Effect of Cr Addition on Corrosion Resistance of Laser-Cladding Ni-Cr-Mo Coatings in Chloride Solution with Thiosulfate

Abstract:

The effect of Cr addition on the corrosion resistance of the laser-cladding Ni-Cr-Mo coatings was evaluated in chloride solution with thiosulfate by microstructure observation and electrochemical measurements. Results show that very similar microstructures and phase compositions are tested by scanning electron microscope and X-ray diffraction. Both eutectic and dendrite structures are observed, and the coatings are mainly composed of the γ-Ni solid solution of Cr, Mo, W, Fe, and Cr0.19Fe0.7Ni0.11 solid solution. The electrochemical results confirm that the laser-cladding coating with the special Cr addition behaves better corrosion resistance. The coating C28 performs higher values in open circuit potential and lower passive current density, especially the larger modulus of the impedance and charger transfer resistance. With increasing Cr content, the passive film is much thicker and the defects of the films are less in chloride solution with thiosulfate. The Mott-Schottky reveals that the passive film formed on the top surface of the laser-cladding coatings in solution behaves as n-type and p-type semiconductors.

Key words:laser cladding;microstructures;electrochemical behavior