The mechanism of face-centered-cubic (FCC)-Al formation at an L12-Al3Sc/liquid-Al interface was investigated on the basis of interfacial structure and misfit strains, by using ab initio molecular dynamics (AIMD). These simulations were performed using Born–Oppenheimer dynamics, where pressure and temperature was controlled using a Parrinello–Rahman barostat and Langevin thermostat, respectively. Through this approach, we compared the relative stability of (001) Al3Sc/liquid-Al and (111) Al3Sc/liquid-Al interfaces and examined their effect on the heterogeneous nucleation of FCC-Al. Enhanced interfacial bonding along ⟨001⟩Al3Sc stabilized the (001) Al3Sc/liquid-Al, and formed in-liquid ordered layer resembling (002) FCC. Subsequently, the (001) Al3Sc/liquid-Al interface was subjected to stepwise cooling from 1450 to 950 K. The (002)-ordered layer was found to promote layer-by-layer epitaxial growth of FCC-coordinated regions to ∼25 fraction. During cooling, the resulting misfit strains—at (001) Al3Sc/(002)-ordered layer and (001) Al3Sc/(002) FCC−Al interfaces—ranged from −7.4 to 0.5 within 1450–950 K. The magnitude of such misfit strains reduced significantly between 1250 and 950 K, and this trend coincided with a sharp increase in FCC coordination. Thus, AIMD simulations revealed heteroepitaxial formation of FCC-Al on the (001) faces of intermetallic Al3Sc, and that this mechanism is closely associated with a reduction in misfit strains. Our findings motivate the search for new elements that will stabilize potent L12-like structures and produce grain-refinement in Al-based alloys.
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机译：采用从头开始的分子动力学（AIMD）方法，研究了L12-Al3Sc/液-Al界面面心立方（FCC）-Al在界面结构和失配应变的形成机理。这些模拟是使用 Born-Oppenheimer 动力学进行的，其中压力和温度分别使用 Parrinello-Rahman barostat 和 Langevin 恒温器进行控制。通过这种方法，我们比较了（001）Al3Sc/liquid-Al和（111）Al3Sc/liquid-Al界面的相对稳定性，并研究了它们对FCC-Al非均相成核的影响。沿⟨001⟩Al3Sc的增强界面键稳定了（001）Al3Sc/liquid-Al，并形成了类似于（002）FCC的液内有序层。随后，将（001）Al3Sc/liquid-Al界面从1450 K逐步冷却到950 K。发现（002）有序层促进FCC配位区域的逐层外延生长至∼25%的比例。在冷却过程中，在（001）Al3Sc/（002）有序层和（001）Al3Sc/（002）FCC−Al界面上产生的失配应变在1450-950 K范围内为-7.4%至0.5%。这种不匹配应变的幅度在 1250 K 和 950 K 之间显着降低，这一趋势与 FCC 协调的急剧增加相吻合。因此，AIMD模拟揭示了FCC-Al在金属间化合物Al3Sc的（001）面上异质外延形成，并且该机制与失配应变的减少密切相关。我们的研究结果促使人们寻找新的元素，这些元素将稳定有效的L12类结构，并在铝基合金中产生晶粒细化。
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