Improving the wear resistance and scratch adhesion strength of TiAlN coatings via Al incorporation

• The highest hardness (∼ 34.5 GPa) was found in the coating containing 20 at. % Al • Improved wear resistance is associated with superior mechanical properties • Enhanced scratch toughness was found in coatings with lower Al concentrations • Scratch-failure modes are influenced by the shape and density of macroparticles The inclusion of Al into the binary TiN crystal structure may impose a significant influence on the tribological properties of titanium aluminium nitride (TiAlN) coatings. In this study, a suite of TiAlN coatings, with different Al concentrations, were deposited onto tool steel substrates through variation in the composition of the Ti-Al cathode using the cathodic arc evaporation process. The primary objective of this investigation was to explore the wear and scratch response of TiAlN coatings, in particular, the underlying deformation mechanisms of these coatings under cyclical or progressive loading. The maximum nanohardness (∼ 34.5 GPa) was realised in the film containing the lowest Al concentration (∼ 20 at. %), which was attributed to Hall-Petch effects, as well as the effects of solid solution hardening. The wear resistance of these coatings exhibits an inverse relationship with the Al content and was noted to be consistent with the hardness and modulus of these coatings. Enhanced scratch adhesion strength, as defined by higher L C1 , L C2 and CPR values, was also observed for the TiAlN coating with the lowest Al concentration (∼ 20 at. %), consistent with its higher H/E r and H 3 /E r 2 ratios, promoting good resistance against adhesive and cohesive failures. In addition, the failure modes under progressive loading were found to be influenced by the geometry and density of macroparticles, arising from the deposition process, accompanied by the residual stresses of the coatings and the hierarchical architecture of these thin film systems.