High-speed steels owe their exceptional cutting performance and wear resistance to a microstructure built from a hardenable steel matrix studded with a uniform dispersion of carbides. The desirable phases are M6C carbides, rich in tungsten and molybdenum, and the extremely hard MC vanadium carbides that also carry smaller amounts of tungsten and molybdenum. Undesirable carbide stoichiometries, such as M2C, M3C, M7C3, M23C6 and various eutectic forms, degrade properties and are precisely what metallurgists try to avoid. Powder metallurgy press-and-sinter processing allows alloying levels that conventional wrought routes cannot reach, but sintering such concentrated compositions demands a precise handle on the thermodynamics of the liquid phase that forms near the optimum sintering temperature.

Nitrogen has long been known to help. Earlier work showed that sintering vanadium-rich high-speed steels in nitrogen-containing atmospheres lowers the optimum sintering temperature and widens the temperature window in which successful densification occurs, a breakthrough that enabled continuous belt-furnace processing on an industrial scale. Yet the underlying absorption mechanism remained murky. The new research set out to identify which alloying elements and processing variables govern nitrogen uptake, using experimental grades deliberately designed beyond conventional composition limits and beyond the validated range of the widely used Thermo-Calc software and its TCFe13 database.

The team produced water-atomized powders at their research centre, including high-vanadium grades containing only vanadium carbides and complex alloys additionally loaded with cobalt, molybdenum and tungsten. Powders were sieved below 100 micrometres, hydrogen-annealed to push oxygen below 0.1 weight percent, mixed with a small amount of organic binder and graphite, uniaxially pressed at 700 megapascals into small cylinders at roughly 70 percent of theoretical density, and sintered for one hour under atmospheres of differing nitrogen potential, each containing 1 percent methane to prevent decarburization. Nitrogen and carbon contents of the sintered samples were then measured with dedicated fusion and combustion analysers, while scanning electron microscopy with energy-dispersive X-ray spectroscopy tracked the microstructural consequences.

The absorption mechanism that emerges is a two-step gas-solid reaction. At sintering temperatures, nitrogen molecules dissociate into atomic nitrogen on the steel surface, and the adsorbed atoms enter solid solution in the austenitic matrix and diffuse inward. When a dissolved nitrogen atom reaches an MC vanadium carbide, an exchange reaction takes place: nitrogen substitutes for carbon in the carbide lattice, converting it into an M(C,N) carbonitride and releasing carbon into the matrix. Because the substoichiometric vanadium carbides typical of these steels, close to V8C7 in composition, contain lattice vacancies, nitrogen initially occupies those vacancies before displacing carbon, which explains why earlier researchers observed nitrogen uptake without the expected immediate carbon release.

Diffusion rates might seem a bottleneck, since nitrogen diffuses far more slowly in austenite than in ferrite, even though its solubility is greater in austenite thanks to larger interstitial sites. But the porous network between powder particles offers a shortcut. Below the onset of liquid formation, the maximum diffusion distance is only about half a particle size, under 50 micrometres, meaning nitrogen can reach carbides at the centre of a particle in less than ten seconds. This also means high heating rates can starve the process: they limit the time available for dissociation, diffusion and carbon substitution before liquid forms, densification closes off the pore network and further nitrogen transport is choked. The team therefore used a comparatively gentle heating rate of 20 degrees Celsius per minute to promote controlled absorption.

Thermodynamic calculations confirmed that the MX carbonitride phase is overwhelmingly the nitrogen sink, containing roughly three orders of magnitude more nitrogen than any other phase and accounting for about 90 percent of the nitrogen in these steels. Vanadium nitrides show the largest drop in Gibbs free energy among the candidate nitrides, which is why vanadium carbonitrides are the only nitrogen-bearing phase observed. The study also found that nitrogen uptake increases markedly once liquid forms through the eutectic reaction between austenite and M6C carbides, because the liquid dissolves less nitrogen and releases it to the carbonitrides. The extent of the carbide-to-carbonitride transformation depends on the nitrogen activity of the atmosphere: higher nitrogen partial pressure consistently drove greater uptake, though the atmospheres tested, below 90 percent nitrogen, were insufficient to convert vanadium carbide fully into vanadium nitride.

The alloying chemistry proved equally decisive. At constant vanadium content, higher carbon suppresses nitrogen absorption, because carbon pushes the exchange reaction back toward the carbide side of the equilibrium. Tungsten and molybdenum, which behave almost interchangeably in these alloys, act as a hindrance through a molybdenum-equivalent parameter that showed a nearly linear decline in nitrogen uptake as their combined content rose. These strong carbide formers demand more carbon to satisfy carbide stoichiometry and partially substitute for vanadium in the carbonitride lattice, forming complex (V,W,Mo)(C,N) phases that reduce the effective vanadium available for nitrogen binding. Comparisons between nearly identical compositions differing only in carbon or in tungsten and cobalt isolated these effects cleanly.

