Microstructural and properties of ultrafast laser selective micro-welding joints of sapphire and Invar alloys

The heterostructure joint of sapphire/Invar alloy was prepared using femtosecond laser selective welding technology, and the effects of laser power on the sealing performance, macro, micro-morphology, and shear strength of the joint were investigated. The interface welding defects, elemental distribution, and fracture behavior of the joint were characterized using scanning electron microscopy, energy dispersive spectroscopy, and laser scanning confocal microscope. The results showed that under ultrafast laser irradiation, sapphire and Invar alloy underwent melting, mixing, and diffusion processes through nonlinear absorption and linear absorption, respectively. This resulted in the formation of interlocking interfaces with intermingled features, indicating the presence of both metallurgical bonding and mechanical interlocking. The shear strength of the joint increases monotonically with the laser power, and the maximum shear strength is 145.3 MPa at a laser power of 10.19 W. The fracture of the sapphire/Invar alloy joint is mainly in the form of cleavage fracture, and both sides of the fracture contain the elements of Fe, Ni, Al, and O, which further suggests that the ultra-fast laser promotes metallurgical reactions of the two materials at the interface.