Evaluation of cyclic oxidation and hot corrosion behavior of HVOF-sprayed WC-Co/NiCrAlY coating

Abstract

Corrosion of metallic structural materials at an elevated temperature in complex multicomponent gas environments are potential problems in many fossil energy systems, especially those using coal as a feedstock. Combating these problems involves a number of approaches, one of which is the use of protective coatings. The high velocity oxy fuel (HVOF) process has been used to deposit WC-Co/NiCrAlY composite powder on two types of Fe-based alloys. Thermocyclic oxidation behavior of coated alloys was investigated in the static air as well as in molten salt (Na<inf>2</inf>SO<inf>4</inf>-60%V<inf>2</inf>O<inf>5</inf>) environment at 700 °C for 50 cycles. The thermogravimetric technique was used to approximate the kinetics of oxidation. WC-Co/NiCrAlY coatings showed a lower oxidation rate in comparison to uncoated alloys. The oxidation resistance of WC-Co/NiCrAlY coatings can be ascribed to the oxide layer of Al <inf>2</inf>O<inf>3</inf> and Cr<inf>2</inf>O<inf>3</inf> formed on the outermost surface. Coated alloys extend a protective oxide scale composed of oxides of Ni and Cr that are known to impart resistance to the hot corrosion in the molten salt environment. © 2014 ASM International.