Inversion of the radiation-induced segregation behaviour at grain boundaries in austenitic steel

Radiation-induced segregation (RIS) in solids leads to enrichment or depletion of solute elements at point defect sinks depending on the coupling of the respective solute atoms to point defect migration. The resulting compositional change at grain boundaries may alter their structural and physical properties and may also result in a loss of mechanical strength and ductility. Most successful techniques for studying RIS at grain boundaries are Auger electron spectroscopy on specimens fractured along grain boundaries and energy dispersive X-ray spectroscopy (EDXS) across grain boundaries in transmission electron microscopes (TEM). Particularly, since TEMs with high brightness field emission guns (FEG) are available, high resolution profiles of elemental concentration variations can be traced across grain boundaries. The latter technique has been used in the present study. It was found that the general segregation behavior at grain boundaries, inclusive of the depletion of Cr and enrichment of Si is reversed at high irradiation doses. It is mainly this discovery that is reported in the present letter.