Effect of Ion-Plasma Surface Treatment on Tribological Characteristics of Polyurethane

The aim of this study is an experimental-based analysis of the effect of surface treatment, leading to the formation of carbonized layers, on the coefficient of sliding friction of two polyurethane materials that differ in mechanical and rheological properties. The properties were determined by the results of indentation on a NanoScan-4D scanning nanohardness tester. A ceramic ball with a diameter of 2.1 mm was used as an indenter, which was pressed into the samples at a given linear velocity. The indentation curves at low and high indentation velocities were used to calculate the longitudinal and instantaneous reduced modulus of elasticity. It was found that the longitudinal elastic moduli differ by more than seven times, and the rheological properties of a more rigid material are weak. Tribological tests were performed on a UMT-3 friction machine in the mode of unidirectional sliding friction at a constant load and velocity. Based on the data, regression equations were calculated and the dependences of the friction coefficient on the load and sliding velocity were obtained. The influence of the surface treatment fluence on the surface roughness, adhesion, and deformation friction force is analyzed, data are correlated with the known experimental and theoretical results. It is shown that surface treatment with a relatively small fluence gives fundamentally different effects for the two studied materials: a slight change in roughness and decrease of friction coefficient for the more rigid polyurethane; a significant increase in roughness and a consistently high coefficient of friction, which varies slightly in the considered ranges of loads and velocities. Thus, surface treatment can be used for controlling the coefficient of friction of polyurethane and ensuring its consistently high frictional properties.