# Elastic stability and lattice distortion of refractory high entropy alloys

## TL;DR

This paper investigates how elements with BCC to HCP phase instability influence the elastic properties and lattice distortion in refractory high entropy alloys, providing insights for material design.

## Contribution

It reveals the impact of BCC/HCP elements on elastic moduli and lattice distortion, and offers predictions for phase stability in HEAs.

## Key findings

- Shear moduli are significantly reduced in HEAs containing BCC/HCP elements.
- Size differences between elements contribute to static lattice distortion.
- Elastic constants and lattice distortion evaluated in four representative HEAs support the findings.

## Abstract

Refractory high entropy alloys containing elements from the Ti, V and Cr columns of the periodic table form body centered cubic (BCC) structures. Elements from the Ti column are noteworthy because they take the BCC structure at high temperature but undergo a shear instability and transform to the hexagonal (HCP) structure at low temperature. We show that the instability of these elements impacts the properties of the HEAs that contain them. In particular, the shear moduli are greatly reduced, causing increased dynamic contributions to lattice distortion. Relatively large size differences between elements of the BCC/HCP column compared with the regular BCC columns create additional static contributions to lattice distortion. These findings are supported by direct evaluation of elastic constants and lattice distortion in four representative HEAs. Comparing moduli of HEAs with those of compositionally averaged pure elements verifies the impact of BCC/HCP elements and allows us to estimate the compositions at which the BCC phases become elastically unstable, predictions that could be useful in material design.