This paper investigates a hypothesis for understanding how the substrate texture influences the adhesive strength. A surface-scale fractal analysis is carried out on measured surface textures obtained from various metallic substrate materials. The results of these area-scale analyzes are correlated with the adhesive tensile strength of the finished coating. The results show that scale-considering fractal parameters predict bond strength better than average roughness, and that they support a hypothesis that relates bond to available surface area at a given scale. Paper includes a German-language abstract.

For the adhesion of thermally sprayed coatings, the substrate roughness, or topography, plays an important role in droplet-substrate interaction. The lack of availability of methods for appropriate characterization of the real topography is a major difficulty in understanding the role that topography plays during droplet impact, wetting and solidification. The complex nature of the usually chaotic substrate topographies cannot be fully characterized by conventional roughness numbers such as Sa or Ra. In our study a scale-sensitive fractal analysis method is used for describing the morphology of grit blasted surfaces. Area-scale analyses are performed on 3D data sets acquired from different substrate materials, treated by various grit blast parameters. From fractal analysis it is known that the apparent area of a rough surface increases as the scale of observation decreases. The area-scale relations are used on one side to guide experimental design for topographical data acquisition and analysis, and on the other side to understand the influence of the grit blast process on the different kind of substrates. The potential of these scale-sensitive analysis techniques for supporting statistical correlations and clear physical interpretations will be discussed.

It is widely recognized that substrate surface roughness, or topography, plays an important role in droplet-substrate interaction and the adhesion of sprayed coatings. A key difficulty in understanding the role that topography plays during droplet impact, wetting and solidification has been the availability of methods for appropriate characterization of the topography. The complex nature of the substrate topographies cannot be adequately characterized by conventional methods such as Ra. In this work, scale-sensitive fractal analyses are considered for advancing the understanding of roughness of grit blasted surfaces in thermal spray applications. Area-scale analysis is performed on 3D data sets acquired from different grit-blasted substrates. From fractal analysis it is known that the apparent area of a rough surface increases as the scale of observation decreases. The area-scale relations are used to guide experimental design for topographical data acquisition and analysis and to better understand the influence of grit blasting on substrates for thermal spray. The potential of these scale-sensitive analysis techniques to fulfill the above bases for supporting statistical correlations and clear physical interpretations is discussed.