Dynamic and static hydrogen effects on mechanical properties in Vanadium alloys

To understand hydrogen behavior in V and V-based alloys, two kinds of tensile tests were carried out for hydrogen-charged miniature specimens: One is with hydrogen charging prior to testing (static charging), and the other is with hydrogen charging during straining (dynamic charging) with the continuous and intermittent ways. Static hydrogen-charging effect: From the results of gas emission and microstructure, it was indicated that hydrogen can be trapped by lattice defects, dislocations, vacancies and voids, which were effective up to 500 C. The static charging prior to straining generally resulted in hydrogen-induced hardening. Dynamic hydrogen-charging effect: The deformation stress dropped just after starting the dynamic charging, and returned to the original level after stopping the charging, which can be called as a hydrogen-induced softening. The significant softening is attributed to fast diffusion and interactions of hydrogen with mobile dislocations. The activation volume from different strain rate experiment was decreased with hydrogen charging, which means that a small amount of hydrogen can reduce Piers potential for mobile dislocations.