The tribological investigations of the hybrid composite Ni-SiC-fluoropolymer layers
Benigna Szeptycka*, Andrzej Skrzyniowski** *Instytut Mechaniki Precyzyjnej, ul. Duchnicka 3, 01-796 Warszawa **Politechnika Krakowska, Instytut Pojazdów Samochodowych i Silników Spalinowych, al. Jana Pawła II 37, 31-864 Kraków
Annals 3 No. 8, 2003 pages 325-331
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abstract The tribological contact of solid bodies results in the two major phenomena of friction and wear. The situations where friction and wear are both low, as in bearings, gears, cams, slideways etc, the surface of contacting bodies are in the elastic stress condition. The conditions for purely elastic deformation of model surface asperities are: E/Y < 70 for very smooth surface and E/Y < 3.5 for rougher surface. The first condition is realised by the ceramic particles, the second - by polymers. In present work the hybrid composite electrochemical coatings were prepared with nickel matrix and SiC as the ceramic particles and PTFE or CFx as polymer particles. Table 1 shows the particle’s character. The particles contents, roughness of surface and microhardness of the hybrid coatings used in the test are given (Tab. 2). Microhardness of hybrid composite coatings is different (Tab. 2) and not always greater than microhardness of Ni coating. The roughness of hybrid composite is low, but it is not connected with content of dispersion of particles in the coating. It is probable that the type of built-in particles also influences the roughness of hybrid coating. SEM micrographs of these coatings are presented in Figures 1-5. In Table 3 the results of the chemical composition analysis of the composite coatings are presented. The sliding wear tests were performed by wheel abrasion test based on microprocessor tribology set T-O5-tester typeroller- block, without lubrication and with lubrication along the specimen surface at a speed range of 0.27÷1 m/s under specific load in the range of 50 and 100 N. In Tables 4 and 5 the coefficients of friction are presented. The results obtained from wear tests for the hybrid composite coatings are summarized in Tables 6 and 7. Data, regarding the substrate are also included for comparison. Comparing results obtained for Ni-SiC-fluoropolymer it has been found that the composites was many times more wear resistant in comparison with steel for the friction with lubrication. The coefficient of friction in these conditions was low and significantly decreased during friction investigations with increase of load and also rubbing speed but it could be caused by lubrication agent as well as self-lubricating properties of these composite coatings. The hybrid composite coating Ni-SiC1000-DT has lower coefficient of friction and higher wear resistance than other investigated layers. This coating has a high microhardness, low roughness and also low content of built-in dispersion particles. Key words: nickel, composites, hybrid, electrochemical coatings, wear, coefficient of friction