金属材料NT和HNT诸结构的实验、原子和理论研究成果

纳米孪晶（NT）和分层纳米孪晶（HNT）面心立方（FCC）金属最近在实验、计算和理论模型方面均取得了较大的研究进展。

来自香港城市大学的吕坚教授（法国技术科学院院士，本刊编委，曾在本刊发表研究论文“Super square carbon nanotube network: a new promising water desalination membrane”） 对此作了全面综述。HNT结构是一种新颖的结构，与NT结构材料相比具有更高的强度/延展性。

综述主要关注金属材料中NT和HNT诸结构的实验、原子和理论方面的最新研究成果：

1）阐述了用于制造NT和HNT结构的几种自下而上和自上而下的先进技术。

2）采用塑性形变技术可成功诱导HNT结构的形成，而采用晶体生长的模式则几乎不能成功合成HNT结构。对NT和HNT FCC金属的分子动力学（MD）研究揭示了诸如双晶间距、晶粒尺寸和塑性取向等纳米尺度效应极大地改变了NT和HNT金属的性能。因而与NT结构相比，HNT结构有可能开启材料学的一些独特现象；

3）人们基于实验和MD模拟观测揭示的现象和机制而提出了一系列理论模型，可有效描述NT和HNT两类金属的力学行为；

4）目前HNT结构的制造技术及其对金属性能的影响研究，均处于起步阶段，迫切需要进一步的探索来推动先进材料的设计。

The recent studies on nanotwinned (NT) and hierarchical nanotwinned (HNT) face-centered cubic (FCC) metals are presented in this review. The HNT structures have been supposed as a kind of novel structure to bring about higher strength /ductility than NT counterparts in crystalline materials. We primarily focus on the recent developments of the experimental, atomistic and theoretical studies on the NT and HNT structures in the metallic materials. Some advanced bottom-up and top-down techniques for the fabrication of NT and HNT structures are introduced. The deformation induced HNT structures are available by virtue of severe plastic deformation (SPD) based techniques while the synthesis of growth HNT structures is so far almost unavailable. In addition, some representative molecular dynamics (MD) studies on the NT and HNT FCC metals unveil that the nanoscale effects such as twin spacing, grain size and plastic anisotropy greatly alter the performance of NT and HNT metals. The HNT structures may initiate unique phenomena in comparison with the NT ones. Furthermore, based on the phenomena and mechanisms revealed by experimental and MD simulation observations, a series of theoretical models have been proposed. They are effective to describe the mechanical behaviors of NT and HNT metals within the applicable scope. So far the development of manufacturing technologies of HNT structures, as well as the studies on the effects of HNT structures on the properties of metals are still in its infancy. Further exploration is required to promote the design of advanced materials.