Characterisation of open volume defects in FeeCr and ODS FeeCr alloys after Heþ and Feþ ion irradiations

Abstract

Different ODS RAF steels with nominal composition Fee14Cre2We0.3-Tie0.3Y2O3 (wt%) and a model Fe e14Cr (wt%) alloy have been subjected to single Feþ or Heþ 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 Feþ 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 Heþ irradiations at RT and high temperatures is considerably lower than for the Feþ irradiations. Regardless of the temperature Heþ 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 Heþ irradiation at high temperatures. Small bubbles were observed, being smaller in the ODS steels as compared to the model alloy