From DLC to Si-DLC based layer systems with optimized properties for tribological applications

Abstract Diamond-like carbon (DLC) coatings are used in many industrial applications like valvetrain-, fuel injection- and piston-systems. For DLC (a-C:H) coatings, prepared by a magnetron based technique using graphite targets, high indentation hardness values of more than 40 GPa were achieved. The wear resistance, the microhardness and the coefficient of friction are shown as a function of the hydrogen concentration in the coatings. In order to reduce the coefficient of friction even more and to increase the operational temperature of the coatings from about 350 °C for DLC to near 500 °C, a new Si-DLC (a-C:H:Si) based layer system was developed using a special magnetron sputter target configuration. This Si-DLC based layer system combines the benefits of a reduced coefficient of friction with a high wear resistance. The DC magnetron cathode based production method allows the deposition of Si-DLC coatings in a wide range of compositions with 4 to 40 at.% Si at low hydrogen contents down to 5 at.%. These new Si-DLC based coatings with a silicon concentration around 25 at.% Si exhibited under dry conditions friction coefficients with only the half of the value of pure a-C:H. This is rather promising for present and future industrial applications.