Designing a new generation of biomaterials is based on the assumption that the appropriate chemical composition of a material, the chemical state of its surface and the surface structure in nanoand micrometer scales are the elements which selected in a planned way decide on the type of cellular response to the material. The use of quantitative fractography enables a quantitative description of the surface. The parameter most frequently used in surface stereometry is the area development coefficient Sdr. Attempts are being made to use other tools for determining additional parameters. One of them may be fractal analysis, in which fractal dimension D is the measure of surface complexity. For the purposes of the study, comparative fractal and multifractal analyses of images showing porous surfaces of Al₂O₃ ceramic coatings were performed. The analyses were carried out for three lenses, namely 20×, 50× and 100×, and the impact of magnification (scale properties) on the obtained results was examined.

Due to its tendency to increase the power of engines, improving their reliability and operational efficiency, the compression ring in combustion engine pistons is embedded in a cast iron insert, which is subjected to the process of “alfining”. This involves covering the insert with an Al–Si alloy, which increases the iron content. Research has shown that the β-Al₅FeSi phases crystallizing in the area of the insert–piston connection are the main cause of an unstable connection between the silumin casting of the piston and the ring insert. Their unfavourable lamellar morphology and large dimensions are the main causes of weakening in the connection between the insert and the piston, resulting in an unacceptable number of defective products. It has also been found that up to approx. 0.59 wt.% Fe, the pore volume fraction is very small (up to 3%), and there is no correlation. However, after exceeding this value, both the volume fraction of the β-Al₅FeSi phase and the number of pores increase monotonically to values of approximately 18% and 14%, respectively, and the correlation between the examined features is statistically significant. These results were compared with known theories of the influence of iron on the porosity of Al–Si alloys, showing that the precipitates of the β-Al₅FeSi phase are more important in the porosity fraction than the two-layer oxide films called “bifilms”. This research was carried out and verified under industrial conditions in one of the largest piston foundries (Federal-Mogul Gorzyce sp. z o.o., F-MG) on a separate line intended for alfining ring inserts intended for combustion pistons.