Ni-SiO2 composite coatings were prepared on surface of 45# steel substrate by plating. Effects of n-SiO2 concentration in nickel bath on the surface morphology and microhardness of composite coatings were studied. The fractal dimension values of surface morphologies were calculated by means of projective covering method. The relationship between fractal dimension of the surface morphology of composite coating and its microhardness was studied. Results showed that the microhardness of composite coatings reaches the maximum value when the n-SiO2 concentration in bath is 5 g/L. The fractal dimension value is 2.7～2.9 and the correlation coefficients are above 0.9. There is a negative correlation between fractal dimension of the surface morphology of Ni-SiO2 composite coating and its microhardness, indicating that the application of fractal theory to the quantitative characterization of microhardness of coating is feasible.%利用电沉积方法在45钢上制得Ni-SiO2纳米复合镀层,研究了镀液中纳米SiO2的浓度对镀层表面形貌和性能的影响；用投影覆盖法计算镀层表面分形维数,并考察分形维数与镀层显微硬度的关系.结果表明,纳米SiO2的质量浓度为5g/L时,镀层的显微硬度最高；镀层的表面分形维数介于2.7～2.9之间,相关系数在0.9以上,分形维数与显微硬度成负相关关系,进一步说明了用表面分形维数定量表征镀层显微硬度的可行性.
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