Search Results (575)

Laser powder bed fusion (L-PBF) enables the integral fabrication of thrust chamber–nozzle and injector assemblies, eliminating some assembly and welding interfaces and reducing structural redundancy. However, under this manufacturing route, as-built geometric deviations act more directly on functional features, creating new challenges for dimensional accuracy and performance stability. To address this issue, this study investigates an additively manufactured 200 N monopropellant thruster and conducts geometric-deviation characterization, deviation–performance mapping, precision allocation, and performance validation. Key forming deviations were characterized using a coordinate measuring machine, industrial CT, micro-focus CT, and confocal microscopy. A first-order geometric deviation–performance mapping model was established through CFD-based sensitivity analysis, and Monte Carlo simulation was used to evaluate performance risk. A priority evaluation system combining the process capability index (Cpk) and performance sensitivity was then developed to guide differentiated finish-machining allowance allocation, CAD model pre-compensation, and process optimization. After two closed-loop iterations, the Monte Carlo-predicted thrust nonconformance probability decreased from 8.5% to 1.2%, and the simulated injection-flow non-uniformity narrowed from ±8.7% to ±4.2%. Cold-flow measurements showed that injection-flow non-uniformity decreased from ±9.3% to ±4.8%. In the rated-condition hot-fire test of the compensated thruster, the measured steady-state thrust deviation was controlled within ±1.5%, while the throat-diameter Cpk increased from 0.56 to 1.45. These results demonstrate that the proposed “inspection–analysis–allocation–compensation” closed-loop method can integrate performance sensitivity with actual manufacturing capability and provide an implementable route for precision-resource allocation and engineering optimization of integrated additively manufactured propulsion components. Full article

This study investigates the application of magnetic Barkhausen noise (MBN) measurements for assessing the microstructural and residual stress characteristics of additively manufactured AISI 4140 steel. The research explores the influence of part geometry, residual stresses, and material hardness on the MBN signal, particularly in thin-walled structures produced using laser-based powder bed fusion (PBF-LB). Results indicate a strong correlation between wall thickness and MBN intensity, attributed to the penetration depth of the magnetic field and the resulting amplification in thinner sections. Furthermore, an anisotropic MBN response is observed due to residual stress distributions, with tensile stresses leading to a higher Barkhausen signal. These findings highlight the potential of MBN as a non-destructive evaluation method for quality assessment in additively manufactured components supporting future approaches for non-destructive assessment of material conditions in additively manufactured components. Full article

Laser powder bed fusion (LPBF) is a disruptive additive manufacturing process for producing high-performance Inconel superalloy parts with complex shapes for the aerospace, energy, and other demanding industries. However, uniform part quality remains a persistent challenge, as process parameters, melt-pool dynamics, microstructural evolution, defect formation, and mechanical performance are closely coupled across a wide range of spatial and temporal scales. In previous reviews, these dimensions have been considered in isolation with limited insight into their interactions and implications for predictive process control. The present review aims to address this lacuna by proposing a unified Process–Structure–Property–Control (PSPC) framework for LPBF-produced Inconel 625, 718, and 738. The discussion begins with material attributes governing alloy processability, and then synthesises the melt-pool physics governing thermal behaviour, solidification, and energy transfer. Attention then turns to a critical assessment of grain evolution, defect formation, and process stability, showing how the thermal history governs microstructural development and, in turn, mechanical performance via linked process–structure–property relationships. Progress in multiscale numerical modelling, such as finite-element analysis, computational fluid dynamics, phase-field modelling, cellular automata, and phase-diagram calculation (CALPHAD), is reviewed to establish a comprehensive modelling ecosystem for predictive LPBF. The review also discusses the potential of emerging technologies, such as beam shaping, multi-laser processing, in situ monitoring, artificial intelligence, and powder recyclability, to increase the robustness and productivity of the process. Building on these advances, a digital-twin-enabled predictive-manufacturing framework that integrates physics-based models, data-driven algorithms, and real-time monitoring is introduced to enable closed-loop process optimisation. The review ends with a scientific synthesis and future research roadmap for intelligent, reliable, and autonomous LPBF of next-generation Inconel superalloys. Full article

