An integrated technology of hollow cathode plasma enhanced chemical vapor deposition (PECVD) with plasma immersion ion deposition (PIID), promoting the deposition rate ranging from10 to 14 µm h −1 , was developed to deposit thick Si-doped diamond-like carbon (Si-DLC) films on the internal surface of 304 stainless steel (SS304) pipes with various inner diameters for corrosion and abrasion protection. After the deposition, the films inside 30 mm and 90 mm diameter pipe have been comprehensively investigated by FESEM, optical 3D profiler, Raman, XPS, nanoindentation, EIS and polarization measurements, salt spray test and friction test. It was found that Si-DLC films were compact and smooth, thick (~11 µm) and hard (~13 GPa). The current density ( 2.38 × 10 −9 A cm −2 ) of Si-DLC films was 1000 times lower than the uncoated steel pipe through the electrochemical polarization test. The EIS data were analyzed by an equivalent circuit model, which presented a highest charge transfer impedance of ~4.5E7 Ω cm 2 . Si-DLC films survived 720 h salt spray test without the presence of corrosion pits and exfoliation. The test results confirmed that Si-DLC films possessed superior performances in corrosion resistance, which was not only attributed to the chemical inertness of DLC and Si incorporation, but also to the multilayered film with few defects. Besides, the friction coefficient of Si-DLC films in air, water and oil environments was low at 0.05-0.06, 0.08-0.12 and 0.08-0.09, respectively, in comparison with 0.55, 0.30 and 0.11 for bare steel. The corresponding wear rates of Si-DLC films were much lower than uncoated steel pipe in the three environments as well.

An energy dissipation model was raised, including the influence of film properties, counterpart, contact stress and adhesion strength between film and substrate. A new plastic deformation-tendency index was introduced. The new index was more appropriate in predicting the wear behavior of a-C films than hardness and H/E. Particularly, the critical value of the new index existed for film failure in the friction test. Realizing the limitation of the model, some improvement directions of the model were also discussed in this study.