Effects of modulation periodicity on microstructure, mechanical and tribological properties of NbN/AlN nanostructured multilayer films

NbN/AlN nano-multilayer films with modulation periodicity (Λ) ranging from 3.9 to 31.6 nm have been deposited on Si (1 0 0) substrate by reactive magnetron sputtering in Ar/N2 mixtures. The Λ dependent structural, mechanical and tribological properties for resulting NbN/AlN multilayers have been explored. As Λ varies from 3.9 to 31.6 nm, the crystal structures of NbN and AlN are face-centered cubic and hexagonal in multilayer films, respectively, favoring formation of a coherent epitaxial growth with crystallographic relationship of image due to total energy minimization, and large Λ can improve mutual coherence and promote coherent growth of fcc-NbN(1 1 1)/w-AlN(0 0 0 2). The remarkable hardness enhancement implements in a wide range of Λ from 3.9 to 31.6 nm for NbN/AlN multilayer system, which can be mainly attributed to hindering the dislocation motion caused by heterostructure coherent interface of fcc-NbN(1 1 1)/w-AlN(0 0 0 2). Although all multilayers show lower friction coefficient than constituent monolayers, great improvements in the wear behaviors only appear in multilayers with Λ = 3.9 and 7.4 nm due to their large content of interfaces.