Hydrogen trapping in metallic glasses investigated by positron annihilation and differential scanning calorimetry

Abstract

Positron annihilation experiments have been performed on the metallic glasses Co58Ni10Fe5 B16Si11, Fe78B13Si9 and Fe81B13.5Si3.5C2 produced by melt-spinning. For the metallic glass Co58Ni10Fe5B16Si11 it has been found that the positron lifetime spectrum is either single-component or resolvable in two exponential terms, depending on the production parameters of the ribbons. The commercial metallic glass Fe78B13Si9 (2605S2) shows a two-component spectrum while the alloy Fe81 B13.5Si3.5C2 (2605SC) exhibits a single-component spectrum. After hydrogen charging no significant changes are observed in the positron lifetime of those metallic glasses which exhibit a single-component spectrum. For ribbons showing a two-term spectrum, the intensity of the long-lived componentl2 decreases with the cumulative charging time. This decrease is interpreted in terms of hydrogen trapping in the structural defects responsible for the long-lived component. Differential scanning calorimetry of ribbons of Co58Ni10Fe5B16Si11 suggest that hydrogen in extended structural defects should induce some local structural change.