Effect of temperature on the microstructure and bonding strength of partial transient liquid phase bonded WC-Co/40Cr joints using Ti/Ni/Ti interlayers

Partial transient liquid phase bonding of WC-Co cemented carbide to 40Cr steel has been performed using a selected Ti/Ni/Ti multi-interlayer in vacuum in the temperature range of 950-1100 °C. The interfacial microstructures of the joints revealed that the two original titanium layers were completely consumed and transformed into active transient liquid phase which would react with the two base materials. The transient liquid phase penetrated into the cemented carbide, leading to the formation of a transition layer consisting of reaction-formed TiC and dispersed WC particles. In contrast, an individual layer of TiC was identified at the steel side. Moreover, two Ni-Ti intermetallic compound (NiTi and Ni3Ti) layers were also observed on both sides of the residual nickel core layer. And the NiTi layer was gradually consumed due to the aggravation of interfacial reaction as the bonding temperature was increased, accompanying with the growth of the TiC layers and Ni3Ti layers. The shear strength of the joints increased firstly and then decreased sharply when the bonding temperature was higher than 1050 °C, since the Ni3Ti layer was greatly thicken where most of the joint failures tended to occur. The maximum strength of 137 MPa was obtained at the moderate temperature of 1000 °C.