High heat flux ablation behaviors of Ir-Hf coatings in wind tunnel tests up to 6.6MW/m²

The Ir-Hf coatings have good resistance to oxidative ablation, in order to investigate the ablation resistance limit and ablation failure mechanism of the Ir-Hf coatings, graphite/Re/Ir/Ir-Hf samples were prepared by an optimized pack cementation method. The Ir-Hf coating samples were tested for anti-ablation properties under stepwise and constant working conditions in a high-frequency plasma wind tunnel, respectively. The results showed that the Ir-Hf coating passed the high-frequency plasma wind tunnel test at a heat flux of 5.7 MW/m2 for 650 s without defects. And the heat flux limit of the Ir-Hf coating was about 6.6 MW/m2 in the plasma wind tunnel with a lifetime no less than 400 s and a surface temperature of about 2200℃, exceeding most of the reported heat flux limits for non-ablative materials, such as SiC, ZrB2 and HfC. The failure mechanism of the Ir-Hf coating is as follows: when the surface temperature reaches a certain level, the interface temperature between Ir and the oxide layer will exceed its low eutectic point and a liquid phase will appear, triggering failure. The Ir-Hf coatings have the advantages of high heat flux resistance, zero ablation, low thermal response and good protection of the graphite substrate, which makes them promising as the thermal protection coatings in ultra-high temperature (over 2000 °C) aerospace applications.