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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. 

Two-photon polymerization direct laser writing (TPP-DLW) is one of the most versatile technologies to additively manufacture complex parts with nanoscale resolution. However, the wide range of mechanical properties that results from the chosen combination of multiple process parameters imposes an obstacle to its widespread use. Here we introduce a thermal post-curing route as an effective and simple method to increase the mechanical properties of acrylate-based TPP-DLW-derived parts by 20-250% and to largely eliminate the characteristic coupling of processing parameters, material properties and part functionality. We identify the underlying mechanism of the property enhancement as a self-initiated thermal curing reaction, which robustly facilitates the high property reproducibility that is essential for any application of TPP-DLW. 

Abstract We demonstrate the use of tip-enhanced Raman spectroscopy (TERS) on polymeric microstructures fabricated by two-photon polymerization direct laser writing (TPP-DLW). Compared to the signal intensity obtained in confocal Raman microscopy, a linear enhancement of almost two times is measured when using TERS. Because the probing volume is much smaller in TERS than in confocal Raman microscopy, the effective signal enhancement is estimated to be ca. 10⁴. We obtain chemical maps of TPP microstructures using TERS with relatively short acquisition times and with high spatial resolution as defined by the metallic tip apex radius of curvature. We take advantage of this high resolution to study the homogeneity of the polymer network in TPP microstructures printed in an acrylic-based resin. We find that the polymer degree of conversion varies by about 30% within a distance of only 100 nm. The combination of high resolution topographical and chemical data delivered by TERS provides an effective analytical tool for studying TPP-DLW materials in a non-destructive way.