Micro-welding of sapphire and metal by femtosecond laser

A direct joining of sapphire and Fe–36Ni alloy was successfully realized via femtosecond laser micro-welding for the first time. A sound joint without any voids or microcracks was obtained with a narrow interface width less than 1 μm. There was no obvious element diffusion or metallurgical reactions at the interface. Sapphire and Fe–36Ni alloy were found chemically bonded and mechanically interlocked evidenced by jagged feature at the interface due to “cold” machining of femtosecond laser ablation. The highly localized femtosecond laser irradiation and smaller heat-affected zone contributed to the shear strength of the joint as high as 108.35 MPa. A higher laser scanning speed corresponded with less jagged feature and thermal stress due to the reduced thermal deposition at the interface. Proper micro-welding parameters were obtained for sapphire/Fe–36Ni alloy, and was verified in the direct joining of sapphire/steel and sapphire/silicon. It appears the femtosecond laser micro-welding technique is promising for direct joining of materials with large physical property disparities, and beneficial for manufacturing of optomechanical components at high precision, efficiency and performance.