On dislocation interaction with radiation-induced defect clusters and plastic flow localization in fcc metals

Abstract

Plastic instability associated with formation of narrow flow channels results from dislocation pinning–unpinning by defect clusters. We investigate the dynamics of dislocation interaction with radiation-induced defect clusters, and specifically with, firstly, sessile self-interstitial atom clusters in dislocation decorations and, secondly, stacking-fault tetrahedra (SFTs) in the matrix. It is shown that the critical stress to free trapped dislocations from pinning atmospheres can be a factor of two smaller than values obtained on the basis of rigid dislocation interactions. The unpinning mechanism is a consequence of the growth of morphological instabilities on the dislocation line. Dislocation sources are activated in spatial regions of low SFT density, where their destruction by glide dislocations leads to subsequent growth of localized plasticity in dislocation channels. We show that removal of SFTs is associated with simultaneous dislocation glide and climb. Jogs of atomic dimensions are formed when a fraction of SFT vacancies are absorbed by pipe diffusion. The width of a flow channel is explained in terms of two length scales: the size of an individual SFT, and the dislocation source-to-boundary distance (d of the order of micrometres). While dislocation segments climb by a few atomic planes with each SFT destruction event, d determines the total number of such events. Numerically computed channel widths (about 70–150nm), and the magnitude of radiation hardening in copper are consistent with experimental observations.