Cold spray (CS) is a solid-state additive manufacturing technique used to produce dense metallic structures with minimal oxidation. However, as-sprayed deposits typically require post-processing to enhance mechanical performance. This study explores the effects of sintering on cold-sprayed Aluminum 6061 (Al6061) and Stainless Steel 316 L (SS316L). Fast Spark Plasma sintering at 400 degrees C for 15 min had negligible impact on Al6061, while SS316L exhibited notable improvements in ductility and strength following sintering at 1200 degrees C. Comparable enhancements were also achieved using an ultra-high heating rate sintering process in under three minutes. These findings underscore the potential of rapid sintering as an efficient and effective approach for strengthening cold-sprayed SS316L in advanced manufacturing applications. (c) 2026 The Author(s). Published by Elsevier Ltd on behalf of Society of Manufacturing Engineers (SME). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The osteo-odonto keratoprosthesis (OOKP) remains a groundbreaking treatment for end-stage corneal blindness after 50 years, but is surgically complex and unsuitable for certain patients, particularly those without healthy teeth. We developed a novel keratoprosthesis (KPro) comprising spark plasma sintered titania-graphene oxide (TiGO) and a 5-mm PMMA optical cylinder, and evaluated its performance as an alternative to the tooth in the OOKP. The KPro's suitability for implantation was first demonstrated through the preservation of surface integrity, chemical structure, and mechanical strength following ethylene oxide sterilization. Mechanical pull-out tests showed that PMMA adhered more strongly to TiGO than to primate teeth after bonding with dental cement, suggesting that the same cement used in OOKP procedures can be used with TiGO skirts. In addition, in vitro studies confirmed TiGO's biocompatibility, supporting adhesion, proliferation, and viability of human corneal stromal fibroblasts. In a rabbit model of OOKP stage 1 surgery, the TiGO integrated successfully into dermal tissue, showing vascularized connective tissue with positive staining for collagen I and III and CD31. In stage 2 simulation, implantation of fibrovascularized KPro onto the ocular surface, under the nictitating membrane, was uneventful with no evidence of tissue melt, PMMA detachment, or adverse inflammatory response over six months. Immunohistological analysis showed that fibrovascular and immune cell markers in the implanted eyes were highest in the nictitating membrane proximal to the PMMA optical cylinder, decreased toward the distal regions, and were low throughout the host cornea. In conclusion, our TiGO-based KPro offers a promising alternative to OOKP, with advantages including a larger PMMA optical cylinder, less complex surgery, and broader surgical indications.

This study investigates the origin of distortion during sintering of 316 L stainless steel components produced by binder jetting, focusing on friction between the sample and the support surface and on density inhomogeneity in the green state. A design of experiments (DoE) approach evaluates the influence of key printing parameters on the sintering behavior of two geometries with different through-hole sizes. Dimensional measurements, and density profiling, are performed in both green and sintered states. Sintering simulations use the Skorokhod-Olevsky viscous sintering (SOVS) model and include experimentally measured density gradients and frictional effects. Results show that green density varies significantly (52% to 58%) depending on printing parameters, especially binder saturation, and exhibits directional dependence. These variations lead to measurable distortions during sintering. Simulations that include both friction and density gradients match experimental deformations with deviations below 4%. A compensation strategy that places parts on co-sintered 316 L support plates with interposed refractory particles reduces distortion to <1.5%. This work demonstrates the combined role of friction and density gradients in sintering distortion and presents a practical method to improve dimensional accuracy in binder jetting.

