Interaction of Surface Roughness of Polypropylene and Steel under Dry Friction Conditions

Abstract

The tribological behavior of metal–polymer friction pairs depends to a large extent on their surface roughness. In this study, we analyze the friction of C45 (1.0503) steel and polypropylene homopolymer (PPH) in terms of the surface roughness characteristics of the material pair subjected to friction. The results of the friction experiments described in the article showed that during the friction process, the investigated roughness parameters of the steel specimen (Ra – average surface roughness, Rz – roughness height or ten-point height, Rp – maximum peak height, Rv – maximum valley depth) remained essentially unchanged, while the same roughness parameters of the polymer surface significantly changed and adapted to the roughness characteristics of the steel. Ellipsometric measurements also confirmed the presence of a 20–30 nm thick polymer transition film on the steel surface, and there were parts of steel on the polymer surface as well. The obtained results indicate that in the case of metal–polymer friction pairs, the change in surface roughness is asymmetric (the surface roughness of the harder material shapes the softer surface). In contrast, material transfer is bidirectional. These must be taken into account in friction modeling and wear prediction.