Magnesia (MgO) particles inevitably exist in liquid Mg and may be used as potential sites for heterogeneous nucleation to achieve effective grain refinement. Understanding of the atomic configurations on MgO surfaces and in the liquid Mg adjacent to the liquid Mg/MgO interfaces is therefore of both scientific and practical interests. We investigate the surface structures of MgO in liquid Mg and the atomic arrangements of liquid Mg adjacent to liquid/substrate interfaces, using an ab initio molecular dynamics (MD) simulation technique. We find that an atomically rough terminating Mg layer forms on the {1 1 1} terminated MgO substrate (octahedral MgO) in liquid Mg. The simulations also reveal that on the structurally flat {0 0 1} terminated MgO substrate (cubic MgO) a rough Mg layer forms due to the unique chemical interactions between the ions on the substrate and the liquid metals. The surface roughness together with the large lattice misfits with solid Mg makes both octahedral and cubic MgO substrates impotent for heterogeneous nucleation of α-Mg. The present results may shed new light on grain refinement of Mg-alloys.

中文翻译：

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MgO和液态镁之间界面的预成核：从头算分子动力学研究

镁（MgO）颗粒不可避免地存在于液态Mg中，并且可以用作异质成核的潜在位点，以实现有效的晶粒细化。因此，理解MgO表面上和邻近液态Mg / MgO界面的液态Mg中的原子构型具有科学和实践意义。我们使用从头算方法研究了液态镁中镁的表面结构以及与液/底物界面相邻的液态镁的原子排列分子动力学（MD）模拟技术。我们发现，在液态镁中{11 1 1}终止的MgO衬底（八面体MgO）上形成了原子粗糙的终止Mg层。模拟还表明，在结构平坦的{0 0 1}终止的MgO衬底（立方MgO）上，由于衬底上离子与液态金属之间独特的化学相互作用，形成了粗糙的Mg层。表面粗糙度以及与固态Mg的大晶格失配使得八面体和立方MgO衬底都无法实现α-Mg的异质成核。目前的结果可能为镁合金的晶粒细化提供新的思路。