Modelling of a transition to the diffusionless dendritic growth in rapid solidification of a binary alloy
The diffusionless growth of dendritic crystals results in microsegregation-free microstructures with an initial (nominal) chemical composition of solidifying systems. Normally, a transition from chemical partition growth to diffusionless solidification is accompanied by the morphological transition in a crystal shape with nonlinearity appearing in the kinetic behaviour of growing crystals. This phenomenon has been studied using a model of local non-equilibrium rapid solidification. In describing the transition from the solute diffusion-limited growth to purely thermally controlled growth of dendritic crystals, the model predicts the abrupt change of growth kinetics with the break points in the dendrite tip velocity-undercooling and dendrite tip radius-undercooling relationships. It is shown that the abrupt change of growth kinetics occurs with the ending of the transition to purely thermally controlled growth and onset of the diffusionless solidification. Using the numerical modeling methods it has been proved that a correct description of kinetics requires all kinds of interface anisotropy to be taken into account simultaneously. This includes the anisotropy of surface energy and that of atom attachment kinetics.