Film properties of Si-DLC intermediate layer with different gas compositions and DLC with C2H2 gas

Diamond-like carbon (DLC) coatings, which improve wear resistance and extend component service life, have gained considerable research attention as an approach for conserving limited resources. The DLC coating is a highly functional film with high hardness and excellent low-friction, wear-resistance, and corrosion-resistance properties; however, it has high residual stress and low adhesion between the substrate and the film. Existing studies focused on using DLC containing metallic elements (Me-DLC) as an intermediate layer to minimize residual stress, thereby improving adhesion. Si-DLC is deposited using a mixture of hydrocarbon gases, such as methane (CH₄) and acetylene (C₂H₂), and silicon gases, such as tetramethylsilane (TMS: Si(CH₃)₄), H, and Si, to form the DLC coating. The composition, hardness, Young's modulus, and friction coefficient of the film can be controlled by changing the composition of the gas mixture. This study investigated the effect of the flow rate ratio of raw material gases (CH₄ and TMS and C₂H₂ and TMS) on the properties of the DLC film when Si-DLC is deposited as an intermediate layer on austenitic stainless steel SUS304 using plasma-enhanced chemical vapor deposition. The coating time was adjusted to ensure that the thicknesses of the Si-DLC layer and DLC film were 1.0 and 0.2 μm, respectively, under both conditions. The results demonstrated that the durability of the DLC film improved and adhesion decreased with a decrease in the TMS ratio in the Si-DLC intermediate layer. When C₂H₂ was used as the raw gas, durability improved and adhesion decreased compared to when CH₄ was used.