Development and characterization of a high-Cr-content Co–Ni–Al–V–Ta–Cr superalloy: Microstructure, mechanical properties and oxidation resistance

Enhancing the oxidation resistance of Co-based superalloys by adding a high content of Cr, while simultaneously ensuring the stability of the γ/γ′ phases, presents a significant challenge. This study evaluated the alloying potential of Co–30Ni–10Al–5V–4Ta using the CALPHAD method, revealing promising characteristics. The developed Co–30Ni–10Al–5V–4Ta–12Cr alloy characterized by high Cr content and γ/γ′ two-phase structure, demonstrating high γ′ solvus temperature of 1139°C, low density of 8.48 g/cm³, minimal γ/γ′ lattice misfit of +0.28%, high compressive yield strength of 651 MPa at 800°C, and excellent oxidation resistance with a weight gain of 6.5 mg/cm³ after 200 h at 1000°C. Examination of the oxidation behavior at 1000°C revealed an oxide layer consisting of a porous outer CoO, NiO, and V₃O₄ (CNV) oxide and a denser inner mixed oxide layer comprising CoO, NiO, and V₃O₄ (CNV) oxide, Al₂O₃, Cr₂O₃, CoO, and NiO (CNAC) oxide, and TaO₂, CoO, and NiO (CNT) oxide.