Effects of grain boundaries and temperature on spinodal decomposition in a binary Fe-Cr alloy: A phase-field simulation

Due to its excellent oxidation resistance, corrosion resistance and mechanical properties, Fe-Cr based stainless steel is a promising candidate for advanced nuclear power systems. At the temperature of 300–600 °C, spinodal decomposition usually occurs in Fe-Cr alloys. However, irradiation can greatly accelerate this process. Fe-Cr based stainless steel decompose into a Cr-enriched α^′ phase and a Fe-enriched α phase during spinodal decomposition, and the Cr-enriched α^′ phase plays an important role in the hardening/embrittlement of Fe-Cr based stainless steels. In the present work, the evolution of vacancy and the Cr-enriched α^′ phase in Fe-Cr alloy is investigated using phase-field method. The simulation results show that the vacancy concentration has a great influence during the spinodal decomposition. The Cr-enriched α^′ phase occurs initially at the positions with high vacancy concentration. During spinodal decomposition, the vacancy forms a defect concentration loop around the Cr-enriched α^′ phase. In addition, with the increase of temperature, the concentration of Cr atoms in the center of the Cr-enriched α^′ phase decreases, and the coarsening rate increases, while the number of the Cr-enriched α^′ phase formed in the alloy decreases. At low temperature, α^′ phase is mainly coarsened by interlinking; while at high temperature, α^′ phase is mainly coarsened by Oswald maturation. Moreover, the Cr-enriched α^′ phase occurs at the grain boundary (GB) and the Fe-enriched α phase occurs at both sides of the GB during the spinodal decomposition. At the same time, in polycrystalline system, GB movement during grain growth is inhibited during the spinodal decomposition.