considering the local equilibrium at the surface region of the Cu-rich particles.