Xiao Jianwei, Yang Huizhen, Wu Xiaozhi, Younus Fatima, Li Peng, Wen Bin, Zhang Xiangyi, Wang Yanbin, Tian Yongjun
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
College of Physics and Institute for Structure and Function, Chongqing University, Chongqing 401331, China.
Sci Adv. 2018 Sep 21;4(9):eaat8195. doi: 10.1126/sciadv.aat8195. eCollection 2018 Sep.
Experimental results (Huang .) indicated that nanotwinned diamond (nt-diamond) has unprecedented hardness, whose physical mechanism has remained elusive. In this report, we categorize interaction modes between dislocations and twin planes in nt-diamond and calculate the associated reaction heat, activation energies, and barrier strength using molecular dynamics. On the basis of the Sachs model, twin thickness dependence of nt-diamond hardness is evaluated, which is in good agreement with the experimental data. We show that two factors contribute to the unusually high hardness of nt-diamond: high lattice frictional stress by the nature of carbon bonding in diamond and high athermal stress due to the Hall-Petch effect. Both factors stem from the low activation volumes and high activation energy for dislocation nucleation and propagation in diamond twin planes. This work provides new insights into hardening mechanisms in nt-diamond and will be helpful for developing new superhard materials in the future.
实验结果（黄.）表明，纳米孪晶金刚石（nt-金刚石）具有前所未有的硬度，其物理机制一直难以捉摸。在本报告中，我们对nt-金刚石中位错与孪晶面之间的相互作用模式进行了分类，并使用分子动力学计算了相关的反应热、活化能和势垒强度。基于萨克斯模型，评估了nt-金刚石硬度对孪晶厚度的依赖性，这与实验数据吻合良好。我们表明，有两个因素导致nt-金刚石具有异常高的硬度：由于金刚石中碳键的性质而产生的高晶格摩擦应力以及由于霍尔-佩奇效应而产生的高非热应力。这两个因素都源于位错在金刚石孪晶面中形核和传播的低激活体积和高激活能。这项工作为nt-金刚石的硬化机制提供了新的见解，并将有助于未来开发新型超硬材料。
