Cascade morphology transition in bcc metals

TL;DR

This paper identifies a morphological transition in collision cascades within bcc metals, characterized by a change in defect production behavior, and provides an empirical formula relating transition energy to material properties.

Contribution

It establishes the existence of a morphological transition in collision cascades in bcc metals and derives an empirical formula for the transition energy based on material parameters.

Findings

Existence of a morphological transition in bcc metals cascades.

Empirical formula relating transition energy to displacement threshold energy.

Comparison of different bcc metals using normalized cascade energy.

Abstract

Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, $b$, in the defect production curve as a function of cascade energy ($N_F \sim E_{MD}^b$). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, $\mu$, between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of $\mu$ as a function of displacement threshold energy, $E_d$, is presented for bcc metals.