Microstructure, mechanical and tribological performance of nanostructured TiAlTaN-(TiAlN/TaN)n coatings: Understanding the effect of quaternary/multilayer volume fraction

Four nanostructured TiAlTaN-(TiAlN/TaN)n coatings were deposited, varying the volume fraction of the top quaternary coating (TiAlTaN) and the base multilayer coating (TiAlN/TaN) with percentages of: 84/16, 66/34, 48/52 and 23/77, and evaluating their effect on mechanical and tribological performance of the nanostructured coatings. The cross-sectional images obtained by FE-SEM showed the interface between each of the constituent monolayer, a well-defined columnar structure for the TiAlN/TaN multilayer coating, while in the quaternary TiAlTaN coating thicker columns were also observed. High-resolution TEM analysis revealed well-defined multilayer architecture followed by the quaternary TiAlTaN. The nanostructured TiAlTaN-(TiAlN/TaN) coatings showed preferential growth in the direction (111) corresponding to the rock-salt-like crystalline structure of the TiN. Additionally, the shift of this peak was observed as the volume fraction of TiAlTaN decreased, associated to the decrease in the residual stresses of the coatings. Regarding tribological properties, nanostructured coatings exhibited relatively high friction coefficients (~0.8) for coatings with higher TiAlTaN volume fraction, with a clear progressive decrease as the volume fraction of multilayer TiAlN/TaN coatings increases. The high friction coefficients are compensated by the low wear rates of coatings compared to the uncoated substrate. Regarding to the mechanical properties, nanostructured coatings, follow the composite rule of mixtures, with a hardness between 32 GPa (TiAlTaN) and 25 GPa (TiAlN/TaN), Young's modulus showed similar behavior. The coatings adhesion increased progressively as the percentage of TiAlN/TaN increased, reaching Lc3 values higher than 28 N. The propagation of the transverse and longitudinal crack were observed by FE-SEM, in radial direction to the direction of application of the load and oblique direction with 45° tangential to the direction of scratching, respectively. •Nanostructured TiAlTaN-(TiAlN/TaN) coatings using substrates speed rotation control.•Switch the architecture between quaternary and multilayer with substrate speed rotation.•Mechanical and tribological properties of coatings follow the composite rule of mixture.•Cracks evolution in scratch tests analysis detected by Focused Ion Beam cuts.