Research On Ni-P/PVDF Electroless Composite Platings

With the industrial development and scientific technical progress, the higher requirement for material surface properties was put forward. Electroless composite plating has become an increasing concern in the field of surface modification with its excellent performance. For optimizing the coating with higher corrosion resistance, Ni-P/PVDF composite coatings are deposited by adding PVDF into electroless Ni-P alloy baths. The structure and properties of composite coatings were tested. The effects of PVDF content on coating morphology and corrosion resistance were estimated. Moreover, the influence of rare earth elements on the structure and properties of Ni-P and Ni-P/PVDF was also studied.The results indicate that after add PVDF into electroless Ni-P alloy baths (NiSO4·6H2O 24g/L, NaH2PO2·H2O 30g/L, C6H8O7 24g/L, CH3COONa 14g/L, Na2S2O3 0.5g/L, CH3CH2COOH 5g/L), the surface morphology of the Ni-P/PVDF composite coatings is uniform and dense. The corrosion resistance is better than Ni-P alloy platings and substrates. The corrosion resistance of the coatings is increased at low PVDF contents, and then decreased with the increased of PVDF contents. In this experiment the optimum contents of PVDF in plating bath is 3g/L.After add the rare earth elements (Y³⁺ and La³⁺) into electroless Ni-P alloy baths, the grain of the obtained Ni-P-RE alloy coating is refined. With a small amount content of rare earth elements, the corrosion resistance of the coating can be improved. And the optimum content of rare earth elements is 0.1g/L. But too much addition will aggravate the corrosion.According to the optimum contents of PVDF and rare earth elements (PVDF: 3g/L, Y³⁺: 0.1g/L, La³⁺: 0.1g/L), Ni-P-RE/PVDF coatings are also deposited by electroless composite plating technology. The self-corrosion potential of the coating was low (about -510mV); the passivation current density was small, and the passivation zone width is relatively large. Under the combined effect of PVDF and rare earth elements, the corrosion resistance of Ni-P-RE/PVDF coatings has been further improved.