Evolution of microstructure and mechanical properties in the PTLP joint between PCBN ceramic and M42 steel

Polycrystalline cubic boron nitride (PCBN) ceramics have been successfully joined with M42 steel via partial transient liquid phase (PTLP) bonding. To advance joint quality, this study systematically investigates element diffusion behavior and interfacial microstructural evolution of a pre-melted CuNi interlayer during joining. Under optimized parameters (1080 °C/30 min/0.1 MPa), a joint with homogeneous microstructure and high shear strength (132 MPa) is achievable. The brazing seam primarily consists of a Cu-based solid solution with minor dispersed CuNi 2 Ti phases. Analysis of the Cu-Ni-Ti ternary phase diagram reveals that elevating the brazing temperature above 1056 °C suppresses brittle Ti-Cu and Ti-Ni intermetallic compound formation. Notably, the relatively low diffusion coefficient (9.2 × 10 -14 m 2 /s) and high activation energy (230 kJ/mol) for Ti diffusion within the CuNi interlayer inhibit excessive Ti penetration into M42 steel and subsequent brittle phase formation, thereby enabling fabrication of high-integrity brazed joints.