Femtosecond laser-induced honeycomb structure on the interface for the micro-welding of YSZ/sapphire

Femtosecond laser welding, a novel technique for material joining, faces challenges such as stringent pre-welding requirements and low joint strength when directly welding ceramics. In this study, we addressed the issues associated with the direct welding of yttria-stabilized zirconia (YSZ) and sapphire by first depositing a nanometer-thick Ti layer on the ceramic surface, followed by femtosecond laser welding. Notably, we observed for the first time that femtosecond laser pulses induced the formation of a honeycomb structure at the interface, forming a YSZ/sapphire micro-welding joint characterized by a continuous structure, a honeycomb structure, and Ti-rich phases. This specific joint distribution significantly enhanced the interface transition and improved the joint strength. Under conditions of 8 W laser power, scanning speed of 50 mm/s, and pulse frequency of 200 kHz, the micro-welding joint exhibited optimal interface performance, achieving a maximum shear strength of approximately 79 MPa. Through calculations of the temperature distribution of the interface and the surface energy of the crystal, we conclude that the honeycomb structure arises from the Ti layer, the temperature gradient distribution, and the tendency of sapphire to melt along directions with lower surface energy. The honeycomb structure effectively enriched the transition between the micro-welding interface and the substrate. The new findings of this study offer valuable insights and potential pathways for the reliable and efficient welding of advanced ceramics.