EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Many metalworking tools, e.g. for milling applications, are made of hard-coated WC-Co hard metals. To date, the damage evolution in the substrate of the substrate-coating composite that leads to the loss of the coating is not completely understood. This is mainly due to the lack of material testing methods that reflect the loading conditions present near the cutting edges of milling tools, that involve multiaxial cyclic high-temperature loads. For this reason, a novel “ball-in-cone” test setup was developed to induce cyclic shear-compression loading at isothermal conditions by cyclic indentation of a spherical indenter in an inclined sample surface. The ball-in-cone tests were performed in a servo-hydraulic testing machine in a vacuum environment with the test temperature of 700°C induced via eddy current heating. The investigated substrate-coating composite was a WC-Co hard metal with a Co binder content of 12 wt.% and an average WC grain size of 2 µm, covered with a TiN-TiB2 hard coating deposited by chemical vapor deposition. The nucleation and accumulation of defects in the nm- and µm size regime was studied for the substrate by means of scanning electron microscopy in cross sections prepared by focused ion beam milling. The local loading situation in the contact area between sample and indenter was examined via finite element-based analysis. Experimentally parameterized material models were applied that considered the cyclic deformation and creep behavior of the substrate material at the test temperature. The experimental results show, that positions on the sample with mainly compressive cyclic stresses showed significantly slower defect accumulation compared to positions with combined compressive-tensile loads. The observed concentration of damage formation near the substrate-coating interface was similar to that observed in cyclically loaded cutting edges of milling tools.