Hydrogen-assisted enhancement of diffusion bonding for Zr-4 alloys with a Ti interlayer

High-temperature joining of Zr alloys entails many challenges, such as performance degradation and excessive deformation, inhibiting the widespread utilization in nuclear reactors. This study employed different charging methods, including cathodic charging and gaseous hydrogen charging, to achieve a reliable Zr-4/Ti/Zr-4 joint at a low temperature of 650 °C. The influence of charging time on the microstructure, mechanical properties, and fracture behavior of the joints was investigated via scanning electron microscope (SEM equipped with EDS), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD), respectively. The diffusion layer thickness and shear strength increased with increasing charging time. The maximum joint strength reached 261 MPa for the hydrogenated Ti interlayer and 296 MPa for the hydrogenated Zr-4 alloys, which were 141.7% and 174.1% higher than that without hydrogenation. Compared with the nonhydrogenated joint, the hydrogenated Ti-interlayer joint failed within the weld instead of at the Ti/Zr-4 interface. Cracks in the hydrogenated Zr-4 joint propagated into substrates, resulting in a higher load-bearing capacity. Furthermore, the mechanisms for joint strengthening induced by different hydrogenation methods were proposed and compared, thus providing a reliable basis for selecting hydrogenation methods and materials in the nuclear industry.