Laser powder bed fusion enables the fabrication of complex Inconel 718 components, but rapid solidification produces pronounced microsegregation that complicates subsequent phase evolution. In this study, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy were combined with JMatPro calculations to examine as-built microsegregation and phase behavior in laser powder bed-fused Inconel 718. The as-built alloy exhibited a continuous cellular and dendritic substructure, a high dislocation density, and interdendritic constituents with pronounced Nb enrichment and weaker local Mo enrichment. Equilibrium calculations based on the measured powder composition predicted γ formation at approximately 1350 °C and a liquid plus γ region between 1195 and 1350 °C. The calculated stability ranges of MC, δ, η, γ′, σ, M₂₃C₆, Laves, and μ phases were also identified. Comparison with the experimental observations showed that calculations using the nominal composition cannot directly represent the strongly segregated interdendritic regions formed during rapid solidification. The TTT and CCT calculations indicated that δ phase precipitation is most sensitive at approximately 900 to 1000 °C. The results clarify the distinction between local nonequilibrium phase formation and bulk phase stability and highlight the role of Nb redistribution among interdendritic constituents, the δ phase, and γ″ and γ′ precipitates. The calculated results should be regarded as a qualitative reference. Further local composition-based calculations and experimental validation are required before they can be applied to heat treatment design. Full article

Powder bed fusion–laser beam (PBF-LB) of nickel–titanium (NiTi) has attracted increasing interest in aerospace, biomedical, and energy applications owing to its shape memory and superelastic properties, combined with the capability to fabricate complex geometries. However, the strong sensitivity of NiTi to thermal history and process variability makes predictive modeling and process parameter selection challenging. In this work, a physics-guided decision-support framework is developed for melt pool prediction and stability assessment during the PBF-LB processing of NiTi. A high-fidelity thermal finite element model incorporating CALPHAD-derived, temperature-dependent material properties was calibrated using a subset of experimental measurements and independently validated against additional experimental melt pool data. The calibrated model demonstrated good agreement with experiments, yielding mean absolute percentage errors of 4.22% and 5.63% for melt pool width and depth, respectively, on the validation dataset. A multi-output random forest surrogate trained on the validated simulation dataset enabled rapid prediction of melt pool geometric features, achieving test-set $R^2$ values exceeding 0.95, together with low MAE and RMSE values, while five-fold cross-validation confirmed robust predictive performance. The proposed framework integrates surrogate predictions with physics-based melt pool stability criteria to rapidly identify physically feasible processing conditions, thereby providing a computationally efficient foundation for future supervisory process control strategies. Full article

A study of thermal post-processing of laser powder bed fusion (powder bed fusion by laser beam for metal, PBF-LB/M)-built Inconel 718 components is presented, evaluating the effects on their mechanical properties, microstructure and deformation behaviour. For this, a variety of heat treatments is conducted to define the impact of the individual processes as well as of combinations of differently sequenced heat treatments. To be precise, solution treatment, hot isostatic pressing and ageing procedures are used as well as subsequently combined for a comprehensive investigation on process successions and the improvement of mechanical properties. The ultimate tensile strength, part density and microhardness are recorded for a quantification of metallographic and mechanical properties, as the heat treatments improve material properties. While an improvement of the material properties for the employment of the heat treatments is achieved, an outstanding hot-isostatic pressing sequence leads to a significant improvement in part density, hardness and mechanical properties with the highest measured tensile strength improving by 50%. Furthermore, microstructural and fractographic analysis is used for a discussion on the mechanisms of thermal post-processing, revealing phase precipitations and microstructural changes. An element analysis for phase identification and the characterization of precipitations is conducted, using an SEM/EDX measurement of the heat-treated samples. Microstructural changes, grain boundary migration as well as Nb-precipitations are shown for the heat-treated samples. Deformation mechanisms of the material states and the microstructure are discussed and reveal differences in fracture behavior caused by the development of shear bands and lengthened grain boundaries. Based on the fractographic analysis, the heat-treated samples could be classified according to whether their microstructures promoted ductile or more brittle fracture behaviour after heat treatment. Full article

