On the kinetics of homogeneous nucleation of incoherent precipitates in solid solutions

TL;DR

This paper revises the understanding of homogeneous nucleation in solid solutions by showing elastic strain effects differ for incoherent precipitates and proposing a new kinetic model incorporating point defect effects.

Contribution

It introduces a new kinetic model for incoherent precipitate nucleation that accounts for point defect absorption and elastic stress relief, challenging traditional elastic strain assumptions.

Findings

Elastic strain increases are valid for coherent precipitates only.

Point defects can be absorbed at interfaces, relieving elastic stresses.

A new nucleation rate prediction model for incoherent precipitates is proposed.

Abstract

By critically examining the traditional theory of homogeneous nucleation of precipitates in solid solutions, it is revealed that the theory's assertion regarding an increase in the nucleation free energy due to elastic strain associated with the difference in atomic volumes between the two phases is applicable to coherent precipitates, but becomes incorrect when applied to incoherent precipitates. This conclusion is obtained by accounting for thermal point defects in the matrix, which can be absorbed at the interface between an incoherent particle and the matrix during nucleation, thereby relieving elastic stresses. Accordingly, a new kinetic model based on the Reiss theory for binary nucleation is proposed for predicting the nucleation rate of incoherent precipitates by agglomeration of solute atoms and point defects, with a further extension to account for excess vacancies formed under non-equilibrium conditions of quenching experiments.