Enhancing the strength of metallic laminates through decreasing the constituent layer thickness from micrometer to nanometer scale is usually accompanied by the degradation of ductility because plastic instability characterized by fatal shear bands inevitably occurs in the early stage of deformation. To overcome the strength-ductility trade-off dilemma, we designed a kind of metallic layered composites (LCs) consisting of nano-grained Ni (grain size: 21–37 nm) and ultrafine nano-grained Ni-W (grain size: 8 nm) constituent layers with layer thickness ranging from microns to tens of nanometers. We found that the strength and ductility of Ni/Ni-W LCs can be simultaneously enhanced by decreasing the layer thickness. Interface-constrained grain growth in the Ni layers with an initial layer thickness of less than 1 μm enhances strain hardening ability. Thus, strain delocalization characterized by the formation of rectangular strain zones instead of crossed micro shear bands appears in the LCs. Based on the above mechanism, we obtained the optimum ratio of the layer thickness to the grain size for the nano-grained Ni layers as about 15:1, which corresponds to Ni0.25/Ni-W0.025 LCs with the highest tensile strength (1.9 GPa) and elongation to failure (5.5 %). These findings may provide a new path for the design principle of metallic LCs with multi-level microstructural and geometrical scales.

中文翻译：

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超细尺度 Ni/Ni-W 层状复合材料通过界面约束晶粒生长实现卓越的延展性

通过将组成层厚度从微米级降低到纳米级来提高金属层压板的强度通常会伴随着延展性的下降，因为在变形的早期阶段不可避免地会出现以致命剪切带为特征的塑性不稳定性。为了克服强度与延展性的权衡困境，我们设计了一种由纳米晶镍（晶粒尺寸：21-37 nm）和超细纳米晶粒镍钨（晶粒尺寸：8 nm) 层厚从微米到数十纳米的组成层。我们发现，通过减小层厚度可以同时提高 Ni/Ni-W LC 的强度和延展性。初始层厚度小于 1 μm 的 Ni 层中界面约束的晶粒生长增强了应变硬化能力。因此，LC 中出现了以形成矩形应变区而不是交叉微剪切带为特征的应变离域。基于上述机理，我们得到了纳米晶镍层的最佳层厚与晶粒尺寸之比约为15:1，对应于具有最高拉伸强度的Ni0.25/Ni-W0.025 LCs (1.9 GPa) 和断裂伸长率 (5.5 %)。这些发现可能为具有多层次微观结构和几何尺度的金属液晶的设计原理提供新的途径。