Structural, chemical, mechanical and corrosion resistance characterization of TiCN coatings prepared by magnetron sputtering

A range of different chemical compositions of TiCxNy coatings were deposited by a magnetron sputter ion plating technique onto highspeed steel (M2) and a medium-carbon steel (1045). Variations of the reactive gas mixture, deposition temperature and substrate bins were carried out for each series of deposition, in order to observe the influence of these deposition parameters on chemical composition and on the X-ray diffraction and mechanical properties of the coatings. Rutherford backscattering spectrometry (RBS) and glow discharge optical spectroscopy (GDOS) techniques were used to analyze and characterize chemically the TiCxNy layers, which could be under-stoichiometric, stoichiometric or over-stoichiometric, depending on the methane content in the gas mixture. Moreover, there was a composition variation within the film thickness for over-stoichiometric coatings. The residual stress characterization was carried out with grazing angle X-ray diffraction, using lattice distance versus sin(2) psi plots. The coating hardness and adherence were observed by ultra-microhardness and scratch test analyses, respectively. The coatings were hard and presented a good adherence to the substrates. Coating stoichiometry affected the intensity of {111} and {200} X-ray diffraction lines, although the characteristic Ti(C,N) diffraction lines were able to be distinguished. The film structure was directly affected by its thickness, and the residual stress values were higher for thinner coatings (1 mu m). Finally, the coating resistance to aggressive environments was observed by using electrochemical impedance spectroscopy (EIS). This result showed that an increasing carbon content in the coating decreased the corrosion resistance. (C) 1997 Elsevier Science S.A.