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Titanium and titanium alloys such as Ti-6Al-4V are generally considered as difficult-to-machine materials. This is mainly due to their high chemical reactivity, poor thermal conductivity, and high strength, which is maintained at elevated temperatures. As a result, the cutting tool is exposed to rather extreme contact conditions resulting in plastic deformation and wear. In the present work, the mechanisms behind the crater and flank wear of uncoated cemented carbide inserts in the turning of Ti6Al4V are characterized using high-resolution scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and high-resolution Auger electron spectroscopy (AES).The results show that, for combinations of low cutting speeds and feeds, crater and flank wear were found to be controlled by an attrition wear mechanism, while for combinations of medium to high cutting speeds and feeds, a diffusion wear mechanism was found to control the wear. For the latter combinations, high-resolution SEM and AES analysis reveal the formation of an approximately 100 nm thick carbon-depleted tungsten carbide (WC)-layer at the cemented carbide/Ti6Al4V interface due to the diffusion of carbon into the adhered build-up layers of work material on the rake and flank surfaces.

Innovative textured alumina coatings have been engineered to boost the performance of cutting tools. Different workpiece materials affect the wear inside the CVD textured alumina coating differently on the crater and flank side of the tools. How the balance in wear changes between the crater and flank side of the tool inside the alumina is not fully understood. Furthermore, any changes in steel elements in the workpiece can affect this balance differently. In this work, the wear of alumina coating has been studied after turning different workpiece materials (low alloy steel with and without Ca, ball bearing steel and stainless steel). The worn surfaces of the inserts were studied and their features related to the different materials. It was found that after machining under similar conditions, each workpiece material leaves a different signature, or worn surface, with unique features in the alumina coating layer. The transition between the sliding to the sticking region was studied in order to help understand the relation to wear when machining different workpiece materials. SEM and topography characteristics were identified on worn surfaces of the coated tools. The resulting worn volume and surface characteristics were related to different wear mechanisms acting on the rake and flank sides of the tool. This work studies the shift in balance between crater and flank wear by identifying different wear mechanisms acting inside the same alumina coating layer when machining different grades of steel. Such work can be a good resource for FEM wear modeling, where good simulation models must take into consideration the physics lying behind the wear types acting on each side of the tool.