Abstract High strength of materials usually comes with low ductility due to the lost or short-lived strain hardening. Here, we uncover a sequentially-activated multistage strain hardening (SMSH) that allows for sustained and effective strain-hardening capability in strong ultrafine-grained eutectic high-entropy alloy (EHEA). Consequently, exceptional ductility is realized in an ultrafine-grained EHEA, accompanied with high ultimate strength. We demonstrate that the SMSH is derived from a coordinated three-level design on structural heterogeneity, grain-size control, and intragranular composition modification, which enables the sequential activation of stress-dependent multiple hardening mechanisms. Furthermore, despite the well-known low twinning propensity due to ultrafine grains and medium-to-high stacking fault energies of prototype EHEAs, our coordinated design sequentially activates three types of deformation twinning to assist this SMSH. This work sheds light on the SMSH effect assisted by multi-type twinning previously unexpected in ultrafine-grained EHEAs, and thereby represents a promising route for improving ductility of high-strength materials.

中文翻译：

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超细晶异质结构共晶高熵合金中多类型孪晶辅助的多级加工硬化

摘要 材料的高强度通常伴随着低延展性，这是由于失去或短暂的应变硬化。在这里，我们发现了一种顺序激活的多级应变硬化 (SMSH)，它可以在强超细晶共晶高熵合金 (EHEA) 中实现持续有效的应变硬化能力。因此，超细晶粒 EHEA 实现了卓越的延展性，同时具有高极限强度。我们证明了SMSH源自结构异质性、晶粒尺寸控制和晶内成分改性的协调三级设计，这使得依赖于应力的多重硬化机制能够顺序激活。此外，尽管众所周知，由于原型 EHEAs 的超细晶粒和中高堆垛层错能导致的低孪晶倾向，我们的协调设计依次激活了三种类型的变形孪晶来辅助这个 SMSH。这项工作揭示了超细晶 EHEAs 中以前意想不到的多型孪晶辅助的 SMSH 效应，从而为提高高强度材料的延展性提供了一条有前途的途径。