Effects of gas trapped in nickel alloy coating on corrosion behavior of coating deposited by HVOF

The NiCrBSi alloy powders were sprayed to a steel substrate using high velocity oxy-fuel(HVOF)after which some coatings were heat treated at 600℃ in vacuum for 2 hours, and corrosion behavior of the as-sprayed coating and heat-treated coating in 3.5%NaCl aqueous solution was investigated using electrochemical impedance spectroscopy.The results show that effects of gas trapped in nickel alloy coating on corrosion potential and corrosion resistance of the coating are great.The corrosion potential of as-sprayed coating is higher than that of the gas-removed coating which has been heattreated in vacuum, because the gas can decrease the electric charge density in electrochemical double layer thus heighten the corrosion potential.The coating can be densified by heat-treatment, but the corrosion resistance of as-sprayed coating is higher than that of the heat-treated coating, so the effects of gas on corrosion resistance are greater than that of microstructure.However, the influence of gas is short-term and the corrosion potential and corrosion resistance decrease dramatically at the early stage of corrosion.The corrosion behavior of coating is determined by microstructure finally.