Factors Affecting Hydrogen Embrittlement at Ta/Zr Bond Interface

In order to clarify the hydrogen embrittlement mechanism at Ta/Zr explosive bonded interface, the effects of the Ta content and microstructure on changes in hardness and toughness during hydrogen charging were investigated by using Zr-Ta binary alloys. Zirconium hydrides were precipitated after hydrogen charging in Zr-Ta alloys with the specific crystallographic relationship to α-Zr substrate, and there was no significant difference in the precipitation behaviour of zirconium hydrides with varying the Ta content and microstructure (α, α' and ωphase structures). The impact absorbed energies of Zr-Ta alloys were drastically reduced with an increase in hydrogen charging time, while their hardness slightly increased with hydrogen charging. A pure Zr was highly sensitive to hydrogen embrittlement, whereas the toughness value after hydrogen-charging was lowest when alloys involved ω phase structure, and it decreased with an increase in the Ta content of the alloy. Furthermore, the sensitivity of hydrogen embrittlement of the Zr substrate was heightened with an increase in the degree of cold working (rolling reduction). The hydrogen embrittlement crack occurring in Zr adjacent to the Ta/Zr bond interface would be attributed to the mechanism that cracks were preferentially initiated and propagated in the precipitated zirconium hydrides which were precipitated on the deformation texture of α-Zr (0001) formed during explosive bonding.