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

The hardness of dc-magnetron sputtered Ag/Ni multilayers with different mod ulation wavelengths Lambda was measured by nanoindentation. A hardness enha ncement of nearly 50% over the rule-of-mixtures value; calculated from the experimentally determined hardnesses of single Ag and Ni thin films, is obs erved. For small Lambda values, the hardness increases with Lambda and reac hes a maximum at 10nm, 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 multil ayer structure such as amorphization or a break-up of the individual layers at very low modulation lengths (Lambda less than or equal to 4nm) are dete cted by the nanoindentation measurements. X-ray diffraction measurements we re performed in order to investigate the correlation between structural par ameters and hardness.