Effect of hydrogen and oxygen on the tensile properties of V-4Cr-4Ti

Flat subsized tensile specimens of the vanadium alloy V-4Cr-4Ti were loaded with different amounts of pure hydrogen in order to study its effect on room temperature tensile properties. It was found that, apart from a slight influence of pretreatment, hydrogen can be tolerated up to about 2.5 at.%, whereas higher hydrogen contents lead to catastrophic failure. It is suggested that this behavior is attributed to coexistence of dissolved hydrogen and brittle hydride at room temperature. In addition, some measurements were made with specimens that had been loaded with about 850 wppm oxygen from a low oxygen partial pressure at 500 degrees C (773 K), prior to hydrogen exposure. In this case room temperature ductility, starting from a decreased level, suffered severe deterioration by hydrogen concentrations of much less than 1 at.%. Apparently, in this case, embrittlement is concentrated at the near-surface grain boundaries, and stresses can no longer be absorbed if the matrix gets hardened by the addition of hydrogen. Thus, under the given conditions, oxygen and hydrogen show a strong synergistic effect on the tensile properties of this material. (C) 1998 Elsevier Science B.V. All rights reserved.