Phase field study of the copper precipitation in Fe-Cu alloy

Fe-Cu low-carbon steels play significant roles in a rich variety of applications. The high strength of Fe-Cu steels originates from the strengthening effect of Cu precipitates. Further optimization of mechanical properties of Fe-Cu and Fe-Cu based steels requires an understanding of precipitation process of Cu particles. In this study, a comprehensive phase field model is developed which captures the microstructure evolution process during the nucleation and growth of BCC Cu precipitates followed by the BCC → 9R phase transformation. Results generated by phase field simulations agree well with previous experimental reports. In addition, the pseudo-spinodal decomposition theory is adopted to analyze the kinetic process of precipitation. Our simulation results and theoretical analyses jointly demonstrate that the kinetic process of precipitation and the initial Cu concentration of precipitates are ageing temperature and composition dependent, which is helpful in solving the mystery of the Cu concentration in precipitates of early stage. Moreover, interfacial energy and internal stress are found to be responsible for the temperature and composition dependence of critical nucleation size of the 9R phase, respectively. The nature of wetting layer and the mechanism that regulates the thickness of wetting layers are revealed as well. The comprehensive phase field model developed in this study offers a powerful tool for investigating precipitations in Fe-Cu alloys. The findings of this study provide new insights on the evolution process of Cu precipitates in Fe-Cu alloys.