Tribological evaluation of biodegradable and mineral hydraulic oil with sliding between the Cu-Zn and WC-CoCr alloys

ABSTRACT The correct selection of lubricating oils and contact surfaces improves performance and reduces the energy consumption of the machines. Therefore, surface engineering proposes new coatings to which their tribological behavior combined with the use of biodegradable oils in hydraulic system components are unknown. The aim of this study was to evaluate the behavior of the mineral oil - HLP and the synthetic biodegradable - HEES, subjected to sliding of a pin made of Cu-35Zn alloy, against a flat surface coated with WC-10Co4Cr by high-speed thermal spraying - HVOF. The combination of biodegradable oils with surfaces of lesser environmental impact is important for the sustainability and growth of the modern industry. The performance of the lubricants was evaluated by means of sliding tests on a pin-on-disc tribometer, modifying the loads, to identify the lubrication, friction and wear regimes. The tests indicated that the average coefficient of friction was μHEES = 0,054 and μHLP = 0,044, so the limit of the lubrication regimes was close. The minimum film thickness hmín was 23 % higher for HLP and the obtained values of the film parameter (λ) were different from the results of other surfaces. In the evaluation of the wear of the pin and disk, it was found to that the higher concentrations of the additives of Zn and P, found in the HLP, reduces the surface damage. Therefore, it is necessary to evaluate the type of surfaces lubricated with oils of the HEES type, as well as changes in additive concentrations should be made.