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 30mm 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 (~13GPa). 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 cm2. 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.