Synchrotron GIXRD and slow positron beam characterisation of Ar ion irradiated pure V and V-4Cr-4Ti alloy: Candidate structural material for Fusion reactor application

Abstract

Pure V and V-4Cr-4Ti has been irradiated with Ar9+ion at 0.4, 2.3, 8.4 and 23 dpa. GIXRD was carried at two different incident angles i.e. at 0.2° and 0.45° using Synchrotron radiation. The XRD data were analyzed to determine the variation of microstructural parameters like domain size and microstrain as a function of dose by modified Rietveld technique. The dislocation density calculated from these parameters show contrasting behaviour in pure V and V-4Cr-4Ti as a function of dose. In pure V the dislocation density increases at the highest dose, whereas in V-4Cr-4Ti it saturates after 8.4 dpa. However, in V-4Cr-4Ti at the highest dpa clear evidence of segregation of the alloying elements is observed. Slow positron annihilation spectroscopy has been used to characterize the irradiation induced depth dependent changes in the microstructure with dose. The positron diffusion lengths in pure V (202 nm) and V-4Cr-4Ti (370 nm) indicate a defect free bulk state. An increase in S-parameter (∼1.07Sbulk) confirms the creation of vacancy type open volume defects in the damaged region (0−300 nm from surface) of the ion-irradiated samples. It was observed that that there is no appreciable change in open volume defect density and type of defects up to 8.4 dpa for pure V except at the highest dose. However, in contrary to pure V, the increase in S-parameter at highest dpa clearly indicates that the type of defects at highest dose is significantly different from the other samples.