Electronic density of states as the descriptor of elastic bond strength, ductility, and local lattice distortion in BCC refractory alloys

TL;DR

This study uses density functional theory to establish that the electronic density of states at the Fermi level is a key predictor of elastic bond strength, ductility, and lattice distortion in BCC refractory alloys, aiding materials design.

Contribution

It reveals fundamental correlations between electronic density of states at the Fermi level and mechanical properties of BCC refractory high entropy alloys, providing a new descriptor for alloy design.

Findings

Low N(Ef) correlates with high elastic constants and bond stiffness.

N(Ef) is linked to ductility via the Pugh ratio (G/B).

N(Ef) correlates with local lattice distortion and yield strength.

Abstract

Although electronic density of states (DOS) is fundamental to materials properties, its general relationship to mechanical properties of alloys is not well established. In this paper, using density functional theory (DFT) calculations, we show that the electronic occupancy at the Fermi level, N(Ef), obtained from DOS is a key descriptor of alloy strength and ductility. Our comprehensive analysis of numerous body centered cubic (BCC) refractory high entropy alloys (RHEAs) shows an overwhelming correlation that low N(Ef) indicates strong bonds that have high stiffness resulting in high elastic constants. High bond stiffness indicates presence of covalent nature of bonds that are directional in nature resulting in resistance to deformation leading to high bulk (B) and shear (G) moduli. Consequently, N(Ef) provides a direct correlation to the tendency of alloy ductility evidenced in the Pugh ratio (G/B). As stiffer bonds result in lower local lattice distortion (LLD), N(Ef) are LLD are also found to be corelated which opens up a correlation to solid solution strengthening and yield strength. Thus, this work unveils fundamental correlations between N(Ef) and (1) elastic bond strength, (2) ductility, and (3) LLD. These correlations open opportunities for the design of high strength high ductile RHEAs.