Accurate microstructural characterizationCharacterization is essential for understanding and optimizing the performance of metallic components produced by powder-based additive manufacturingAdditive manufacturing (PBAM). While two-dimensional (2D) cross-sectional imaging is widely used due to its accessibility, conventional image processing methods are labor-intensive and insufficient for reliably capturing three-dimensional (3D) particle contact features. This study introduces a machine learningMachine learning (ML) framework for predicting 3D particle contact areas (PCAs) directly from 2D microstructural images, eliminating the need for complete 3D X-ray computed tomography (CT) datasets. The framework leverages contact-line statistics extracted from 2D images to predict 3D contact areas. Validation using 316L stainless steelStainless steel PBAM samples demonstrates that the model achieves an average accuracy of 98.5

Direct Laser Metal Deposition (DLMD) is an additive manufacturing process in which a laser and metallic powder are used to build or repair metal components. The mechanical performance and microstructure of DLMD parts are governed by the thermal conditions during processing, which are commonly monitored using in-situ infrared pyrometers and thermal cameras to record surface temperature fields. Bulk temperature evolution and final material response can be predicted with thermal models that couple material properties, measured surface temperatures, and energy conservation. However, the reliability of these models strongly depends on accurate knowledge of the material’s laser absorptivity. Absorptivity governs the interaction between the laser and the material, offering critical insight into the high-temperature, transient, and highly localized phenomena occurring near the laser spot. This work proposes novel in-situ technique for numerically estimating the material’s absorptivity to the laser beam by using surface temperature data from the solid region of the substrate, where reliable calibration of the thermal-camera measurements is possible. In contrast to conventional approaches, the method does not rely on estimating the optical properties of the molten material. Instead, it exploits calibrated temperatures outside the melt pool, detailed knowledge of the thermal properties of the solid material, and the specific characteristics of Rosenthal’s analytical approximation of the temperature field for a moving point heat source. The approach was validated using experimental surface temperature data acquired during the deposition of a nickel-based superalloy. The absorptivity values obtained using our method closely match those reported in the literature using established techniques.

Hydroxyapatite scaffolds with controlled porosity were fabricated using robocasting to investigate the influence of additive manufacturing and sintering on microstructure, mechanical performance, and bioactivity. A printable ink containing 50 vol% nano-acicular HAp was developed to achieve stable filament deposition and well-defined lattice architectures. Thermal analysis confirmed complete removal of organic additives below 600 degrees C with no phase transformation. Dilatometry revealed a two-stage sintering process characterized by densification between 900 and 1200 degrees C and grain coarsening above 1200 degrees C. The relative density increased from 37% to 94% as the sintering temperature increased from 900 degrees C to 1400 degrees C, accompanied by grain growth from similar to 200 nm to similar to 2.5 mu m. Analytical modeling quantified activation energies of similar to 240 kJ/mol at low temperatures and similar to 740 kJ/mol at high temperatures, enabling predictive description of grain growth, densification kinetics, and shrinkage behavior in lattice-structured scaffolds. Predictive FEM modeling was developed to study the loss of shape uniformity during sintering. X-ray diffraction confirmed the phase stability of HAp up to 1400 degrees C without decomposition. Scaffolds sintered at 1200 degrees C exhibited compressive strengths in the range of 0.5-5 MPa, with the highest strength for the denser infill pattern and the shortest strand distance, comparable to trabecular bone, while maintaining an interconnected porous architecture. In vitro bioactivity evaluation in simulated body fluid demonstrated rapid apatite nucleation within 7 days and the formation of a continuous apatite layer after 21-28 days. These results demonstrate that sintering conditions assisted by additive manufacturing were systematically optimized to tailor porosity, mechanical performance, and bioactivity in robocast HAp scaffolds.

