High-resolution transmission electron microscope was used to observe and characterize the different formation stages of zero-strain twins in uniaxial tensile-deformed 120Mn13 steel at the atomic scale, which revealed the growth process of zero-strain twins in coarse-grained austenitic manganese steels. Here, plenty of zero-strain twins are observed in deformed 120Mn13 steel and they can be formed by three types of precursors. Their processes of expansion and connection, thickening and thinning can be carried out through the transformation of 9R phase with the matrix and the twin. A new 9R phase with different stacking sequences is firstly discovered and defined as 9R-Ⅱ to distinguish it from the classical 9R phase (9R-Ⅰ). 9R-Ⅰ and 9R-Ⅱ have the same lattice structure but different internal atomic arrangements and satisfy a twin-like relationship. In addition, a new formation mechanism of zero-strain twins based on the 9R phase transformation is proposed.

中文翻译：

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单轴拉伸变形 120Mn13 钢变形孪晶的原子尺度观察和表征

利用高分辨率透射电子显微镜在原子尺度上观察和表征单轴拉伸变形120Mn13钢中零应变孪晶的不同形成阶段，揭示了粗晶奥氏体锰钢中零应变孪晶的生长过程。在这里，在变形 120Mn13 钢中观察到大量零应变孪晶，它们可以由三种类型的前驱体形成。它们的膨胀连接、增厚和减薄过程可以通过9R相与基体和孪晶的转变来进行。首次发现了一种具有不同堆积顺序的新9R相，并将其定义为9R-Ⅱ，以区别于经典的9R相（9R-Ⅰ）。 9R-Ⅰ和9R-Ⅱ具有相同的晶格结构，但内部原子排列不同，满足类孪晶关系。此外，还提出了一种基于9R相变的零应变孪晶形成新机制。