Mechanical properties and load bearing capability of nanocrystalline nickel-tungsten multilayered coatings

Nanocrystalline nickel-tungsten alloys are of high industrial interest owing to their mechanical properties, wear and corrosion resistance, as well as their thermal stability. Since the patterning of their structures potentially enhances mechanical and tribological characteristics, layered nickel-tungsten alloys were developed by sequential electrodeposition of bi-layers (two different concentrations of tungsten) in the current study. The layer thickness was modulated in the range of 90 to 3000 nm. Using a modified pulse reverse current technique, all the layers were deposited from a fixed citrate-based electrolyte. Studying the material by microhardness and Palmqvist techniques revealed that the microhardness of the coatings was improved by reduction of layer thicknesses, in accordance with Hall-Petch relation. Wear test results indicated that layered coatings were more resistant in comparison with the monolithic counterparts. Furthermore, microscopy investigations showed that by reducing the layer's thickness, the plastically deformed region underneath the wear front narrows, thus increasing the load-bearing capabilities.