A study on the effect of the number of clusters at the phase transformation kinetics

Abstract

This work aims to study cluster nucleation, whose solid–solid phase transformation kinetics considerably deviates from that forecasted by the Kolmogorov–Johnson–Mehl–Avrami (KJMA) model. In this scenario, nuclei do not appear homogeneously within the matrix; however, they appear in preferred regions called clusters. One of the principal parameters of this nucleation is the number of clusters in the matrix. This work uses a numerical model to simulate nucleation and growth reactions, which occur explicitly in spherical clusters. It was thus possible to analyze the cluster number variation affecting the microstructural evolution. During the numerical experiments, we compare the simulation outcomes with the analytical model from Villa & Rios. It was possible to observe that analytical solutions from Villa & Rios equations corroborated the numerical results. The computational model of this study agrees with the analytically exact modeling. This study expanded the analytical solution showing the microstructural evolution in 3D. The simulations also proved that the slower the phase transformation reaction occurs, the fewer clusters per unit volume. Also, the generated microstructures have their particular characteristics. Studies in cluster matrices that use only qualitative and visual analyses can lead to wrong interpretations regarding microstructural evolution when using conventional models of formal kinetics. Thus, the computer simulation study presented that Villa & Rios model is the most suitable for this case involving clustering nucleation. The research shows that clustering introduces microstructural heterogeneity into the matrix. This heterogeneity can be harmful to the materials' final properties that underwent a microstructural transformation with these characteristics.