On the shear strength of laser brazed SiC–steel joints: Effects of braze metal fillers and surface patterning

Within the development of a laser brazing process for joining non-oxide ceramics (SiC) to steel, we examined the effect of different braze filler metals on the shear strength of the joint. Specific surface patterns were applied on the surface of the ceramic in order to study changes of the joint strength by an additional mechanical anchoring at the ceramic–braze metal interface. The study compared a commercial AgCuTi brazing foil with SnAgTi-alloys, which contained various Sn/Ag fractions, with regard to their implementation in the laser process, which is characterized by localized heat input and short processing times in contrast to conventional furnace brazing. The microscopic investigations on laser brazed cross-sections indicated, that the application of the AgCuTi foil developed porous metal–ceramic interfaces with a poor mechanical stability and a high failure rate. The application of SnAgTi-alloys within the laser process resulted in an interface, which is free of pores. The characteristic fracture shear stress increased with increasing Sn fraction up to τ0 = 20 MPa and a Weibull modulus of m = 4.9 for the 50Sn48Ag2Ti alloy. A further enhancement of the shear strength could be achieved by generating specific patterns on the surface of the ceramic prior to the laser brazing process.