Efficient Induction Brazing for Ceramic-Steel Joints

Recently, advanced ceramic cutting materials with high fracture toughness have been developed for various applications, especially high-speed machining of difficult materials like Ni- or Co-based superalloys. However, their use is limited to turning and milling with solid ceramic tools due to a lack of suitable joining techniques. This challenge can be addressed with a novel joining technique that involves metallizing the ceramic through vacuum brazing, followed by induction brazing with metal in air using flux. In this study, Si3N4 and X37CrMoV5-1 are joined with a stress-reducing Cu interlayer and active filler metal APA5. Joint quality is assessed via wetting test and microstructure analysis using SEM/EDS, while mechanical properties are evaluated through nanoindentation, shear tests, and fractography analysis. The investigations demonstrate that the new joining technique successfully produces metal-steel joints. With a brazing temperature of T = 780 °C, an average shear strength of τ = 155 MPa is achieved. Fractography analysis indicates that fracture primarily occurs in the brazing seam, suggesting a strong bond between the ceramic and the filler metal. This method enables the creation of high-strength ceramic-metal joints, enhancing productivity in the machining of difficult-to-cut materials.