Pattern Selection in Model Alloys Under Additive Manufacturing Conditions

Brian Rodgers, Colorado School of Mines

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Predicting the patterns formed during metallic alloy solidification is of fundamental interest to additive manufacturing. Dendrites are the most commonly encountered solidification pattern under additive manufacturing conditions. Conventionally, dendrites in face centered cubic systems such as aluminum are expected to solidify along <100> directions. In contrast, experiments conducted at the Advanced Photon Source (APS) and with Dynamic Transmission Electron Microscopy (DTEM) have revealed dendrite growth along <110> directions in the Al-Ag system. The preferred crystallographic growth direction of dendrites is predicted by the minimum solid-liquid interface stiffness, generally corresponding to the maximum interfacial energy. The change in preferred crystallographic growth direction can be explained by a shift in the interfacial energy profile. To verify this, the interfacial energy profile of the system must be determined. This can be accomplished with Molecular Dynamics (MD), but there are currently no potentials well suited to modelling liquid behavior in the Al-Ag system. To support the development of a potential for this system and inform subsequent phase field modelling of microstructure development, recent work during a residency LANL focused on developing an automated system for performing MD simulations. This code base, called LAVA, is capable of performing a number of simulation types in LAMMPS. Work on this code base involved verifying baseline simulations and making improvements where possible. One such improvement was in the melting point calculation routine, where the algorithm testing for convergence was upgraded from the relative error method to the bisection method. This change made the convergence behavior more consistent and reliable.

Abstract Author(s): Brian Rodgers, Saryu Fensin, Joseph McKeown, Amy Clarke