Radio-frequency plasma-enhanced chemical vapour deposition of carbon films on AISI 316LVM steel: Formation of a transition layer and metal whiskers, and their influence on coating properties

Abstract

The process parameters for carbon coating synthesis can affect the entire zone of modification, including the coating itself and the transition layer close to the surface of the metal substrate. In this study, diamond-like carbon (DLC) coatings were synthesised using the radio frequency plasma-enhanced chemical vapour deposition method with a variable negative potential of the electrode called self-bias (Vb) that affects the temperature of the process. Three types of modification were distinguished according to the thickness and properties of the modification zone.The hardness of the mentioned zones was two to three times greater than that of the core material (AISI 316 LVM steel). Coatings deposited at temperatures up to 450 °C (Vb lower than 1000 V) have thicknesses lower than 5 μm. These coatings have good corrosion resistance but hardness on the level of 9 GPa. By increasing the process temperature above 500 °C (Vb above 1000 V), the corrosion resistance of the modification zone was depleted, an increase in hardness to a level of 14 GPa was observed. In these cases, the thickness of the modification zone was over 9 μm. The reason for the weak corrosion resistance was the formation of metal whiskers across DLC coating.