Ultra-high strength of Ir-Hf-Nb ternary alloys with an fcc/L12 microstructure at 1950 °C

► Ir-Hf-Nb ternaries with different fcc to L12 fraction ratios were prepared. ► Fcc is the strengthening phase in the fcc/L12 microstructure. ► Fcc-dominant microstructure shows higher strength than L12-dominant one. ► Fcc-dominant alloy Ir-5Hf-7Nb shows the highest strength of 270 MP at 1950 °C. ► Interface strengthening is the key role on high-temperature strength.