Experimental study on high temperature oxidation and hot corrosion behaviour of superalloys coatings using thermal spray technique

Abstract

Materials used in components of boiler, such as water walls, superheaters, reheaters, and steam tubes, must resist corrosion and oxidation at high temperatures in flue gas and steam environments. Prolonged exposure to high temperatures degrades the component material at a rapid rate through oxidation and corrosion, thereby reducing its span. To overcome this, surface modification such as thermal spray coating is one of the cost-effective techniques that makes the component resistive to degrading factors. Therefore, corrosion-resistive materials SS304 and SS316 are taken as base substrate materials, and superalloy powder Inconel-625 and a mixture of Tungsten Carbide (WC), Nichrome (Ni-Cr-B), Aluminium (Al), and Cobalt (Co) are taken as coating materials to study and compare their oxidation and corrosion behaviour at air and salt environments. Initially, Inconel-625 and an optimized coating mixture of WC-NiCrB-Al-Co are coated separately on the selected substrates SS304 and SS316 through the Atmospheric Plasma Spray technique. Optimization of the WC-NiCrB-Al-Co mixture is carried out using I-Optimal Mixture Design (DoE), and the optimum weight percentages obtained based on high hardness and low porosity are 65, 25, 5, and 5, respectively. The oxidation kinetics is studied by placing all the samples (both coated and uncoated) in a tubular furnace (1000 and#8451; capacity) for 50 cycles at 800 and#8451; in an air environment. The hot corrosion kinetics is studied by following a similar procedure but in a molten salt environment newline