Development and Characterization of a High-Cr-Content Co-Ni-Al-V-Ta-Cr Superalloy: Microstructure, Mechanical Properties, and Oxidation Resistance

Abstract

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 a high Cr content and a γ/γ′ two-phase structure, demonstrated a high γ' solvus temperature of 1139°C, low density of 8.48 g/cm³, a 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/cm² after 200 hours at 1000°C. Examination of the oxidation behavior at 1000°C revealed an oxide layer consisting of a porous outer CNV oxide and a denser inner mixed oxide layer comprising CNV, CNAC, and CNT oxides.

Keywords: Cobalt-based superalloys, strength, γ′ phase solvus temperature, γ′ phase stability, oxidation resistance