The practical payoff lies in the sintering window. Increasing the nitrogen potential lowered the optimum sintering temperature by 20 to 40 degrees Celsius and expanded the window from roughly 40 to about 100 degrees Celsius, an almost threefold widening, while the liquid fraction at the optimum temperature remained essentially constant at around 12 weight percent. Phase diagrams showed that nitrogen, a strong austenite stabilizer comparable to carbon, widens the temperature interval between the solidus and the austenite disappearance line, enlarging the liquid-plus-austenite-plus-carbide region that defines supersolidus liquid phase sintering. A flatter liquid-fraction-versus-temperature slope means the process is less sensitive to small temperature fluctuations, reducing the risk of undersintering or dimensional distortion.

The authors caution that their calculations should be read as qualitative trends rather than absolute predictions, since some compositions exceeded the database limits and kinetic factors such as diffusion are not captured by equilibrium thermodynamics. Even so, the guidelines are clear: tailor vanadium content and atmospheric nitrogen activity to promote uptake, manage carbon and molybdenum-equivalent levels to avoid tipping the equilibrium the wrong way, and exploit the widened processing window for energy-efficient, more controllable sintering of next-generation tool steels, including alloys that could eventually feed additive manufacturing routes beyond current compositional limits.

Subject of Research: Nitrogen absorption mechanisms in powder metallurgy high-speed steels sintered in nitrogen-rich atmospheres

Article Title: Nitrogen absorption mechanism in powder metallurgy high-speed steels sintered in nitrogen-rich atmospheres

Article References: Iraola-Arregui, I., Lozada, L., Mancisidor, A. M., & Iturriza, I. (2026). Nitrogen absorption mechanism in powder metallurgy high-speed steels sintered in nitrogen-rich atmospheres. Journal of Materials Science: Metallurgy, 1(1), Article 9. https://doi.org/10.1007/s44492-026-00009-x

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00009-x

Keywords: high-speed steel, powder metallurgy, sintering, nitrogen absorption, vanadium carbide, carbonitrides, Thermo-Calc, liquid phase sintering, alloy design, sintering window, thermodynamics, tool steels

The oxide problem is deceptively simple to state and maddeningly difficult to solve. Every aluminum particle, the instant it is exposed to air, develops a native Al₂O₃ film that is chemically stable, thermodynamically tenacious, and electrically and thermally insulating. When loose powders are compacted and heated, these films sit at every would-be bond between particles, acting as a continuous network of brittle ceramic that throttles densification, poisons interparticle bonding, and caps the achievable strength and ductility. In conventional press-and-sinter processing, where powders are heated slowly in a furnace, the oxide largely survives the journey, lingering at grain boundaries as a weak link that cracks initiate from under load. The review emphasizes that the central engineering question of aluminum powder metallurgy is therefore not merely how hot or how long to sinter, but how to disrupt, dissolve, fragment or bypass that oxide network — because once interparticle contact becomes true metallic bonding, the powder route can rival or exceed casting and forging in performance.

Each sintering family attacks the film in a different way, and the review dissects these mechanisms in detail. Conventional sintering relies on extended heating to promote diffusion and, where alloying permits, the formation of transient liquid phases that can penetrate and erode oxide films; it is inexpensive and scalable but slow, and densification is often incomplete. Pressure-assisted routes such as hot pressing, spark plasma sintering and hot isostatic pressing bring mechanical force to bear, rupturing oxide layers by plastic flow and shear at particle contacts while simultaneously accelerating densification — the reason these methods routinely achieve near-full density where furnace sintering falls short. Field-assisted techniques add pulsed electrical currents, whose localized Joule heating and possible electrochemical effects clean contact asperities and promote rapid neck formation within minutes. Microwave sintering heats volumetrically rather than from the surface inward, shortening the time the oxide has to thicken and enabling rapid densification at lower temperatures, while flash and induction sintering push heating rates to extremes that reshape precipitation behavior itself.

What elevates the review beyond a catalog of techniques is its insistence on processing–microstructure–property linkage. The authors trace how each route governs pore elimination, grain evolution, liquid-phase formation, precipitation sequences and interface development, and then connect those microstructural outcomes to hardness, tensile strength, ductility, fatigue life, wear resistance and fracture behavior. Densification alone, they stress, does not guarantee performance: aggressive rapid sintering can produce full density yet leave residual oxide clusters that become fatigue crack nucleation sites, while gentle conventional sintering may preserve fine grains that boost strength but retain porosity that kills ductility. The strength–ductility trade-off that dominates structural metallurgy is reframed here as a processing choice — controllable, in principle, by tuning how heat, pressure, fields and time are combined.

