Mechanical and Corrosion Behaviour of DLC and TiN Coatings Deposited on Martensitic Stainless Steel

The ceramic and carbon coatings such as titanium nitride (TiN) and diamond-like carbon (DLC) coatings are characterised by good mechanical properties and chemical inertia. The objective of this work is to compare the wear, friction, adhesion and corrosion behaviour of commercial TiN and DLC coatings deposited on AISI 420 stainless steel, by plasma-assisted techniques. The microstructure of the coatings was characterised by optical and electronic microscopy and X-ray diffraction. The hardness and Young’s modulus were measured by nanoindentation. Pin-on-disk, fretting and abrasive wear tests were performed. Adhesion was evaluated by means of Scratch Test and Rockwell C Indentation. The corrosion behaviour was evaluated by Salt Spray Fog and electrochemical tests in chloride solutions. The thickness of both coatings was between 1 and 1.5 µm. The hardness was 26 GPa and 34 GPa for DLC and TiN coating, respectively. The results showed that the TiN coatings presented better abrasive wear resistance than the DLC coatings; however, the latter was more resistant to the pin-on-disk test, fretting and it had a lower friction coefficient. Both coatings showed far better wear resistance than the untreated steel. Finally, TiN coatings had better adhesion to the substrate than DLC coatings, proved in both tests. Regarding the corrosion behaviour, both coatings exhibited acceptable corrosion resistance in the Salt Spray Fog Test, but only the DLC coatings had both nobler corrosion potential and higher breakdown potential than the TiN coatings in electrochemical tests.