Microstructural evaluation and mechanical properties of Ir-Hf-Zr ternary alloys at room and high temperatures

Iridium is one of the most promising base metals for future high-temperature structural materials. Attempts to improve the high-temperature strength of Ir have involved solid-solution hardening and coherent hardening. Hf and Zr having a larger atomic size misfit with Ir were found to be the most effective solid-solution hardening and coherent hardening elements on Ir. The idea of multi-component alloying Ir by Hf and Zr was used for the improvement of high-temperature properties of Ir-based alloys in this work. The results show that the monolithic saturated fcc phase has an outstanding Vickers hardness at room temperature, whereas a dual-phase fcc/L1₂ structure is favorable for high-temperature strength and creep resistance. With a dual-phase fcc/L1₂ structure composed mostly of fcc phase, the Ir-5Hf-5Zr alloy has a 0.2% yield strength as high as 175 MPa, and a stable creep rate as low as 1.33 × 10^-7 S^-1 at a stress of 40 MPa even at 1950 °C. Finally, a principle for the design of Ir-based alloy based upon the composition and microstructural morphology was discussed.