The review then marches through the major aluminum alloy families and shows how alloy chemistry interacts with sintering strategy. Pure and low-alloyed aluminum, with little solute to drive liquid-phase sintering, depends heavily on mechanical oxide disruption, making pressure-assisted routes especially attractive. The Al–Cu 2xxx series and the Al–Mg–Si 6xxx series benefit from transient liquid phases that sweep oxide from interfaces and from subsequent precipitation strengthening, so sintering schedules must be balanced to allow both densification and controlled precipitate formation. The high-strength Al–Zn–Mg–Cu 7xxx alloys, prized in aerospace, are notoriously sensitive to over-heating during sintering because incipient melting can degrade their carefully engineered microstructures; the authors highlight how field-assisted, short-duration routes can densify them while avoiding the thermal damage of long furnace holds. Hypereutectic Al–Si systems, used where wear resistance matters, depend on sintering conditions that control the size and distribution of primary silicon particles, and aluminum-matrix composites add yet another variable: the reinforcement interface, whose integrity determines whether added ceramic particles strengthen the metal or embrittle it.

From this cross-system comparison the review distills a unified framework linking sintering strategy to densification mechanism, microstructural control and mechanical response. The framework treats oxide-film disruption, densification and microstructural evolution as three coupled channels through which any sintering process acts, and argues that rational alloy-and-process pairing — rather than trial and error — should guide the next generation of sintered aluminum components. The practical implications reach into automotive powertrains, aerospace structures, additive manufacturing feedstocks and lightweight consumer hardware, all domains where near-net-shape powder processing promises to cut machining waste and energy use. Because powder metallurgy shapes parts to final dimensions with controlled composition and fine, tunable microstructure, the review argues it is uniquely positioned to meet industry’s simultaneous demands for weight reduction, mechanical performance and manufacturing sustainability.

Equally valuable is the authors’ candor about what remains unknown. The review identifies limited characterization of the residual oxide network itself as a first major gap: researchers rarely map how much oxide survives sintering, where it sits, or in what form, leaving the true role of oxide films in fatigue and fracture under-quantified. A second gap is the weak correlation between ductility and fatigue behavior in sintered aluminum — most studies report tensile data, but fatigue, the property that matters most for structural service, is comparatively neglected. Third, sintering parameters across the literature are poorly standardized, making it nearly impossible to compare results between laboratories or to build reliable process–structure databases. Finally, the authors call for data-driven process maps that could let engineers select sintering routes computationally, an approach they see as essential for next-generation sintered aluminum alloys designed for electric vehicles, aerospace and beyond.

The significance of this synthesis lies in its reframing of an old bottleneck as a solvable design problem. For half a century the oxide film has been treated as an inevitable tax on aluminum powder metallurgy, paid in reduced performance and restricted applications. By showing that the film can be systematically disrupted through the deliberate combination of pressure, fields, fast heating and liquid phases — and that the optimal combination is alloy-specific — the review converts a materials limitation into a processing design space. The proposed unified framework gives researchers a common vocabulary for comparing radically different sintering technologies, and the identified gaps sketch a research agenda: map the surviving oxide, close the fatigue data gap, standardize parameters and build predictive process maps. If those steps are taken, the powder route could become the default manufacturing path for high-performance aluminum, replacing energy-intensive melting and machining with a cleaner, near-net-shape alternative.

For a world racing to lightweight everything from aircraft to battery enclosures, the timing could hardly be better. Aluminum demand is rising across electrified transport and renewable-energy hardware, and every percentage point of density savings compounds into range, payload or efficiency gains. The review’s message to engineers is quietly radical: the strongest, most ductile sintered aluminum parts will not come from a single breakthrough furnace, but from matching each alloy system — pure aluminum, 2xxx, 6xxx, 7xxx, hypereutectic Al–Si or metal-matrix composite — to the sintering physics that best defeats its oxide skin and sculpts its microstructure. With peer-reviewed synthesis now connecting the dots across half a century of scattered process literature, the humble aluminum powder particle may finally be ready to shed its ceramic cloak and step into structural duty at scale.

