# Mechanistic origin of high retained strength in refractory BCC high entropy alloys up to 1900K

## TL;DR

This paper develops a parameter-free theory explaining the high temperature strength retention in BCC high entropy alloys, revealing an edge dislocation mechanism and enabling rapid composition screening for stronger alloys.

## Contribution

It introduces a novel, parameter-free theoretical model for edge dislocation strengthening in BCC HEAs, facilitating efficient alloy design.

## Key findings

- The theory accurately predicts strength versus temperature for MoNbTaW and MoNbTaVW alloys.
- Edge dislocation motion, rather than screw dislocation, controls high-temperature strength in BCC HEAs.
- Screening over 600,000 compositions identified new alloys with improved strength and reduced density.

## Abstract

The body centered cubic (BCC) high entropy alloys MoNbTaW and MoNbTaVW show exceptional strength retention up to 1900K. The mechanistic origin of the retained strength is unknown yet is crucial for finding the best alloys across the immense space of BCC HEA compositions. Experiments on Nb-Mo, Fe-Si and Ti-Zr-Nb alloys report decreased mobility of edge dislocations, motivating a theory of strengthening of edge dislocations in BCC alloys. Unlike pure BCC metals and dilute alloys that are controlled by screw dislocation motion at low temperatures, the strength of BCC HEAs can be controlled by edge dislocations, and especially at high temperatures, due to the barriers created for edge glide through the random field of solutes. A parameter-free theory for edge motion in BCC alloys qualitatively and quantitatively captures the strength versus temperature for the MoNbTaW and MoNbTaVW alloys. A reduced analytic version of the theory then enables screening over >600,000 compositions in the Mo-Nb-Ta-V-W family, identifying promising new compositions with high retained strength and/or reduced mass density. Overall, the theory reveals an unexpected mechanism responsible for high temperature strength in BCC alloys and paves the way for theory-guided design of stronger high entropy alloys.