Effect of hydrogen on the low-temperature mechanical properties of V-5 at % Ti alloys

The effects of grain size and hydrogen in solid solution or as hydrides on the strength and ductility of V--5 at.% Ti were studied over the temperature range 15-448K. Comparison of the strength and ductility characteristics of hydrogenated alloys where hydrides were not observed down to 78K (1.8 and 1.9 at.% H alloys) or where hydrides were observed to form near 230K (3.8 and 3.9 at.% H alloys) indicated that the presence of hydride precipitates had no apparent influence on the strength or ductility characteristics. It appears that the main consequence of hydride precipitation is that H is removed from solid solution, making strengthening less effective than expected based on the total H content. Decreasing grain size from 31 to 8 mu m had no apparent effect on ductility in the nonhydrogenated alloys ( < 0.05 at.% H), but it did increase the strength over most of the temperature range and especially at 15K. In the hydrogenated alloys, this decrease in grain size lowered the transition temperature approx 10K, and it appreciably increased the degree of ductility return at 78K and below. The ductility return < 78K peaked near 50K before decreasing < 30K with the improvement in ductility being greatest in the alloys with the lower H contents.