How to design ultra-strong face-centered cubic (FCC) metals is a grand challenge in materials community. In general, nanotwinned (NT) FCC metals manifest the maximum strength as the intrinsic size ratio of twin thickness–to–grain size is achieved, above which softening caused by detwinning occurs, whereas below this intrinsic size ratio strengthening caused by dislocation–twin boundary interactions occurs. In this work, we used the room temperature creep as an effective pathway to strengthen NT-Ni with the high stacking fault energy by controlling microstructure in terms of the intrinsic size ratio. We experimentally discovered in NT-Ni at the room temperature steady-state creep stage that there is a critical grain size of ∼230 nm for the intrinsic size ratio transition from 0.04 in the large grain size regime to 0.14 in the small grain size regime. In particular, this intrinsic size ratio can be taken as a signature to estimate the microstructural stability, which linearly scales with the twinnability of FCC metals. Compared with the as-deposited NT-Ni foils, their counterparts undergoing the steady-state creep stage manifest significantly enhanced strength without losing their elongation to failure. This work provides new insights into designing the strongest NT metals via the creep process.

如何设计超强面心立方（FCC）金属是材料界面临的巨大挑战。通常，纳米孪晶（NT）FCC金属表现出最大强度，因为达到了孪晶厚度与晶粒尺寸的内在尺寸比，高于此值则发生了脱孪现象引起的软化，而低于此固有尺寸比，则由位错-孪晶边界引起了强化发生互动。在这项工作中，我们使用室温蠕变作为有效途径，通过根据固有尺寸比控制微观结构来增强具有高堆垛层错能的NT-Ni。我们在室温稳态蠕变阶段的NT-Ni中实验发现，本征尺寸比从大晶粒尺寸状态下的0.04过渡到0，存在约230 nm的临界晶粒尺寸。在小粒度体制下为14。特别地，该固有尺寸比可以作为估计微观结构稳定性的标志，该微观结构稳定性与FCC金属的孪生性成线性比例。与沉积后的NT-Ni箔相比，经受稳态蠕变阶段的对应物表现出明显增强的强度，而不会失去其断裂伸长率。这项工作为通过蠕变工艺设计最强的NT金属提供了新的见解。