APVV-24-0038: New-generation hard coatings with enhanced fracture toughness and oxidation resistance

The research aims to develop next-generation hard coatings based on transition metal diborides with advanced architectures designed to mitigate the detrimental effects of micro-cracks on their exceptional mechanical properties and oxidation resistance. This includes the use of innovative technological methods and the development of material concepts to suppress the formation and propagation of microcracks in naturally brittle ceramics. Furthermore, it seeks to establish a regeneration strategy for micro-crack-containing structures through targeted oxidation of grain boundaries. As the appropriate approaches are identified, advanced physical vapor deposition techniques, such as high-power impulse magnetron sputtering (HiPIMS) and high-target utilization sputtering (HiTUS), enable control of chemical composition, microstructure densification, defect control, and internal stress tuning to tailor the coatings for specific applications. The second approach involves designing multilayer systems and superlattices with sharp interfaces and nanometer-scale bi-layer periods. The alternation of different layer´s materials at these interfaces is intended to arrest propagating micro-cracks. The third approach is based on alloying hard coatings with oxide-forming metals or semi-metals that diffuse to grain boundaries and form stable oxides upon thermal exposure, effectively sealing micro-cracks. These multi-element coatings will be developed using co-sputtering configurations. Comprehensive characterization and calculation techniques—including X-ray diffraction and scanning and transmission electron microscopy, ab initio calculations—will elucidate the coatings' compositional and microstructural evolution. Mechanical properties and fracture toughness will be assessed through nanoindentation and micro-mechanical bending tests, offering insight into the coatings' brittleness/ductility. Oxidation behavior will be investigated via in situ XRD, and using gravimetric techniques.