Hot corrosion behavior of plasma-sprayed NiCrAlY/TiO2 and NiCrAlY/Cr2O3/YSZ cermets coatings on alloy steel

Abstract

The objective of the Present research work is to evaluate the hot corrosion resistance of plasma-sprayed 70% NiCrAlY+ 30% TiO<inf>2</inf> and 70% NiCrAlY+ 25% Cr<inf>2</inf>O<inf>3</inf>+5% YSZ coatings on MDN 420 alloy. Hot corrosion tests are carried out under molten salt environment of Na<inf>2</inf>SO<inf>4</inf>+60 % V<inf>2</inf>O<inf>5</inf> salt mixture at 700°C for 50 cycles. Each cycle consisting of 1 hour heating in a silicon carbide tubular furnace followed by 20 min of cooling. The thermogravimetric technique was used to determine the kinetics of corrosion. The scanning electron microscopy (SEM), energy dispersive analysis (EDAX), electron probe microanalyser (EPMA) and X-ray diffracton (XRD) techniques were used to evaluate the characterization of coatings with regard to coating bondstrength, thickness, microhardness and porosity. The parabolic rate constants of coated steels are lower when compared to the uncoated substrate. The NiCrAlY+ Cr<inf>2</inf>O<inf>3</inf>+YSZ coating is found to be more protective when compared to NiCrAlY+ TiO<inf>2</inf> coating. The oxides of Al<inf>2</inf>O<inf>3</inf>, NiCr<inf>2</inf>O<inf>4</inf>, and Cr<inf>2</inf>O<inf>3</inf> are formed on the outermost layer of the coatings which gives the resistance the coatings to high-temperature corrosion. © 2020