The wear properties and adhesion strength of the diamond-like carbon film coated on SUS,Ti and Ni–Ti with plasma pre-treatment

Diamond-like carbon (DLC) films were deposited on stainless steel (SUS), titanium (Ti) and nickel titanium (Ni–Ti) substrates using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the substrates were exposed to O₂ and N₂ plasma to enhance the adhesion strength of the DLC film to the substrate. After the plasma pre-treatment, the chemical composition and the wettability of the substrate surface was investigated by X-ray photoelectron spectroscopy (XPS) and water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated substrates.

The XPS results showed that the N₂ and O₂ plasma pre-treatment produced nitride and oxide on the substrate surfaces, such as TiO₂, TiO, Fe₂O₃, CrN and TiNO. In the pull-out test, the adhesion strengths of the DLC film to the SUS, Ti and Ni–Ti substrates were improved with the plasma pre-treatment. In the ball-on-disc test, the DLC coated SUS, Ti and Ni–Ti substrates without the plasma pre-treatment showed severe film failure following the test. The DLC coated SUS and Ni–Ti substrates with the N₂ plasma pre-treatment showed good wear resistance, compared with that with the O₂ plasma pre-treatment.