| Ni-P alloy coatings has been widely used in chemical, textile, aerospace, automotive and computer fields for its excellent corrosion resistance, wear resistance and good weldability. The Ni-P-PTFE composite coating can be prepared by dispersing the polymer PTFE (polytetrafluor-oethylene) in the Ni-P alloy plating solution.This composite coating has excellent corrosion resistance, wear resistance, unique self-lubricating nature and is applicable to a wide range of temperatures (-250～300℃). Ni-P-PTFE composite coating microstructure mainly affected by the P content of the coating. With the P content increases, the corrosion resistance will increases, But the mechanical properties of coating will become deterioration and brittle. The dispersion ability, deep bath plating capabilities and current efficiency of the electroplating solution can be improved by adding a small amount of rare earth compounds, and these greatly improve the corrosion resistance and wear resistance of the coating. In this thesis, research work are as follows:1. For the purpose of dispersing PTFE particles in Ni-P plating solution, the dispersion effect of mechanical mixing, slotted ultrasound and ultrasound probe was compared by experiments. The effects of dispersion time on particle size and dispersion stability were investigated. Ultrasound probe was selected as the optimum method, the optimum dispersion time is 45 min.2. The mechanism of the rare earth elements in Ni-P-PTFE composite plating was investigated, the effects of rare earth dosage on plating speed and the PTFE content of coating were also studied, Then determined the optimum rare earth dosage is 1.2g/L3. The main process parameters of the bath PTFE content, pH, bath temperature, cathode current density and stirring speed on the composite coating performance were discussed by the method of single-factor test. Then optimum plating process parameters were determined as follows:PTFE 10mL/L, current density 3.5 A/dm~2, temperature 70℃, stirring speed 180r/min, pH 5.0, adding amount of sodium hypophosphite is 20g/L.The coating has the maximum amount of PTFE content 9.32% and P content 11.71% with these plating process parameters. SEM images revealed that the modified composite coating had a flat and smooth surface and compact structure with the PTFE particle uniformly dispersed in it.4. The corrosion electrochemical behavior of the Ni-P alloy coating, Ni-P-PTFE composite coating and modified Ni-P-PTFE composite coating in different media were investigated by anodic polarization curves (Tafel curves) and electrochemical impedance spectroscopy. The results showed that, compared with Ni-P alloy coating and Ni-P-PTFE composite coating, the corrosion potential of modified Ni-P-PTFE composite coating in 10% hydrochloric acid was increased by 316 mV and 84 mV respectively. The corrosion current density was decreased by 2 and 1 orders of magnitude respectively. The impedance value was increased by 7 and 4 times respectively. The corrosion potential of modified Ni-P-PTFE composite coating in 10% NaOH was increased by 330 mV and 40 mV respectively. The corrosion current density was decreased by 2 and 1 orders of magnitude respectively. The impedance value was increase by 3 and 2 times respectively.5. The wear resistance, antifriction, porosity, corrosion resistance and bonding strength of the composite coating ware measured. The results indicate that the composite coatings prepared by the optimum plating process show fine grain size, brightness surface, smooth, compact organization, less porosity, good adhesion and good PTFE particles distribution in the composite coating. When the rare earth dosage is 1.2g/L, the coating has the minimum friction coefficient 0.063. The composite coating has the supreme antifriction when the PTFE content is about 9%. The rare earth modified composite coating compared to the unmodified composite coatings and Ni-P alloy coatings has shown a more excellent corrosion resistance in different media environment.
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