Executive Summary : | Metal-based additive manufacturing (AM) processes produce parts with improved properties compared to conventional manufacturing processes. However, most metal alloys cannot be reliably printed due to the non-equilibrium nature of melting and solidification dynamics during AM. This proposal aims to understand the underlying physical mechanisms of microstructure formation during ultrarapid cooling rates typical of AM to suggest approaches to minimize and control microstructural heterogeneities for improved printability and microstructure robustness. The physical effects of cooling rates and alloy parameters on rapidly moving complex solid-liquid interface shapes during non-steady thermal conditions in heterogeneous liquid during AM need to be well-understood to control grain size and final microstructure. Mesoscale phase-field simulations will be used to study the solidification dynamics and microstructure formation in metal alloys under AM conditions. The simulation results will lead to strategies to improve composition homogeneity and phase control. Solidification maps will be constructed in view of various solidification morphologies as a function of AM solidification conditions, i.e., thermal gradient and rate of solidification, to guide microstructure formation and control during additive processing. The research directions will develop a detailed understanding of the underlying mechanisms of microstructure formation under AM conditions, potentially advancing strategies to identify "AM-friendly" robust microstructures to achieve targeted properties. The overall framework proposed will apply to diverse families of materials, including alloys, superalloys, and intermetallics, accelerating broad adoption of AM and enabling the design of new alloy systems specifically for additive processing. |