THE CHARACTERIZATION OF DISPLACEMENT-CASCADE COLLAPSE IN NI-CR-FE ALLOYS

Displacement cascades produced by energetic lattice recoils are the pr imary damage state in neutron-irradiated metals, among which austeniti c stainless steels are an important class of technological alloys. The vacancy constituent of this damage that survives in the form of colla psed vacancy loops is a major component of this damage state, and has been investigated in the present work as a function of alloy compositi on and the temperature. This has been done by irradiating single cryst al foils of a range of high-purity model ternary Fe-xNi-15%Cr alloys ( x = 15-70%) with heavy ions, and then analysing the resulting damage b y transmission electron microscopy. A full analysis has been achieved by measuring the areal density of loops and their size distribution fo r each irradiation condition, and hence obtaining the important parame ters defect yield and collapse efficiency. By appropriate choice of io n energy, ion mass, ion dose and specimen temperature, we have been ab le to vary the factors such as cascade size, cascade energy density, c ascade defect density and cascade overlap, and thus study their influe nce on cascade collapse. The results have been assessed in terms of cu rrent models of cascade processes in pure metals and alloys.