Wear mechanisms of PCD tools with different diamond grain sizes in milling tungsten carbide

Tungsten carbide, owing to its high hardness, compressive strength and wear resistance, is widely used in precision molds and wear-resistant components; however, these properties also make its machining highly challenging. Polycrystalline diamond (PCD), as a superhard tool material, possesses excellent mechanical properties and shows great potential for machining such difficult-to-cut materials. Among the factors influencing the performance of PCD tools, diamond grain size is particularly critical, yet its effect on tool wear mechanisms in tungsten carbide machining has been insufficiently studied. In this study, milling experiments on tungsten carbide were carried out using PCD tools of three grain sizes to examine their effect on tool wear. The results indicated that the wear rate decreased as the diamond grain size increased. Tool wear was mainly characterized by large-scale spalling on the rake face, as well as adhesive and abrasive wear on the flank face. It was further inferred that the large-area spalling of the rake face was associated with the cobalt-catalyzed phase transformation of diamond grains at elevated temperatures and the scraping of the chips. In addition, abrasive wear was strongly dependent on the diamond grain size: tools with finer grains were dominated by intergranular fracture, whereas those with coarser grains tended to transgranular fracture. This behavior was primarily attributed to the direct mechanical impacts between the diamond grains of the tool and the WC grains of the workpiece during machining.