Additive manufacturing (AM), particularly laser power bed fusion (LPBF) technique, enables the formation of hierarchical heterogeneous microstructures that markedly enhance the mechanical performance of materials. However, a quantitative, kinetics-based understanding of how AM-induced heterostructures govern the evolution of deformation mechanisms and hetero-deformation-induced (HDI) strengthening during plastic flow remains lacking. Here, we employ metastable 304 L stainless steel, with its intrinsically low stacking fault energy that activates slip, twinning, and martensitic transformation, as a model system to elucidate the interplay between deformation kinetics and hetero-deformation in AM alloys. By integrating strain-rate jump and stress-relaxation experiments with loading–unloading hysteresis measurements and multiscale microstructural characterisation, we quantitatively resolve the evolution of dislocation mobility, dislocation storage, and HDI back stress across different deformation stages. The results reveal a sequential yet overlapping transition of dominant plasticity carriers: from dislocation slip in sub-micron cellular structures and planar slip band, to deformation twinning, and finally to deformation-induced martensitic transformation. This mechanistic evolution is manifested by a continuous reduction of activation volume from over 100 b³ to tens of b³, coupled with a non-monotonic evolution of mobile dislocation density. Throughout deformation, HDI back stress contributes up to ~75% of the flow stress, primarily associated with the massive accumulation of geometrically necessary dislocations at cellular walls, twin boundaries, and martensitic interfaces. These findings establish a quantitative linkage between AM-induced heterogeneous microstructures, deformation kinetics, and HDI strengthening, providing a kinetics-based framework for the mechanistic design of AM-enabled heterostructured materials. • Kinetics-based framework links AM microstructures to plastic deformation. • Activation volume drops from ~120 b³ to ~30 b³ across deformation stages. • Multi-modal deformation mechanisms govern rate control and sustain work hardening. • HDI back stress contributes ~75% of flow stress in LPBF 304 L stainless steel. • Transient tests quantify dislocation mobility, exhaustion, and back-stress evolution.

Additive manufacturing of silicone parts using Direct Ink Writing is interesting for producing parts with complex geometries, especially for medical applications and soft robotics. Using commercially available off-the-shelf solutions, the process currently relies on the choice by the user of a standardized rigid nozzle prior to printing. The nozzle orifice dimensions must then respect a trade-off between resolution and control over manufacturing time: a small-diameter nozzle allows for higher printing precision, but at the cost of longer printing times. Furthermore, in the case of a non-Newtonian fluid such as silicone, the internal geometry of the nozzle channel directly affects the shape of the extruded bead. A solution based on a variable-geometry nozzle is presented to contribute to the development of active nozzles. It relies on a deformable body, actuated by nine independent actuators, permitting continuous variation of the shape and dimensions of the orifice during the printing process, and also independently of the internal geometry of the nozzle. The proposed solution enables the independent displacement of the orifice from the printer end-effector. The staged configuration of the nozzle also makes it possible to act on flow dynamics. The behavior of the nozzle is assessed in printing conditions, and the associated results show that the nozzle is capable of producing beads of variable diameter, reducing printing time. The displacement of the position of a printed bead, independently of the end-effector of the printing structure, is highlighted, and a direct influence on fluid dynamics at the nozzle output is observed. • A nozzle with active control of orifice size and overall shape is proposed. • Orifice size can vary from 0.32 to 1.11 mm, reducing a sample printing time by 50%. • The nozzle mobilities can be used in conjunction with the printing system motion. • The nozzle motions are shown to provide possible improvement of printing accuracy. • Using nozzle shape modification can help to control the material flow.

Inconel 718 dominates laser powder bed fusion (PBF-LB/M) builds as the benchmark Ni superalloy for its γ′/γ″ hardenability, weldability, and qualification pedigree, yet its fatigue resistance remains limited by porosity, tensile residual stresses, and microstructural heterogeneity. Hot isostatic pressing (HIP) reduces porosity but induces grain growth and twinning, which degrade fatigue performance. Prior attempts to control grain size using micron-scale carbides often led to reduced ductility. We introduce a powder modification strategy for reused Inconel 718 feedstock by adding 0.6 wt.% micron-sized niobium and titanium carbides. During PBF-LB/M, these carbides dissolve and reprecipitate as nanoscale carbide-nitrides that pin grain boundaries and refine the microstructure during heat treatment. Neutron diffraction measurements reveal a redistribution of residual stresses, linked to interactions between nano-precipitates and the alloy structure. Fatigue life improves by 150–200% in the 10 5 –10 6 cycle regime, with fatigue limits up to 200 MPa higher than wrought or unmodified, additively manufactured (AM) IN718. This approach enables powder reuse while enhancing mechanical performance, offering a scalable route for fatigue-critical components in aerospace and energy sectors. By integrating powder chemistry and process control, this method demonstrates a sustainable strategy for upcycling aged AM powders into high-performance materials. • Powder-level NbC/TiC addition refines grains and suppresses HIP coarsening • Nano carbide–nitrides pin boundaries and redistribute residual stress • Fatigue life improved by 150–200% with +200 MPa fatigue limit • Compatible with existing IN718 reuse and qualification routes • Enables circular powder use and scalable fatigue-critical AM parts