Deposition and characterization of non-isostructural (Ti0.7Al0.3N)/(Ti0.3Al0.7N) multilayers

Non-isostructural Ti0.7Al0.3N(cubic B1)/Ti0.3Al0.7N(hexagonal B4) nanoscale multilayers were deposited by dc magnetron sputtering on steel substrates, with nominal periods of 6, 10, 20 and 40 nm. The structure, composition, periodicity, and interface abruptness of the samples were characterized by X-ray diffraction, glow discharge optical spectroscopy, medium energy ion scattering, and narrow resonant nuclear reaction profiling. The nanohardness and elastic modulus of the samples were determined, revealing superhardness of up to 57 GPa for the lowest nanoscale multilayer period. The H3/E2 ratios were found to be superior to those of most metal nitride multilayers commonly used as protective coatings, which indicates a superior wear resistance for the present nanostructured coating. The results are discussed in terms of the present stage of understanding of nanoscale multilayer effects on the tribological properties of protective coatings.