Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off

Abstract

Metals have been mankind’s most essential materials for thousands
of years; however, their use is affected by ecological and economical
concerns. Alloys with higher strength and ductility could alleviate
some of these concerns by reducing weight and improving energy
efficiency. However, most metallurgical mechanisms for increasing
strength lead to ductility loss, an effect referred to as the strength–
ductility trade-off1,2. Here we present a metastability-engineering
strategy in which we design nanostructured, bulk high-entropy
alloys with multiple compositionally equivalent high-entropy
phases. High-entropy alloys were originally proposed to benefit
from phase stabilization through entropy maximization3–6. Yet
here, motivated by recent work that relaxes the strict restrictions
on high-entropy alloy compositions by demonstrating the weakness
of this connection7–11, the concept is overturned. We decrease phase
stability to achieve two key benefits: interface hardening due to
a dual-phase microstructure (resulting from reduced thermal
stability of the high-temperature phase12); and transformationinduced
hardening (resulting from the reduced mechanical stability
of the room-temperature phase13). This combines the best of two
worlds: extensive hardening due to the decreased phase stability
known from advanced steels14,15 and massive solid-solution
strengthening of high-entropy alloys3. In our transformationinduced
plasticity-assisted, dual-phase high-entropy alloy (TRIPDP-
HEA), these two contributions lead respectively to enhanced
trans-grain and inter-grain slip resistance, and hence, increased
strength. Moreover, the increased strain hardening capacity
that is enabled by dislocation hardening of the stable phase and
transformation-induced hardening of the metastable phase
produces increased ductility. This combined increase in strength
and ductility distinguishes the TRIP-DP-HEA alloy from other
recently developed structural materials16,17. This metastabilityengineering
strategy should thus usefully guide design in the nearinfinite
compositional space of high-entropy alloys.