In this paper, a new way for synthesising nanoscale AlN and Si3N4 co-reinforced aluminium matrix composites (AMCs) by means of laser powder bed fusion (LPBF) is presented. The method entails irradiating AlSi10Mg powder with a laser beam, thereby forming an Al matrix melt pool in an atmosphere of dilute nitrogen (N2) concentration; simultaneously, the nearby N2 undergoes pyrolysis, generating reactive nitrogen ions that react with dissolved Al and Si atoms within the melt pool to form AlN and Si3N4 precipitates. Benefiting from rapid solidification characteristic of LPBF, these nitrides nucleate and grow in an extremely short temporal window before precipitating in the melt pool. Finally, the (AlN + Si3N4)/AMC is fabricated through successive layer-by-layer application of this synthesis strategy. Herein, a comparative investigation was conducted between AMCs processed under varying N2 concentrations (2 vol%, 5 vol%, and 10 vol%) and a reference AlSi10Mg alloy produced in a pure argon (Ar) atmosphere (0 vol% N2). Multiple analytical techniques (XRD, SEM, EDS, HR-TEM, and XPS analyses) verified nitrides incorporation into the AMCs matrix, meanwhile, EBSD characterised the grain morphology, dimension, and orientation. The strengthening-toughening mechanisms of the composites were systematically elucidated through comprehensive microstructural and mechanical property evaluations.

Studies on the intermediate-temperature brittleness (ITB) of gamma '-strengthened LPBF-fabricated Ni-based alloys mainly focus on the evolution of deformation mechanisms under different temperature conditions, while the effects of LPBF-induced microstructure on ITB remain less explored. In this work, effects of LPBF-induced microstructure on the ITB were investigated by comparing the microstructural differences between LPBFfabricated and cast IN738 alloy (denoted as AM738 and CA738), both before and after tensile testing. The results indicate that AM738 exhibits micron-sized columnar grains with straight grain boundaries (GBs) parallel to build direction and the cellular sub-grain structure, whereas CA738 has near-equiaxed millimetre-sized grains with tortuous GBs and gamma ' phase distributed in both grains and GBs. Tensile tests over a wide temperature range show that AM738 exhibits a more pronounced ITB, with a broader temperature range and lower ductility. Post-fracture observations indicate that LPBF-induced supersaturated solid solution causes gamma ' phase to precipitate within grains during tensile loading, increasing intragranular strength and the strength mismatch of intragranular/GB in the AM738. Consequently, strain concentrates at weakened GBs, leading to crack initiation and rapid propagation along flat GBs, resulting in brittle fracture. In the CA738, however, the gamma ' phase in grains and GBs remains stable, maintaining minimal strength mismatch, which enables synergistic deformation and inhibits crack initiation. In addition, the residual stress from LPBF promotes oxygen ingress along GBs, forming brittle oxides and further facilitating GB decohesion. These findings will advance the understanding of ITB failure mechanisms in gamma '-strengthened LPBF-fabricated Ni-based alloys and promote the development of reliable high-temperature components.

Powder bed anomalies in the laser powder bed fusion (LPBF) additive manufacturing process may cause various defects, potentially reducing the mechanical properties of the fabricated components. Although deep learning methods have been successfully employed to identify various powder bed anomalies, the categorization of "powder spreading anomaly" has been oversimplified into a single class, neglecting multi-layer insufficient powder spreading conditions. The correlation between insufficient powder spreading and mechanical properties also remains unclear, and the threshold at which insufficient powder spreading leads to a decline in mechanical properties has not been investigated. This study develops a novel powder spreading anomaly detection system (PSADS) for LPBF that includes a deep learning-based segmentation algorithm, known as Full-scale Feature Adaptive UNet++ (FFA-UNet++). FFA-UNet++ addresses challenges such as brightness homogenization, texture homogenization, and boundary blurring caused by multi-layer insufficient powder spreading. The algorithm enables the detection of six types of insufficient powder spreading, achieving a mean intersection over union (mIoU) close to 57 %, representing a 4 %-11 % improvement over six widely used segmentation networks, with a maximum IoU exceeding 90 % for individual anomaly categories. The study also investigates the effects of the six types of insufficient powder spreading on the mechanical properties of LPBF-fabricated 316 L stainless steel and proposes a process control guideline: The cumulative number of insufficient powder layers per part should not exceed three layers. This study provides a novel vision-based powder spreading anomaly detection method used for LPBF process and furnishes valuable insights for LPBF quality control within industrial applications.

