Dissimilar Diffusion Brazing of WC-Co to AISI 4145 steel using RBCuZn-D interlayer

Diffusion brazing mechanism of two dissimilar alloys WC-CO and AISI 4145 steel by RBCuZn-D filler metal with different bonding times of 1, 2.5, 5, 7.5, 10 and 12.5 min was investigated. Shear strength and microhardness tests were performed to evaluate mechanical properties. The microstructure and compositional changes in the joint zone was characterized using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The results revealed that there are γ, α and β solid solution phases and Co3W3C intermetallic compound in the joint zone of the bonds made in 5 and 10 min due to the inter-diffusion of elements across the interface. The optimum shear strength of 412 MPa was achieved for the bond made in 5 min. With increase of bonding time to more than 5 min, a reduction in the strength occurred which may be due to the increase in formation of brittle Co3W3C compound, zinc evaporation and heterogeneity of interface. It is also indicated that hardness mapping exposed the microstructure heterogeneity very well while linear hardness measurement was incapable to show the variations accurately.