We report a novel material processing using ultra-intense nanopulse electric current to achieve unprecedentedly high dislocation densities in metallic materials. By applying electrical current nanopulses with intensities exceeding several 1010A/m2, we observed a high-density dislocation formation across with multiple scales, including micro-, sub-micrometer, nano- and sub-nanometer scales. Unlike conventional deformation or thermal processing, this method enables the creation of dislocation densities beyond the limits of cold-worked metals, reaching up to 1018/m2 at the nanoscale. Our results indicate that while microscale dislocations reach densities less than or similar to 1015/m2, a threshold typical for heavily cold-worked metals and alloys, nanoscale screw dislocations achieve densities around 1018/m2. This remarkable enhancement in defect density suggests a new pathway of tailoring mechanical and physical properties of metallic materials. We think this increase stems from significant stress concentration at grain boundaries (GBs) due to electron wind forces, which substantially heightens shear stress levels within grain interiors, particularly near lattice defects. Additionally, we demonstrate that higher pulsing frequencies lead to a greater degree of dislocation formation, revealing a frequency-dependent mechanism that enhances lattice distortion through localized shearing. Our findings suggest that ultra-intense nanopulse electric current promotes the significant generation of dislocations, which could significantly alter material properties, paving the way for advanced defect engineering in metallic materials. This innovative approach holds promise for applications in high-strength materials, microelectronics, and functional materials where defect engineering plays a critical role.

In the binder jetting (BJ) process, as in most of powder bed additive manufacturing technologies, the powder is periodically recoated onto the substrate layer-by-layer. The elements of the current deposited layer corresponding to the part being manufactured are bonded together using a polymeric binder. In all cases that require a thermal process for sintering, the internal structure of the finished part is defined by the internal structure of the powder bed. This article focuses on the discrete element modelling (DEM) of various powder spreading methods during recoating and their impact on the powder bed structure particularly applied to binder jetting technology. The article demonstrates that despite the thinness of the deposited layers, they typically exhibit porosity and particle and pore size non-uniformities along the build-up direction. These irregularities contribute to the anisotropic sintering shrinkage observed in green BJ bodies during experiments. However, the experiments presented confirmed by modelling show that without binder deposition, the powder bed – except for a narrow surface layer – remains relatively uniform, regardless of the recoating method used. It is the binder injection into the porous structure of the powder bed that disrupts this homogeneity, locks in large surface pores, and exacerbates the effects of powder segregation during spreading. Finally, several strategies, explored via simulation, are proposed to reduce porosity variations during BJ: using a combined roller-wide blade method for powder spreading and a two-hopper approach, where each layer consists of small particles deposited over larger ones.

This study proposes a strategy using triple-layered composite powder prepared by electroless deposition to achieve efficient densification in sintering. Fe-Cu-Ni-P alloys can be effectively densified with low-temperature, pressure-less sintering. The microstructure and mechanical properties of Fe-based alloys with varying Cu content are analyzed. The 1 wt% Cu nano-layer yields the highest compressive strength (2711 MPa) and yield strength (1538 MPa). This method can be extended to 3D-printed materials needing full densification through pressureless sintering.

Thermally activated precipitation imparts a strengthening effect on many alloys through solution-aging treatment. A major challenge for precipitation-hardening alloys is their microstructural instability, which results in the formation of detrimental phases and a loss of strength during prolonged thermal exposure. The strategy of rare-earth microalloying and high-intensity electrical nano pulsing (ENP) has been proposed to suppress the thermal degradation and promote the ultra-rapid field-activated Ce-rich precipitation in Ni-based alloy with cerium micro-addition. Single electric pulse at ultra-high intensity (1.30 x 1011A/m2) and ultra-short duration (330 ns) is applied, leading to the thermally stable hexagonal Ni5Ce intermetallic with a semi-coherent interface in this alloy. The increased corrosion potential (-194.5 mV) and ultimate tensile strength (831.1 MPa) indicate that the ENP treatment significantly improves both the corrosion resistance and work-hardening performance of Ni-based alloy. The uniqueness of field-activated precipitation behavior has been rigorously demonstrated, with intense electromigration effect driving the significantly enhanced diffusivity responsible for this transformation behavior. These findings provide a critical foundation for understanding microstructural evolution under highintensity electric fields and for advancing the field-assisted material processing technologies.

