Magneto-chemical effects in the elastic properties of Co3Al-based compounds

Abstract

The thermodynamic and mechanical properties of the L12 Co3Al type of compounds are fundamental for understanding and designing Co-based superalloys. In these systems, both compositional and magnetic changes can occur upon service due to the elevated temperature. Here, using first-principle calculations, we study the bulk properties of three families of Co3Al-based compounds: (Co1−𝑥Ni𝑥)3Al (0 ⩽ 𝑥 ⩽ 0.5), Co3(Al1−𝑦W𝑦) (0 ⩽ 𝑦 ⩽ 1), and (Co0.5Ni0.5)3(Al0.5Ti𝑧Ta0.5−𝑧) (0 ⩽ 𝑧 ⩽ 0.5). The calculated lattice constants, Curie temperatures, and formation energies show good agreement with the limited available theoretical and experimental data. Our results reveal the impact of chemistry and magnetism on the elastic parameters. We find that both chemical composition and magnetic state alter the elastic parameters and the elastic anisotropy, which in turn makes the predictions based on common ductile–brittle criteria challenging. We separate the volume and chemical effects for both ferromagnetic and paramagnetic states and show that in most cases, the chemical effect gives the dominant contribution to the alloying trends in the elastic parameters. The present findings reveal the complex relationship between alloying elements and elastic parameters in the Co3Al-based precipitates, providing insights into their mechanical properties for engineering applications.