High emittance plasma sprayed ZrO2-Y2O3/La2Zr2O7 thermal barrier coatings for potential application in scramjets

In this study, an investigation was conducted on the thermal barrier coatings, focusing on their applicability for radiative cooling in the external airframe of the scramjet intake. ZrO2-8 wt% Y2O3 and La2Zr2O7 were plasma sprayed onto Inconel 718 substrate with a bond coat of NiCrAlY. The findings revealed that a maximum emittance of 0.83 ± 0.02 at 973 K was exhibited by Inconel/NiCrAlY/ZrO2-Y2O3 (INY) and maintained good thermal stability up to 1373 K for 2 h in the air. Inconel/NiCrAlY/ZrO2-Y2O3/La2Zr2O7 (INYL) showed a maximum emittance of 0.92 ± 0.02 at 773 K but experienced degradation at higher temperatures. In the thermal exposure temperature range of 298–1373 K, an average emittance of 0.81 ± 0.02 was possessed by INY, while INYL had an average emittance of 0.85 ± 0.05. The thermal stress-induced coating failure and the sintering effect led to the degradation of INYL, while INY exhibited reliable performance while exposed to high temperatures. Computational analysis indicated a reduction of ∼ 230 K wall temperature in the Mach 7 scramjet intake upon using the coatings on Inconel. In summary, the developed plasma spray coatings on Inconel substrate have potential use in scramjet for radiative cooling-based passive thermal management.