Effect of hexane precursor diluted with argon on the adherent diamond-like properties of carbon films on steel surfaces

• Hard DLC coatings can be deposited on steels by bipolar pulsed-DC PECVD method.
• Using an amorphous silicon interlayer the adhesion increases considerably.
• Hexane–argon atmosphere improves the mechanical and tribological proprieties.

Various precursors of diamond-like carbon (DLC) growth have been studied in order to find the best set of mechanical and tribological proprieties. Gaseous hexane (C6H14) stands out as an option because of its high vapor pressure and the fact that it accepts dilution with other hydrocarbons or even nanoparticles, forming convenient colloidal substances. Therefore, in the present paper, hexane will be studied using argon as an inert additional gas, in order to determine the mechanical and tribological properties and microstructure of DLC films deposited via a modified and asymmetrical bipolar pulsed-DC plasma enhanced chemical vapor deposition system. The addition of argon to the hexane precursor atmosphere is expected to increase the ratio of ion to neutral radicals on the surface of the growing film without changing the H/C ratio of the gas mixture. The film's microstructure and the hydrogen contents were probed by means of Raman spectroscopy. The internal stress was determined through measurement of the change in the substrate curvature by means of a profilometer, while nanoindentation experiments showed the hardness of the film. The adhesion of the films was evaluated via the scratch test. In order to overcome the low adhesion of these films on AISI 304 stainless steel surfaces, a silicon interlayer, obtained by using low-energy ion implantation and silane as a precursor gas, was used. The results show that the precursor hexane atmosphere diluted with argon induces modifications in the properties of the films when a high quantity of argon is used. The importance of the effect of ion bombardment during film growth on the properties of the films was confirmed.