Hardness enhancement and elastic modulus behaviour in sputtered Ag/Ni multilayers with different modulation wavelengths

Abstract

The hardness of de-magnetron sputtered Ag/Ni multilayers with different modulation wavelengths Λ was measured by nanoindentation. A hardness enhancement of nearly 50% over the rule-of-mixtures value, calculated from the experimentally determined hardnesses of single Ag and Ni thin films, is observed. For small Λ values, the hardness increases with Λ and reaches a maximum at 10 nm, whereafter it decreases again. This behaviour agrees qualitatively with model calculations which have been developed to explain the hardness enhancement in multilayers composed of layers with different shear moduli and lattice parameters. Instabilities of the metastable multilayer structure such as amorphization or a break-up of the individual layers at very low modulation lengths (Λ≤4nm) are detected by the nanoindentation measurements. X-ray diffraction measurements were performed in order to investigate the correlation between structural parameters and hardness.