We report the discovery of a rigorous nucleation mechanism for $\left\{10\overline{1}2\right\}$ twins in hexagonal close-packed (hcp) magnesium through reversible hcp-tetragonal-hcp martensitic phase transformations with a metastable tetragonal phase as the intermediate state. Specifically, the parent hcp phase first transforms to a metastable tetragonal phase, which subsequently transforms to a twinned hcp phase. The evanescent nature of the tetragonal phase severely hinders its direct observation, while our carefully designed molecular dynamics simulations rigorously reveal the critical role of this metastable phase in the nucleation of $\left\{10\overline{1}2\right\}$ twins in magnesium. Moreover, we prove that the reversible hcp-tetragonal-hcp phase transformations involved in the twinning process follow strict orientation relations between the parent hcp, intermediate tetragonal, and twin hcp phases. This phase transformation-mediated twinning mechanism is naturally compatible with the ultrafast twin growth speed. This work will be important for a better understanding of the twinning mechanism and thus the development of novel strategies for enhancing the ductility of magnesium alloys.

中文翻译：

---

可逆马氏体相变在镁中{101¯2}孪晶的形核

我们报告发现了一种严格的成核机制 $\left\{10\overline{\mathrm{1个}}2\right\}$通过亚稳态四方相为中间态的可逆hcp-四方-hcp马氏体相变，在六方密堆积（hcp）镁中形成双胞胎。具体而言，父hcp相首先转换为亚稳态四方相，然后再转换为孪生hcp相。四方相的逝性质严重阻碍了其直接观察，而我们精心设计的分子动力学模拟严格揭示了该亚稳相在核的成核中的关键作用。$\left\{10\overline{\mathrm{1个}}2\right\}$双胞胎在镁。此外，我们证明了孪生过程中涉及的可逆hcp-tetragonal-hcp相变遵循父hcp，中间四方和孪生hcp相之间的严格取向关系。这种由相变介导的孪生机制与超快孪生生长速度自然兼容。这项工作对于更好地了解孪生机理，从而开发出增强镁合金延展性的新策略至关重要。