Multilayered decorative a-C:H/CrC coating on stainless steel

A nano-structured multilayer coating of a combination of a soft layer (a-C:H) produced by PECVD together with a hard layer (Cr/Cr3 − xCx) produced by PVD allows to tailor the coating properties by choosing the thickness of the individual layers. The resulting coating is well adherent, may have the elastic properties compatible with the substrate and is much harder than the substrate. The best coating properties were found for about 7–8 nm thick layer thickness for both CrC/Cr and a-C:H. The adhesion (LC1 > 30 N) and abrasion resistance (Rösler test > 1 h) indicate a coating resistant to normal handling of a handheld consumer product. The colour of the coating may be chosen by adjusting the thickness of the top Cr layer between black (5 nm thick Cr layer) and metallic Cr like (> 30 nm thick Cr layer). The colour and the adhesion (as verified by tape test) did not change during a 6 d humidity cycle tests or 3 month exposure to normal atmospheric conditions.