An important, but insufficiently described in the literature aspect of tribological tests of surface modified materials is the contact geometry in friction systems. Relatively little attention is paid to the observation and description of the phenomena that occur in the friction area of biomaterials modified with thin layers. The aim of the study was to analyze the chaos phenomena in pin-on-disc wear tests of TiN-modified Ti6Al4V alloys. The counter material was AISI 52100 bearing steel. Friction force evolvement was registered during 2h tests performed in non-lubricated conditions. For the purpose of the analysis of time and amplitude characteristics of the obtained signals, the Matlab® software and the Cross Reference Plot Toolbox (Potsdam Institute for Climate Impact Research) were used. According to the results, the breakdown of the TiN layer results in a significant decrease in the recurrence of the analyzed signals. The analysis of the phenomena of deterministic chaos allows the clear identification of changes in tribological systems dynamics. What is more, it can be used in order to determine the exact sliding distance before the breakdown of the anti-wear layers. Acknowledgements: This scientific work was supported by the Faculty of Mechanical Engineering, Bialystok University of Technology, project No MB/WM/XX/2016.