Reactions of hydrogen with V–Cr–Ti alloys

The interest in vanadium alloys for use as a first-wall material in fusion reactor applications has led to a study to determine the effects of hydrogen on the mechanical properties of certain V–Cr–Ti alloys. Hydrogen uptake by the alloys is a function of temperature and pressure. In the absence of increases in oxygen concentration, additions of up to 400 wpm hydrogen to V–4Cr–4Ti did not result in any significant embrittlement. However, when hydrogen approached 500 wppm, rapid embrittlement occurred at 325°C that was suggested to result from formation of a hydride phase upon cooling. When oxygen was added as well, either during or prior to hydrogen exposure, synergistic effects depending on grain size occurred that led to significant embrittlement by 35–130 wppm hydrogen. Because of its synergism with hydrogen and ubiquitous presence in most environments, oxygen pick-up remains as one of the major concerns for use of V–Cr–Ti alloys in fusion reactor applications.