Microstructure and Properties of a YG18/40Cr Joint Vacuum–brazed by Cu–Sn–Ti Filler Metal

YG18 cemented carbide and 40Cr steel were brazed using Ag-Cu-Ti filler metal under vacuum, and the microstructural evolution of the YG18/Ag-Cu-Ti filler metal/40Cr steel brazed-joint interface was investigated to determine how brazing temperature affected the brazed-joint microstructure, bonding strength, and fracture behavior. At the YG18 cemented carbide/filler metal interface, Ti atoms in the filler metal and C atoms in the YG18 cemented carbide formed a continuous TiC layer, reducing the difference in thermal expansion coefficients between the YG18 cemented carbide and filler metal. At the 40Cr steel/filler metal interface, Ti atoms in the filler metal and C atoms in the 40Cr steel formed a continuous TiC layer, preventing the diffusion of Fe atoms to the cemented carbide side and formation of a hard, brittle phase. YG18 cemented carbide/TiC/Cu2Ti/Ag-Cu eutectic + TiCu granules/TiC/40Cr steel-brazed joints were obtained. With increasing brazing temperature from 860 to 920.C, the bonding strength of the YG18 cemented carbide/40Cr steel joint initially increased and then decreased. The joint brazed at 900 degrees C for 10 min failed in the middle of the brazing seam, and its average bonding strength was 235 MPa.