  Energy efficiency is motivating the search for new high-temperature metals.
Some new body-centered-cubic random multicomponent "high entropy alloys (HEAs)"
based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional
strengths at high temperatures but the physical origins of this outstanding
behavior are not known. Here we show, using integrated neutron-diffraction
(ND), high-resolution transmission electron microscopy (HRTEM), and theory,
that the high strength and strength retention of a NbTaVTi alloy and a new
high-strength/low-density CrMoNbV alloy are attributable to edge dislocations.
This is surprising because plastic-flow in BCC elemental metals and dilute
alloys is universally accepted to be controlled by screw dislocations. We use
the insight and theory to perform a computationally-guided search over $10^7$
BCC HEAs and identify over $10^6$ possible ultra-strong high-temperature alloy
compositions for future exploration.
