Samples were irradiated, at 473 or 573K, to between 0.0003 and 0.14dpa. In specimens which had been irradiated at 573K to 0.0003dpa, the number of vacancies which accumulated in the largest stacking-fault tetrahedron was 276. It was equal to 470 in the case of the smallest voids. This was explained by a model in which, at 573K, a stacking-fault tetrahedron changed into a void when the number of vacancies exceeded about 400. In samples which were irradiated at 573K, the numbers of vacancies in a stacking-fault tetrahedron and a void of average size increased with the neutron fluence. The number of vacancies in a void increased more rapidly than that in a stacking-fault tetrahedron. The reason was suggested to be that small vacancy clusters relaxed, at 573K, to a string-like cluster. They then moved as a cluster and coalesced. Experimental results revealed the movement of voids. In material which was neutron-irradiated at 573K, the number-density of stacking-fault tetrahedra and voids peaked at 0.0003dpa and decreased with fluence. The reason for this was suggested to be a low sink efficiency of dislocations for point-defect absorption at 0.0003dpa. Due to a low sink efficiency, straight extended dislocations were decorated with many interstitial clusters. When jogs formed on dislocations by joining with grown interstitial loops, the absorption efficiency of point defects increased significantly and, with increasing dpa, lowered the density of stacking-fault tetrahedra at voids.

Development of Vacancy Clusters in Neutron-Irradiated Copper at High Temperature. Y.Shimomura, I.Mukouda: Journal of Nuclear Materials, 2000, 283-287, 249-54