Microstructure and oxidation behaviour of Ir-rich Ir–Al binary alloys

• Oxide scale’s structure resembles to their former alloy for Ir–23Al and Ir–30Al.
• In oxidation, Ir(Al)ss and β-IrAl individually form porous and dense Al2O3 scale.
• Ir–45Al exhibits the best oxidation resistance and basically complies with parabolic law.
• Only β-IrAl can perform selective oxidation and form continuously dense Al2O3.

In the current study, alloys of Ir–11Al, Ir–23Al, Ir–30Al, Ir–41Al and Ir–45Al (at.%) were prepared to investigate the microstructure and oxidation behaviour of Ir-rich Ir–Al alloys. Ir(Al)ss and/or β-IrAl intermetallic phases were found to exist in the prepared alloys. During isothermal oxidation at 1100 °C, the Ir(Al)ss and β-IrAl individually changed to porous and dense Al2O3. The microstructure of the oxide scale formed on Ir–23Al was similar to that of its former alloy which possessed a dendrite-like configuration. It was found that the mass change of Ir–45Al followed a parabolic law, showing the best oxidation resistance among the Ir–Al alloys.