DLC coating on Mg-Li alloy

The Mg-14mass%Li alloy is an ultra-light metallic material that is lighter than pure magnesium. However, this alloy has some disadvantages, in particular its poor wear and corrosion resistance. In this study a diamond-like carbon (DLC) coating was applied to the surface of the Mg-14mass%Li alloy and the extent to which it improved the wear and corrosion resistance was evaluated. As pretreatment, certain specimens of Mg-14mass%Li were coated with a Si interlayer using the ion beam sputter method and others were peened using a silicon carbide (SiC) medium, before the deposition of the DLC film. All specimens were coated with DLC using the RF capacitively coupled plasma CVD method. The DLC formed an adhesive coating on the specimen that had undergone the SiC peening process. This specimen showed a relatively low friction coefficient and relatively low wear. However, the DLC coating did not form adhesively on the specimen with a Si interlayer. None of the DLC coated specimens were able to withstand the corrosion effects of the acidic and alkaline artificial perspiration solutions. A de-lithium phenomenon was responsible for preventing effective DLC deposition on the Mg-14mass%Li alloy, therefore reducing adhesion and corrosion resistance.