Enhancement of Corrosion Resistance of Al2O3 + Sm2SrAl2O7 Composite Thermal Barrier Coatings by Laser Treatment

Abstract

The rare earth aluminate Sm<inf>2</inf>SrAl<inf>2</inf>O<inf>7</inf> was synthesized in the laboratory through a molten salt synthesis technique at 1100 °C. A composite thermal barrier coating system on Inconel 718 substrate was developed with Al<inf>2</inf>O<inf>3</inf>–Sm<inf>2</inf>SrAl<inf>2</inf>O<inf>7</inf> composite as the top coat and NiCrAlY as the bond coat using atmospheric plasma spraying. The surface of the plasma-sprayed coatings was treated using an Nd: YAG fiber laser to seal off the open porosities and reduce surface roughness. Hot corrosion tests on the laser-modified samples were performed at 700 °C and 900 °C, in aviation and marine corrosive conditions using 50 wt.% Na<inf>2</inf>SO<inf>4</inf> + 50 wt.% V<inf>2</inf>O<inf>5</inf> and 90 wt.% Na<inf>2</inf>SO<inf>4</inf> + 5 wt.% V<inf>2</inf>O<inf>5</inf> + 5 wt.% NaCl, respectively. The laser-treated samples showed higher resistance to failure than the as-coated samples under similar conditions. The corrosion products are identified, and the mechanisms involved are discussed in detail. The effect of surface modifications on the hot corrosion resistance of the coatings is investigated. © The Indian Institute of Metals - IIM 2023.