Growth, microstructure, and microhardness of W/Mo nanostructured multilayers

Abstract

Artificially modulated W/Mo multilayers on polished stainless-steel substrates with modulation wavelength Λ ranging from 4.0 to 60.0 nm and total film thickness of 2.0 μm were prepared by magnetron sputtering. X-ray diffraction (XRD) and cross-sectional transmission electron microscopy showed that though the polycrystalline films exhibited coherent interfaces, the interfaces have a wave-like appearance due to the different orientations of individual crystals. The interplanar spacings of the W and Mo layers determined by the XRD method in W/Mo multilayers varied with the modulation wavelength. The mechanical properties of these films were investigated by a low-load microhardness indentation technique. The maximum hardness enhancement is about 51% higher than the value calculated from the role of mixtures at wavelength Λ=10.0 nm. The Koehler’s modulus difference model and Cahn’s coherent stress model have been used to estimate the hardness enhancement of W/Mo multilayers. From the comparison of theoretical calculation results with experimental dates, it is obvious that the combination of the two models can explain the hardness enhancement in W/Mo multilayers.