Despite the fundamental importance of solid-solid transformations in many technologies, the microscopic mechanisms remain poorly understood. Here we explore the atomistic mechanisms at the migrating interface during solid-solid phase transformations between the topologically closed-packed A15 and body-centred cubic phase in tungsten. The high energy barriers and slow dynamics associated with this transformation require the application of enhanced molecular sampling approaches. To this end, we performed metadynamics simulations in combination with a path collective variable derived from a machine-learning classification of local structural environments, which allows the system to freely sample the complex interface structure. A disordered region of varying width forming at the migrating interface is identified as a key physical descriptor of the transformation mechanisms, facilitating the atomic shuffling and rearrangement necessary for structural transformations. Furthermore, this can directly be linked to the differences in interface mobility for distinct orientation relationships as well as the formation of interfacial ledges during the migration along low-mobility directions.

中文翻译：

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界面局部无序驱动的结构转变

尽管固-固转变在许多技术中具有根本重要性，但其微观机制仍然知之甚少。在这里，我们探讨了钨中拓扑密堆积 A15 相和体心立方相之间固-固相变过程中迁移界面的原子机制。与这种转变相关的高能垒和缓慢的动力学需要应用增强的分子采样方法。为此，我们结合从局部结构环境的机器学习分类导出的路径集体变量进行了元动力学模拟，这使得系统能够自由地采样复杂的界面结构。在迁移界面处形成的不同宽度的无序区域被认为是转变机制的关键物理描述符，促进结构转变所需的原子改组和重排。此外，这可以直接与不同取向关系的界面迁移率差异以及沿低迁移率方向迁移过程中界面凸缘的形成相关。