Effect of Strain Rate on Ductile-Brittle-Ductile Transition in Nb-0.5 at%H Alloy

It is well known that a small addition of hydrogen to niobium(1)(2) or vanadium(3)(4) causes a ductile-brittle-ductile (DBD) transition. The DBD transition occurs between room temperature and 80K; a ductility minimum is observed in an intermediate temperature range and the ductility is increased by either raising or lowering temperature from this range. A typical DBD transition(5) was observed in a Nb0.5at%H alloy. In more diluted alloys, the ductility minimum disappeared with decreasing hydrogen content. In a low temperature range the alloys containing more than 0.5at%H did not show the increase in ductility with increasing hydrogen content. Some different result has been obtained for the strain rate dependence of ductility. Hardie and McIntyre(1) found the dependence of ductility on the strain rate; at higher strain rate, a predominant increase in ductility was observed in the intermediate range and the ductility minimum was shifted to lower temperatures. On the other hand, Wood and Daniels(2) reported that the strain rate had little effect on the ductility. In this note, the effect of strain rate on DBD transition in Nb-0.5at%H alloy is shown and discussed. Niobium wire (containing 500ppm Ta, 100ppm W, 300ppm Fe, and each of other metallic impurities being less than 10ppm) in the size of 1mm diameter and 30mm length