# Aging‐Induced Ductile‐Brittle‐Ductile Transition in High‐Entropy Alloys and its Implications

## TL;DR

Aging a high-entropy alloy causes a surprising shift from ductile to brittle and back to ductile behavior, driven by changes in chemical order and phase boundaries.

## Contribution

The study reveals a novel ductile-brittle-ductile transition in high-entropy alloys caused by dynamic chemical ordering and phase boundary evolution.

## Key findings

- Aging in the embrittlement-prone regime increases chemical ordering and jagged phase boundaries, causing a ductile-to-brittle transition.
- Aging outside this regime suppresses excessive ordering and restores ductility through the formation of interphase transition zones.
- The findings challenge the traditional understanding of thermal embrittlement in alloys.

## Abstract

Temper embrittlement, characterized by a dramatic loss of ductility within a narrow temperature window, is ubiquitous in conventional alloys but is not reported in compositionally complex or high‐entropy alloy systems. Here, an unexpected ductile–brittle–ductile transition is discovered in a multiphase high‐entropy alloy (HEA) aged in an intermediate temperature regime. Unlike the classical thermal embrittlement driven by grain boundary effects, this transition originates from the dynamic evolution of local chemical order (LCO) and phase boundary (PB) configurations in HEAs. Aging within the embrittlement‐prone regime enhances chemical ordering, increases the density of ordered domains, and induces jagged PBs, collectively triggering plastic instability and the ductile−to−brittle transition. In contrast, aging outside this regime suppresses excessive ordering and promotes the formation of ductile interphase transition zones, facilitating a brittle−to−ductile recovery. The findings offer new insights into the thermal behavior of HEAs and challenge the established paradigm of thermal embrittlement. These insights provide valuable guidance for the design and processing of high‐performance HEAs, thereby unlocking their potential as advanced high‐temperature structural materials.

We discover a ductilebrittleductile transition in a multiphase high‐entropy alloy during intermediate‐temperature aging. The loss and recovery of ductility are controlled by dynamic evolution of local chemical order and phase boundary structure. Excessive ordering and jagged boundaries trigger localization and fracture, whereas moderated order and CRPs‐free PBs restore plastic stability, defining a processing window for strong, damage‐tolerant HEAs.