Effects of exposure to 40MPa hydrogen on DLC films

This paper describes the behaviors of DLC (diamond-like carbon) films exposed to high pressure hydrogen. Two types of DLC, i.e. a-C:H (hydrogenated amorphous carbon) and ta-C (tetrahedral amorphous carbon) DLC films, were exposed to 40 MPa hydrogen at 373 K for 20 and 200 hours. Reciprocating sliding experiments were conducted with the exposed specimens. The specimens after the exposure and those after sliding tests were observed and analyzed with scanning Auger microprobe, Raman spectroscopy, dynamic-mode secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. It was found that the two DLCs were partly or totally fractured at the film-substrate interface after the exposure to high pressure hydrogen. The results of the surface analyses suggested that hydrogen permeated, diffused and accumulated in the DLC films, which might be the cause of the film failure. It was also found that wear of ta-C DLC was reduced by the exposure to high pressure hydrogen.