Combined TEM, PAS and SANS investigation of neutron-irradiated pure iron

Fission spectrum neutron irradiation of pure Fe at irradiation temperatures of about 300 °C gives rise to the formation of two populations of defects: planar dislocation loops and spherical vacancy-type clusters. Knowledge of the type and size distributions of these populations is important for the purpose of multi-scale modelling of the mechanical behaviour of Fe-based alloys. Among the experimental techniques with nanometer size resolution, transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) allow to gain information on both nature and size distribution of particular types of defects. Furthermore, positron annihilation spectroscopy (PAS) is sensitive to sub-nanometer size open-volume defects. However, there is no single experimental technique capable of providing the full set of information required for calibration and validation of advanced models. The complementarity between the three techniques to identify and quantify the defects created by irradiation in pure Fe is emphasised in the paper. It is shown that while TEM allows direct size-resolved evidence of dislocation loops, PAS a qualitative appreciation of the existing sub-nanometer size vacancy-type clusters, SANS yields indirect size-resolved evidence of vacancy-type clusters, which form a sound basis for the quantification of the size distributions.