Publication
WC-Co cemented carbides are widely used in the cutting tool industry due to their mechanical properties. These composite materials indeed combines hardness and toughness, two properties that are generally contradictory. WC-Co is composed of hard WC grains joined together by a ductile Co binder. Tools produced from WC-Co are the most popular choice for cutting operations. For these applications, the tools are coated with thin films to increase their mechanical and chemical wear resistance. The most commonly used coating is TiAlN. Due to the extreme temperature and stress conditions during the use of the tools, understanding the evolution of their microstructure as well as how they interact with the coating and the working piece is essential for improving their life. This study focuses on the behavior of WC-Co cemented carbides, with an emphasis on the behavior at the interface between the coating and the tool. The objective is to present innovative ways to use this traditional protective layer. Mechanical spectroscopy is used to investigate the mobility of defects at the interface and possible phase transformations. Three peaks are revealed, with the two first ones being in the range of the temperatures reached during cutting operations. These peaks are attributed to the binder phase. The first one seems to reveal a thermodynamical equivalent of a glass transition. Its thermal activation indeed follows a VFT model, and evidences of broken ergodicity are found. The role of an interlayer between the coating and the WC-Co substrate to reduce the temperature of the peak is also discussed. A decrease of the peak temperature can be beneficial to the tool life so stabilizing the fcc ductile phase of the cobalt. The second peak returns fitting parameters that define it as a point defect peak of Zener type, with the diffusion of W elements in the Co phase. This study also proposes a 3D finite element model obtained from a real WC-Co sample to observe the distribution of the residual stresses in the two phases during the cooling following the sintering process and during compression cycles. A good correspondence between the simulation and neutron diffraction data used as a reference is obtained. During the unloading cycle, a modification of the plastic model of the Co phase is needed to maintain the quality of the fit. The influence of the addition of a coating during a compression cycle is also tested. A comparison with WC-Ni, another cemented carbide studied as a potential substitute for WC-Co, is proposed as well. A new direct application of the TiAlN is finally presented. The tool and its coating are used to produce a thermocouple able to follow the evolution of the temperature of the cutting edge during machining. The tests performed with continuous and interrupted cutting return a very stable and repeatable signal. A calibration procedure is given, and a simulation of the thermoelectric power of the couple WC-Co/TiAlN is shown.