Effect of methane and acetylene pre-gases on the corrosion resistance of DLC coatings

Abstract

Diamond-like carbon (DLC) coatings were applied to 304 stainless steel specimens using two different pre-gases: methane and acetylene.Compared to DLC prepared with acetylene pre-gas(DLC-C2H2). DLC prepared with methane pre-gas(DLC-CH4) has a denser coating body and a smoother surface.The DLC-C2H2 film shows crack defects on the surface, and the DLC-CH4 film has a lower sp2/sp3 ratio than DLC-C2H2. DLC-CH4 has better electrochemical characteristics and salt spray corrosion testing results than DLC-C2H2 films in NaCl solution. DLC-CH4 has a high charge transfer resistance of 9.54 × 103 Ω/cm2. Compared to DLC-C2H2, DLC-CH4 coatings form a more complete, continuous, smooth surface and a minor porosity in the coating body, inhibiting localized corrosion processes. The DLC-CH4 coatings have less sp2 phase, which results in lower electrical conductivity and limited electron transport at the coating surface. DLC-CH4 shows more excellent corrosion resistance.