# Deformable Eutectic Alloy With Near‐Theoretical Yield Strength via Hierarchical Nanoscale Multiphases and Sessile Defects

## TL;DR

A new eutectic alloy achieves near-theoretical strength and good flexibility by using a complex nanostructure to reduce material mismatch.

## Contribution

Designing a CoCrFeNiTa0.4 alloy with hierarchical nanostructures to achieve high strength and ductility by reducing phase mismatch.

## Key findings

- The CoCrFeNiTa0.4 alloy reaches a yield strength of 2.6 GPa with 13.6% plasticity.
- Hierarchical nanostructures reduce modulus/hardness mismatch between FCC and Laves phases.
- Sessile defects and precipitates synergistically strengthen and toughen the alloy.

## Abstract

Eutectic high‐entropy alloys (EHEAs), a typical bioinspired lamellar composite, have the potential to achieve high strength and good ductility simultaneously for structural applications through microstructure modification. However, an extreme modulus/hardness mismatch between constituent phases leads to premature fracture and severely limits the achievable yield strength by impeding plasticity at room temperature. Here, a CoCrFeNiTa0.4 EHEA designed via suction casting followed by precise thermal treatment, which exhibits sessile interface defects and hierarchical nano‐multiphase structures consisting of FCC‐Laves eutectic lamellae, L12 and D022 coprecipitates, attains a near‐theoretical yield strength of 2.6 GPa alongside sufficient plasticity of 13.6%. This breakthrough is attributed to multiple mechanisms, characterizing soft‐FCC nanolamellae strengthened by coherent L12 precipitates, sessile planar faults, and misfit‐interface dislocations, while hard‐Laves nanolamellae are toughened by deformable D022 precipitates. All of these factors lead to the reduced modulus/hardness mismatch between FCC and Laves lamellae. The results indicate that the long‐range modulus/hardness‐matching and short‐range heterostructure, via hierarchical multiple phases and defects, are pivotal for next‐generation dual‐ and multi‐phase alloys to achieve theoretical strength while retaining impressive plasticity.

A CoCrFeNiTa0.4 eutectic high‐entropy alloy achieves a near‐theoretical yield strength of 2.6 GPa with 13.6% plasticity. This breakthrough stems from a hierarchical nanostructure (FCC‐Laves lamellae with L12/D022 precipitates), which alleviates the inter‐phase modulus/hardness mismatch through synergistic strengthening and toughening, guiding the design of next‐generation strong‐ductile alloys.