The increasing demand of the industry for high quality coatings with a low cost aspect has led to the development of ultra thin, nearby finishing free carbide coatings. The R&D work performed for this publication was focused on the tailoring of carbide powders together with the development of a new generation of HVOF-Systems working on higher combustion chamber pressures. An as-sprayed surface roughness of less than 1,5µm has to be envisaged for a thin nearly finishing free coating. Therefore, the starting powder has to have fine particles size with a homogenous distribution of carbides and matrix metals. To ensure the corrosion resistance, the matrix metals have to be completely alloyed and the coatings have to be dense. The used HVOF-System must be able to feed and spray these fine powders without any blockage of the powder feeder or nozzle clocking. The coating quality has to fulfil the requirements of hardchrome plating as wear and corrosion resistance is concerned. The low cost level of thin hard-chrome coatings shall be matched. The suitability for using this coating on applications like hydraulic cylinders has been proven. Generally, this technique of thermal spraying can be used as a hard-chrome alternative as well as for new applications where thermal spraying was not put into account due to cost and technical reasons. The aim was to fill the gap between thin film technologies as PVD or CVD techniques and conventional thermal spraying. The new technology enables the industry to coat large components with nearly no restrictions in size and for competitive prices.

Advanced spraying technologies as High Pressure-HVOF Spraying or Cold Gas Spraying as well as new concepts for the next generation of plasma sprayed TBC's demanding spray powders with strongly decreased powder grain sizes (< 15µm or even less). Although, with decreasing powder grain size the flowability of the powder is also decreased, causing finally problems in the transport of powder. Within this paper a new powder feeder design will be presented, that makes the precise feeding of ultrafine powders possible, even through feeding lines several meters in length. All known powder feeders for thermal spraying use the pneumatic convey for powder transport through the feeding line. In opposite, the new developed powder feeder is using the dense phase convey of powders. The powder transport can be compared with the transport of a liquid in an hydraulic system. The new powder feeder shows no restrictions in the flowability of a powder. The feeding of normal spray powders (carbides, oxides, metals) as well as submicron powders were successfully tested. Feeding rates from several grams per hour to hundred kilogram and more per hour can be realised, depending on the design of the system. The transport through feeding lines longer than 10 meters also causes no difficulties. The system is self-cleaning and there are no mechanical parts in contact with the powder.