Enhancing sapphire/Kovar alloy brazed joint through combined effect of TiB whisker reinforcement and surface micro-nano structures

The brazed joining between Kovar alloy and sapphire was successfully achieved by using TiB whisker reinforcement and applying the surface micro-nano structure. We systematically studied the composition and mechanical properties of Kovar/Sapphire joint. The typical interfacial structure of the joint brazed at 825 °C for 10 min was determined as Sapphire/ γ-TiO/ Ti₃(Cu,Al)₃O/ Ag(s,s) + Cu(s,s) + TiB/ Ti₂Cu + TiFe₂ + TiNi₃/ Kovar alloy. The addition of B forms tiny TiB whisker reinforcement phase in situ, which refines the interface structure. The presence of micro-nano structures improves the interface products on the sapphire side: reducing the generation of Ti₃(Cu,Al)₃O and replacing it with γ-TiO. This makes the phase transition on the sapphire side smoother and reduces thermal expansion coefficient mismatch, thereby enhancing joint strength. Under suitable brazing parameters, the maximum shear strength of the joint is 137 MPa. This study provides new insights for optimizing and improving connections between sapphire ceramics and metals, with potential applications in more ceramic/metal joining.