Theory of nucleation with cluster loss and injection: Application to plastic deformation and irradiation

Abstract

Conventional nucleation theory considers the growth and decay of clusters only by thermally activated single atom addition or subtraction. Many environments of interest, including plastic deformation and energetic particle irradiation, induce numerous dynamic processes to create a host of defects which may produce a new nucleation regime. Creation and movement of dislocations and point defects and passage of thermal and stress waves could readily destroy or remove atoms from subcritical clusters, which typically contain at most only a few tens of atoms. Displacement cascades could destroy subcritical precipitates or vacancy clusters. It is also possible that clusters are injected into the system, as with vacancy-rich displacement cascades which may act as precursors for dislocation loop or void nuclei. This article modifies the nucleation equation to account for such cluster loss and injection and solves the resulting equation analytically for the steady state. The effects of cluster loss are described by several dimensionless groupings of kinetic and thermodynamic parameters. Cluster loss is found significant only if the probability of destruction is comparable to or greater than the probability of growth by single atom capture. The effects of cluster loss are predicted to be greatest for phases which form with large critical nuclei or complex unit cells. Athermal single atom loss, as by radiation resolution in ion mixing, appreciably reduces the nucleation rate only when the rate of loss approaches or exceeds the rate of solute atom capture.