Subject of Research: How sintering methods disrupt oxide films and control microstructure and mechanical properties in aluminum powder metallurgy

Article Title: From oxide disruption to strength-ductility optimization: a review of sintering methods, microstructural evolution and mechanical properties of Al alloys

Article References: Raj, R., Patel, P., Ghosh, A., Shrivastava, P., Mabuwa, S., & Msomi, V. (2026). From oxide disruption to strength-ductility optimization: a review of sintering methods, microstructural evolution and mechanical properties of Al alloys. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02079-w

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02079-w

Keywords: aluminum alloys, powder metallurgy, sintering, oxide-film disruption, densification, microstructure, mechanical properties, spark plasma sintering, strength-ductility, Al-Si alloys, composites, Advanced Composites and Hybrid Materials

The review systematically summarizes recent progress across the major 3D printing technologies used for energy storage applications, including direct ink writing, electrohydrodynamic printing, fused deposition modeling, stereolithography and binder jet printing. Particular emphasis is placed on the critical role of post-processing in regulating microstructural evolution, phase stability, interfacial bonding and electron and ion transport pathways. The authors, led by Xiaowen Zheng and Qing Sun, critically discuss how key sintering parameters such as temperature, dwell time and heating rate govern densification behavior and, ultimately, electrochemical performance. They also highlight emerging strategies involving rapid sintering, high-throughput experimentation and machine-learning-assisted optimization as promising approaches to accelerate process development and improve reproducibility.

The field traces its origins to 2013, when researchers used direct ink writing to fabricate the first interdigitated lithium-ion microbattery. Since then, battery components made with fused deposition modeling, electrohydrodynamic printing, stereolithography and binder jetting have been reported in rapid succession, spanning electrodes, electrolytes, separators and current collectors. The appeal of these approaches lies in the architectural freedom they provide. Hierarchical porosity can be engineered so that macropores facilitate electrolyte infiltration, mesopores enhance ion diffusion and micropores increase accessible surface area, collectively reducing transport resistance and improving rate performance. Complex geometries such as interdigitated, lattice and honeycomb structures can shorten ion transport pathways, while multi-material printing allows electrodes, electrolytes and current collectors to be integrated monolithically, minimizing interfacial contact resistance.

Yet the review stresses a fundamental mismatch: 3D printing primarily addresses spatial shaping rather than imparting electrochemical functionality. Electrochemical reactions and charge carrier transport occur at the nanoscale to microscale, far below the manufacturing resolution of most printing techniques. Printed green bodies generally exhibit high porosity, low density, substantial organic binders or photocurable resins, and insufficient interlayer bonding. Consequently, their electronic conductivity, ionic transport capability and mechanical strength often fail to meet the demands of battery applications. Among post-processing techniques, sintering is singled out as the most critical step, determining not only final densification and grain morphology but also the quality of interlayer adhesion, the evolution of porosity and the continuity of electronic and ionic transport pathways.

Each printing technique imposes its own post-processing requirements. Direct ink writing, the most widely applied and material-versatile method, relies on viscoelastic inks extruded through nozzles, with successful printing demanding carefully tuned rheological properties such as yield stress, shear thinning and thixotropic behavior. Electrohydrodynamic printing applies high voltage between nozzle and substrate, forming a Taylor cone that emits filaments one to two orders of magnitude finer than the nozzle itself, enabling micrometer and sub-micrometer deposition ideal for high-resolution electrode patterns and flexible substrates. Fused deposition modeling compounds active materials with thermoplastic binders into printable filaments, while stereolithography uses ultraviolet light to crosslink photosensitive resins loaded with active particles. Binder jetting selectively deposits liquid binders onto powder beds, accommodating ceramics, metals and multiphase composites without high temperatures or energy beams.

In every case, the printed structure must be transformed through curing, debinding and sintering. Pre-curing steps such as ultraviolet curing, freeze drying and solvent evaporation provide preliminary shape fixation before high-temperature treatment. Debinding, typically conducted between 200 and 600 degrees Celsius, thermally decomposes organic binders and releases them as gases, exposing functional particles and establishing initial interparticle contacts. Solvent debinding can complement this by selectively dissolving soluble binder fractions and creating interconnected pore channels that vent gaseous decomposition products, preventing blistering, cracking or large voids. Only after these stages can high-temperature sintering promote solid-state diffusion and particle necking, forming a densified skeleton with interconnected porosity and continuous transport networks.

The review devotes detailed attention to the four core dimensions of the sintering profile. Temperature governs atomic diffusion kinetics, crystal-phase transformation, grain growth, pore elimination and grain-boundary quality. Moderate elevation improves lattice ordering in intercalation-type oxide cathodes, while solid electrolytes such as LLZO and LATP require high temperatures to eliminate secondary phases, though overheating induces lithium volatilization and secondary phases that degrade ionic conductivity. Dwell time controls how far diffusion-driven processes progress, with insufficient holding leaving carbonaceous residues and trapped gases, and excessive holding causing abnormal grain coarsening. Heating rate determines how organic decomposition and gas release unfold, with rapid heating risking blistering and delamination, and the sintering atmosphere regulates defect chemistry, oxygen vacancy concentration and phase stability, with oxygen-rich conditions shown to suppress lithium oxide loss and stabilize the fast-ion-conducting cubic garnet phase.

