| Electroless Nickel Plating(ENP) have been widely applied in production with its advantages such as simple processing, low-cost, uniformity, thickness and large-area plating. However, with the technology development and actual production's needs, composite coatings were gradually developed with their specific functions. Using some of the unique performance of nano-materials, combining traditional surface technology so as to prepare nanoparticles reinforced surface coating of composite materials become one of the hot topics in the surface area. This paper studied the preparation of a kind of coating on 45 steel surface with the performance of high wear resistance and self-lubricating that compounded with nano-Al2O3 powder and PTFE, so as to meet the needs of actual production.The microstructure, surface morphology, hardness, wear resistance and also formation mechanism of the test samples were systematic studied by Micro-hardness tester, Optical Microscope, Scanning Electron Microscope, X-ray diffraction and Friction-Wear tester. The results show as follow:The optimized dispensation of electroless plating of nikel through the experiments are showed as follows:NiSO4 25g/L, NaH2PO2 30g/L, CH3CH(OH)COOH 25ml/L, CH3COONa 15g/L, C2H5NO2 3g/L, CH4N2S 3-5mg/L; pH=4.8, the temperature is 88±2℃; The addition of nano-Al2O3 was 2-3g/L, the addition of PTFE emulsion was 10ml/L. Using the optimized technology, the Ni-P-Al2O3-PTFE composite coating with nano-Al2O3 enhanced, PTFE antifriction of high wear-resistant and low coefficient on the 45 steel surface was successfully prepared.The prepared coating of Ni-P,Ni-P-Al2O3,Ni-P-PTFE and Ni-P-Al2O3-PTFE after plating was non-crystalline, the hardness were followed by 516HV,684HV,380HV and 452HV. The plating coating became crystalline after heat treatment temperature at 300℃, and totally crystalline at temperature 400℃. The maximum hardness of Ni-P coating achieved to 894 HV after 400℃heat treatment; Ni-P-Al2O3 composite coating achieved up to 1215 HV also after heat treatment at 400℃. Because the melting point of PTFE is 327℃, the hardness of Ni-P-Al2O3-PTFE multiple composite coatings after heat treatment at 375℃was 894 HV and 1187 HV at 400℃, which illuminated PTFE in coating had gasified and escaped at evaporation temperature 375℃, so the self-lubricating properties reduced. Thus this paper choose the heat treatment temperature at 350℃for one hour, then the hardness can be relatively achieved up to 756 HV and will not damage PTFE in the coating. The wear performance showed that, the wear rate of Ni-P-Al2O3-PTFE multiple composite coatings was reduced evidently, and had lower friction coefficient. The wear resistance of Ni-P-Al2O3-PTFE multiple composite coating was the best after heat treatment of 350℃for 1h, the wear losses was 1.6mg and the friction coefficient 0.11.In the Ni-P-Al2O3-PTFE multiple composite coatings, as a kind of hard particle, Al2O3 particles and nickel-phosphorus coating form a complex phase through composite deposition. The hard particles greatly enhance the property of the coating hardness and wear-resistance. The PTFE particles have nice property of self-lubricating, when they were rubbed, they enabled to form a spreading layer by the lamellar delamination in the coating containing PTFE, so the uniform thickness anti-resistance layer was formed on the samples surface to reduce the friction coefficient and wear losses. The co-action of both particles enabled the Ni-P-Al2O3-PTFE coating with properties of high wear resistance and self-lubricating.
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