Magnetron sputtered SiC coatings as corrosion protection barriers for steels

Silicon carbide films between 2.3 and 3.0 μm were deposited on AISI 304 stainless steel (SS), carbon steel (CS) and crystalline silicon from a SiC target in a magnetron sputtering system. Good mechanical properties were obtained for the films by carefully controlling the deposition parameters. Results of scratch tests revealed that adhesion of the films is a function of deposition parameters and substrate type. Additionally, an influence of substrate preparation prior to deposition was also observed. Critical loads of 20 N, 8 N and 5 N were obtained in case of Si, SS and CS substrates, respectively. Vickers micro-hardness values were between 10 and 30 GPa, films on SS being harder than films on CS. The behavior of the films as corrosion protection barriers in aggressive environments was evaluated by immersion tests and electrochemical impedance spectroscopy measurements. Films on SS exhibited a better corrosion resistance than those on CS. Their adhesion to the SS was outstanding, even after a long time of immersion in a HCl 0.8 M solution, showing that they are efficient protection barriers. The corrosion process of the substrates starts at micro-pores present in the films so that corrosion pits all over the surface of the samples can be observed.