Wang Jiangwei, Zeng Zhi, Wen Minru, Wang Qiannan, Chen Dengke, Zhang Yin, Wang Peng, Wang Hongtao, Zhang Ze, Mao Scott X, Zhu Ting
Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Sci Adv. 2020 Jun 3;6(23):eaay2792. doi: 10.1126/sciadv.aay2792. eCollection 2020 Jun.
Nanomaterials often surprise us with unexpected phenomena. Here, we report a discovery of the anti-twinning deformation, previously thought impossible, in nanoscale body-centered cubic (BCC) tungsten crystals. By conducting in situ transmission electron microscopy nanomechanical testing, we observed the nucleation and growth of anti-twins in tungsten nanowires with diameters less than about 20 nm. During anti-twinning, a shear displacement of 1/3〈111〉 occurs on every successive {112} plane, in contrast to an opposite shear displacement of by ordinary twinning. This asymmetry in the atomic-scale shear pathway leads to a much higher resistance to anti-twinning than ordinary twinning. However, anti-twinning can become active in nanosized BCC crystals under ultrahigh stresses, due to the limited number of plastic shear carriers in small crystal volumes. Our finding of the anti-twinning phenomenon has implications for harnessing unconventional deformation mechanisms to achieve high mechanical preformation by nanomaterials.
纳米材料常常以意想不到的现象让我们感到惊讶。在此，我们报告了在纳米级体心立方（BCC）钨晶体中发现了以前认为不可能的反孪生变形。通过进行原位透射电子显微镜纳米力学测试，我们观察到直径小于约20 nm的钨纳米线中反孪晶的形核和生长。在反孪生过程中，与普通孪生中相反的剪切位移不同，在每个连续的{112}面上会发生1/3〈111〉的剪切位移。这种原子尺度剪切路径上的不对称导致反孪生比普通孪生具有更高的阻力。然而，由于小晶体体积中塑性剪切载体数量有限，在超高应力下纳米尺寸的BCC晶体中反孪生会变得活跃。我们对反孪生现象的发现对于利用非常规变形机制来实现纳米材料的高机械性能具有重要意义。
