Mechanical and tribological properties of nanostructured TiAlN/TaN coatings deposited by DC magnetron sputtering

In this research, nanoscale TiAlN/TaN multilayer coatings was deposited by DC magnetron sputtering, controlling the substrate rotation speed in order to obtain different periods and to evaluate their effect on mechanical and tribological properties. FE-SEM images showed multilayer architecture of coatings with larger bilayer period, TEM analysis were necessary to observe the architecture for coatings with periods below 25 nm. Mechanical properties exhibited a parallel behavior. Hardness, Young's modulus and recovery percentage increase progressively as the bilayer period of multilayer coatings decreases. Regarding to the residual stresses, a significant reduction of residual stress was observed for multilayer coatings compare to monolayer constituent monolayers, decreasing the residual stress from -8 GPa up to -1 GPa. By FIB, it was possible to study the deformation mechanisms in nanoindentation tests; inter-columnar shear was the main mechanisms observed. The increase in critical load of coatings was one of the most relevant results obtained in the investigation, it was possible to increase two times the critical load of multilayer coatings with Lambda = 10 nm, compare to TiAlN and TaN monolayer coatings. With Regard to tribological properties, it was clearly observe the influence of multilayer architecture and the bilayer period. TiAlN/TaN coatings with Lambda = 5 mn exhibited friction coefficients lower than 0.2 and wear rates 2 time lower than the bare substrate. The optical images suggest the presence of tribooxidation reactions and with EDS it was possible to confirm the oxidation of coatings.