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

Plastic instability associated with formation of narrow flow channels resul ts from dislocation pinning-unpinning by defect clusters. We investigate th e dynamics of dislocation interaction with radiation-induced defect cluster s, 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 disloca tions from pinning atmospheres can be a factor of two smaller than values o btained on the basis of rigid dislocation interactions. The unpinning mecha nism is a consequence of the growth of morphological instabilities on the d islocation line. Dislocation sources are activated in spatial regions of lo w SFT density, where their destruction by glide dislocations leads to subse quent 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 te rms of two length scales: the size of an individual SFT, and the dislocatio n source-to-boundary distance. d of the order of micrometres). While disloc ation segments climb by a few atomic planes with each SFT destruction event , d determines the total number of such events. Numerically computed channe l widths (about 70-150 nm), and the magnitude of radiation hardening in cop per are consistent with experimental observations.