H. Pokhmurska, B. Wielage, T. Grund, S. Schuberth, TU Chemnitz, Chemnitz, Germany; V. Pokhmurskii, M. Student, G.V. Karpenko Physico-Mechanical Institute, Lviv, Ukraine
Boiler heating surfaces of thermal power plants are operated under conditions of elevated temperatures and gas-abrasive wear caused by coal dust particles. Arc sprayed Fe-based coatings with the effect of dispersion hardening are developed to protect these surfaces against oxidation and wear under operation temperatures up to 700 °C. Cored powder wires of 1.6-1.8 mm diameter were used as feeding materials. As filling material, different powder mixtures containing FeCr, FeCrB, Al, W, Mo, Ni and other components are proposed. Microstructure, mechanical properties and abrasive wear resistance of as-sprayed coatings as well as coatings after dispersion-hardening at 550 °C are investigated. It is established that dispersion hardening of electric arc sprayed coatings takes place due to precipitation of intermetallic phases (FeAl, Ni3Al), borides (Fe2B and CrB) and special carbides (for example Me23C6 alloyed with W, Mo, V) from the oversaturated solid solution. After dispersion hardening at 550 °C during 1 h the coating microhardness increases from 600 - 800 HV0.3 to 1000 -1200 HV0.3. The results of gas-abrasive wear testing demonstrate that abrasion wear resistance of electric arc sprayed coatings dispersion-hardened at 550 C° is 2.5-4 times higher than that of the low alloyed boiler steel.
Summary: Oxidation kinetics of arc sprayed Fe-based coatings with the effect of dispersion hardening have been investigated. An improvement by 2.5-4 times of gas-abrasive resistance of electric arc sprayed coatings dispersion-hardened at 550 C° is observed.
