Microstructure and nanoindentation hardness of TiN/AlN multilayer films prepared by pulsed laser deposition

Abstract

TiN/AlN nanoscale multilayer films were deposited on silicon by pulsed laser depositions, with nominal periods of 10, 20, 40 and 100 nm and total thickness of the TiN/AlN multilayer of ∼500 nm. The microstructure, composition and period of samples were characterised by SEM, nanoindentation and friction tests. The SEM result indicates that the microstructure of the TiN/AlN multilayer film has a good period. The nanoindentation test shows that the hardness of the TiN/AlN multilayer films range from 22 to 30·6 GPa, which is higher than that of a single TiN film (17 GPa). The TiN/AlN multilayer film with a maximum hardness value of 30·6 GPa is associated with more effective combination of solid solution hardening (TiAlN) on the interface. This point is confirmed by X-ray photoelectron spectroscopy. The influences of the period on the microstructure and mechanical properties of films are also investigated. The X-ray diffraction patterns indicate that TiN film exhibits nanocrystalline columns, whereas AlN shows a crystallite structure. The TiN/AlN multilayer film presents typical microstructural features for both materials. In tribological tests, a ball on disc test is used to determine the friction coefficients. The coefficient of steady state friction against a Si3N4 ball varies considerably between films grown by different periods. The lowest friction coefficient of μ = 0·33 is shown at the TiN/AlN multilayer film, whereas the TiN and AlN single layer film ranges from 0·33 to 0·82.