Abstract
In order to obtain a wear and oxidation resistant surface, hydraulic cylinders are commonly coated with electrodeposited hard chromium. However, due to the wear, this type of coating exhibits a gradual increase of the bearing area for the sealing elements, interfering in the lubrication of the hydraulic rod, causing damage to the sealing elements and, consequently, oil leakage. Currently, the High Velocity Oxygen Fuel (HVOF) process appears as an alternative coating technique to Hard Chrome Plating, using composites (metal-ceramic), which provide low wear rates and a low friction. This work aims to compare the mechanical and tribological properties of hard chrome plated and WC-CoCr HVOF coated AISI 1045 steel for the use as hydraulic rods. The selected coatings thickness was in the order of 100-170 μm aiming to meet best wear test conditions, to facilitate the analysis of the microstructure, and to obtain better results regarding the hardness of each coating. Roughness measurements, hardness, bending and wear tests, including the measurements of friction coefficients were carried out for the coatings. Additionally, a microstructural analysis was performed by optical and Scanning Electron Microscopy (SEM) supported by Energy Dispersive Spectroscopy (EDS). The results indicated superior properties of the WC-CoCr HVOF coated steel in comparison to the chrome hard plated one, especially regarding roughness, friction and wear.
Highlights
As a power transmission element, the hydraulic cylinder can continuously transmit a wide range of power, which can be controlled and with accuracy
The samples were coated with two different types of coating: Hard Chrome, which is an electroplating process, and WC-CoCr - High Velocity Oxygen Fuel (HVOF) which is a thermal spraying process
Based on the presented results, it is possible to state that the WC-CoCr coating presented better performance in relation to the main parameters, roughness values (Ra) and Rmr, because was found the best indexes applied to the sealing surfaces in application of hydraulic cylinders [2]
Summary
As a power transmission element, the hydraulic cylinder can continuously transmit a wide range of power, which can be controlled and with accuracy. The electrodeposited hard-chrome layer, as the wear progresses, causes a gradual increase of the supporting area to the sealing elements and guides This interferes directly in the lubrication of the rods, causing damage to the sealing elements and promoting fluid leakages. This is because the roughness peaks are broken during slippage and, the height of the valleys decrease dramatically, not holding the lubrication oil anymore. Another problem in the use of Hard Chrome Plating is the presence of Cr6+ hexavalent chromium in high levels, leading to high carcinogenic and environmental contamination [2, 3]
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