An Xinlai, Bao Weikang, Zhang Zuhe, Jiang Zhouwen, Yuan Shengyun, You Zesheng, Zhang Yong
Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.
Nanomaterials (Basel). 2021 Sep 18;11(9):2437. doi: 10.3390/nano11092437.
Gradient-nanostructured material is an emerging category of material with spatial gradients in microstructural features. The incompatibility between gradient nanostructures (GNS) in the surface layer and coarse-grained (CG) core and their roles in extra strengthening and strain hardening have been well elucidated. Nevertheless, whether similar mechanisms exist within the GNS is not clear yet. Here, interactions between nanostructured layers constituting the GNS in a Ni alloy processed by surface mechanical rolling treatment were investigated by performing unique microtension tests on the whole GNS and three subdivided nanostructured layers at specific depths, respectively. The isolated nanograined layer at the topmost surface shows the highest strength but a brittle nature. With increasing depths, isolated layers exhibit lower strength but enhanced tensile plasticity. The GNS sample's behavior complied more with the soft isolated layer at the inner side of GNS. Furthermore, an extra strain hardening was found in the GNS sample, leading to a greater uniform elongation (>3%) as compared to all of three constituent nanostructured layers. This extra strain hardening could be ascribed to the effects of the strain gradients arising from the incompatibility associated with the depth-dependent mechanical performance of various nanostructured layers.
梯度纳米结构材料是一种新兴的材料类别，其微观结构特征具有空间梯度。表层的梯度纳米结构（GNS）与粗晶（CG）核心之间的不相容性及其在额外强化和应变硬化中的作用已得到充分阐明。然而，GNS内部是否存在类似机制尚不清楚。在此，通过分别对整个GNS以及特定深度处的三个细分纳米结构层进行独特的微拉伸试验，研究了经表面机械轧制处理的镍合金中构成GNS的纳米结构层之间的相互作用。最顶层表面的孤立纳米晶粒层强度最高，但具有脆性。随着深度增加，孤立层强度降低，但拉伸塑性增强。GNS样品的行为更符合GNS内侧较软的孤立层。此外，在GNS样品中发现了额外的应变硬化，与三个组成纳米结构层相比，其均匀伸长率更大（>3%）。这种额外的应变硬化可归因于与各纳米结构层随深度变化的力学性能不相容相关的应变梯度效应。
