Segregation of cascade induced interstitial loops at dislocations: possible effect on initiation of plastic deformation

In metals and alloys subjected to cascade damage dislocations are frequently found to be decorated with a high density of small clusters of self-interstitial atoms (SIAs) in the form of dislocation loops. In the present paper it is shown that this effect may be attributed to the glide and trapping of SIA loops, produced directly in cascades (rather than to the enhanced agglomeration of single SIAs), is the strain field of the: dislocations. Tnt conditions for the accumulation of glissile SIA loops near dislocations as well as thr dose and temperature dependencies of this phenomenon are discussed. II is suggested that the decoration of dislocations with loops may play a key role in radiation hardening subjected to cascade damage. It is shown, for example, that the increase in the upper yield stress followed by a yield drop and plastic instability in metals and alloys subjected to cascade damage cannot be rationalized in terms of conventional dispel-sed barrier hardening (DBH) but may he understood in terms of cascade induced source hardening (CISH) in which the dislocations are considered to be locked by the loops decorating them. Estimates for the stress necessary to pull a dislocation away from its loop 'cloud' are used to discuss the dose and temperature dependence of plastic flow initiation. (C) 1997 Elsevier Science B.V.