Hardmetal interlayered butt-joints made by diffusion bonding and pressure bonding

The metallurgical structure and strength of inter layered joints between a WC–6Co hardmetal and Co, Cu, Ni, mild steel, and tool steel, and between two WC–Ni hard metals and Ni have been studied for diffusion- and pressure-bonding treatments at 1000°–1400°C for typical times of 5 and 1500 min under pressures of 1 and 20 MPa in vacuum. Strengths of up to 1·4 GNm⁻² were obtained in pressure-bonded Ni joints, but diffusion-bonded Co joints were weak, and pressure-bonded Co, Cu, and steel joints were of intermediate strength. The formation of an η-phase in the hardmetal at bond interfaces with Co and mild steel was due to decarburizatiotz which could be prevented by treating the mating surfaces with graphite before bonding. At the bond interface in hardmetal/Cu bonds, Cu replaced Co as the binder phase in the hardmetal without adversely affecting the strength of the joint. Diffusion-bonded joints had similar strengths to those required for brazed joints, and it is likely that they could be used with advantage in applications where overheating of brazed joints in hardmetal tools is a problem.