Investigation of the equilibrium morphology of fcc [formula omitted] in Fe–Cu alloys using a non-local Allen–Cahn model

Abstract

Cu-precipitation is one of the main concerns of the degradation of mechanical properties in reactor pressure vessel steels. It is especially prominent in the over-aged state, where the Cu-rich phase possesses an equilibrium face-centered cubic crystal structure. In this study, we develop and implement a non-local phase-field model to study the equilibrium morphology of precipitates in the over-aged state. The model reveals that the precipitates should possess oblate lath-like morphology, which is supported by novel experimental data. The orientation of the precipitates agrees well with the available literature. The mechanism of the morphology accommodation is explained using a theoretical framework of the invariant-line method. Also, morphology was analyzed quantitatively in the sense of its elongation. It was found that the equilibrium values deviate significantly from experimental data in this metric, which is assumed to be due to the metastable state of the precipitates during the coarsening process.