Departmental Bulletin Paper Surface Modification on Tribological Properties of Diamond-like Carbon Films by means of Elements Incorporation and Plasma Treatment(Outline of Doctor Thesis)

Chavin, Jongwannasiri

Diamond-like carbon (DLC) is a metastable amorphous film that exhibits unique properties, such as chemical inertness, a high hardness, a low friction coefficient, and high wear and corrosion resistance. However, a large number of limitations exist regarding the use of DLC. Depending on the environment, the films can exhibit a poor friction coefficient and limited thermal stability. One of the ways to solve these problems is surface modification. DLC surface modification has been performed by doping with suitable elements and plasma treatment. Hence, the focus of this study was to improve the tribological properties of DLC films by means of surface modification, i.e., elements incorporation (Si-O-DLC and Si-N-DLC) and plasma treatment (O2 and CF4 plasma post-treated DLC) using plasma-based ion implantation (PBII) technique. Firstly, surface modification by means of elements incorporation, the results indicated that the Si-N-DLC (23 at.%Si, 8 at.%N) film showed good tribological performance at 500°C when compared with the non-coated substrate. Furthermore, the friction coefficients of Si-O-DLC and Si-N-DLC films insignificantly varied and exhibited lower friction coefficients than as-deposited DLC film when measured under ambient air. Secondly, surface modification by means of plasma treatment, the results indicated that hydroxyl (−OH) and fluorinated (−F) groups were generated on the DLC film surfaces treated with O2 and CF4 plasma, respectively. Both O2 and CF4 plasma treatments also influenced the friction coefficient more when it was measured under dry air than when it was measured in a high relative humidity environment. The DLC films post-treated by O2 or CF4 plasma exhibited lower or higher friction coefficients, respectively, compared with the as-deposited DLC film when they were measured under dry air. On the other hand, the friction coefficients of all the films were very similar when they were measured in a high relative humidity environment. Due to aforementioned reasons, it can be concluded that the surface modification by means of elements incorporation and plasma treatment can be considered beneficial for applying to improve the tribological properties of DLC films.

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