Microstructural evaluation and mechanical properties of WC-6%Co/AISI 1045 steel joints brazed by copper, brass, and Ag-based filler metals: Selection of the filler material

Abstract

Due to the higher production cost of the monolithic carbide tools as well as their brittle nature, cemented carbides such as WC-Co are frequently joined to tool steel. To overcome the joining complications that arise due to notable differences in thermal expansions between the components and the poor wettability, various investigators have used copper-based and silver-based filler metals to dissimilarly braze the cemented carbides to steels. However, researchers do not agree about the selection of filler material. This research investigates the use of pure copper, brass, and silver-based filler metals to join the WC-Co cemented carbide to AISI 1045 steel. In this regard, microstructural features and mechanical properties including microhardness and shear strength were studied. The results indicate the formation of Cu(Fe,Co) solid solution and η carbides at the joint interfaces as well as the development of various precipitated phases in the joint area comprising Fe-Zn and Co-Zn intermetallic compounds. The reaction layers at both sides of the joints accompanied by cobalt-depleted zone on the hard metal side were observed. While using the $\alpha -\beta$ brass interlayer, the increase in hardness of the joint area through the presence of (Cu,Zn) solid solution compared to pure copper, the joint shear strength was enhanced from 161 to 173 MPa. On the other hand, the utilization of silver-based filler alloy with a distribution of hard copper-rich solid solution phase (182 HV) embedded in a silver-rich ductile matrix (88 HV), presenting a dispersion hardening effect, improved the shear strength of the joint to 203 MPa.