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A compact and adherent Al2O3 diffusion barrier was obtained between a Ni coating and stainless steel 316 (316SS) through double-pulse composite plating coupled with in-situ thermal growth. To promote the formation of α-Al2O3 at low temperature, a Cr2O3 film was firstly prepared by pre-oxidation of 316SS. Then a Ni-Al/NiO composite coating was deposited on 316SS in a modified Watts’ bath with a Zeta potential of about +21.89 mV, a favorable condition for the co-deposition of double particles and nickel, followed by heat treatment in Ar at 800 ℃ for 12 h. Results of diffusion resistance tests at 750 and 800 ℃ for 100 h in Ar suggest that the Ni/α-Al2O3 composite coating changes slightly during the annealing treatment and significantly prevents the diffusion of Fe and Cr from 316SS substrate to the upper Ni layer. Furthermore, corrosion resistance of the composite coating is higher than that of the 316SS/Ni sample.
Wang et al. (Fri,) studied this question.