In this study, laser powder bed fusion (PBF-LB) 022Cr17Ni12Mo2 steel plates with dimensions of 50 mm × 50 mm × 2 mm were fabricated using a laser power of 206 W, a scanning speed of 900 mm/s, a hatch spacing of 90 μm, a layer thickness of 30 μm, and an interlayer scanning rotation of 67°. The specimens were then subjected to solution treatment at 900–1100 °C for 30 min and at 950 °C for 30–120 min. Unlike previous ultrasonic studies on additively manufactured metals, which mainly focused on defect detection, elastic-constant characterization, or residual stress evaluation, this work investigates whether solution-treatment-induced changes in grain size and dislocation density can be quantitatively reflected by laser-ultrasonic attenuation and further correlated with yield strength. Laser ultrasonic nondestructive testing using a 1064 nm pulsed laser with a pulse width of 8 ns and a pulse energy of 500 mJ was combined with metallographic observation, EBSD characterization, XRD analysis, tensile testing, and microhardness measurement. The results show that the solution-treated samples retained a single-phase γ-austenitic structure, while microstructural recovery, weakening of PBF-LB-induced cellular substructures, and partial annihilation of cell-wall dislocations led to a reduction in KAM-derived dislocation density from 2.04 × 10¹⁴ m⁻² to 1.45 × 10¹⁴ m⁻² and a decrease in yield strength from 466.9 MPa to 407.4 MPa. Within the present dataset, the EBSD-equivalent grain size showed an apparent positive correlation with ultrasonic attenuation, while the KAM-derived dislocation density showed an empirical negative correlation with ultrasonic attenuation. However, ultrasonic attenuation should be interpreted as a combined microstructure-sensitive response rather than as a response controlled only by EBSD-equivalent grain size or dislocation density. Based on the empirical correlations among ultrasonic attenuation, EBSD-equivalent grain size, KAM-derived dislocation density, and yield strength, a preliminary attenuation-based calibration model was established for the present solution-treated samples. The model should be regarded as an in-sample empirical calibration within the present experimental range rather than a general Hall–Petch-based predictive model. The model showed good in-sample fitting performance, with (R²) values higher than 0.85 and a maximum in-sample fitting error of 3.85%. However, because the model was established and assessed using the same eight solution-treatment conditions, it should be regarded as a preliminary calibration model within the present experimental range rather than a general predictive model. This study demonstrates the potential of laser ultrasonic attenuation for non-contact evaluation of microstructural and mechanical-property variations in solution-treated PBF-LB 022Cr17Ni12Mo2 steel. Full article

Traditional bone plates provide reliable fracture fixation; however, their high stiffness can cause stress shielding, thereby reducing mechanical stimulation of the bone tissue and slowing its regeneration. The biomechanical performance of a titanium plate with a localized porous structure for osteosynthesis of the radial shaft was investigated in this study. Three designs were considered: a solid plate and two plates with localized porous regions measuring 10 × 10 mm and 10 × 15 mm. The finite element analysis of the bone–plate system was performed using MSC Patran/Nastran, with rigid fixation of the proximal end of the bone and sequential application of an axial compressive load of 100 N, bending, and torsion with a moment of 1 N·m. Biomechanical performance was evaluated based on von Mises equivalent stress, fragment displacement (FD), interfragmentary movement (IFM), interfragmentary strain (IFS), and strain energy density (SED). To confirm the manufacturability of the design, the plate was fabricated from Ti–6Al–4V alloy using laser powder bed fusion (LPBF), and the geometry of the porous structure was verified by scanning electron microscopy. The results showed that the localized porous structure altered the load distribution between the plate and the bone, resulting in an increase in local stresses in the bone under the investigated loading conditions. These changes indicate an alteration in the mechanical environment within the bone, which may potentially affect conditions related to fracture healing. Among the investigated configurations, the plate with a 10 × 10 mm porous insert demonstrated the most balanced mechanical characteristics in terms of stresses in the implant, stress distribution in the bone, and structural stability. Full article

Additively manufactured components require machining of functional surfaces to meet geometric requirements. Due to low stiffness and non-nominal as-built geometry, they are susceptible to milling-induced shape deviations. This paper presents a geometric–numerical milling process simulation for predicting shape errors in compliant metallic laser powder bed fusion components. The method combines real-geometry-based technological numerical control simulation, quasi-static force prediction, finite element-based structural response simulation, and surface reconstruction between roughing and finishing to enable multistage operation. The approach is validated for linear and non-linear toolpaths with varying immersion angles and compliance conditions. The results show reproduced force profiles, while magnitude deviations highlight the relevance of deformation-dependent engagement feedback in high-compliance regions. An analytical back-calculation based on the effective engagement cross-section reveals that accounting for deflection-induced engagement reduction reduces force deviations. During roughing, maximum shape errors for linear and non-linear toolpaths are overestimated by 4–5%, and critical high-error regions are identified. The reconstructed intermediate geometry after roughing is essential for finishing, since neglecting geometry feedback underestimates finishing forces. With geometry feedback, the maximum finishing shape error is predicted as 0.090 mm, while the measured value is 0.086 mm. The simulation captures dominant quasi-static shape-error regimes and supports process-chain-oriented prediction in additive–subtractive manufacturing. Full article

