Electrochemical behavior of diamond like carbon coating on AISI 4340 steel deposited using a chemical vapor deposition (CVD) technique

As a high strength material, AISI 4340 steel is extensively used in automotive industry, plastic (cut blades), gear components, machinery, and the palm oil industry (shaft pressure press). But in a corrosive environment, it will cause the performance decline due to corrosion. As we know that all damages always start from the surface. The component’s surface layer must be enhanced to overcome this problem. Among the available techniques for surface modification, chemical vapor deposition (CVD) is popular and always being developed. This paper presented the results of research on the effect of diamond like carbon (DLC) coated on AISI 4340 steels on its corrosion behavior. For the purpose, a home-made CVD to coat the DLC was utilized, and a mixture 24%: 76% of Argon (Ar) and Methane (CH4) was used as a carbon source. The experiments were conducted at 400°C for 3 and 5 hours, and variation of gas pressures (1.2, 1.4, 1.6, 1.8, and 2.0 mbar). Corrosion behavior was investigated using a 3-electrodes cell potentiostat/ galvanostat. It was found that corrosion current density for raw material is 68.448 µA/cm2 or the corrosion rate is 31.332 mpy. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to examine cross-section morphology. After being coated for 5 hours, at 1.4 mbar, the current density is 2.360 µA/cm2 or the corrosion rate is 1.08 mpy or there is an increasing by factor 29. At this condition, the carbon content is 23.93 % mass and the thickness of DLC coating is 126.16 µm.