Factors controlling heteroepitaxial phase formation at intermetallic- Al₃Sc/liquid interfaces

H Wilkinson and B Boyd and JM O'Connell and R Knox and AJ Rinehart and BS Majumdar and D Choudhuri, JOURNAL OF APPLIED PHYSICS, 133, 124902 (2023).

DOI: 10.1063/5.0142117

The mechanism of face-centered-cubic (FCC)-Al formation at an L1(2)-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 similar 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 L1(2)-like structures and produce grain-refinement in Al-based alloys.

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