Molecular dynamics simulations of Al-Al2Cu phase boundaries

Potential based molecular dynamics simulations were performed for Al-Al2Cu phase boundaries (PBs) at a temperature of 50 K using a newly designed computation geometry that enables modeling hetero-interface configurations for an arbitrary pair of phases. The computational method and geometry were validated for symmetric grain boundaries in Al, both [0 0 1] and [1 1 0] tilt boundaries, followed by extensive simulations of Al-Al2Cu PBs. For randomly oriented Al and Al2Cu as well as randomly oriented phase boundary planes the average PB energy reaches γav. = 0.456 ± 0.002 J/m2. Two special orientation relationships (ORs), known to prevail in Al-Al2Cu eutectics after unidirectional solidification, were characterized in detail. For each OR the 3D phase boundary energy surface was mapped and the energy minima were carefully analyzed. Computational results were compared to experimental observations based on EBSD measurements and allowed concluding that lamellar eutectic interfaces select a shallow energy minimum γα4 = 0.407 J/m2 for one OR, but a deep, cusp-like energy minimum γβ6 = 0.253 J/m2 for the second OR. The calculations thus substantiate the experimentally observed behavior of lamellar eutectic interfaces, being nearly isotropic in the first case, but strongly anisotropic in the latter.