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Recently a demand-driven development of iron-based coatings that could be an alternative for self-fluxing and cermet coatings for the protection of screen tubes of boilers of power stations has been observed. Electric arc spraying is an advantageous method in many applications due to its high deposition rate and economical operation (Crawmer, 2004) [1] . The fast development of cored wires as a feedstock material over the past few decades has made it possible to extend the metallurgical choice of sprayed coatings significantly. In the present work, the results concerning the development of arc-sprayed iron-based coatings for application at elevated temperatures are presented. Powder-cored wires have a diameter of 1.8 mm with a filling coefficient of 20–27%, a 0.4 mm thick cover, made of low-carbon steel (0.08% C), and contain a filling powder (Al, Cr, Mg, B). High resistance of coatings against hot-gas corrosion and erosion at elevated temperatures in oxidising atmosphere is ensured by the appropriate choice of an alloying system as well as the optimisation of deposition and, if needed, post-treatment processes. Oxidation kinetics, phase transformation and an evolution of the residual stresses in the coatings have been investigated at a temperature up to 700 °C for the time interval 100–2000 h. It has been established that the oxidation resistance of arc-sprayed coatings depends on the coating microstructure, phase transformation and oxidation processes, which take place during the high-temperature exposure, as well as on the level of chemical inhomogeneity of the arc-sprayed coating. The high resistance against gas abrasion is provided due to the favourable changes in the coating microstructure at the service temperature (600–700 °C) namely dispersing strengthening, desired oxidation sealing effect and formation of the beneficial compressed residual stresses. |
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