With the advancement of laser powder bed fusion (LPBF) additive manufacturing, efficient utilization of powders outside conventional particle size range (15-53 mu m) has become critical to improving powder efficiency. This study investigated process optimization, microstructure, and mechanical properties of coarse AlMgScZr alloy powders (53-150 mu m) in LPBF. The controlled variable method employed to analyze parameter effects on density, defects, microstructure, and mechanical properties. Results show that the coarse powder exhibits a narrow process window with high sensitivity of forming stability to parameter fluctuations. The optimized parameters are a thickness of 100 mu m, a laser power of 450 W, and a scanning speed of 900 mm/s. This parameter set achieves a relative density of 99.3%+/- 0.2%. Microstructural analysis reveals fine equiaxed grains near fusion boundaries transitioning to columnar grains within molten pools, without observable secondary precipitates. The as-printed samples show a microhardness of 99.7 +/- 8.9 HV0.1, tensile strength of 336.5 +/- 8.0 MPa, elongation of 12.7%+/- 0.4%.

This work challenges the conventional size constraints for laser powder bed fusion (LPBF) powders by demonstrating that coarse AlMgScZr powder (53-150 μm) can be successfully fabricated via a laser remelting (LR) strategy to prevent mechanical degradation. The optimized LR strategy simultaneously regulated building quality and grain structure. Porosity and lack-of-fusion defects have been effectively mitigated, achieving a relative density exceeding 99.5%. LR strategy reduced the heterogeneity of the bimodal grain structure, increased the area fraction of fine equiaxed grains to 76.5%, and weakened the columnar texture. Consequently, the aged alloy exhibited an ultimate tensile strength of 508 ± 8 MPa and an elongation of 14.1% ± 0.7%, approaching the standard powder counterpart, which had an ultimate tensile strength of 528 ± 7 MPa and an elongation of 14.3% ± 0.4%. This study presents a practical approach to reducing feedstock costs and broadening the range of applicable powder sizes in LPBF.

This study presents a design-for-additive-manufacturing (DFAM) workflow for developing lightweight patient-specific mandibular reconstruction plates (PSMRPs). Topology optimisation (TO) was employed to generate two new designs (PSMRP1 and PSMRP2) from an original plate (PSMRP0), achieving approximately 25% mass reduction. Their biomechanical performance was comparatively evaluated against the original design using finite element analysis (FEA) under two physiologically relevant occlusal conditions - incisal biting and right group clenching. The results indicate that the TOed plates maintained comparable structural safety and stability while offering adequate fatigue durability, despite a moderate reduction in resilience. PSMRP1 demonstrated more balanced biomechanical behaviour across both occlusal scenarios than PSMRP2. All three PSMRP designs were additively manufactured as physical prototypes using laser powder bed fusion (LPBF) in Ti6Al4V and assembled onto three anatomically accurate 3D printed mandibular bone models via PolyJet in VeroWhitePlus, confirming both manufacturability and anatomical fit. This study establishes a closed-loop DFAM workflow from virtual design to physical prototype, demonstrating that topology optimisation enables the development of lightweight, manufacturable patient-specific implants without compromising biomechanical integrity.

Multi-material laser powder bed fusion (MM-LPBF) presents a promising route for property customisation in precise additive manufacturing. However, its application to immiscible material systems, such as Cu-steel combinations, sought for their synergistic strength and thermal conductivity, is fundamentally challenged by the unreliable interfacial bonding. Here, an experimental study is presented with a mechanism-based discussion to elucidate the formability, molten-pool dynamics, and interfacial bonding mechanisms of an immiscible 18Ni300/CuSn10 structure fabricated via MM-LPBF, as a model material combination. The track morphology is governed by the line energy density (LED), evolving from discontinuous forms (<0.19 J/mm) to continuous tracks (>0.26 J/mm). Crucially, the top-surface morphology of the previously deposited 18Ni300 steel is found to critically influence the structure-building process. Under the present process window, surface depressions with depths greater than 37 μm in overlapping 18Ni300 tracks induce CuSn10 necking defects by reducing the actual energy input and geometrical restriction. The interfacial bonding mode is dictated by the energy input, and transitions through three distinct modes: Type I (flat geometrical interface) under low energy ( ≤ 0.22 J/mm) with sharp elemental transitions and penetration microcracks; Type II (gradual interlaced geometrical interface) at moderate energies (0.24–0.30 J/mm), characterised by partial 18Ni300 peninsulas; and Type III (deep-penetration mixing interface) under sufficient energy (≥0.32 J/mm), which generates a deep molten-pool (∼100 μm) and an alternating elemental distribution. Electron back-scatter diffraction analyses confirm random grain orientations and smaller grain-size differences at Type III interfaces during solidification. The micro-hardness distribution across the interface further reflects the bonding quality: Type III interfaces exhibit gradual transitions with fluctuations from elemental segregation, whereas Type I interfaces present abrupt changes. The Type III bi-metallic joint achieves a tensile strength of 471 MPa, indicating favourable interfacial bonding. Importantly, a framework is established linking the LED to a cascade of physical processes and final interface characteristics, revealing how energy input governs the molten-pool heterogeneity in immiscible steel/Cu systems fabricated via MM-LPBF. In conclusion, this work provides an understanding of the fundamental interface formability and heterogeneity in immiscible steel/Cu systems, which serve as a basis for the future development of multi-material structures in other immiscible material systems via LPBF.

