Co segregation on WC grain formed in an interfacial reaction between WC-Co cemented carbide and Ag-Cu eutectic brazing material

The interfacial structure between Cu and WC-Co cemented carbide after Ag-Cu vacuum brazing was evaluated. No Co was present on the surface of the WC grains before brazing. The vacuum-brazed specimen was heated at 850 degrees C for 0.5 h, and Ag and Cu were found to penetrate the grain boundary phase, which initially consisted of Co, over a distance of about 1 mu m from the surface of the WC-Co cemented carbide. A Co-containing segregated layer with a thickness of about 2-7 nm formed at both the Cu-rich phase/WC grain interface and the Ag-rich phase/WC grain interface. In addition, a Cu-containing segregated layer with a thickness of about 2 nm formed on the Ag-rich phase side against the Co-containing segregated layer at the Ag-rich phase/WC grain interface. This suggests that the formation of the Co-containing segregated layer originated from the local interfacial reaction between the Co dissolved in molten Ag-Cu phase and the WC grains during brazing.