Rapid sintering techniques are presented as a way to balance energy consumption, dimensional stability and compatibility with thermally sensitive materials. Field-assisted sintering applies pulsed direct current to generate intense Joule heating at particle microcontacts, enabling near-theoretical densities at lower furnace temperatures and shorter dwell times while suppressing excessive grain growth. Microwave sintering converts electromagnetic energy directly into heat within the material, achieving volumetric heating with rapid temperature rise and reduced thermal stress. Laser-assisted sintering uses focused beams for localized densification with a small heat-affected zone, making it compatible with polymer substrates and flexible current collectors. Emerging ultrafast high-temperature sintering and blacklight sintering, which achieve heating in milliseconds to seconds, have so far been limited to structural ceramics but could eventually accelerate the debinding-densification of battery electrodes and electrolytes.

Looking forward, the authors argue that no universal processing window exists because temperature, dwell time and heating rate are strongly interdependent and different printing techniques and material systems exhibit markedly different sintering tolerances. They advocate a shift from empirical optimization toward mechanism-guided design, coupled with high-throughput experimentation and machine learning. Machine-learning approaches, including Bayesian optimization workflows, can extract hidden relationships between sintering parameters, material structure and performance, capturing nonlinear interactions that conventional one-factor-at-a-time analyses miss. By coupling the parallel manufacturing capability of 3D printing with data-driven modeling in a closed loop of data, model and experiment, researchers can rapidly identify optimal sintering windows that balance densification, conductivity and structural stability. The review concludes that while 3D printing provides unprecedented structural design freedom, post-processing ultimately determines whether printed architectures become stable, high-performance electrochemical devices, and that continued advances in mechanistic understanding, rapid processing and data-driven optimization will position 3D printing as a viable manufacturing paradigm for next-generation energy storage.

Subject of Research: The role of printing technologies, post-processing and sintering in fabricating functional 3D-printed energy storage devices

Article Title: From printed architectures to functional batteries: printing technologies, post-processing, and sintering

Article References: Zheng, X., Mejia-Centeno, K. V., Khan, M. D., Cabot, A., & Sun, Q. (2026). From printed architectures to functional batteries: printing technologies, post-processing, and sintering. Advanced Materials Joining, 1(1), Article 2. https://doi.org/10.1007/s44500-026-00002-3

Image Credits: AI Generated

DOI: 10.1007/s44500-026-00002-3

Keywords: 3D printing, batteries, sintering, direct ink writing, solid-state electrolytes, electrodes, additive manufacturing, debinding, machine learning, energy storage, post-processing, lithium-ion batteries

The appeal of ceramics is easy to understand. Materials such as alumina, zirconia, silicon nitride, and bioactive calcium phosphates combine exceptional hardness, thermal stability, and chemical resistance with, in some formulations, genuine bioactivity. They survive in jet engine hot sections, power electronics substrates, thermal protection systems, and patient-specific orthopedic implants. Yet conventional shaping routes, including pressing, injection molding, and tape casting, falter when designers demand tortuous internal channels, triply periodic minimal surfaces, hierarchical porosity, or geometries derived directly from medical scans. Every design iteration traditionally required new tooling, inflating both cost and timeline.

Among the competing additive manufacturing technologies, direct ink writing occupies a distinctive niche. Stereolithography and digital light processing deliver fine resolution but depend on photosensitive slurries with limited solids loading and suffer from light-scattering problems. Binder jetting separates shaping from sintering but struggles with powder bed management, weak green strength, and residual porosity. Laser-based methods impose punishing thermal loads and narrow processing windows that invite cracking. Direct ink writing, by contrast, works under ambient or near-ambient conditions, requires no photochemistry or powder bed, and welcomes multi-material integration, compositional gradients, and functional fillers such as conductive carbons, catalytic particles, piezoelectric phases, and magnetic components.

The technique’s history is a study in steady accumulation. Researchers at Sandia National Laboratories first extruded high-concentration ceramic slurries with partial organic binders in 1997, laying the foundation for modern robocasting. In the early 2000s, Jennifer Lewis’s group systematically studied high-solid-loading pastes, established the principles of filament stability and interlayer adhesion, and demonstrated layer-by-layer assembly of silica-based inks into three-dimensional grids. By 2006, programmable deposition systems were fabricating ceramic microstructures with sub-100-micrometer resolution. The 2010s brought alumina, zirconia, hydroxyapatite, and graphene-based composite inks, followed by multi-material printing, functionally graded structures, and fiber-reinforced ceramic matrix composites. Since 2021, the field has entered its data-driven era, with artificial intelligence optimizing processes, digital twins simulating entire workflows, and one-step debinding-sintering routes such as microwave heating compressing production cycles.

