Enhancing the laser sealing of borosilicate glass/Kovar alloy joint via picosecond laser welding at varying power levels

The sealing of the Kovar alloy (Fe–Ni–Co) to borosilicate glass has traditionally been achieved using an intermediate oxide layer formed through high-temperature isothermal furnace treatment. However, this conventional furnace sealing process requires prolonged exposure to elevated temperatures, which can degrade the functional properties of the glass-to-metal seal. Laser welding technology offers an alternative approach, enabling high shear strength in glass-to-metal seals, which is crucial for industrial applications across various fields. Nevertheless, modern femtosecond laser welding techniques remain costly and necessitate optical contact between the materials. To develop a more efficient sealing method, this study proposes a novel approach that replaces traditional preoxidation with laser surface texturing of the Kovar alloy, followed by laser transmission welding using a picosecond laser. The welding results were compared with those obtained via conventional preoxidation. After laser surface texturing, the Kovar alloy surface exhibited the formation of oxygen-containing compounds, facilitating well-formed borosilicate glass/Kovar alloy joints. Key welding parameters—including laser power, scanning velocity, and surface texturing—significantly influenced the laser energy input and thermal accumulation during welding, thereby affecting the interfacial characteristics and mechanical properties of the resulting joints. The achieved shear strength reached 160 N, demonstrating the viability of this method. Furthermore, the underlying welding mechanism was investigated, revealing that metallurgical bonding (from interfacial reactions) and mechanical interlocking are the primary contributors to the joint’s high shear strength. This study presents a promising strategy for joining materials with significant differences in thermophysical properties, offering potential advancements in high-performance sealing applications.