Revealing extra strengthening and strain hardening in heterogeneous two-phase nanostructures
Revealing extra strengthening and strain hardening in heterogeneous two-phase nanostructures
复制标题
揭示异质两相纳米结构中的额外强化和应变硬化
DOI：
10.1016/j.ijplas.2019.11.005
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发表时间：
2020-03-01
影响因子：
9.8
通讯作者：
Liu, Chunhui
中科院分区：
文献类型：
--
作者：
Li, Jianjun;Lu, Wenjun;Liu, Chunhui
异质金属及合金是近年来兴起的一类新型材料，具有优异的强度-延性协同、显著的减摩磨损和高疲劳极限等力学性能。实验表明，背应力对增强强度-延性平衡具有重要作用。然而，背应力是如何发挥作用的仍未完全解决。对于两相非均质纳米结构Cu，我们提出了由于晶粒尺寸变化大而具有高机械对比度的相之间的强应变分配产生显著的应变梯度和几何必要的位错（GNDs）。gds在相界面处的堆积会对位错源产生高背应力，从而产生新的位错。上述物理图像被纳入到一个新开发的理论模型中，其中不同晶粒尺寸的组成相的力学响应由基于位错密度的模型描述，而整体响应通过割线方法获得包涵矩阵复合材料。结果表明，软相得到了明显的强化。非均相复合材料的应变硬化能力也得到了很大程度的增强，甚至远高于粗晶Cu。较强的应变硬化能力使非均质铜克服了均质铜通常存在的强度-塑性折衷问题。预测的应力应变响应与已有实验数据吻合较好。为设计具有强韧性的非均相铜材料，选择较小的硬相晶粒尺寸、较大的软相晶粒尺寸和较少的软相材料，给出了一种强度-塑性图。所建立的模型可以很容易地扩展到研究其他非均相纳米结构的强化和应变硬化行为，如梯度、层压、纳米管强化和金属玻璃/金属衬底结构。
Heterogeneous metals and alloys are a new class of materials that emerged recently with outstanding mechanical performances such as excellent strength-ductility synergy, significant friction and wear reduction and high fatigue limits. Experiments demonstrated that back stress plays an important role in enhancing the strength-ductility balance. However, how does the back stress play the role remains fully unsolved. Here for a two-phase heterogeneous nanostructured Cu we proposed that the strong strain partitioning between the phases with high mechanical contrast due to the large variation of their grain sizes produces significant strain gradient and geometrically necessary dislocations (GNDs). The piling up of the GNDs at the phase interface generates high back stress towards the dislocation source in order to emit new dislocations. The above physical picture is incorporated into a newly developed theoretical model, in which the mechanical responses of the constituent phases with various grain sizes are described by a dislocation density based model, while the overall response is obtained by a secant method for an inclusion-matrix composite. The results show that the soft phase is considerably strengthened. The strain hardening capability of the heterogeneous composite is also enhanced to a large extent, even much higher than that the coarse-grained Cu. The strong strain hardening capability makes the heterogeneous Cu overcome the strength-ductility tradeoff that is usually the case of the homogeneous counterparts. The predicted stress-strain response agrees well with the existing experimental data. A strength-ductility map is also given for designing strong and ductile heterogeneous Cu by selecting smaller grain size in the hard phase, larger grain size in the soft phase and less soft materials. The developed model can be easily extended to investigate the strengthening and strain hardening behavior of other heterogeneous nanostructures such as gradient, laminate, nanotube strengthened and metallic glass/metallic substrate structures.