Melt-pool depth governs interlayer bonding and porosity in laser powder bed fusion and underpins part qualification, yet predicting it reliably remains difficult. Fast conduction models reach useful accuracy only after the absorptivity is fitted to the depths they are meant to predict, and inverse analyses have been used the same way, to recover a calibrated parameter rather than to test the model. Here, the absorptivity is fixed independently instead, a measured coupling for IN718 and, for IN625 and 316L, a published closed-form relation never fitted to the present depths. This converts a moving-source conduction model from an object of calibration into one of validation. The melt boundary is located by root-finding rather than on a grid, so no discretization error enters the diagnosis. Across 231 single tracks, the model reproduces conduction-regime depth and half-width to within a few percent and underpredicts increasingly once keyholing begins. Inverting each measured depth for the absorptivity conduction would require yielding a fitting-free diagnosis: no conduction-regime track demands a non-physical value, and the inferred value converges near 0.38 against inputs of 0.27 to 0.34, whereas every keyhole-classified track demands a value above unity. Because an inferred absorptivity also absorbs unmodeled transport, downward convection was emulated as an anisotropic effective diffusivity; at the enhancement reported for Marangoni flow, no keyhole track becomes explicable. A measured Ti-6Al-4V absorptivity rise of a factor 1.9 supports the mechanism. An enthalpy-indexed correction and data-driven baselines remain alloy-specific, whereas the physics-based model retains its advantage under cross-alloy extrapolation. All findings are for single tracks on bare plates. Full article

This study investigates the laser powder bed fusion (LPBF) fabrication of 17-4 PH stainless steel triply periodic minimal surface (TPMS) structures and the wettability response of corresponding flat plates subjected to selected post-processing treatments. Five TPMS geometries were fabricated and visually examined to document their overall condition and manufacturing irregularities. Thermal aging, steel shot blasting, commercial hydrophobic coating, and selected treatment combinations were evaluated on flat plates manufactured using the same material and LPBF process. Wettability was assessed using time-dependent static contact angle (CA) measurements and a preliminary comparison of three steel shot grades. The fabricated TPMS structures retained their overall geometries but exhibited localized burnt edges, distortion of thin boundary features, and differences in surface appearance. The untreated LPBF-fabricated surface was hydrophilic and exhibited time-dependent wetting, with the CA decreasing from approximately 81° to as low as 48° within 4 min and complete wetting occurring within approximately 8–10 min. Among the evaluated blasting media, S-330 produced the highest CA values; however, blasted surfaces remained hydrophilic, and the response depended on whether the plate was untreated or aged. The coating produced CA of approximately 153–170° across all coated regions, both with and without prior blasting. These findings identify manufacturing considerations for LPBF-fabricated TPMS structures and demonstrate the effects of the investigated treatments on the wettability of corresponding flat surfaces, thereby providing insights for future studies of TPMS-based condensation surfaces in atmospheric water generation applications. Full article

Heat treatment significantly improves the ductility of additively manufactured Zr–2.5Nb alloy, but the mechanisms responsible for this improvement remain poorly understood. In this study, the effects of heat treatment on the microstructure and room-temperature tensile behavior of Zr–2.5Nb fabricated by laser powder bed fusion (LPBF) were investigated by comparing as-built (AB) and heat-treated (HT) specimens. The HT specimens were held at 800 °C for 2 h and subsequently air-cooled. A microstructure-based crystal plasticity fast Fourier transform (CPFFT) model was constructed directly from two-dimensional electron backscatter diffraction (EBSD) orientation and phase maps to quantify the local stress, strain, and slip responses of the α and β phases in the HT microstructure. Heat treatment caused the acicular α′ martensite to decompose, producing a coarser lamellar α + β microstructure. In a representative EBSD field of the HT specimen, β-Zr accounted for 6.0% of the analyzed area and was distributed predominantly between the α lamellae. Compared with the AB condition, heat treatment reduced the mean 0.2% proof stress and ultimate tensile strength from 840 and 1033 MPa to 792 and 881 MPa, respectively, while increasing the mean uniform strain from 4.02% to 6.94%. At an applied axial strain of 3.2%, the β/α ratios of phase-averaged equivalent strain and accumulated absolute slip were 1.59 and 2.51, respectively, whereas the corresponding ratios for von Mises stress and axial stress were 0.57 and 0.81. These results reveal pronounced stress–strain partitioning between the phases: β-Zr accommodated greater equivalent strain and more extensive slip, whereas α-Zr carried higher stresses. This interphase partitioning helps explain the increased uniform strain of the HT specimens, while the reduction in strength is primarily associated with α′-martensite decomposition and α-lamella coarsening. Full article

