High temperature erosion wear of flame and plasma-sprayed nickel–chromium coatings under simulated coal-fired boiler atmospheres

This study concerns the behaviour of plasma and flame sprayed modified nickel–chromium alloy (with small aluminium and titanium additions) subjected to the action of simulated post-combustion gases from a coal-fired boiler combustor. The study first evaluates the effects of thermal exposure at high temperature on the adherence between the substrate (austenitic stainless steel) and coatings. Then, the oxidation rates of these coatings in atmospheres with 3–3.5% of free oxygen at 500 and 800°C (773 and 1073 K) were evaluated. The low velocity corrosion–erosion behaviour produced by the impact of fly ashes in the gas stream at high temperatures (773 and 1073 K) was also evaluated under impact angles of 30 and 90°. Finally, the eroded surfaces were analysed using scanning electron microscopy in order to characterise the ash embedment phenomena and the operating erosive micromechanisms.