RADIATION HARDENING REVISITED - ROLE OF INTRACASCADE CLUSTERING

Experimental observations related to the initiation of plastic deforma tion in metals and alloys irradiated with fission neutrons have been a nalyzed. The experimental results, showing irradiation-induced increas e in the upper yield stress followed by a yield drop and plastic insta bility, cannot be explained in terms of conventional dispersed-barrier hardening because (a) the grown-in dislocations are not free, and (b) irradiation-induced defect clusters are not rigid indestructible Orow an obstacles. A new model called 'cascade-induced source hardening' is presented where glissile loops produced directly in cascades are envi saged to decorate the grown-in dislocations so that they cannot act as dislocation sources. The upper yield stress is related to the breakaw ay stress which is necessary to pull the dislocation away from the clu sters/loops decorating it. The magnitude of the breakaway stress has b een estimated and is found to be in good agreement with the measured i ncrease in the initial yield stress in neutron irradiated copper. (C) 1997 Elsevier Science B.V.