Study On Preparation And The Properties Of Duplex Ni-P/Ni-B Layer

In order to identify the better scheme, the writer studies the performance of Ni-B coating in the orthogonal experiment from the perspectives of deposition rate, crystal structure, surface morphology and microhardness. Orthogonal experiment and Chinese-based orthogonal table are applied in this thesis. Finally, orthogonal experiment 4 and 9 are identified as preferred schemes. The four factors in this experiment are:the concentration of nickel sulfate (the primary salt), the concentration of complexing agent ethylenediamine, the concentration of reducing agent sodium borohydride, the concentration of sodium hydroxide. To further optimize the orthogonal experiment 4 and 9, the writer changes the content of boron by changing the concentration of the reducing agent because the content of boron in coating determines the structure and properties of the coating. The writer compares the deposition rate, crystal structure, surface morphology, and microhardness ect. by optimizing the orthogonal experiment 4 and 9. The result shows that the deposition rate of the orthogonal experiment 4 is faster than that of the orthogonal experiment 9. However, the crystal structures of the two types are basically the same and the reason is the content of boron in the coating is probably of the same quantity. The coating's surface of the optimized orthogonal scheme 4 is dense and uniform, yet the coating's surface of the optimized orthogonal scheme 9 has more defects and the surface is of low density. Furthermore, the microhardness of the optimized orthogonal scheme 4 is obviously higher than that of the optimized orthogonal scheme 9. However, the two types'coatings all have pinholes and the pinholes in the optimized orthogonal scheme 9 are more obvious. Based on the above analysis, the optimized orthogonal scheme 4 is a better scheme.The orthogonal optimized scheme 4 is optimized again by adding sodium acetate in it. The writer studies the deposition rate, crystal structure, surface morphology, microhardness, the abrasion resistance and the corrosion resistance in this orthogonal optimized scheme 4 with sodium acetate. The deposition rate of the coating with sodium acetate is reduced. Meanwhile, the coating changes from blended structure to microcrystalline structure; the surface morphology of the coating is more dense and uniform than the former one without sodium acetate; the microhardness is improved; both of the abrasion loss and the average friction coefficient are reduced.Based on the preparation of Ni-P/Ni-B, the writer studies the crystal structure, surface morphology, abrasion property, porosity rate, polarization curves of Ni-P/Ni-B coating in details for the improvement of the single-layer coating's performance is limited. Furthermore, the writer also analyzes the abrasion resistance and the corrosion resistance of the coating.The crystal structure of the Ni-P/Ni-B coating does not change though the coating's bottom is changed. The surface morphology of the coating is influenced by the bottom coating. The abrasion property Ni-P/Ni-B of the coating is influenced by the coating's microhardness and average friction coefficient. The corrosion potential of the Ni-P coating and Ni-B coating influences the corrosion potential of Ni-P/Ni-B coating. When the corrosion potential difference is about 100-130mV, the corrosion potential of Ni-P/Ni-B coating is higher.The writer studies the abrasion resistance and corrosion resistance of the coating by reducing the coating's thickness. Both the abrasion resistance and corrosion potential of Ni-P (high phosphorus)/Ni-B coating is basically lower. As for the Ni-P (low phosphorus)/Ni-B coating, the change rules of the abrasion resistance and corrosion resistance is the same as Ni-P (high phosphorus)/Ni-B coating.