Development of low-density γ/γ′ Co–Al–Ta-based superalloys with high solvus temperature

The present paper reports the development of W-, Mo-, and V-free and Ni- and Cr-containing Co–Al–Ta-based superalloys. In particular, the presence of a metastable L1₂-γ′ phase is experimentally verified in Co–12Al–2Ta alloy. The results show that the γ′ phase stability is improved and the γ/γ′ composition range is broadened by rising the Ni content in alloys under study. Moreover, elemental partitioning proves that Cr was a γ-phase former, which addition reduces the γ/γ′ lattice misfit and the γ′ precipitate coarsening rate. Moreover, the developed Cr-containing alloys exhibit excellent γ′ phase stability even at high temperatures of 800–1100 °C. In particular, Co–30Ni–12Al–4Ta–12Cr (12Cr) alloy possesses a good combination of high solvus temperature (∼1152 °C), low density (∼8.38 g/cm³), low γ/γ′ lattice misfit (∼+0.33%), and low coarsening rate of γ′ precipitate (∼1.95 × 10⁻²⁷ m/s at 900 °C). Besides, nominal and specific yield strength values of the developed 12Cr alloy at ambient and high temperatures are no worse than those of other available Cr-containing and W-free cobalt-based superalloys.