Morphology and microhardness of Ni-W alloy nanocrystalline coatings prepared by electrodeposition

Abstract

Ni-W alloy coatings prepared by electrodeposition have been studied by means of X-ray diffraction, transmission electron microscopy, energy dispersive spectrometer and scanning electron microscope. The results showed that the sizes of Ni-W alloys' crystal grains are determined within 30 nm and they are recognized as the nanocrystalline coatings. During electrodeposition, the coating grows at the nicks or corrosive holes firstly. Surfaces close cyst-form and uniform of Ni-W alloy coatings under the optimum process condition, and the microstructures are compact and well-distributed. The microhardness of Ni-W alloy electrodeposited coatings comes to more than 600HV and can attain to 1 132.88HV after heat treatment at 550 ℃. When the concentration of Na2WO4·2H2O is 30~50 g/L, the current density is 15 A/dm2, the pH value is 7 and the temperature is about 60~70 ℃, then optimum Ni-W alloy coatings of electrodeposition will be obtained.