Cooperative Effects in Microstructural Evolutions Under Irradiation: Fundamental Aspects

Abstract

Microstructural development under high temperature irradiation corresponds to the coupled evolution of various solute and defect sink strengthes, resulting from the continuous absorption or emission of point defects at these sinks. The coupling results from the fact that each class of sink exchanges point defects and solute with the same unique reservoir. We propose a novel technique for studying the coupling of the evolution of the various components of the microstructure. The state of the microstructure is represented by a point in an appropriate state space; a microstructural evolution corresponds to a trajectory in this space. Standard techniques are used for studying the topology of all a priori possible trajectories. The practical use of this technique is exemplified by the study of the evolution of dislocation lines or dislocation interstitial loops in the presence of cavities. The state of the microstructure is represented by the curvature radii of these two classes of sinks. The model reveals the following possible behaviours, some of which have been experimentally observed but not properly accounted for by existing theories: - existence of an incubation dose for swelling. The amplitude of the incubation dose depends on the dislocation density and on the irradiation flux and temperature; - possibility of transient swelling (cavity growth followed by decay); - large dose divergence of evolutions which are very similar at lower doses (swelling heterogeneities); - irradiation induced enhancement of the rate of sintering: a new mechanism has been revealed by the model. Preliminary results obtained for precipitates-containing microstructures are briefly discussed.