Dissipative structure formation during crystallization of alloys under high-nonequilibrium conditions

TL;DR

This paper models the crystallization process in alloys under high nonequilibrium conditions, revealing a morphological transition characterized by a sudden increase in dendrite growth velocity during rapid solidification.

Contribution

It introduces a computer model that accounts for temperature-dependent diffusion and nonequilibrium partitioning, identifying a critical undercooling for morphological transition.

Findings

Discontinuous increase in dendrite growth velocity at critical undercooling.

Transition from diffusion to thermal growth regime.

Dependence of critical undercooling on anisotropy and activation energies.

Abstract

The crystallization of a binary system is investigated in computer model which takes into account a temperature dependence of diffusion coefficient and a nonequilibrium partition of dissolved component of the alloy. The dependence of interface velocity on an undercooling at the dendrite tip is obtained during rapid solidification of Fe-B and Ni-B systems. The morphological transition which is conditioned by change from a diffusion growth regime to thermal growth at some critical undercooling is detected. This transition is characterized by discontinuous magnification of the dendrite growth velocity. Values of a critical undercooling and a growth velocity discontinuity depend both on a degree of an anisotropy of a kinetic coefficient, and on difference in energies of activation for atomic kinetics and for diffusion on an interface.