Role of thermally grown oxide and oxidation resistance of samarium strontium aluminate based air plasma sprayed ceramic thermal barrier coatings

Samarium Strontium Aluminate (SSA) based ceramic oxide was synthesized and coated on a bond coated (NiCrAlY) Inconel 718 superalloy by air plasma spray (APS) process. Thermally grown oxide (TGO) thicknesses were controlled at different pre-oxidation times of 10, 20 and 30 h at 1050 °C in the argon atmosphere, the highest TGO thickness being found for 30 h pre-oxidized samples. The percentage elastic recovery of pre-oxidized samples increased (45, 48, and 50%) with an increasing pre-oxidation time at 1050 °C. The isothermal oxidation test was performed on pre-oxidized samples at 1100 °C for 15 h in air. The parabolic oxidation rate constant decreased from 6.08 × 10− 5 to 3.90 × 10− 5 mg2 cm− 4 s− 1 (from 10 to 20 h) and then increased up to 4.55 × 10− 5 mg2 cm− 4 s− 1 for 30 h pre-oxidized SSA samples at 1100 °C. SSA based TBCs showed 65% lower weight gain as compared to conventional YSZ TBCs after oxidation at 1100 °C in air. Cross-sectional SEM results revealed that the threshold TGO thickness of SSA TBCs is about 5.3 to 5.8 μm. Failure of SSA TBCs was observed at the interface of TGO and ceramic top coat due to the formation of SmAlO3 along with spinel oxides.