Effect of hafnium on radiation-induced inter-granular segregation in ferritic steel

Ferritic steels with and without hafnium (Hf) addition were irradiated by 250 keV nickel ions at 300 °C in an ion accelerator attached to the multi-beam high voltage electron microscope (JEOL ARM1300) to study the influence of Hf additions on radiation-induced segregation in a ferritic/martenitic steel. Grain boundary segregation of phosphorus, silicon, chromium and molybdenum were measured by field-emission-gun transmission electron microscopy with an energy dispersive analyser. The results show that radiation induces the enrichment of undersized atoms (P) and the depletion of oversized atoms (Cr) in the materials without Hf addition. The addition of Hf suppresses radiation-induced undersized atom enrichment and oversized atom depletion. A radiation-induced non-equilibrium segregation (RIS) model is developed to predict undersized and oversized atom segregation behaviour at the grain boundary. The effect of hafnium on freely migrating defect population is discussed and estimated to indicate the effect of the element on segregation behaviour of the elements like P and Cr in the ferritic steel. The predicted results are compared with experimental data.