  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.
