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

Abstract

It is crucial to design a novel active filler metal for brazing WC–Co cemented carbide–steel joints at low temperatures. 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 °C were systematically analyzed. On both sides of the filler metal, WC and α-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 °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.