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Microstructure and Corrosion Resistance of Ni-P/Ni-W-P/Ni-P Three-layer Coating Prepared on 45# Steel by Chemical Deposition Method

Ni-P/Ni-W-P/Ni-P three-layer coating is prepared on 45# steel substrate by chemical deposition method. Meanwhile, the Ni-P coating with medium phosphorus content is as the bottom layer, Ni-W-P coating is as the intermediate layer and the Ni-P coating with high phosphorus content is as the outer layer. The surface morphology, composition, microstructure and corrosion resistance of three-layer coating are characterized by scanning electron microscope, energy dispersive spectrometer, X-ray diffraction and electrochemical workstation respectively. The results show that three-layer coating has an amorphous structure with a small amount of microcrystalline structure, its porosity is only 1.54% and the surface compactness is better than that of Ni-P single-layer coating. The main composition of three-layer coating is Ni, P and W elements, which belongs to the coating with high phosphorus content. The corrosion current density of three-layer coating without immersion is 7.24×10 -7 A/cm 2 , which is nearly two orders of magnitude lower than that of 45# steel substrate. The corrosion rate of three-layer coating without immersion is only 0.044 g/(cm 2 ·a), which is lower than that of 45# steel substrate. After immersion in 3.5% sodium chloride solution for 14 days, the corrosion degree of three-layer coating is very light, and the corrosion current density increases very slowly, indicating that the corrosion resistance of three-layer coating is better than that of single-layer coating, which can provide better protection for 45# steel substrate.