Fractal Feature And Wear Resistance Of Rough Coating Surfaces

The coating technology, for its vital function of improving the surface quality and material performance, is widely applied in surface protection, strengthening and repair of mechanical components. However, the research of friction and wear processes about coating surfaces is not sufficient. Much work is still required to be done. And this essay provides a new method for the explanation of coating abrasion. In this paper, the relation of the real contact area and the wear resistance for coating surfaces is investigated, which bases on their surface micro-topography and contact behavior.Measuring the coating surface firstly, the fractal dimension and coordinates of some regular grid points are obtained simultaneously. Then this case develops fractal model of coating rough surface parametrically by APDL and application of fractal interpolation theory. Similarly, more coating surface models are established to contact with a rigid plane respectively. And combined with the finite element method, those contact problems can be solved by numerical calculation. At last, the orthogonal test is designed to study effects on the real contact area of these factors, such as surface fractal dimension, materials’ tangent modulus, coating thickness and indentation depth.According to the numerical calculation and orthogonal tests, the following conclusion can be drawn:(1) there are only a few asperities to real contact with each other, and it makes the contact regions to present discontinuously on coating surface. Simultaneously, the plastic and the elastic contact areas produce on the surface.(2) The contact area of those surfaces decreases obviously when the surface fractal dimension increases from2.1to2.6, while the fractal dimension is greater than2.6, the contact area changes slightly.(3) On coating surfaces, the real contact area increases slowly before the indentation depth up to2.5um, but after that, it will amplifies rapidly and accelerates with the indentation depth continuous increase to5um.(4) Through the variance analysis of orthogonal test, the influence extent of real contact area is investigated. The indentation depth has significant influence on the real contact area of coating surface, and it is the primary factor, then the surface fractal dimension, the coating thickness behind, and the materials’tangent modulus is the weakest factor.The friction and wear experiment is conducted to15coating samples with Taber test in the certain load and the same wear distance. And the results are indicated that, the wear loss of coating varied with the fractal dimension at2.05-2.46is approximately exponential distribution. Combined with the classical theory of adhesive wear, it takes the experimental result to compare with the numerical calculation, then the change of the real contact area is great consistent with the wear loss under the different surface fractal dimension.