Surface hydrogenation treatment facilitating ultra-low temperature diffusion bonding of Zr-4 alloy

To meet the low-temperature bonding requirements in the nuclear industry, a surface hydrogenation treatment method was introduced for the diffusion bonding of the Zr-4 alloy. The evolution of the hydrogenated layer thickness was investigated with the current density and electrolytic time. The microstructure of the hydrogenated layer was detected as δ-ZrH 2 and ε-ZrH 2 . γ-ZrH phase was detected on the interface between the hydrogenated layer and α-Zr base metal. The surface hydrogenated Zr-4 alloy (SHy-Zr-4) bonded at 650 °C was achieved. The tensile strength of the joint was 415 MPa, reaching 90 % of the Zr-4 base metal. The ultra-low temperature diffusion bonding mechanism was discussed in detail. At the diffusion-bonded interface of the SHy-Zr-4, there was no residual hydrides and nano-sized α-Zr crystals were formed, which were the key factors for obtaining the high-performance joints. This work provided new ideas for achieving other alloys' high-strength diffusion bonded joints at ultra-low temperature.