Effects of carbon doping on mechanical, tribological, structural, anti-corrosion and anti-glass-sticking properties of CrNbSiTaZr high entropy alloy coatings

Abstract

CrNbSiTaZr high entropy alloy (HEA) coatings with different carbon contents were deposited on tungsten carbide (WC) disks by radio frequency magnetron sputtering. Half of the disks were retained in an as-deposited condition, while the remainder were annealed at 750 °C for 60 minutes. The microstructure, adhesion properties and hardness of the HEA coatings were measured via X-ray diffraction, scratch tests and nanoindentation tests, respectively. In addition, the tribological properties were examined using a ball-on-disk tribometer. The anti-corrosion properties were tested under 0.1 M NaCl using a potentiostat system. Finally, the anti-glass-sticking properties were tested in a nitrogen atmosphere at a temperature of 750 °C. The results showed that the HEA coating with no carbon addition had the highest hardness (20.12 GPa) and highest critical load (100 N), but the poorest tribological properties. Among the carbon-doped coatings, the coating prepared with an acetylene flux rate of 19 sccm displayed the highest hardness (14.00 GPa), the highest critical load (64.5 N), the lowest coefficient of friction (0.05), the lowest wear depth (0.29 μm) and the lowest wear rate (0.16 × 10−6 mm3/N.m). The corrosion tests showed that the annealed coatings generally provided a better anti-corrosion performance than the non-annealed coatings or bare WC substrate. The coating without acetylene addition showed a better anti-glass-sticking performance than the native WC substrate. The addition of acetylene in the deposition process further improved the anti-sticking performance of the HEA coatings. However, the coatings prepared with a higher acetylene flux rate (i.e., 22 sccm, or more) showed a greater diffusion of carbon and chromium into the glass under high temperature conditions. Consequently, in fabricating moulds for glass component production, a lower acetylene addition (e.g., 19 sccm) is preferable for improving the quality of the moulded components.