Effects of nitrogen on the mechanical behavior of hydrogenated V, Nb, and Ta

The effects of hydrogen, nitrogen, and combined nitrogen and hydrogen on the strength and ductility of V, Nb, and Ta have been investigated for temperatures from 295 to 78 K. The influence of nitrogen and hydrogen on the yield stress appeared to be additive. The effect of nitrogen on ductility was minimal, while hydrogen induced brittle behavior. The combined effect of nitrogen and hydrogen on ductility was generally similar to that of hydrogen alone. However, the addition of nitrogen decreased the temperature where hydrides were observed to form. In all cases studied the ductile-brittle transition temperature (DBTT) occurred above the temperature where hydride precipitation (Ts) was observed. However, there was no apparent correlation between DBTT andTs when the results for V, Nb, and Ta were taken as a group. Current models relating the strength and ductility in these metals to hydride precipitates appear inadequate for explaining the results showing that the DBTT can occur at temperatures significantly aboveTs (up to 140 K) and that the strengthening may not occur until temperatures are significantly belowTs (up to 70 K).

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