DLC coatlng on magnesium alloy sheet by low-temperature plasma

Magnesium alloy sheets were coated with diamond-like carbon (DLC) using low-temperature plasma for the improvement of formability. For the better adhesion between Mg and DLC, Si-containing intermediate layer was necessary. In SEM observation, Si-containing layer formed by tetraethoxysilane (TEOS) plasma exhibited Very tight and regular wavlng pattern, Which was inherited to DLC layer deposited successively, and showed good adhesion. From the X-ray photoelectron spectroscopy (XPS) measurement, Si-C bond was found at the interface after DLC coating. Concerning the surface chemical structure, both sp³ fraction and hydrogen content measured by XPS and glow discharge spectroscopy, respectively, decreased with increaslng CH₄ concentration in the mixed gas with H₂ in DLC coating. The friction coefficient was reduced by the TEOS and DLC coatlng tO a compatible level with MoS₂ lubricated one, but its clear dependence on CH₄ conCentration was not found. The formability by deep drawing of DLC coated Mg alloy sheet was as good as that of MoS₂ 1ubricated one.