Characterisation of open volume defects in Fe-Cr and ODS Fe-Cr alloys after He+ and Fe+ ion irradiations

Different ODS RAF steels with nominal composition Fe&-14Cr&-2W&-0.3-Ti&-0.3Y2O3 (wt%) and a model Fe&-14Cr (wt%) alloy have been subjected to single Fe+ or He+ ion irradiations to simulate the effect of a fusion environment at different doses and temperatures. The irradiation induced open volume defects have been characterised by positron annihilation spectroscopy and transmission electron microscopy. For low temperature Fe+ irradiations, positron annihilation spectroscopy results show a high concentration of irradiation induced vacancy clusters, much more evident in the model alloy as compared to the ODS steels. The extent of damage due to He+ irradiations at RT and high temperatures is considerably lower than for the Fe+ irradiations. Regardless of the temperature He+ irradiations introduced changes in the chemical environment of open-volume positron traps possibly due to the creation of He-vacancy complexes. Positron annihilation spectroscopy results also suggest that irradiation induced vacancy-type defects in ODS steels are not associated with nanoparticles but are mainly in the ferritic matrix. The presence of irradiation induced bubbles was studied after He+ irradiation at high temperatures. Small bubbles were observed, being smaller in the ODS steels as compared to the model alloy.

Characterisation of open volume defects in Fe-Cr and ODS Fe-Cr alloys after He+ and Fe+ ion irradiations Articles