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 mu m. 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 irra-diation 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.