Functionally graded diamond-like carbon coatings on metallic substrates

Various functionally graded diamond-like carbon (DLC) coatings were developed to improve the coating adhesion of DLC onto 304 stainless steel and Ti–6Al–4V substrates. The functionally graded coating systems investigated were Ti/TiN/TiNC/DLC and Ti/TiC/DLC on titanium alloy substrates, and Ti/TiN/TiNC/DLC on stainless substrates. These coatings were fabricated using a magnetron sputter ion plating technique. The structure, composition and mechanical properties of the coated substrates were characterised using a combination of X-ray diffraction, Raman spectroscopy, scanning electron microscopy, scratch test and pin-on-disc methods. The deposited functionally graded DLC films consisted of amorphous hydrogenated carbon with graphitic domains. Both functionally graded structures improved the adhesion and wear resistance of the DLC coatings on metallic substrates. The effects of the graded structures on the adhesion and wear of DLC coatings on metallic substrates were established. For all the coating systems, the coefficient of friction of the DLC film against a chrome steel ball was about 0.2.