PREPARATION AND PROPERTIES OF NANOSIZED MUL- TILAYERED Ni COATINGS BY ULTRASOUND-ASSISTED ELECTRODEPOSITION

Nanosized multilayered Ni coatings were deposited on Q235 steel substrates by ultrasound-assisted electrodeposition.The multilayered Ni coating has a laminated structure of ordinary Ni layer/ultrasonic Ni layer.In order to determine the corrosion and wear property of this novel multilayered Ni coating, conventional Ni coating and bilayered Ni coating were prepared.The phase structure and average grain size of the Ni coatings were determined by X-ray diffraction analysis.Cross section morphologies were observed by scanning electron microscope.Corrosion properties of the Ni coatings were investigated by the immersion test in 7%HCl solution at room temperature, and then their corrosion morphologies were examined by scanning electron microscope.Another way to evaluate the corrosion resistance of the Ni coatings is to calculate the porosity of the Ni coatings using porosity analysis software on an optical microscope.Wear resistance of the Ni coatings were evaluated by rubber wheel test method.The test condition was 400 # SiC emery paper and the applied load on the samples is 6.3 N.Moreover, after 1500 cycles, cross sections of the worn Ni coating samples along the wear direction were observed by means of scanning electron microscope.The results indicate that the growth orientation of the multilayered Ni coating is (111) preferably.Its microstructure is obviously a smooth stacker-up laminated structure.Hence, the epitaxial columnar growth of the conventional Ni coating is annihilated by the formation of the multilayered structure.Compared with the conventional Ni coating, not only the wear resistance of the multilayered Ni coating is improved obviously, but also the corrosion resistance of the multilayered Ni coating is enhanced dramatically.With multilayered structure, the pinholes were obviously inhibited.That is because the multilayered Ni coating can cover the whole surface of the substrate without pinhole interruption.The multilayered structure can extend the pinhole passages extremely for the multilayered