COMPARATIVE-STUDY OF HIGH CORROSION-RESISTANT TICXN1-X AND TIN HARD COATINGS

TiCxN1-x coatings with compositions ranging from TiN to TiC were deposited by cathodic are plasma deposition (CAPD) technique onto HSS M35 tool substrates. TiN films were also obtained by plasma-assisted chemical vapour deposition (PACVD) on the same substrates. A comparative study of the corrosion resistance of these films is presented. The potentiodynamic corrosion tests were carried out in 0.1 and 1 N H2SO4 aqueous solutions at 25 degrees C. Results of adherence, hardness, as well as morphology and crystalline structure of the films are included. The microstructural characterization of the films before and after the corrosion test was carried out using SEM, XRD, XPS and EPMA techniques. PACVD and CAPD TiN films gave a columnar morphology with different textures. CAPD-TiCxN1-x and TiC films consisted of a mixture of dense columnar and granular morphology. The corrosion tests showed that the films themselves are inert and that the corrosion process of the film-substrate system occurred through the cracks around the microdefects of the films. The corrosion resistance of the film-substrate system was dependent on the TiCxN1-x film composition and showed a close correlation with the adherence and the hardness of the films. The corrosion resistance of the different TiCxN1-x films was in general worse than that of TiN films, but the film with stoichiometric TiC0.5N0.5 composition showed the highest resistance. This film combined good adhesion and corrosion resistance, and had a higher hardness than TiN films.