Effect of solid-solution W addition on the nanostructure of electrodeposited Ni

Electrodeposition method was employed to produce freestanding Ni-W alloy foils. The foils consist of nanograins. The structure of the foil, e.g. texture, grain morphology, size distribution, and the nature of grain boundaries, were characterized using X-ray diffraction and high-resolution electron microscopy. The deposited foils exhibit an equiaxed nanocrystalline structure having a grain size value of about 6 nm. Two types of grain boundary structure were observed. One type of grain boundary is essentially one atomic layer thin and another type consists of a structureless layer of about 0.5-1 nm in thickness. Angular dark field (Z-contrast) image of the deposited foils showed an inhomogeneous distribution of W solutes. In some local regions, the W content actually exceeds the equilibrium solid solution limit. Many grain boundaries with a structureless layer of about 0.5-1 nm are probably a result of local supersaturation of W.