At the heart of the technology lies a deceptively simple rheological trick. A printable ceramic ink must flow smoothly under the high shear rates of roughly 100 to 1,000 per second inside the nozzle, then instantly rebuild its internal structure after deposition to resist gravity and surface tension. This shear-thinning, yield-stress behavior is commonly captured by the Herschel-Bulkley model, where a sufficiently high yield stress keeps deposited filaments from slumping while a shear-thinning exponent between 0.3 and 0.6 allows dramatic viscosity reduction during extrusion. Oscillatory rheometry adds further criteria: the storage modulus must exceed the loss modulus at low strain to signal solid-like behavior, and thixotropic recovery times shorter than one second are considered ideal for stacking tall, unsupported features.

Formulating such inks is a balancing act across four essential ingredients: ceramic particles, binders or thickeners, dispersants, and solvents. High solids loadings of 40 to 60 percent by volume are preferred because they minimize sintering shrinkage, but excessive loading compromises dispersion stability and green strength. Bimodal particle distributions, mixing coarse micrometer-scale grains with finer submicrometer particles, fill interstitial spaces and reduce viscosity at a given loading, and studies of bimodal glass bead mixtures show they consistently extrude at higher mass flow rates than monomodal inks. Binders such as polyvinyl alcohol, methylcellulose, and the thermoresponsive copolymer Pluronic F127 impart the viscoelasticity and yield stress needed for shape retention, while dispersants stabilize particles against agglomeration, with a zeta potential exceeding plus or minus 30 millivolts generally indicating robust electrostatic stabilization. Non-oxide ceramics such as silicon carbide and silicon nitride demand even stricter control, often requiring non-aqueous solvents to prevent surface hydrolysis.

Hardware and process control translate ink design into reproducible parts. Extrusion systems come in pneumatic, screw- or piston-driven, and direct-drive varieties, each trading cost against precision and response speed; direct-drive actuators respond in under 50 milliseconds and enable programmable retraction for clean start-stop transitions. Nozzle diameters range from 50 micrometers for micro-features to several millimeters for rapid prototyping, with tapered tips reducing shear stress on particles and preventing clogging. Layer height is typically set at roughly 60 percent of the nozzle diameter to ensure interlayer bonding without excessive squeezing. Dimensionless metrics guide the process: a Bond number below one predicts stable overhangs, while the yield-capillary ratio quantifies shape retention after deposition. Environmental chambers holding temperatures between 15 and 30 degrees Celsius and humidity between 40 and 60 percent stabilize solvent evaporation and prevent nozzle drying and differential shrinkage.

Modern systems increasingly close the loop with real-time sensing. Optical cameras track filament diameter and layer alignment to about 10 micrometers, laser profilometers map surface topology and detect warping, pressure sensors flag nozzle clogging through abrupt backpressure drops, and acoustic emission sensors catch microcracks and filament slippage before they become failures. Machine learning algorithms analyzing these sensor streams can adjust extrusion rate, print speed, or nozzle height within milliseconds; in one reported study, a convolutional neural network trained on filament images reduced print errors by 87 percent in a zirconia lattice structure. Embedded printing, in which inks are extruded into self-healing support baths, further offloads anti-sagging constraints and has been validated with preceramic polymers and titanium, titanium-aluminum-carbide, and alumina inks.

Post-processing remains the most defect-prone phase of the workflow. Green bodies containing 20 to 40 percent solvent must dry gently to avoid capillary-stress cracking, sometimes requiring days of controlled humidity or solvent exchange. Debinding, the thermal decomposition of organic binders between roughly 200 and 600 degrees Celsius, often consumes 10 to 50 hours and demands slow heating ramps through critical decomposition intervals identified by thermogravimetric analysis. Sintering then densifies the part, and the choice of route matters enormously: conventional furnace sintering is cheap but slow, spark plasma sintering has pushed printed silicon carbide to 98 percent theoretical density in minutes at 2,050 degrees Celsius, microwave sintering cuts cycle times by 50 to 70 percent, and ultrafast high-temperature sintering can merge debinding and densification into a single step lasting seconds to minutes. Well-optimized dense alumina and zirconia components now reach flexural strengths of 250 to 500 megapascals, approaching conventionally sintered engineering ceramics.

