Corrosion behaviour of electrodeposited Ni/Al2O3 composite coating covered with a NaCl salt film at 800°C

The electrodeposited Ni/Al2O3 composite coatings were prepared by direct current (DC), pulse current (PC) and pulse reversal current (PRC) deposition, respectively. The corrosion behaviour of electrodeposited Ni/Al2O3 composite coatings covered with NaCl salt films at 800 degrees C in air was investigated by SEM/EDX, XRD and thermogravimetric analysis. It is found that corrosion of the three types of coatings is seriously aggravated with a present NaCl salt film, and a corrosion layer with a poor adherence to the matrix has been formed. Furthermore, chlorine enrichment at the interface between the matrix and the corrosion product has been observed. The corrosion resistance of the three types of coatings has improved with the increase of Al2O3 content. The corrosion resistance of the Ni/Al2O3 composite coatings prepared by PRC deposition is the best, and that by DC deposition is the worst. The corrosion mechanism of Ni/Al2O3 composite coatings will also be discussed.