Ir–Zr coating through a pack cementation method for ultra-high temperature applications

Abstract

An Ir–Zr intermetallic coating was prepared onto Re/Ir coated graphite through a pack cementation method. The microstructure, nanoindentation and ablation behaviors of the coating system were investigated. The Ir–Zr coating was about 20 μm thick and consisted of 4 intermetallic phases which showed a quasi-gradient transition in composition. Nanoindentation measurements indicated that most of the intermetallic phases had higher hardness but lower Young's modulus compared to pure iridium. By ablation test in a high-frequency plasma wind tunnel, the heat flux limit of the Ir–Zr coating was measured to be about 6.1 MW/m2, and the endurance time was about 100 s under this condition. The coating failed at ∼2240 °C during the ablation test when the iridium melted, but the unfused parts remained complete and in good adhesion with the iridium beneath. The average normal emissivity between 2 and 5 μm of the sample was measured to be ∼0.82 at around 2092 °C before failure, which was higher than pure iridium and bulk ZrO2.