Understanding the ultrashort laser microwelding process of ceramics to metals by numerical and experimental investigations

Ultrashort laser microwelding is an advanced technology with significant potential and benefits for welding dissimilar materials, including ceramics and metals. Details of the microwelding process involving ceramics and metals with ultrashort lasers remain somewhat unclear, especially regarding phase transformation and the underlying mechanism of joint formation. In this study, we utilized the ultrashort laser microwelding technique to join sapphire and Invar alloy. We have developed a predictive numerical model to calculate the interfacial temperature during the laser irradiation process. The relative contributions of heat diffusion, heat radiation, and heat accumulation in the welding process of two materials were investigated under single and multiple pulses. Upon implementing laser pulse energies of 35, 40, and 50 μJ, the maximum temperatures of sapphire were 3027.8, 4179.89, and 4533.30 K, respectively. The maximum temperature of the Invar alloy exceeded the vaporization temperature (3223.15 K). This resulted in various phase transformations, including evaporation, ionization, and melting, that occurred on both substrates. These transformations also caused the intermixing and diffusion of materials. It then resulted in the formation of the final joint. Based on the findings, we aim to provide a more comprehensive understanding and practical applications of the ultrashort laser microwelding technique.