Non-equilibrium processing science of additive friction stir deposition

This paper presents a perspective of the non-equilibrium processing science underlying additive friction stir deposition, focusing on its unique shear-driven kinetic pathways for synthesizing new materials. We explore the extreme thermal and deformation histories and analyze each processing stage through the lens of non-equilibrium thermodynamics. The resulting phase and microstructural states arise from the competition between the shear-driven stage, characterized by distinct atom transport mechanisms, and the subsequent stages dominated by thermally activated processes. Leveraging the scalability of additive friction stir deposition, we argue for the possibility of simultaneously synthesizing and printing bulk-scale driven alloys with novel, non-equilibrium defect–phases.