Effect of Hydrogenation on the Microstructure and Mechanical Properties of Low‐Temperature Diffusion Bonding Joints of Zirconium Alloy

To address the limitations of high‐temperature diffusion bonding in zirconium alloys, the effect of controlled hydrogenation is investigated on bonding behavior, microstructure evolution, and joint performance. Zirconium alloy with 0, 200, and 2000 ppm hydrogen are prepared for diffusion bonding at 700–800 °C under 15 MPa for 30–120 min. At 200 ppm hydrogen, hydrides decomposed during bonding and reprecipitated along the interface upon cooling, eliminating interfacial voids and preserving finely dispersed second‐phase particles around equiaxed α ‐Zr grains with minimal coarsening. At 2000 ppm hydrogen, incomplete hydride decomposition resulted in residual hydrides, while β ‐Zr at grain boundaries softened the interfacial grains without extensive recrystallization, maintaining grain sizes below 7 μm. Hydrogenation lowered the required bonding temperature, where joints bonded at 700 °C with 200 ppm hydrogen achieved shear strengths of 220 MPa, comparable to un‐hydrogenated joints bonded at 750 °C. Similarly, 2000 ppm hydrogen enabled comparable strength at 720 °C to that of un‐hydrogenated joints bonded at 780 °C. Molecular dynamics simulations confirmed that hydrogen‐induced hydrogen‐vacancy clusters enhanced atomic diffusion, while finite‐element modeling demonstrated that hydrogen‐induced softening lowered local stress concentrations and promoted void closure during bonding. These multiscale insights clarify the mechanisms where hydrogen enhances diffusion bonding efficiency and joint properties in zirconium alloys.