Solid-State Metal Additive Manufacturing: A Review

Although a significant amount of technical, commercial, and academic resources have been invested in laser and electron beam-based additive manufacturing (AM) of metals and alloys over several decades, challenges and limitations associated with repeated local melting and processing complexity along with the cost of equipment and operation have sparked interest in research on solid-state AM methods as an alternative. This paper reviews the capabilities and challenges of major solid-state metal AM techniques by dividing it into two broad categories (plastic deformation based and sinter based) depending on the metallurgical bonding mechanisms, range of processible alloys, and resulting microstructures. The limited and recent data available in literature show that, while deformation-based AM techniques are primarily limited to relatively ductile alloys, a larger variety of materials are suitable for manufacturing through sinter-based AM. Deformation-based methods generally refine the microstructure by recrystallization, while in most cases sinter-based AM methods lead to grain growth due to high-temperature processing and a more isotropic microstructure. Among the solid-state AM methods summarized here, the binder jetting and additive friction stir AM methods stand out with isotropic microstructures and mechanical properties close to the wrought properties.