Hot corrosion behaviour of HVOF sprayed Ni3Ti and Ni3Ti + (Cr3C2 + 20NiCr) coatings in presence of Na2SO4-40%V2O5 at 650 °c

Abstract

Ni<inf>3</inf>Ti and Ni<inf>3</inf>Ti + (Cr<inf>3</inf>C<inf>2</inf> + 20NiCr) coatings were deposited on gas turbine based ASTM B265 titanium (Ti-15) and AISI 420 stainless steel (MDN-420) substrate materials using HVOF technique. Thermocyclic hot corrosion tests were carried out at 650 °C in molten salt environment of Na<inf>2</inf>SO<inf>4</inf>-40%V<inf>2</inf>O<inf>5</inf> for about 50 cycles. Thermogravimetric analysis was carried out to study the hot corrosion kinetics of uncoated and coated titanium and stainless steel substrates. The weight gain per unit area showed that the coated substrate materials displayed better resistance to hot corrosion when compared with that of uncoated substrate materials. The surface morphology of uncoated and coated substrate materials were analysed using scanning electron microscopy and elemental analysis. The formation of different types of oxides and compounds were analysed using x-ray diffraction. The uncoated substrates surface showed microspalling at several regions while coated substrates surface were composed of protective oxide layers. The presence of ternary NiCr<inf>2</inf>O<inf>4</inf> protective oxides on the surface of Ni<inf>3</inf>Ti + (Cr<inf>3</inf>C<inf>2</inf> + 20NiCr) coated substrates leads to reduction in the diffusion of corrosive species inside the coating. © 2019 IOP Publishing Ltd.