Microstructure evolution and mechanical properties of a novel γ′ phase-strengthened Ir-W-Al-Th superalloy

The present work introduces a novel γ′ phase-strengthened Ir-W-Al-Th superalloy for ultrahigh-temperature applications. First, the as-cast microstructure and phase transformation of Ir-13W-6Al-0.15Th (at%) alloy during solid solution and aging were investigated. Phase transformation was observed during heat treatment. The primary γ′ phase disappeared via the redissolution of γ′ → γ at 1800 °C. The recrystallization took place at 1450 °C and very fine equiaxed γ′/γ grains formed after 240 h. The cold-rolled microstructure indicated that the room-temperature γ phase was brittle and cracks mainly emerged along grain boundaries. Ir-13W-6Al-0.15Th alloy exhibited a higher nanohardness than other Ir-based superalloys and pure Ir, which can be attributed to the solid solution and precipitation (γ′) strengthening. In addition, the as-cast Ir-13W-6Al-0.15Th alloy shows a medium room-temperature compressive yield strength and good ductility.