Mechanism of wettability enhancement of the AgCuTi-SiO_2f/SiO₂ system with a laser-manufactured bioinspired sinusoidal interface

The poor wettability of filler metals on the SiO_2f/SiO₂ composite surface adversely affected the brazing joint strength, constraining the application of SiO_2f/SiO₂ composite. In this paper, the bioinspired sinusoidal structure interface was designed and manufactured by the picosecond laser, aiming to enhance wettability. The wetting angles of the Ag-Cu-Ti filler metal on the SiO_2f/SiO₂ composite surface with different bioinspired sinusoidal structures were compared. Effects of the structural morphology and surface reaction state of bioinspired sinusoidal structures on the wetting mechanism were investigated. The results indicated that, as the amplitude of the sinusoidal structure decreased, the surface energy barrier that hindered wetting and the capillary force that promoted droplet spreading decreased simultaneously. Furthermore, active defects, such as ODC(II) and NBOHC, were generated on the structured surface. The surface rich in defects easily reacted with the Ag-Cu-Ti filler metal, which was beneficial for promoting the reactive wetting. An optimized double sinusoidal structure with 25 μm amplitude and 100 μm wavelength reduced the wetting angle from ~110° to ~70°. Dense and continuous Ti₅Si₃ + TiO₂/Cu₃Ti₃O reaction layers with a thickness of over 2 μm were formed, which indicated a reliable metallurgical bonding. Attributed to the promoted wettability and enhanced interfacial bonding, the SiO_2f/SiO₂ composites brazed joint was strengthened from 5 MPa to 23 MPa. This bioinspired sinusoidal structure could also be introduced in further ceramics-metal dissimilar interfaces to enhance wettability and interfacial bonding.