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

•No different phases existed on the surface of WC grains before brazing.•Cu was vacuum brazed to WC–Co cemented carbide using Ag–Cu eutectic brazing foil.•The binder Co was contained in the segregated layer formed at the brazing interface.•The double segregated layer containing Cu and Co was formed at the Ag/WC interface. 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 °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 μm 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.