Aging-Induced Ductile-Brittle-Ductile Transition in High-Entropy Alloys and its Implications.

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.