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Abstract The ablation and surface heating behaviors of iridium and Ir-Al coatings on graphite substrates under non-equilibrium conditions were investigated in a plasma wind tunnel. The results showed that the iridium coating had a much higher thermal response than the Ir-Al coating in non-equilibrium conditions. The iridium coating melted at a heat flux of 2.03 MW/m2 with the surface temperature up to 2494 °C, while the surface temperature of the Ir-Al coating was only 1330 °C at this condition. When the heat flux rose to 3 MW/m2, the surface temperature of the Ir-Al coating stayed at ~1520 °C. After continuous ablation at this condition for 500 s, the Ir-Al coating remained intact. It can be concluded that the Al alloying modification could largely improve the ablation resistance of an iridium coating. The present research proposed a novel idea for ultra-high temperature coating for hypersonic applications. Highlights • Pure iridium coating had a heat response of over 2440°C at a heat flux of 3MW/m2 in plasma wind tunnel • Ir-Al coating could withstand a heat flux of more than 3 MW/m2 in plasma wind tunnel • Surface temperature of Ir-Al was about 1000°C lower than iridium coating at the same condition [ABSTRACT FROM AUTHOR]

Iridium (Ir) does not form a protective oxide barrier in high-temperature oxidizing environments, leading to a limited lifetime at high temperatures. To improve the oxidation resistance, pure Ir was modified by pack cementation to produce a double-layer iridium-aluminum (Ir-Al) coating. The oxidation behavior investigation on the Ir-Al coatings at temperatures from 1400 °C to 2000 °C demonstrated that the oxidation resistance of the Ir were significantly enhanced after the pack cementation treatment. Further detailed studies showed that the morphology and mass loss of the oxidized Ir-Al coating are considerably affected by the melting and oxidation of the IrAl 2.7(3) . [ABSTRACT FROM AUTHOR]