Self‐ion irradiation on hydrogenated amorphous carbon films at depth of adhesion interlayer: Radiation‐induced atomic intermixing and degraded film properties

Hydrogenated amorphous carbon (a‐C:H) films consisting of a top a‐C:H layer, a gradient transient a‐C:H:Ti layer, and a bottom Ti layer were irradiated by 1.1‐MeV C+ ions, resulting in a maximum displacement damage of 1.0 dpa and a projected range inside the Ti layer. Time‐of‐flight secondary ion mass spectrometry, electron energy loss spectroscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy analyses were performed to investigate the compositional and structural transitions of a‐C:H films after self‐ion irradiation. The results revealed that C+ ions passing through the top a‐C:H layer induced C–H fracture and hydrogen diffusion in this layer and then resulted in atomic intermixing in the multilayered adhesion interlayer. After local energy deposition of C+ ions, the initial sharp interfaces in the a‐C:H:Ti layer became ambiguous due to interfacial mixing. In addition, titanium carbides formed in the Ti layer, with a gradual phase transition from TiCx to TiC with a diffusion depth of 200 nm. The broken compositional gradients of the adhesion interlayer resulted in a significant decrease in the adhesion strength of the films, which eventually resulted in degraded antiwear properties of the irradiated film in dry sliding tribotests.