The application landscape is expanding accordingly. Printed silicon carbide and silicon nitride lattices serve as heat-exchanger cores, turbine filters, and lightweight aerospace panels. Hydroxyapatite and beta-tricalcium phosphate scaffolds with hierarchical porosity above 300 micrometers promote osteointegration, and drug-releasing binder systems add therapeutic function. Piezoelectric actuators, solid oxide fuel cell electrodes with engineered tortuosity that boost efficiency by 20 to 30 percent, microchannel heat sinks, and hierarchically porous catalytic frameworks for hydrogen production and wastewater treatment all showcase the method’s breadth. Significant challenges persist, including long-term ink stability at high solids loadings, the trade-off between sub-100-micrometer resolution and throughput, multi-material compatibility, and sintering shrinkage of 15 to 25 percent that distorts geometry. But with machine-learning-guided process optimization, digital twins reporting roughly 94 percent defect-prediction accuracy in early studies, one-step sintering, and functionally graded multi-material printing on the horizon, the review’s authors conclude that direct ink writing is well on its way to becoming a foundational platform for next-generation ceramic manufacturing across aerospace, energy, electronics, and biomedicine.

Subject of Research: Direct ink writing as an additive manufacturing technique for fabricating complex ceramic components from ink formulation through industrial applications

Article Title: Direct ink writing of ceramics: from fundamentals to industrial applications

Article References: Direct ink writing of ceramics: from fundamentals to industrial applications. (n.d.). https://doi.org/10.1007/s44500-026-00001-4

Image Credits: AI Generated

DOI: 10.1007/s44500-026-00001-4

Keywords: direct ink writing, ceramics, additive manufacturing, 3D printing, rheology, sintering, ceramic inks, robocasting, biomedical scaffolds, machine learning, ceramic matrix composites, thermal materials

The material at the heart of this work is lunar regolith, the loose, fragmented layer of rock, mineral grains, and glassy particles that blankets the lunar surface to depths of several meters. Regolith is the product of billions of years of meteorite impacts that pulverized the lunar crust, and its composition varies across the Moon but generally includes silicate minerals, oxides of iron, titanium, calcium, and aluminum, and a significant fraction of agglutinates, which are irregular glassy particles welded together by micrometeorite impacts. Because this material is already sitting on the lunar surface in essentially unlimited quantities, it represents the single most obvious feedstock for any serious attempt at in-situ resource utilization, the strategy of living off the land beyond Earth.

Additive manufacturing, more commonly known as 3D printing, offers a natural fit for this challenge. Unlike conventional construction, which relies on large machinery, formwork, and a skilled workforce, additive manufacturing builds structures layer by layer from a digital design, using only the material that is actually needed. On the Moon, where every machine must be shipped from Earth and operated in a vacuum, under extreme temperature swings, and amid abrasive dust, the appeal of a compact, automated, digitally controlled fabrication system is hard to overstate. A single printer, paired with a regolith harvesting and processing system, could in principle fabricate walls, foundations, radiation shields, landing pads, and infrastructure components on demand, adapting each design to local terrain and mission requirements without waiting for resupply missions.

What distinguishes the new study is its emphasis on reconfigurability. Most visions of printed lunar habitats assume a one-way process: a structure is designed, printed, and fixed in place forever. But mission planners increasingly recognize that lunar bases, like the missions that precede them, will need to evolve. Equipment will be replaced, modules will be repurposed, and habitats will need to expand or contract as crew rotations and scientific priorities change. Building blocks that can be printed, assembled, disassembled, and reassembled into new configurations would give lunar architects a flexibility that monolithic printed structures cannot provide. Instead of demolishing a wall to build a new room, crews could simply take the wall apart and reprint or reposition its elements elsewhere.

Achieving this vision requires solving a chain of interlocking technical problems, and the researchers address them across the full workflow. The first step is feedstock preparation. Raw lunar regolith, whether actual Apollo-era samples or, more commonly in laboratory research, lunar regolith simulants that replicate the mineralogy and particle size distribution of the real material, must be sieved, sorted, and in some cases processed into a form suitable for printing. The sharp, irregular, and glassy nature of regolith particles makes them abrasive and difficult to flow uniformly, so particle engineering plays a crucial role in producing a feedstock that a printer can handle reliably.

The second step is the printing process itself, and here the study examines how regolith-based materials behave when deposited layer by layer. A central tension in lunar construction chemistry is the binder problem. On Earth, concrete gains its strength from Portland cement, whose production requires water and generates carbon dioxide through the calcination of limestone. Neither the water nor the emissions are acceptable on the Moon, where water is a precious resource and there is no atmosphere to pollute. Alternatives under investigation across the field include geopolymer chemistry, in which alkaline solutions activate the aluminosilicate minerals in regolith to form cement-like binders; sintering, in which concentrated heat from lasers, microwaves, or focused sunlight fuses regolith particles into solid masses without any binder at all; and small quantities of imported bonding agents, such as polymers, used as economically as possible.

