Solute trapping and diffusionless solidification in a binary system

TL;DR

This paper develops a model explaining how rapid solidification in binary systems leads to metastable phases through solute trapping, transitioning from partitioned to diffusionless growth, and matches experimental data across various velocities.

Contribution

It introduces an analytical model describing the transition from partitioned to diffusionless solidification considering interface and bulk diffusion speeds.

Findings

Model accurately predicts solute trapping at various velocities.

Analytical conditions for complete solute trapping are derived.

Experimental data on Si-As alloys are well explained by the model.

Abstract

Numerous experimental data on the rapid solidification of binary systems exhibit the formation of metastable solid phases with the initial (nominal) chemical composition. This fact is explained by complete solute trapping leading to diffusionless (chemically partitionless) solidification at a finite growth velocity of crystals. Special attention is paid to developing a model of rapid solidification which describes a transition from chemically partitioned to diffusionless growth of crystals. Analytical treatments lead to the condition for complete solute trapping which directly follows from the analysis of the solute diffusion around the solid-liquid interface and atomic attachment and detachment at the interface. The resulting equations for the flux balance at the interface take into account two kinetic parameters: diffusion speed $V_{DI}$ on the interface and diffusion speed $V_D$ in bulk phases. The model describes experimental data on nonequilibrium solute partitioning in solidification of Si-As alloys [M.J. Aziz et al., J. Cryst. Growth {\bf 148}, 172 (1995); Acta Mater. {\bf 48}, 4797 (2000)] for the whole range of solidification velocity investigated.