Microstructural Evolution in Metallic Alloys under Additive Manufacturing Conditions

In metal additive manufacturing (AM), an alloy (in powder or wire form) is melted by a rapidly moving heat source. A solid layer forms upon cooling, and successive layers are built by melting and solidification to form a three-dimensional part. AM processes typically produce large temperature gradients, high solidification rates, and repeated cycles of heating and cooling. The local processing conditions experienced during AM (e.g., thermal gradients and solid-liquid interface velocities during solidification) dictate microscopic structure (i.e., microstructure) evolution. Here we visualize melt pool dynamics and solidification during simulated AM by real-time imaging (e.g., synchrotron x-ray and dynamic transmission electron microscopy) and computational modeling to link local processing conditions to microstructural evolution. We also highlight novel microstructures produced by solid-state phase transformations. A deeper understanding of solidification and solid-state phase transformations under AM conditions is needed to optimize processing parameters across AM technologies, control microstructural evolution and resulting properties, and design metallic alloys for AM.