Fast Joining of the 40Cr/WC-8Co Combination with Ag28Cu Interlaer Through the Spark Plasma Sintering Process

The solid joining between the WC-8Co cemented carbide and alloy steels has great significance for their extensive applications. In this study, the WC-8Co and 40Cr steel were joined with the Ag-28Cu interlayer through the SPS method. The microstructure and mechanical properties of the joints obtained at three temperatures—740 °C, 760 °C, and 780 °C—were analyzed. The joining mechanism was studied, and the relationship between the microstructure and shear strength of the joints was also revealed. When processed at 740 °C, the poor bonding between the interlayer and the 40Cr substrates damaged the joint strength. Higher bonding temperature helped to eliminate the interfacial defects. The joint bonded at 760 °C consists mainly of Ag, Cu within the interlayer and Co-rich Fe(s,s) at the substrate/interlayer interfaces, without any defects. In such a case, the shear strength of the joints reached the maximum level of 236 MPa. However, the increased residual stresses at higher bonding temperatures (780 °C) spoiled the strength of the joints, resulting in the decreasing of the shear strength to 173 MPa. The study shed light on the fast joining of the WC-Co and alloy steels at relatively low temperatures.