The effects of interstitials and hydrogen-interstitial interactions on low temperature hardening and embrittlement in V, Nb, and Ta

The effects of combined C and H on the temperature dependence of the yield stress and ductility of V, Nb, and Ta have been investigated at temperatures between 295 and 78 K. Because of the limited solubility of C in these metals, there was little solid solution hardening (S.S.H.). The combined effect of C and H on ductility was similar to that of H alone. There was no correlation between the ductile-brittle transition temperature (DBTT) and the temperature where hydrides formed (T s. Comparison of the effects of C, N, and O on strengthening in both nonhydrogenated and hydrogenated V, Nb, and Ta showed that in general the contributions of C, N, or O and H were additive. C, N, and O produced athermal S.S.H. whereas the H contribution to the strengthening was thermally activated. The effect of these interstitials on ductility in nonhydrogenated V, Nb, and Ta was minimal, while their effect in hydrogenated V, Nb, and Ta was to decrease T s but have very little effect on the DBTT, which was determined primarily by the H content. There was no common correlation between the DBTT and T s or between the temperature where pronounced strengthening occurred and T s in the different alloys. Comparison of the results indicated that current models based on either hydride precipitates or H in solution as the cause of strengthening or embrittlement are incapable of explaining the observed effects of H on both the yield stress and the ductility in V, Nb, and Ta