Morphology, Structure, Microhardness and Corrosion Resistance of Ni-W Coating Annealed in Hydrogen and Argon Atmosphere

In this paper, an amorphous Ni-W coating was electrodeposited on the low-carbon steel and then annealed in hydrogen and argon atmosphere. Their characterization was carried out using scanning electron microscopy and x-ray diffraction. The corrosion characterization was carried out using the potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy. The results show that microcracks inevitably exist on the surface of Ni-W coating when annealed at 750 degrees C or higher temperature. After annealing treatment, amorphous structure transforms to crystalline and some new phases are precipitated, which is significantly affected by the annealing temperature and atmosphere. The microhardness of annealed Ni-W coatings is much higher than that of as-deposited coating, while an adverse corrosion performance is observed for the annealed Ni-W coatings. The coating annealed in hydrogen at 500 degrees C shows a huge improvement in hardness and a fairly acceptable corrosion resistance compared with the as-deposited Ni-W coating.