Evolution of defects in Ti6-4 under Ti2+ ion irradiation: Focus on radiation-induced precipitates

Ion irradiations on the Ti6-4 titanium alloy were conducted at the JANNUS French platform in two different conditions of temperatures, doses and fluxes, to simulate neutron irradiation damage. Quantification of defects and chemical microanalyses were carried out thanks to Transmission Electron Microscopy and Atom Probe Tomography. -type loops and radiation induced precipitates (a vanadium-rich β BCC phase) were observed for both irradiation temperatures. During an irradiation at 300 °C, there was no notable influence of the dose and flux for the considered doses and fluxes ranges on the -type defects. The influence of raising the irradiation temperature up to 430 °C was a lowering of their density and an increase of their mean diameter for both defects. In addition, a lower flux seemed to enhance this temperature effect. These phenomena were very significant for precipitates whereas it appeared very modest for -type loops. The probable mechanism to explain the distribution of vanadium-rich β precipitates inside the α phase is the heterogeneous nucleation. The nucleation is dominated by the Radiation Induced Segregation (RIS) phenomenon at 430 °C and could be dominated by the mechanism of vanadium-rich clusters formation by ballistic effects in the cascades at 300 °C.