Coherent twin boundaries (CTBs) are internal planar defects that offer a promising pathway for designing advanced metallic materials with superior strength-ductility synergy. However, incorporating nanoscale CTBs into additive manufacturing (AM) microstructures is highly challenging without severe plastic deformation. Here, by utilizing the intrinsic cellular structures in AM alloys, we for the first time achieved a high density of multi-scale annealing twins in a laser powder bed fusion (LPBF) NiCoCrTiAl medium-entropy alloy. These multi-scale annealing twins, together with nanoprecipitates and dislocations, resulted in gigapascal strength (∼1.4 GPa) and substantial tensile ductility (∼25 %). We reveal that the AM-induced cellular structures, decorated with entangled dislocations and Ti segregation at the cellular boundaries, facilitate the abundant nucleation of multi-scale annealing twins through interactions with migrating recrystallization boundaries. Additionally, the cellular precipitation networks enhance the thermal stability of nanoscale annealing twins. Frequent dislocation-TB interactions during deformation contribute to superior strain hardenability and thus good ductility. Synergized multiple strengthening mechanisms, i.e., boundary strengthening, precipitation strengthening, and dislocation strengthening, are responsible for the excellent strength. Our present findings advance the design of AM microstructures by harnessing the beneficial effects of cellular structures and provide valuable guidance for developing alloys with exceptional mechanical properties.

中文翻译：

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多尺度退火孪晶在增材制造的高强度中熵合金中产生卓越的延展性


相干孪晶边界（CTB）是内部平面缺陷，为设计具有卓越强度-延展性协同作用的先进金属材料提供了一条有前途的途径。然而，在没有严重塑性变形的情况下，将纳米级 CTB 融入增材制造 (AM) 微观结构极具挑战性。在这里，通过利用AM合金中的固有胞状结构，我们首次在激光粉末床熔合（LPBF）NiCoCrTiAl中熵合金中实现了高密度的多尺度退火孪晶。这些多尺度退火孪晶与纳米沉淀物和位错一起产生了千兆帕强度（~1.4 GPa）和显着的拉伸延展性（~25%）。我们揭示了AM诱导的胞状结构，在胞状边界处装饰有纠缠位错和Ti偏析，通过与迁移再结晶边界的相互作用促进多尺度退火孪晶的丰富成核。此外，细胞沉淀网络增强了纳米级退火孪晶的热稳定性。变形过程中频繁的位错-结核相互作用有助于获得优异的应变淬透性，从而获得良好的延展性。边界强化、析出强化、位错强化等多种强化机制协同作用，带来优异的强度。我们目前的研究结果通过利用多孔结构的有益效果推进了增材制造微结构的设计，并为开发具有卓越机械性能的合金提供了宝贵的指导。