A phase-field model investigating the role of elastic strain energy during the growth of closely spaced neighbouring interphase precipitates

A multi-phase field method is developed to investigate the effects of transformation strain on the transformation kinetics, thermodynamic stability and pairing of interphase precipitates in micro-alloyed steels. The model conserves homogeneity of stress in the diffuse interface between elastically inhomogeneous phases and provides an explanation of the mechanism resulting in the pairing of two adjacent interphase precipitates. Several scenarios of inhomogeneous elastic conditions have been considered. The simulations for a situation where only the interfacial energy is considered to contribute to the transformation show that this energy can lead to the establishment of a neck between two neighbouring precipitates. However, if sufficient time is given, one of the precipitates will completely dissolve into its neighbouring particle. On the other hand, when both strain and interfacial energies act on the system, the bridge between the particles becomes stabilised leading to the pairing of the particles. This is a result of the particles tendency to minimise the strain energy due to the excessive strain field generated by the neck between the two particles.