This paper is devoted to achieving accelerated densification, optimized microstructure, and improved mechanical properties of AlCoCrFeNi complex concentrated alloys (CCAs) by applying cyclic phase transition (CPT) process in spark plasma sintering (SPS) at low temperature. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were performed to correlate the sintering shrinkage with associated microstructural changes. Experimental results show that CPT process promotes the formation of refined intragranular BCC/B2 structure and networked dendritic FCC phase at grain boundaries in the CCAs. The proposed CPT-assisted sintering not only promotes these CCAs to have a fully dense structure that is unobtainable in regular sintering at lower-limit temperature (800 °C), but also promotes these CCAs to have an accelerated densification that does not exist in regular sintering at upper-limit temperature (1000 °C). This better densification outcome is contributed by distinctive elemental redistribution and nano-grain clusters, which promote the mass transfer and the superplasticity behavior in the CCAs. Given this, hardened BCC phase (471HV) and softened FCC phase (188HV) can be obtained in AlCoCrFeNi CCAs after CPT-assisted sintering, which brings a synergistic effect to overcome the strength–ductility trade-off in CCAs. This work is expected to provide more insights into the efficient sintering of complex alloys.

Understanding the anisotropic sintering behavior of 3D-printed materials requires massive analytic studies on their grain boundary (GB) structures. Accurate characterization of the GBs is critical to study the metallurgical process. However, it is challenging and time-consuming for sintered 3D-printed materials due to immature etching and residual pores. In this study, we developed a machine learning-based method of characterizing GBs of sintered 3D-printed materials. The developed method is also generalizable and robust enough to characterize GBs from other non-3D-printed materials. This method can be applied to a small dataset because it includes a diffusion network that generate augmented images for training. The study compared various machine learning methods commonly used for segmentation, which include UNet, ResNeXt, and Ensemble of UNets. The comparison results showed that the Ensemble of UNets outperformed the other methods for the GB detection and characterization. The model is tested on unclear GBs from sintered 3D-printed samples processed with non-optimized etching and classifies the GBs with around 90% accuracy. The model is also tested on images with clear GBs from literature and classifies GBs with 92% accuracy.

Rotary furnaces are used as reactors to intensify chemical processes between the powder and gas atmosphere around it. The furnace rotation leads to relative motion and dilation of the powder layers, facilitating gas access. The paper is devoted to the modeling of nickel oxide powder behavior in a rotary furnace to estimate the contribution of furnace rotation speed to gas permeability when the nickel oxide granules are reduced in a hydrogen atmosphere. Discrete element modeling of powder granules in a rotary furnace was conducted employing Altair EDEM commercial software to estimate the powder gas permeability at different stages. The powder bed in a horizontal cylindrical rotary furnace was modeled as a packing of identical spherical granules with diameters equal to those of the nickel oxide granules. The furnace rotation led to periodic oscillations of the powder along the furnace wall with an amplitude that gradually diminished to some steady value. Gas permeability of the powder bed was evaluated through the porosity function, derived from the Carman permeability equations. Greater gas permeability resulting from significant powder dilation was observed only in active shear zones on the powder bed surface and in the contact area between the powder and the furnace wall. Sizes of the shear zones depended on the furnace rotation speed but never exceeded several granule diameters for all rotation speeds. The efficiency of a rotary furnace as a chemical reactor was shown to be determined not only by the powder dilation but also by the regeneration rate for the powder bed surface. The regeneration rate can be calculated and changes nonlinearly with the furnace rotation speed.

This study explores the impact of electric field and temperatureTemperature on flash sinteringFlash sintering of zirconia nanoparticlesNanoparticles using molecular dynamics simulationsMolecular dynamics simulation. The findings suggest that the electric field effect is secondary to the temperatureTemperature effect. A comparison of simulations varying temperatureTemperature and electric field reveals a more significant difference in diffusion coefficient with temperatureTemperature variations. Furthermore, the electric field effect does not exhibit a consistent monotonic trend, as seen in the changing order of curves when temperatureTemperature increases. The induced electric field contributes to crystal orientation alignment and promotes surface mechanisms throughout the sinteringSintering stages. While a higher electric field leadsLead to greater atomic motion in the initial stage, the relationship is not strictly monotonic. However, it consistently enhances the diffusion coefficient of surface atoms, highlighting its role in surface mechanisms. Further research is warranted to fully understand the interplay between electric field, temperatureTemperature, and sintering mechanismsSintering mechanisms.

