Investigation of cyclic oxidation and corrosion behavior of plasma-sprayed NiCrAlY/Cr3C2/h-BN coatings on T22 boiler steel alloy

The present study examines the hot cyclic oxidation and corrosion behavior of NiCrAlY/Cr3C2/h-BN coating sprayed with a plasma gun on ASTM SA213-T22 boiler steel. The newly developed coating underwent testing for hot cyclic corrosion at high-temperature in a molten salt environment containing (Na2SO4-60%V2O5) and a test of cyclic oxidation was conducted in static air at 700 °C. Hot corrosion and oxidation were evaluated over 50 cycles at a temperature of 700 °C. The oxidation kinetics were determined using a thermogravimetric method, and the produced oxide scale was characterized using FESEM, EDS, and XRD. The oxidation rate of the NiCrAlY/Cr3C2/h-BN coated substrate was found to be 8.7 times lower than that of the uncoated substrate. When exposed to oxidation in air, the coated substrate showed gradual scale growth kinetics, leading to the development of oxides like NiO, and Cr2O3 on the surface, and the results showed that the addition of solid lubricant boron nitride (h-BN) greatly increased their resistance to high-temperature corrosion and oxidation. The coating and underlying substrate did not deteriorate as much because the h-BN particles served as barriers to the migration of oxygen and corrosive species. The enhanced performance of the coatings under challenging operating conditions was also aided by the development of protective oxide layers including silicon and boron.