Abstract: Developed in early 80-s of last century HVOF sprayed coatings were result of looking for new solution in thermal spray technology directed on increasing of kinetic energy of powder grains. Nowadays HVOF spraying have found a lot of applications in different branches of industry [1, 2, 3, 4, 5, 8]. Properties of thermally sprayed coatings cause that the processes of wear are more complex than in the case of monolithic materials. The phenomenon, however, has not been fully explained [6]. Thermally sprayed elements are exposed to high loads, variable rotational speeds and high temperatures, which may result in undesirable under-lubrication or no lubrication at all. The problem refers mainly to such elements as, e.g. piston rings in combustion engines or synchroniser rings [3]. All forms of failure wear can be observed on the surfaces of mating elements. Intensive adhesive or thermal wear leads to the occurrence of local grafting and adhesion and, consequently, shorter life and scuffing. The interaction of ZrO2-MgO and Al2O340TiO2 coatings and cast iron under dry friction conditions is discussed in Ref. [7]. Ref. [9] deals with the development of scuffing for plasma sprayed ceramic and metal coatings interacting with bearing steel under dry friction conditions. The behaviour of oil-lubricated Cr3C2 coatings interacting with steel is described in [10]. Investigations on the problem of scuffing resistance of cylider bore are presented in paper [11]. Former investigations of properties of HVOLF sprayed coatings are presented in paper [12]. Two carbides produced by HC Stark tungsten carbide WC-Co (FST k-674.23) and chromium carbide Cr3C225%NiCr) (1375 VM), were used. For HVOLF spraying a JP-5000 (TAFA) gun was applied. Before the spraying, faces of cylindrical samples 12.7 x 10 made of steel 45 were grit blasted with 12 grade electrocorundum at a pressure of 0.5MPa. In this test a tribological tester, T-09 type Falex which has a friction pair with a pin and vee block association was applied to investigate scuffing resistance of thermally sprayed coatings under dry friction conditions. The microstructure of the sprayed coatings was analysed with a scanning microscope JOEL JSM-5400, whereas the element distribution with a microprobe ISIS 300 Oxford Instruments. The roughness of coatings was measured with a profilographometer Talysurf 4, whereas to study their hardness a Zwick 3210 hardness tester was used. The tests were carried out under dry friction conditions and had a comparative character. It was assumed that scuffing occurs when the pin clamping the rotating antisample is sheared. For each sprayed coating, the tests were repeated three times. HVOLF sprayed WC-Co coatings demonstrated better scuffing resistance (seizure observed at 1205 +, - 163 N), the most homogeneous structure and higher hardness (1218 HV0.1), respectively in the case of Cr3C225%NiCr scuffing resistance 1161 +, - 141 N and microhardness 945 HV0.1. The friction force oscillations are different in the case of WC-Co and Cr3C225%NiCr coatings. The oscillations for chromium carbide appear earlier and they were more intensive then in the case of tungsten carbide. Scuffing resistance of HVOLF sprayed WC-Co and Cr3C225%NiCr coatings was studied using a Falex type tester. It was established that HVOF sprayed wolfram carbide demonstrated the greatest resistance to scuffing, the most homogeneous structure and the highest hardness, whereas Cr3C225(Ni 20Cr) sprayed coating was characterised by the lower hardness. During the testing of the scuffing resistance of all interacting coatings, considerable oscillations of friction force could be observed. They were present also in the case of both coatings, but occurred earlier and were more intensive in the case of Cr3C225%NiCr coating.
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YADDA/CEON