Effect of ion bombardment on structural, mechanical, erosion and corrosion properties of Ti–Si–C–N nanocomposite coatings

This study is one part of a series of efforts to optimize the microstructure and tribological properties of the Ti–Si–C–N coatings for a wide range of industrial applications. In this study, Ti–6Al–4V samples were coated with thick Ti–Si–C–N coatings (25–35 μm) using a plasma enhanced magnetron sputtering (PEMS) process, in which Ti was sputtered from two magnetrons at fixed power of 4 kW for each magnetron in a reactive environment of Ar, N₂ and trimethylsilane (TMS). The substrate power density (ion bombardment power density) was varied by varying the bias voltage and the ion flux, which was varied by changing the electron emission current in the PEMS process. After the depositions, scanning electron microscopy (SEM) and X-ray diffractometry (XRD) were used to study the microstructure and morphology of these coatings. Nano-indentation was performed to study the surface hardness H and modulus of elasticity E, from which the ratios of H/E* and H³/E*² were calculated, where E* = E / (1 − ν²) and ν is the Poisson's ratio. The solid particle erosion (SPE) resistance of the coatings was evaluated using a sand blaster with 50 μm alumina particles at two incident angles of 30° and 90°. Finally, an electrochemical test was conducted to determine the coating corrosion resistance. It was found that all coatings had a nanocomposite microstructure. But the coatings produced at the higher substrate power densities (0.13–0.20 W/cm²) had a smaller crystallite size (5.2–5.8 nm) with a better morphological quality, i.e. free from columnar structure, defects or delamination. The substrate power density has a strong influence on the surface hardness and the ratios of H/E* and H³/E*². The higher the substrate power density, the higher these values. The solid particle erosion resistance and corrosion resistance of the coatings also correlated well with the substrate power density. Coatings deposited at higher power densities of ion bombardment exhibited better erosion resistance and corrosion resistance than those deposited at lower substrate power densities.