Effect of yttrium on dynamic strain aging of vanadium alloys

In order to improve the performance of vanadium alloys for fusion reactors, yttrium (Y) was added to reduce the interstitial O in the matrix by enhanced precipitation with Y. Effect of Y on interstitial C, N and O, however, remains to be investigated since they affect mechanical and fracture properties for vanadium alloys by pinning dislocations, such as dynamic strain aging (DSA). In this study, tensile tests were carried out on annealed V-4Cr-4Ti and V-4Cr-4Ti-Y alloys from 473 to 1073 K at strain rates ranging from 6.67 × 10−5 to 6.67 × 10−1 s−1 to investigate the performance of DSA. In the case of high-purity alloys, DSA regime was narrowed due to Y addition and the reduction in O content. In the case of O doped V-4Cr-4Ti alloys, DSA regime was also narrowed. This may be because the enhanced Ti-O precipitation reduced the O level in the matrix. Also, coarse precipitates (<500 nm) were observed in O doped V-4Cr-4Ti-Y alloy. Y might enhance the coarsening of Ti-precipitates. From activation energies for DSA, the diffusion of C and O is considered to induce the observed DSA. Y does not influence the diffusion of C and O, and might enhance the nucleation to form coarse precipitates.