Microstructure and mechanical properties of brazing bonded WC-15Co/35CrMo joint using AgNi/CuZn/AgNi composite interlayers

Abstract

The present study investigated the nucleation and fracture mechanisms of WC-15Co/Ag-16Cu-23Zn-7.5Mn-4.5Ni (AgNi)/Cu-38Zn-4Mn (CuZn)/Ag-16Cu-23Zn-7.5Mn-4.5Ni (AgNi)/35CrMo joints. The effect of brazing temperature and holding time on the mechanical properties of the joints were analysed. High-frequency induction brazing was used to join the WC-Co/Steel joints with the AgNi, AgNi/CuZn/AgNi and AgNi/Ni-15.5Cr-8.5Si (NiCr)/AgNi interlayers. The results showed that the α-Cu solid solution (s.s) and CuZn interlayer disappeared, while the β-Cu (s.s) phases nucleated in the joint. With increasing brazing temperature and holding time, the composition of the filler alloy changed from hypoeutectic to eutectic and hypereutectic. The β-Cu changed from columnar phase to island-like phase in the brazing seams. The mechanical properties of the joints depend on the distribution form of α-Cu, Cu interlayer and β-Cu phases. The WC-Co/steel joints brazed with the AgNi/CuZn/AgNi interlayer had the highest shear strength of 338MPa when brazing at 740°C for 30s. The joints fractured along the hard, brittle eutectic phase under a high applied stress.