Investigating a novel Hf-enriched iridium alloy: High-temperature oxidation and microstructural evolution

Iridium is mainly used in aerospace propulsion systems and has excellent high-temperature stability, but its high price and difficult processing characteristics limit its application. In order to reduce the content of iridium, Ir-alloy compositions were optimized using Thermo-Calc software and two high-Hf-content iridium alloys, Ir–40Hf and Ir–40Hf–1.9Al, were successfully prepared. For microstructural characterization results of scanning electron microscopy and energy dispersive X-ray detector were combined with X-ray diffraction data. Alloys were mainly composed of two phases: HfIr and HfIr3.Through the systematic high-temperature oxidation experiments and microstructural characterization, the oxidation behavior of the alloys under cyclic oxidation at 1350 °C was revealed. The oxidation kinetics curves of both high-Hf iridium alloys follow a parabolic-like law, demonstrating a good short-term oxidation resistance. For Ir–40Hf, a porous HfO 2 oxide scale was formed on the surface, whereas Ir–40Hf–1.9Al grew a dense Al 2 O 3 protective scale, indicating that the introduction of Al can significantly enhance the ultra-high-temperature oxidation resistance. Cross-sectional microstructural observations further revealed distinct stratification after oxidation.