Interfacial structure and joint strength on $\mathrm{\text{Ti(C, N)}}$–${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ cermet/40Cr steel joints with diffusion bonding

The $\mathrm{\text{Ti(C, N)}}$–${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ cermet to 40Cr steel joint was conducted by liquid phase diffusion bonding under the auxiliary pulse current and using 73Cu–27Ti amorphous foil/Cu foil/72Ag–28Cu foil sandwich foils as the interlayer. The effect of holding time and duty ratio of the pulse current on interfacial structure at the $\mathrm{\text{Ti(C, N)}}$–${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ cermet side and joint strength were studied. The results showed that the longer bonding time can improve the melting of Cu–Ti foil and the dissolution of Cu interlayer to obtain a higher joint strength. The interfacial structure was composed of the TiCu compounds and Cu solid solution at the cermet side, and ${\mathrm{\text{TiCu}}}_4$ compounds and Cu solid solution at the Cu interlayer side. The auxiliary pulse current was beneficial to reach a higher joint strength in a shorter holding time. A higher duty ratio would accelerate the dissolution and reaction of cermet to the interlayer, but continuous increase on the duty ratio would result in the over dissolution of cermet into the interface to produce the Ti(C, N) and ${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ ceramic particles and the decrease on the joint strength.