Each route involves trade-offs that the researchers weigh in detail. Sintering produces genuinely binder-free structures, a major advantage for long-term self-sufficiency, but the vacuum environment complicates heat transfer and can trap gases released from the regolith, causing porosity and cracking. Thermal expansion mismatches between layers and the extreme thermal cycling between lunar day and night, where surface temperatures can swing by more than two hundred degrees Celsius, add further stresses. Geopolymers and chemical binders can deliver strong, dense components at lower processing temperatures, but they introduce dependence on reactants that must either be sourced locally or transported from Earth. The study’s framework for reconfigurable blocks is designed to accommodate this uncertainty: because the blocks are modular, a printing process can be refined or even replaced over time without abandoning the structures already built from earlier batches.

Mechanical performance is, of course, the bottom line for any structural material, and the reported work includes evaluation of the printed blocks under conditions relevant to lunar service. Compressive strength is the primary metric, since lunar habitats will mostly experience compressive loads from overlying regolith shielding piled on top of habitats to protect crews from galactic cosmic rays and solar particle events. Several meters of regolith cover are typically proposed for radiation protection, which means the underlying structure must bear substantial static loads in one-sixth of Earth’s gravity. The blocks must also tolerate internal pressurization, because habitats will hold breathable atmosphere at pressures that push outward on the walls, creating tensile stresses that brittle, sintered regolith handles poorly. Strategies to address this include placing habitat pressure vessels inside regolith-block shells, reinforcing blocks with fibers or mesh, and designing interlocking geometries that distribute loads across many contact surfaces rather than relying on mortar joints.

The interlocking geometry is where the reconfigurable concept becomes tangible. Rather than printing large monolithic panels, the researchers envision blocks with engineered shapes, analogous to LEGO bricks or precision masonry units, that can be stacked into curved walls, domes, and vaults and later separated without destructive force. Digital design tools allow each block’s geometry to be optimized for its position in a structure, embedding channels for cables and pipes, sockets for mounting hardware, or keying features that align with robotic grippers. This last point matters because much of the assembly on the Moon will likely be performed by robots rather than astronauts. Robotic arms placing regolith blocks in a vacuum environment avoid the hazards of EVA, and modularity suits robotic manipulation far better than amorphous printed masses, since discrete units with well-defined geometry can be grasped, positioned, and verified with existing machine-vision techniques.

Looking toward actual missions, the researchers situate their work within the broader context of NASA’s Artemis program and international plans for a sustained lunar presence, including the proposed Moon Village concept championed by the European Space Agency. The surface of the Moon is expected to host multiple cooperating installations in the coming decades, from the Gateway-linked Artemis Base Camp at the lunar south pole to landing infrastructure, power plants, telescopes, and pilot plants for extracting oxygen and metals from regolith. All of these will need construction materials, radiation shielding, thermal management, and foundations, and all of them will benefit from a standardized, printable, reconfigurable building system. The authors position their building blocks not as a finished habitat but as a scalable construction primitive, a verified unit of lunar architecture around which future designs, standards, and robotic systems can converge.

Significant engineering hurdles remain before regolith blocks are stacked on the lunar surface. Testing with genuine lunar samples is rare and limited by the tiny quantities of Apollo material available, so validation ultimately depends on simulants whose fidelity to the real thing is imperfect and whose behavior under vacuum, radiation, and thermal cycling differs in ways that are still being characterized. Printing at useful scale in vacuum, with lunar gravity and without Earthlike supply chains, has yet to be demonstrated in an operational setting, although parabolic flights and vacuum-chamber experiments continue to close the gap. The new study contributes a coherent pathway through this landscape: a demonstration that regolith can be additively manufactured into discrete, mechanically sound, reconfigurable blocks, and a design philosophy in which habitats grow and change with the missions they serve. If the approach matures as hoped, the first permanent structures on the Moon may not be transported there at all, but printed in place from the ground beneath future astronauts’ boots, one reconfigurable block at a time.

Subject of Research: Additive manufacturing of lunar regolith into reconfigurable building blocks for lunar habitation.

Article Title: Additive manufacturing of lunar regolith for reconfigurable building blocks toward lunar habitation

Article References: McCallum, C., Liang, Y., Tushar, N., Xu, B., Zhao, B., Zeng, H., & Shou, W. (2026). Additive manufacturing of lunar regolith for reconfigurable building blocks toward lunar habitation. npj Advanced Manufacturing. https://doi.org/10.1038/s44334-026-00111-x

Image Credits: AI Generated

DOI: 10.1038/s44334-026-00111-x

Keywords: lunar regolith, additive manufacturing, 3D printing, lunar habitation, in-situ resource utilization, Moon base, space construction, sintering, geopolymer binders, reconfigurable building blocks, Artemis program, radiation shielding