PocketQube-class satellites have emerged as a cost-effective platform for space access; however, their extreme mass, volume, and dimensional constraints challenge conventional manufacturing approaches. This systematic review examines the state of the art of additive manufacturing (AM) for PocketQube structural systems between 2015 and 2026, focusing on materials, manufacturing processes, design methodologies, qualification frameworks, and flight heritage. A PRISMA-guided review methodology combined with a PICO/SPIDER-based selection framework was applied to analyse the peer-reviewed literature, technical standards, and documented mission data. The results indicate that AM has evolved from a prototyping tool into a viable production technology for picosatellite structures, enabling mass reductions of 30–60%, increased geometric complexity, functional integration, and improved packaging efficiency within the 50 × 50 × 50 mm PocketQube envelope. Polymer-based selective laser sintering, particularly Windform XT 2.0, currently represents the highest-maturity solution, while laser powder bed fusion of AlSi10Mg and Scalmalloy^® shows significant potential for future primary structures. The review further identifies a persistent gap between technological maturity and qualification readiness, as existing ECSS, NASA, and ISO/ASTM standards remain insufficiently tailored to PocketQube-class hardware. Future research should prioritise dedicated qualification pathways, in-orbit validation of metallic AM structures, and multifunctional topology-optimised architectures to enable the next generation of ultra-small spacecraft. Full article

Nickel-based superalloy components prepared by laser powder bed fusion (LPBF) are increasingly being used in the hot ends of aeroengines, which still need to be laser-welded to realize the assembly connection of large closed structures. However, the unique microstructural characteristics of LPBFed parts render them more poorly weldable than casts and wroughts, especially in cracking-sensitive superalloys. In this study, cracking mechanisms were analyzed by performing laser deep fusion welding on an LPBFed Haynes 230 alloy. The key factors leading to weld cracking were strongly correlated with the low-melting-point TCP phases enriched with W, Si, Al, and silicides, both of which tended to be distributed in the boron(B)-rich region and exhibited poor coherence with the matrix. In addition, the flow behavior of the molten pool affected the solidification rate of the weld, resulting in large solidification shrinkage stresses in the cracking-sensitive zone (CZ) part of the weld. In order to minimize the development conditions of the cracking-sensitive phases, reducing the content of W (from 14.96 to 13.56 wt.%) and Si (from 0.47 to 0.25 wt.%) was chosen to alleviate the segregation of W, Si and C elements in the solid phase at the end of solidification. Thus, TCP phase and silicides were transformed into carbides, which successfully suppressed weld cracking, reducing the crack depth ratio from 0.70 ± 0.08 to zero. New insights into the weldability improvement and crack inhibition mechanism of laser-welded additively manufactured cracking-sensitive superalloys are provided, accelerating the rapid application of large assemblies. Full article

High-entropy alloys (HEAs) offer attractive combinations of mechanical performance, thermal stability, and compositional flexibility, making them promising candidates for advanced structural applications. Laser-based additive manufacturing, particularly laser powder bed fusion (LPBF) and laser-directed energy deposition (LDED), enables the fabrication of geometrically complex HEA components with non-equilibrium microstructures. However, the distinct thermal histories of LPBF and LDED, with typical cooling rates of approximately 10⁵–10⁷ K s⁻¹ and 10²–10⁴ K s⁻¹, respectively, strongly govern solidification behavior, elemental segregation, residual stress development, defect formation, and mechanical properties. Although previous reviews have discussed additively manufactured HEAs, an integrated framework linking composition design, printability, LPBF/LDED processing, microstructural evolution, post-processing, and industrial qualification remains limited. Therefore, this review establishes a unified composition–process–structure–property framework for laser additively manufactured HEAs. Fundamental HEA concepts, LPBF/LDED process characteristics, solidification behavior, phase formation, defect evolution, and mechanical performance from ambient to elevated temperatures are systematically discussed across representative FCC, refractory, and dual-phase HEA systems. This review emphasizes that printability should be considered during alloy design by correlating composition-dependent solidification characteristics, cracking susceptibility, phase stability, and defect formation with mechanical performance. Post-processing treatments are shown to modify residual stress, microsegregation, precipitation behavior, porosity, and deformation mechanisms, although their benefits must be balanced against thermal softening or brittle phase formation. Finally, CALPHAD, integrated computational materials engineering (ICME), machine learning (ML), and in situ monitoring are identified as promising tools for accelerating alloy and process optimization, while reproducible process windows, defect-control criteria, databases, and qualification protocols remain essential for industrial implementation. Full article