Research On Nano-Al₂O₃/Ni-P Composite Coating

With development of aviation, machinery, metallurgy, marine industry and so on, existing single coating material is difficult to meet some specific requirements of material performance. In recent years, the study founds that composite coating by adding nano-particles is provided with better material properties than a single coating. Therefore nano-composite plating becomes an advanced method to prepare composite materials in modern industry.The using of nano-composite electrochemical plating method on low-carbon steel isdiscussed in this paper. In the experiment, the process parameters of pure Ni coating,nano-Al₂O₃/Ni composite coating, Ni-P coating and nano-Al₂O₃/Ni-P composite coating are optimized.The best process parameters are: plating time is 8min, plating temperature is at 60℃and currentdensity is 3.2A·dm^-2,the best content of nano-Al₂O₃ is 8g/L for nano-composite coatings.The hardness, wear resistance, anti-oxidation and corrosion resistance of coatings are compared under the optimum condition. Compared with pure Ni coating, the hardness of nano-Al₂O₃/Ni composite coating increases 101HV, the wear loses 0.0279mg·min^-1·mm^-2,the oxidation weight gain loses 3.2189mg·h^-1.Compared with Ni-P coating, the hardness of nano-Al₂O₃/Ni-P composite coating increases 105HV, the wear loses 0.0393mg·min^-1·mm^-2,the oxidation weight gain loses 4.2459mg·h^-1.The research shows that nano-Al₂O₃/Ni-P composite coating has the best performances of hardness, wear resistance, anti-oxidation and corrosion resistance. The X-ray diffraction pattern shows that pure Ni coating and nano-Al₂O₃/Ni composite coating have crystal structure, and Ni-P coating and nano-Al₂O₃/Ni-P composite coating have amorphous structure which are crystallizated to form new biological phase Ni₃P after crystallization treatment.The research shows that coating presents lamellar growth. The growth of composite coating involves two processes of weak adsorption and strong adsorption. The strengthening mechanism is analyzed from two aspects of matrix metal strengthening and nano-particle dispersion strengthening.