Two high copper irradiated welds, one containing very low Ni and the other containing very high Ni, have been examined using 3-D atom probe (3DAP) microscopy, small angle neutron scattering (SANS) and field emission gun-scanning transmission electron microscopy (FEG- STEM).

Irradiation induced clusters were observed in both welds. They were found to be significantly smaller and exist at a higher number density in the high Ni weld. A new algorithm was developed to precisely identify the shape, composition and size of clusters observed in the atom probe data. Representative irradiation induced clusters from each weld were then examined in greater detail. They were shown to be ramified and have a significant Fe content (∼60at.%). Cu was found to be more strongly associated with the core of the clusters than Mn or Ni. In the low Ni weld, there was evidence for P at the interfaces between the clusters and matrix. Cluster composition estimates from FEG-STEM analyses were consistent with those observed by 3DAP microanalysis. For each weld, the mean radius of gyration of the clusters was found to be almost identical to the radius of gyration determined directly from SANS analyses of these materials. Finally, the number density of features was estimated from the SANS data by using the compositional information from the 3DAP observations. Consistency with the number density calculated directly from the 3DAP data was obtained provided that it is assumed that the clusters exhibit some magnetic properties.