Interfacial microstructure and mechanical properties of WC-Co/40Cr joints brazed at low-temperature with Ag-Cu-Ti plus Sn novel filler

It is crucial to design a novel active filler metal for brazing WC-Co cemented carbide-steel joints at low tem-peratures. In this study, we designed a low-melting-point multi-component active filler metal (Ag-Cu-Sn-Ti) based on Ag-Cu-Ti filler metal to achieve perfect combination of WC-Co/40Cr steel joints. The interfacial microstructure of the WC-Co/40Cr steel joint was comprehensively characterized, and the joint-bonding mechanism, mechanical properties, and fracture behavior after brazing at 700-780 degrees C were systematically analyzed. On both sides of the filler metal, WC and alpha-Fe combined with the TiC layer, enhancing the bonding of the filler metal to base materials. The typical structure of the joint is WC-Co/TiC layer/Co2SnTi + Cu-doped Cu81Sn22 + Ag [s, s] + Ti-Cu granules/TiC layer/40Cr. The maximum shear strength of 241 MPa was obtained when the joint was brazed at 740 degrees C for 10 min, which is approximately 50% higher than those of previous low-temperature vacuum-brazed WC-Co/steel joints. The main factors leading to premature failure of joint include the distribution of phases in filler metal layer and defects of WC-Co caused by Co diffusion.