Scratch and wear resistance of hydrophobic CeO2-x coatings synthesized by reactive magnetron sputtering

CeO2-x coatings were deposited under variable oxygen flow ratios (%fO2) onto Si substrates by reactive magnetron sputtering. Nanoindentation testing revealed an increase in the hardness, elastic modulus, H/E and H3/E2 ratio with increasing oxygen flow ratio, which in turn increased the adhesion and tribological performance of the coatings. Scratch testing yielded the highest critical load (LC2 = 28.8 N) and CPRS = 103 for the coating deposited with the highest oxygen flow ratio (57 %fO2). Cracking events during scratch testing were initiated by tensile forces behind the scratch stylus, which led to the formation of semi-circular ring cracks. As the normal load increased, transverse cracks emerged extending outwards from the scratch track towards the edge causing the exposure of substrate. Beyond LC2, severe spallation of the CeO2-x coatings led to coating failure. Furthermore, the specific wear rates of the CeO2-x coatings were determined to be within the ~10−15 m3/Nm range influenced by three-body abrasive wear. In-depth analyses from scratch and wear data indicates that these coatings possess good adhesion and durability