This work studied spark plasma sintered Ti48Al48Cr2Nb2 alloy for their nanoindentation and wear properties. Results showed an improvement in nanoindentation properties of the compacts with an increase in holding time from 5min to 7.5min for the heating rate of 50°C/min and 100°C/min. X-ray diffraction (XRD) analysis showed the intensity of diffraction peaks of two major crystalline phases of Ti3Al2.25Nb0.75 and γ-TiAl. Scanning electron microscopy (SEM) images of sintered compacts possessed varied microstructures due to different sintering parameters. The nearly lamellar structure showed a good balance of yield stress and fracture toughness. Wear tracks SEM analysis revealed the worn surface morphologies and the sample sintered for 7.5 min at the eating rate of 50°C/min sustained the least damage evident by the shallow grooves and narrow wear track. Profilometer measurements revealed the wear track depth and width, confirming the degree of wear for the samples sintered at varied conditions.

Spark plasma sintering (SPS) is one of the most promising technologies for producing polycrystalline transparent ceramics. However, it has limitations regarding the complexity of the geometries that can be produced. This study addresses these limitations by combining additive manufacturing techniques with spark plasma sintering. Additionally, a Multiphysics sintering model based on the continuum theory of sintering is employed to predict the outcomes of the SPS process, particularly the microstructure of the densified parts. As a result, the geometrically complex Al2O3 transparent parts manufactured in this study exhibit a uniform microstructure, high density (∼99%), and a linear transmittance of 16% at 490 μm.

Despite many efforts, the outcomes obtained with field-assisted processing of materials still rely on long-term coupling with other electroless processes. This conceals the efficacy and the intrinsic contributions of electric current. A new device utilizing electrical nano pulsing (ENP) has been designed and constructed to bring quasi-instantaneous modifications to the micro- and nano-structure in materials. Featuring ultra-high intensity (~ 1011 A/m2) and ultra-short duration (< 1 μs), the ENP technology activates non-equilibrium structural evolutions at nanometer spatial scale and nanosecond temporal scale. Several examples are provided to demonstrate its utility far outpacing any conventional materials processing technology. The ENP technology gives a practical tool for exploring the intrinsic mechanism of electric-field effects and a pathway towards the rapid industrial manufacturing of materials with unique properties.

Sintering is an important consolidation step employed in sinter-based metal additive manufacturing processes. Binder Jetting (BJT) starts with green components with low green density (40-60%) that results in large sintering shrinkages and geometrical shape distortions caused by external forces (e.g. gravity). Consequently, the prediction of the final sintered geometry is crucial during the design process. In this work, a novel sintering simulation framework for gravity-affected sintering of stainless-steel components is presented, including the Rios-Olevsky-Hryha sintering model and the methodology for the identification of the required material parameters. The constitutive law includes material constants to account for the powder packing effects and the delta-ferrite transformation occurring at high temperatures. The material shear viscosity was explicitly related to the equilibrium phase fraction of austenite and delta-ferrite during sintering temperatures. Dilatometry experiments were conducted and followed by the data postprocessing for the model calibration. The calibrated model was incorporated in a FEM code and validated against experimental data from BJT sintered components, showing the remarkably accuracy of the numerical simulations, with small geometric deviations (0.56 mm) related to the assumption of isotropic shrinkage in the model proposed. In parallel, other alternative models were implemented based on different normalized bulk viscosity formulations, which underestimate/overestimate the sintered distortions.