The influence of femtosecond laser surface texturing on the microstructure and mechanical properties of sapphire-ZrO₂ brazed joints

When faced with challenges such as poor wettability of the brazing filler metal and low joint strength in the brazing of dissimilar ceramics, femtosecond laser surface treatment offers a new solution. In this study, we used a femtosecond laser to create periodic patterns on the sapphire surface, applied AgCuTi metal paste to form a metallization layer, and then completed the brazing process with AgCuZnSn filler metal. Following laser texturing, periodic microcone arrays were formed on the sapphire surface. Subsequent cladding on this laser-textured sapphire surface resulted in a more homogeneous microstructure within the joint, along with a reduction in the quantity of brittle intermetallic compounds. The shear strength of the treated joint reached 158 MPa, representing a 50 % increase over the untreated joint. This enhancement is attributed to the microstructures generated by laser processing, which increased the density of reactive sites between Ti and sapphire. This enabled more Ti to react with the sapphire surface, rather than forming brittle Ti-Cu compounds within the joint. On the other hand, when cracks spread along the microstructures, their paths change, which uses up energy. Additionally, the mechanical interlocking effect of the laser-pre-treated periodic microstructures at the interface also contributes to increasing the strength. We hypothesize that this study offers a novel design strategy for joining dissimilar ceramics, with direct applicability to brazing pretreatment of optical windows and microelectronic components.