Coating WC deposited by thermal spraying (HVOF) as an alternative to hard chrome electroplated on hydraulic equipments

Abstract

In order to obtain a surface resistant to wear and oxidation, hydraulic cylinders are typically coated with hard chromium through electroplating process. However, this type of coating shows an increase of the area to support sealing elements, which interferes directly in the lubrication of the rod, causing damage to the seal components and promote leakage oil therefore. Another disadvantage in using the electroplated hard chromium process is the presence of high level hexavalent chromium Cr+6 which is not only carcinogenic, but also extremely contaminating to the environment. Currently, the alternative process of high-speed thermal spraying (HVOF - High Velocity Oxy-Fuel), as opposed to hard chrome coating, uses composite materials (metalceramic) possessing low wear rates. Research has shown that some mechanical properties are changed positively with the thermal spray process using, for electrodeposition of hard chromium for industrial applications. It is evident that coatings based on WC have characteristics such as hardness, wear resistance, roughness and friction coefficient, superior with respect to hard chrome coatings. These characteristics were analyzed by optical microscopy, wear tests (ASTM G65 and G99), roughness measurements and profilometry