Hot corrosion behaviour of HVOF sprayed NiCrAlY–0·4 wt-%CeO₂ coatings on superalloys in aggressive environment at 900°C

Abstract

The NiCrAlY–0·4 wt-%CeO₂ coated superalloys were subjected to aggressive environment of 40%Na₂SO₄–60%V₂O₅ at 900°C under cyclic conditions for 100 cycles and weight gain was monitored after each cycle. Techniques like X-ray diffraction, field emission scanning electron microscopy with energy dispersive X-ray analysis and X-ray mapping were used to analyse the corrosion products. The NiCrAlY–0·4 wt-%CeO₂ coated specimen showed negligible microspalling of the oxide scale. The incorporation of cerium oxide in NiCrAlY powder has contributed to the development of very high resistance to oxidation in the given molten salt environment. Other oxides formed were Cr₂O₃, Al₂O₃ and spinel of Ni and Cr which are highly protective at elevated temperature. CeO₂ in the form of streaks present along the splat boundaries and possible formation of CeVO₄ perhaps led to improved oxidation resistance.

Keywords:

• SUPERALLOY
• HIGH VELOCITY OXYFUEL PROCESS
• CERIUM OXIDE
• NICRALY
• AGGRESSIVE ENVIRONMENT