Effects of Ni and Cr additions on γ + γ’ microstructure and mechanical properties of W-free Co–Al–V–Nb–Ta-based superalloys

The effect of Ni and Cr additions on microstructure, lattice misfit, oxidation, creep properties are investigated for six W- Mo-free cobalt-based superalloys with compositions Co-xNi-5Al-yCr-3V–2Ti-1.5Nb-1.5Ta-0.08B (at.%), where x = 10, 20, or 30 y 4 8. In all alloys, the γ + γ′ microstructure is stable up to 1000 h upon aging at 850 °C. As increases from 10 at.%, area fraction 32 49% in three low-Cr while remaining constant (45%) high-Cr alloys. All alloys show positive γ/γ′ misfits 0.8 ± 0.2%, consistent γ’ rafting observed after creep. Both increase oxidation resistance, more so 8% than 30% Ni, as expected high stability chromium oxide. Increasing 8 at.% slightly resistance °C increasing has a similar effect.