Abstract
There is a variety of components, which are subject to high wear and/or corrosion stress on the one hand and are used to transfer heat on the other hand. Two examples are drying cylinders in paper production and condensing boilers. Up to now there are no data available for the thermal design of thermal spray coated components except for some MCrAlY and thermal barrier coatings for turbine applications. Also guidelines for the optimization of thermally sprayed coatings concerning heat transfer including the effect on the wear resistance are missing. HVOF sprayed cermet coatings are widely used for combined wear and corrosion protection these days. In addition to WC-CoCr 86 - 10 4 and 75 Cr3C2 - 25 Ni20Cr conventional Ni5Al and Ni20Cr bond coats are evaluated concerning their thermal conductivity in the range between room temperature and 600 °C. Also the thermal contact resistance is determined depending on the substrate material: mild steel S355J2G3 (1.0570), grey cast iron GG25 (0.6025) and austenitic stainless steel X5CrNi18-10 (1.4301, AISI 304). The applied Laser- Flash method requires knowledge of the heat capacity, thermal expansion and density, which are determined before. HVOF spraying has only negligible influence on the heat capacity of WC-CoCr feedstock, as the temperature depending functions are almost identical. The use of spraying feedstock with average WC particle sizes of 800 nm, 3 µm and 5 µm permits to investigate the influence of the specific surface area of the hard phases both on the thermal conductivity and wear resistance. Furthermore the influence of the coating porosity is determined. In accordance to the drying cylinder application the wear resistance is determined by Taber-Abraser wear tests. Bond coats are produced by HVOF, HVCW and arc spraying and compared concerning microstructure and thermal conductivity. A comparison to the properties of electroplated hard chromium coatings is drawn.
