Corrosion Resistance of Ni/Cu Directional Structure Coatings in Different Concentrations of H2SO4 Solution

Abstract:

In order to study the influence of Cu element on the corrosion resistance of directional structure coating of Ni-based alloy, 5%Cu element was added to Ni60 alloy powder, and the directional structure Ni60/Cu composite coating was prepared. The electrochemical corrosion properties and immersion corrosion properties of the coatings in different concentrations of H₂SO₄ solutions were evaluated by electrochemical tests and immersion tests, and the corrosion behavior of the coatings in different concentrations of H₂SO₄ solutions was discussed. The results showed that the corrosion of the coatings in different concentrations of H₂SO₄ solution shows the process of activation -passivation-overpassivation, and the electrochemical impedance spectroscopy has typical capacitive reactance characteristics in the whole time constant. The charge transfer resistance decreased firstly and then increased, and the corrosion resistance of the coating showed a trend of first decreasing and then increasing when the concentration increased from 5% to 80%. With the increase of H₂SO₄ concentration, the corrosion degree of the coating surface first intensified and then gradually slowed down, and the corrosion potential shifted to the most negative and the corrosion current density increased to the maximum when the concentration of H₂SO₄ solution was 40%. However, the surface of the coating is accompanied by the formation of a dense and uniform corrosion reaction passivation film mainly composed of NiO, Cr₂O₃ and Cu₂O when the concentration of H₂SO₄ solution reaches 80%. These reactive passivation films effectively prevent the H₂SO₄ solution on the coating surface, making the coating exhibit good corrosion resistance in high concentrations of acid.

Key words:Ni60/Cu directional structure coating; corrosion resistance; H₂SO₄ solution