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Cold spray additive manufacturing (CSAM) is a solid-state deposition process that largely preserves feedstock microstructural features in the bulk deposit, making tuning of powder properties a direct lever for engineering deposit performance. This characteristic is particularly attractive for the fabrication of components subjected to extreme, directionally biased thermomechanical environments, such as the walls of rotating detonation engines (RDEs), where GRCop-42 (Cu-4Cr-2Nb at.%) is a leading candidate material. Realizing feedstock-driven microstructural design in CSAM requires upstream control of the powder itself. Ultrasonic atomization (UA) offers systematic control over droplet solidification conditions, and therefore over powder microstructure, prior to deposition. In this work, 17-4 precipitation-hardening (PH) stainless steel is used as a model system to establish process-structure linkages across the UA parameter space. A two-factor full-factorial study varied torch current and gas recirculation rate, and the resulting powders were characterized by particle size distribution (PSD) analysis, scanning electron microscopy (SEM), backscattered-electron imaging, inert gas fusion, and instrumented microhardness. A single-particle micropillar compression test within a SEM was also performed. The results demonstrate that UA processing parameters systematically influence powder impurities concentration and internal porosity, with dissolved oxygen and nitrogen content tracking together in a manner consistent with a cavitation-driven gas-entrainment mechanism. Single-particle testing further revealed ductile deformation without fracture, indicating feedstock deformability relevant to cold spray consolidation. Together, these findings lay the groundwork for feedstock-informed materials design in CSAM. 

Abstract Metallic materials under high stress often exhibit deformation localization, manifesting as slip banding. Over seven decades ago, Frank and Read introduced the well-known model of dislocation multiplication at a source, explaining slip band formation. Here, we reveal two distinct types of slip bands (confined and extended) in compressed CrCoNi alloys through multi-scale testing and modeling from microscopic to atomic scales. The confined slip band, characterized by a thin glide zone, arises from the conventional process of repetitive full dislocation emissions at Frank–Read source. Contrary to the classical model, the extended band stems from slip-induced deactivation of dislocation sources, followed by consequent generation of new sources on adjacent planes, leading to rapid band thickening. Our findings provide insights into atomic-scale collective dislocation motion and microscopic deformation instability in advanced structural materials. 

Microstructural control is both a major challenge and an opportunity in additive manufacturing of parts, and plays a particularly dominant role in the performance of components with complex geometries. Much effort has gone into metal additive manufacturing of metamaterials; yet a thorough understanding of microstructural controllability toward optimized part performance is lacking. Of interest is the development of functionally graded metamaterials, which locally optimize part properties to enhance overall part performance. 17‐4 precipitation hardened (PH) stainless steel has previously been shown to exhibit phase control as a function of printing parameters; yet the influence of geometry on phase evolution in printing of complex structures and metamaterials has so far remained unexplored. The present study aimed at elucidating the relationship between phase evolution and geometry in gyroid shell metamaterials printed in 17‐4 PH steel via laser powder bed fusion. Local hardening is demonstrated to occur as a function of geometry, likely prompted by topology‐induced variations in cooling profiles. The associated phase evolution is governed by the gyroid geometry and strongly correlates with geometry‐dependent loading paths therein. This demonstrates the possibility of inducing functional grading through geometric complexity, highlighting the possibility of significant property enhancements through local microstructural control.