Atomic number contrast imaging and microanalysis of copper precipitates in irradiated ferritic pressure vessel steels

Nanometre-scale copper-rich precipitates in irradiated ferritic pressure vessel weld surveillance samples have been imaged directly in the field emission gun scanning transmission electron microscope. This is achieved by using the atomic number sensitivity of the high-angle elastically scattered electron signal. Microanalysis after location using this technique indicates that the precipitates contain phosphorus and manganese as well as copper. Preliminary results show that the smallest (sub-2 nm) precipitates to be observed have a high content of phosphorus and manganese relative to copper while in samples with larger precipitate sizes, in which thermal effects have been significant, copper predominates.