Influence of acetylene precursor diluted with argon on the microstructure and the mechanical and tribological properties of a-C:H films deposited via the modified pulsed-DC PECVD method

• Hard a-C:H films can be deposited on steels by modified bipolar pulsed-DC PECVD.
• An active screen as an additional cathode allowed the adherent film deposition.
• Acetylene–argon atmosphere improves the mechanical and tribological proprieties.
• Using a Si interlayer adhesion increased considerably.

Amorphous hydrogenated carbon (a-C:H) films were deposited employing an asymmetrical bipolar pulsed-DC plasma enhanced chemical vapor deposition (PECVD) system and an active screen that worked as an additional cathode. The influence of the acetylene (C2H2) precursor diluted with argon on the microstructure and the mechanical and tribological properties of a-C:H films were studied. Raman spectroscopy was used to estimate the film's atomic arrangements and the hydrogen content of the films. A profilometer was used to evaluate the total stress through measurement of the change in the substrate curvature, and nanoindentation experiments allowed the determination of the hardness and the elastic modulus of the films. The friction coefficient and the wear rates of the films were determined using a tribometer in unlubricated sliding friction experiments, while the critical load of failure was determined via a classic scratch test. In order to improve the adhesion of the a-C:H films to AISI 304 and AISI 1020 steel substrates, a thin amorphous silicon interlayer was deposited as an interface between the substrates and the films, using silane as a precursor. The results showed that the atmosphere of acetylene diluted by argon induced modifications in the properties of the a-C:H films. Hard, adherent, low-stress, and high wear resistant a-C:H films were deposited on steel substrates by means of a combination of a modified asymmetrical bipolar pulsed-DC PECVD system and acetylene–argon atmospheres.