The state of hydrogen in Nb-based Nb-Mo alloys analyzed by the channelling method

In order to locate hydrogen dissolved in metals a channelling method utilizing a nuclear reaction H-1(B-11, alpha)alphaalpha with a B-11 beam has been developed. This method has been applied to study the effect of metallic solutes on the state of hydrogen in metals. The lattice location of hydrogen in Nb-based Nb-Mo alloys with different concentrations (C-Mo) of undersized Mo atoms of 3, 10, 20 and 26 at% has hitherto been investigated. These results are summarized in this paper and the interaction of hydrogen with metal solutes is discussed. At low Mo concentrations less than 10 at% hydrogen is trapped by Mo atoms at room temperature due to attractive interaction to be located at sites displaced from tetrahedral (T) sites by about 0.6 Angstrom toward the nearest neighbour Mo atom. In the case of C-Mo = 3 at%, hydrogen is detrapped at 373 K and enter a T site. The number of H atoms trapped by one Mo atom is limited. It is 0.7-1.0 for C-Mo = 3 at% and decreases with increasing C-Mo. The excess H atoms are located at T sites. For C-Mo = 20 at% such trapped site occupancy is not observed, and 70-80% of the H atoms are located at T sites and the rest are at octahedral (O) sites at low H concentrations. For C-Mo = 26 at%, most of the H atoms are located at T sites.