He Yang, Fang Zhengwu, Wang Chongmin, Wang Guofeng, Mao Scott X
Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
Nat Commun. 2024 Apr 6;15(1):2994. doi: 10.1038/s41467-024-47343-z.
Twinning, on par with dislocations, is critically required in plastic deformation of hexagonal close-packed crystals at low temperatures. In contrast to that in cubic-structured crystals, twinning in hexagonal close-packed crystals requires atomic shuffles in addition to shear. Though the twinning shear that is carried by twinning dislocations has been captured for decades, direct experimental observation of the atomic shuffles, especially when the shuffling mode is not unique and does not confine to the plane of shear, remains a formidable challenge to date. Here, by using in-situ transmission electron microscopy, we directly capture the atomic mechanism of the twinning in hexagonal close packed rhenium nanocrystals. Results show that the twinning is dominated by the (b, h) twinning disconnections. In contrast to conventional expectations, the atomic shuffles accompanying the twinning disconnections proceed on alternative basal planes along 1/6 , which may be attributed to the free surface in nanocrystal samples, leading to a lack of mirror symmetry across the twin boundary.
孪生与位错一样，在低温下六方密堆积晶体的塑性变形中起着关键作用。与立方结构晶体不同，六方密堆积晶体中的孪生除了剪切之外还需要原子重排。尽管由孪生位错承载的孪生切变已被观测数十年，但对原子重排的直接实验观测，尤其是当重排模式不唯一且不限于剪切面时，至今仍是一项艰巨的挑战。在此，通过使用原位透射电子显微镜，我们直接捕捉到了六方密堆积铼纳米晶体中孪生的原子机制。结果表明，孪生主要由(b, h)孪生位错分解主导。与传统预期相反，伴随孪生位错分解的原子重排在沿1/6的交替基面进行，这可能归因于纳米晶体样品中的自由表面，导致孪生界面前后缺乏镜面对称性。
