Non-beam-based metal additive manufacturing enabled by additive friction stir deposition

Beam-based processes are popularly used for metal additive manufacturing, but there are significant gaps between their capabilities and the demand from industry and society. Examples include solidification issues, anisotropic mechanical properties, and restrictions on powder attributes. Non-beam-based additive processes are promising to bridge these gaps. In this viewpoint article, we introduce and discuss additive friction stir deposition, which is a fast, scalable, solid-state process that results in refined microstructures and has flexible options for feed materials. With comparisons to other additive processes, we discuss its benefits and limitations along with the pathways to widespread implementation of metal additive manufacturing.