As the intersecting line of three grain boundaries (GBs), triple line is in non-equilibrium state with large stress concentration and extra energy, which makes it the optimal site for twin nucleation. However, it is very difficult to verify this conjecture by direct experiments, so no one has done it so far. In present work, we try to use molecular dynamics (MD) simulation on nanocrystalline Cu to confirm such hypothesis. We found that 25 out of 28 twins were emitted from triple lines. The related atomic micro-mechanism has been analysed. Stress relaxation and energy reduction were considered to be the driving factors for twinning from triple lines. This could be proved by changes of dihedral angles, relative GB energy sum, average atomic von Mises shear stress and average atomic energy. Experimentally, the transmission Kikuchi diffraction (TKD) characterization on nanocrystalline Cu revealed that the fraction of the triple junction-twin intersection was 81.7% in all twinned nanograins. The underestimation of experimental results might be caused by invisible triple lines in the orientation mapping.

作为三晶界（GBs）的相交线，三重晶线处于非平衡状态，应力集中度大，能量额外，是双晶核形成的最佳场所。但是，很难通过直接实验来验证这一猜想，因此到目前为止，还没有人做过。在目前的工作中，我们尝试对纳米晶Cu使用分子动力学（MD）模拟来证实这种假设。我们发现28个双胞胎中有25个是从三重线发出的。分析了相关的原子微观机制。应力松弛和能量减少被认为是三重线孪生的驱动因素。这可以通过二面角，相对GB能量总和，平均原子冯·米塞斯切应力和平均原子能的变化来证明。实验上，纳米晶Cu的透射Kikuchi衍射（TKD）表征表明，在所有孪晶纳米颗粒中，三重结-孪生相交的分数为81.7％。实验结果的低估可能是由于方向映射中看不见的三线所致。