Influence of deposition parameters on the structure and mechanical properties of nanocomposite coatings

Nanocomposite coatings based on TiC nanoparticles embedded in an amorphous hydrocarbon (a-C:H) matrix are deposited via reactive closed field unbalanced magnetron sputtering, employing Ti targets and acetylene gas as material precursors. The composition of the coatings is varied by changing the acetylene gas flow during the depositions. Different values of substrate bias are employed. Electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) monitor the variation of composition and the formation of TiC. Nanoindentations with a Berkovich indenter measure the coatings hardness (H) and effective Young's modulus (E*), and a cube corner indenter is employed to probe the coatings toughness. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) investigations confirm the formation of TiC nanoparticles and are employed to determine the particle size and size distribution, respectively, both as a function of the applied substrate bias and of the composition. The TiC volume fractions (VF) and interparticle distances are calculated based on the compositional analysis and the measured particle sizes. As a consequence of the different nanostructures, the coatings exhibit different toughness. The highest toughness is observed for low TiC volume fractions (0.2) and particle size (≈ 2 nm). The evolution of the H/E and H3/E*2 parameters as a function of the nanostructure is investigated, and opportunities for their optimization are described.