Application of TiC reinforced Fe-based coatings by means of High Velocity Air Fuel Spraying

Abstract

Abstract. In the field of hydraulic applications, different development trends can cause problems for coatings currently used as wear and corrosion protection for piston rods. Aqueous hydraulic fluids and rising raw material prices necessitate the search for alternatives to conventional coatings like galvanic hard chrome or High Velocity Oxygen Fuel (HVOF)-sprayed WC/Co coatings. In a previous study, Fe/TiC coatings sprayed by a HVOF-process, were identified to be promising coating systems for wear and corrosion protection in hydraulic systems. In this feasibility study, the novel High Velocity Air Fuel (HVAF)-process, a modification of the HVOF-process, is investigated using the same feedstock material, which means the powder is not optimized for the HVAF-process. The asserted benefits of the HVAF-process are higher particle velocities and lower process temperatures, which can result in a lower porosity and oxidation of the coating. Further benefits of the HVAF process are claimed to be lower process costs and higher deposition rates. In this study, the focus is set on to the applicability of Fe/TiC coatings by HVAF in general. The Fe/TiC HVAF coating could be produced, successfully. The HVAF-and HVOF-coatings, produced with the same powder, were investigated using microhardness, porosity, wear and corrosion tests. A similar wear coefficient and micro-hardness for both processes could be achieved. Furthermore the propane/hydrogen proportion of the HVAF process and its influence on the coating thickness and the porosity was investigated. IntroductionAn important point for components in hydraulic applications is their lifetime. In the hydraulic steelwork, a lifetime of 30-50 years is a common demand [1]. To fulfil this requirement, the used piston rod has to be protected against wear and corrosion. Typical coatings for highly loaded hydraulic components are WC/CoCr and Cr 3 C 2 /NiCr sprayed by HVOF. These coatings exhibit a good corrosion and wear protection. Raw material prices have, however, risen over the last years. Therefore, researchers and the industry are investigating possible alternative cost efficient systems with comparable resistance to mechanical and corrosive attack. One alternative is the reduction of the carbide content of the coating. Another alternative is to investigate cost-efficient and ecological [2] Febased matrix materials with alternative hard materials, like TiC. Moreover, it can be noted that the additives in lubricants are often optimized for Fe-based materials, in order to increase the corrosion protection of the technical components [3].In a previous study of the authors, TiC reinforced Fe-based (Fe/TiC) coatings with a relatively low carbide contend (34 wt.-%) has been developed considering the above-mentioned issues. Fe/TiC coatings were applied on the carbon steel C45 using two different HVOF systems; one operated with liquid fuel and one operated with gaseous fuel. Electroplated hard chrome and WC/CoCr HVAF