Study of TiAlSiN coatings post-treated with N and C+N ion implantations. Part 2: The tribological analysis

Ion implantation has found to be an effective approach to modify surface properties of materials. The present research investigates the effect of (1) nitrogen (N), and (2) carbon subsequently with nitrogen (C+N) implantations on the mechanical and tribological properties of the titanium–aluminium–silicon–nitride (Ti–Al–Si–N) coatings. Superhard TiAlSiN coatings produced by magnetron sputtering, of approximately 2.5μm thickness, were post-treated by implantations of N or C+N at an energy level of 50keV. The dose range was between 5×10 ¹⁶ and 1×10 ¹⁸ ionscm ⁻² . After implantation, the tribological performance of the coatings was investigated by a ball-on-disk tribometer against WC–6wt.%Co ball under dry condition in ambient air. The wear performance of the samples was examined by a variety of characterization techniques, such as secondary electron microscopy (SEM), 3D profilometry, atomic force microscopy (AFM), and micro-Raman. The results showed that the wear performance of the samples depended strongly on the implanted elements and doses. There was slight improvement on the samples implanted with N whereas significant improvement was found on the C+N implantations. Particularly, the friction coefficient of the sample with 5×10 ¹⁷ C ⁺ cm ⁻² and 5×10 ¹⁷ N ⁺ cm ⁻² could reach 0.1. In addition, the specific wear rate of the sample was extremely low (0.85×10 ⁻⁷ mm ³ /Nm), which was nearly two orders of magnitude below that of the un-implanted coating. The speculation of the mechanical and tribological analyses of the samples indicates that the improvement of the N implanted and C+N implanted TiAlSiN samples could be due to a combined effect of improved hardness, plus enhanced adhesive and cohesive strength. In addition, the improved performance of the C+N implanted samples could be explained by the formation of lubricating implanted-layer, which existed mostly in sp ² C–C and C–N forms. The formation of such implanted layer could lead to a change of wear mode from strong abrasive wear to mostly adhesive wear, and result in a drop of friction coefficient and wear rate.