Direct joining of sapphire and Invar alloy by nanosecond laser

The direct joining of single-crystal sapphire and Invar alloy using a nanosecond laser is demonstrated for the first time in this study. The macro- and microstructures of the sapphire/Invar alloy joints were analyzed, along with an investigation of their compositional characteristics. Based on this, the effects of nanosecond laser processing parameters on the joint’s macro- and microstructures and its mechanical performance were explored. The typical fracture morphologies of the sapphire/Invar alloy joints were examined, revealing the fracture mechanisms involved. The laser-irradiated area exhibited a conical molten zone, predominantly composed of sapphire with a small amount of Invar alloy particles. No new phases were detected in the joint region, and the primary joining mechanism was identified as mechanical interlocking and embedding. After optimizing the nanosecond laser welding parameters, the joint’s shear strength reached 123.2 MPa. Additionally, the sealed sapphire/Invar alloy samples welded by nanosecond laser passed a 336-hour water resistance test without any leakage. The mechanical interlocking effect generated by the conical weld seam structure in the laser-irradiated area played a key role in enhancing shear strength.