First principles study on structural stability, mechanical and thermodynamic properties of <i>γ'</i>-Co<sub>3</sub>(V, <i>M</i>) (<i>M</i> = Ti, Ta) phase

Abstract

This research focuses on enhancing Co-based high-temperature alloys by using <i>γ'</i> precipitate phases to address the structural metastability of <i>γ'</i>-Co<sub>3</sub>(Al, W). By adding Ti and Ta, the <i>γ'</i>-Co<sub>3</sub>(V, Ti) and <i>γ'</i>-Co<sub>3</sub>(V, Ta) of Co-V alloys are stabilized, surpassing the performance of traditional Co-Al-W alloys. Utilizing a 2×2×2 supercell model and density functional theory (DFT), we investigate these alloys' phase stabilities and mechanical, thermodynamic, and electronic properties. Our findings show that <i>γ'</i>-Co<sub>3</sub>(V, Ti) phase and <i>γ'</i>-Co<sub>3</sub>(V, Ta) phases are stable at 0 K, evidenced by negative formation enthalpies and stable phonon spectra. Mechanical analysis confirms their stabilities through elastic constants and detailed evaluations of properties such as bulk modulus, shear modulus, and Young’s modulus, revealing excellent resistance to deformation and ductility. The electronic structure analysis further distinguishes <i>γ'</i>-Co<sub>3</sub>(V, Ta) for superior electronic stability, which is attributed to its lower state density and deviation from “pseudogap” peaks. Thermodynamically, the quasi-harmonic Debye model highlights the <i>γ'</i>-Co<sub>3</sub>(V, Ti) phase’s temperature-sensitive thermal expansion coefficient, while <i>γ'</i>-Co<sub>3</sub>(V, Ta) maintains higher stability at elevated temperatures. As temperature rises, both phases show decreased resistance to deformation, though they maintain comparable heat resistance due to low-temperature dependency. These results suggest that Co-V-Ti alloy and Co-V-Ta alloy can maintain their <i>γ'</i> phase stability at higher temperatures, enhancing Co-based high-temperature alloys’ performances and phase stabilities. This progress is crucial for developing new Co-based superalloys, and is of great significance for their applications and performance optimization.