Effect of WC grain size and cobalt content on the tribological behavior of WC-Co cemented carbides

Sammanfattning

Cemented carbides are composite materials, most commonly comprising tungsten carbide (WC) grains embedded in a metallic matrix of cobalt (Co). The high hardness and wear resistance properties make it popular in a wide range of tribological applications. However, the effect of WC grain size and Co content is not yet clear under sliding and abrasive conditions. In the present study, tribological behavior of the cemented carbides with varying WC grain size (less than 0.5 to 1.5 μm) and cobalt content (3,6,10 wt%) has been investigated under scratching and abrasion conditions. After tribological testing, a combination of white light profilometry, high-resolution scanning electron microscopy (SEM), and energy-dispersive Xray spectroscopy (EDS) was used to characterize the tribological behavior and understand the effect of microstructure and composition. The results showed that the microstructure degradation of WC-Co cemented carbides starts with cobalt removal, followed by crushing and fragmentation of WC grains which are mixed up with binder again as a modified surface layer. It was observed that cemented carbides with coarse grain size are more prone to fragile within individual WC grain, generating WC fragments as wear debris. Further the results indicated that the cemented carbides with higher cobalt content display desirable tribological behavior under both sliding and abrasion conditions due to the formation of a stable tribo-layer, which is in contradiction to the traditional belief that the wear resistance increase with the bulk hardness of WC-Co.