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In this paper, one of the tribological tests for the evaluation of friction properties is introduced. The test, named “Block-on-Ring”, (in accordance with the standard ASTM G77) was carried out by the SKODA VÝZKUM Ltd. company and realized on renovated apparatus. The brief description of the measurement is as follows: the flat surface of the sample is pressed against the cylindrical surface of the rotating wheel. Arbitrary oil is fed to the materials’ contact surface and the increasing temperature can be detected using the thermocouple that is placed in close proximity of the contact materials. Using the strain-gauge dynamometer, the friction force is recorded. The test is run on a number of periods and, including after the first expiration time, the wear track formed in the sample is measured and evaluated. The final results are the summary of partial results of the long-standing tests, which serve for the preliminary detection of the friction behaviour of the materials. The friction properties of the thermally sprayed coatings were investigated. The Cr3C2-NiCr, 13% Cr and Cr2O3 coatings were tested. The thin-base babbit was selected as the counter-part. The main interest was in the characterization of the friction properties in the dependence on the amount of added lubricant and on the normal load of sliding couples.

The friction between a piston, piston rings and a cylinder is responsible for almost 55% of total power loss in engines. The decrease of friction in the piston area leads to a significant fuel saving and also to emission reduction. Application of a surface treatment, such as PEO, PVD, HVOF, plasma sprayed coatings, surface texturing, etc. on engine components is a way to reduce corrosion, friction, wear and weight of engines. In the paper, the potential of the application of HVOF sprayed coatings on the engine components is discussed with respect to their sliding friction properties. The technology of thermal spraying enables one to create the surface coating approximately 50 µm thick, which provides functional surface protection of the coated parts. HVOF technology offers the possibility of creating the coatings of materials based on the principle of hardmetals with high wear resistance and favourable sliding properties. Such a combination predestinates HVOF sprayed coatings for sliding applications, such as pistons of combustion engines, pumps and other hydraulic devices. In this application area they are used on a regular basis. In practice, the producers and users of thermally sprayed coatings face the problem of the interaction of the coatings and their counterparts with the presence of other media, fuels, or, in the case of sliding wear more often, lubricants. The paper describes the methodology of measurement suitable for lubricated HVOF coatings using the pin-on-disc test according to ASTM G-99 and on the evaluation of the influence of lubricants on the friction properties, wear rate and mechanism of HVOF sprayed coatings. The pin-on-disc test according to ASTM G-99 was performed on the thermally sprayed Cr3C2-25%NiCr coating to determine and describe their sliding wear behaviour under different test conditions. The influence of various test parameters (load, wear track diameter, temperature, lubrication, counterpart

The tribological properties of the surfaces of parts, namely their wear resistance and friction properties, are in many cases decisive for their proper function. To improve surface properties, it is possible to create hard, wear resistant coatings by thermal spray technologies. Using these versatile coatings it is possible to increase the lifetime, reliability and safety of parts. For proper function of the surface treatment it is necessary to find and keep the optimal condition and parameters during preparation, deposition and further processing of the sprayed part. The spraying angle is one of the deposition parameters that influence the quality of thermally sprayed coatings. According to the theory, with decreasing spraying angle the process deposition efficiency decreases, whereas the porosity of coatings increases, being a cause of aggravated microstructure and mechanical properties. In this paper, the microstructure together with the basic mechanical properties and wear of WC-Co and Cr3C2-NiCr HVOF sprayed coatings were investigated in dependence of the spraying angle. For each coating, the marginal spraying angle that can be used without a significant decrease of the coating’s quality was identified. With respect to the change in coating properties as well as to process deposition efficiency, the maximum 30° diversion from a normal spray direction is recommended in the case of WC-Co and 15° diversion in the case of Cr3C2-NiCr.

One of the tribological tests for the evaluation of friction properties is introduced in this paper. The test, named “Block-on-Ring”, is in accordance with the standard ASTM G-77 and in SKODA VÝZKUM Ltd. is realized on the VRS-3 renovated apparatus. The measurement is as follows: the flat surface of the sample is pressed against the cylindrical surface of a rotating wheel of the rotor material. Arbitrary oil is fed to the material contact surface and the increasing temperature is detected using a thermocouple. The friction force is recorded using the strain-gauge dynamometer. The test is performed in a number of periods and always after one expiration time the wear track formed in the sample is measured and evaluated. The final results are the summary of the partial results of the long-standing tests and are used for the preliminary detection of the friction behavior of individual material couples.