Wear and Corrosion Resistances of Arc-Sprayed FeCr Alloy and Fe-Based Coatings for Boiler Heat Exchanger Pipelines

Abstract

Wear and corrosion of boiler tubes in coal-based boilers are one of the serious problems. Trying to solve this issue, FeCr alloy with 45%Cr-content coating and Fe-based coating with 13%Cr-content were arc sprayed onto carbon steel substrates to enhance both the wear and corrosion resistance of boiler heat exchanger pipelines. The microstructure, chemical compositions, and phases of the coatings were analyzed using a scanning electron microscopy, energy-dispersive spectrometer, and x-ray diffraction, respectively. The wear resistance of the coatings was assessed at 25 and 300 °C using a ball-on-disk wear tester. The corrosion resistance of the coatings was evaluated based on seawater immersion, electrochemical impedance, and polarization tests. The porosities of FeCr alloy and Fe-based coatings were 4.05 and 5.75%, respectively. The microhardness values of FeCr alloy and Fe-based coatings were 377.50 ± 46.88 HV_0.5 and 666.69 ± 57.64 HV_0.5, respectively. FeCr alloy coating with lamellar structure was mainly composed of FeCr solid solution phase and a small amount of Cr oxide and Fe₃O₄ phases, and Fe-based coating was composed of a mixture phase of amorphous and crystalline, and a small amount of Fe₃O₄ phase. FeCr alloy coating had better wear resistance than Fe-based coating at both 25 and 300 °C. The wear mechanisms of the coatings were also studied. The corrosion resistance of FeCr alloy coating was better than that of Fe-based coating in corrosive solutions. Therefore, FeCr alloy coating can provide better high-temperature wear resistance and anticorrosion performance for boiler heat exchanger piping, compared with Fe-based coating.