A comparison of microstructural, mechanical and tribological properties of WC-10Co4Cr - HVOF coating and hard chrome to use in hydraulic cylinders

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.