Heterogeneous design offers a promising pathway to overcome the strength-ductility trade-off. However, current additively manufactured multi-material titanium systems critically lack compatible post-processing strategies and frequently suffer from severe interfacial strain localization, leading to premature fracture. To address this fundamental research gap, we engineered a novel dual-titanium architecture combining Ti64 (Ti-6Al-4V) and Ti55511 (Ti-5Al-5Mo-5V-1Cr-1Fe) via multi-material laser powder bed fusion (MM-LPBF), paired with a pioneering compatible solution-quench-age treatment. The heat-treated structure achieves an exceptional ultimate tensile strength of 1143.7 +/- 13.2 MPa and an elongation of 11.26 +/- 0.64% (increasing by 51.5% and 286.5% over monolithic Ti64 and Ti55511, respectively). This strength-ductility synergy originates from a similar to 200 mu m continuous interfacial transition band with coupled compositional and microstructural gradients, evolving smoothly from alpha-dominated basketweave Ti64 to beta-dominated bimodal Ti55511. During deformation, the architecture exhibits pronounced strain partitioning and sequential yielding. This hetero-deformation induced (HDI) strengthening is quantitatively supported by the dynamic evolution of long-range back stress, evidenced by the unloading-reloading hysteresis loop width expanding from 0.015% at 2% strain to 0.027% at 4% strain, alongside the continuous accumulation of geometrically necessary dislocations (GNDs). While the current investigation is limited to quasi-static room-temperature conditions, this work demonstrates that leveraging intrinsic strength contrasts via MM-LPBF and precise thermal control effectively breaks the strength-ductility trade-off, establishing a robust framework for developing high-performance multi-material titanium structures for advanced aerospace applications.

Significance With the rapid development of modern industry,demands for product functionality and performance are escalating.Single-material components often fall short of such stringent requirements as multi-functional integration and robust environmental adaptability.By harnessing the complementary superior properties of different materials,the integrated manufacturing of multi-material structural components provides a potent new impetus for industrial advancement.In this context,multi-material laser powder bed fusion(MM-LPBF)technology has garnered extensive attention in the field of multi-material additive manufacturing,owing to its exceptional forming precision and high design flexibility. However,MM-LPBF technology still confronts several critical challenges.Disparities in physical properties-such as melting point,coefficient of thermal expansion,and thermal conductivity-between dissimilar materials tend to induce interfacial defects at bonding regions,which significantly compromise the quality of components fabricated via MM-LPBF.Moreover,the design and evaluation of multi-material components remain still in a relatively rudimentary stage,with a lack of standardized metrics and systematic criteria.This issue severely dampens industrial initiatives for the development of multi-material parts.Additionally,powder cross-contamination,along with the recycling and separation of distinct powder materials post-printing,remains a pressing challenge that demands urgent resolution in the context of MM-LPBF technology.A viable strategy to mitigate these issues lies in the adoption of appropriate powder spreading techniques. This paper aims to explore and summarize the latest domestic and international research advances and challenges in powder spreading technology for MM-LPBF.It first provides a brief overview of single-material powder spreading technology,followed by an analysis of the specific challenges associated with multi-material powder spreading compared to its single-material counterpart.Subsequently,the focus shifts to recent progress and development trends in MM-LPBF powder spreading technology,along with auxiliary techniques designed to enhance powder spreading quality. Progress Compared to single-material powder spreading,MM-LPBF powder spreading poses several distinct challenges.It is widely acknowledged that powder cross-contamination can exert an adverse impact on product performance.In certain scenarios,even trace levels of cross-contamination can significantly compromise the mechanical properties,structural integrity,and functional performance of printed components.Notably,however,powder cross-contamination in MM-LPBF is often a systematically induced issue.From an economic perspective,the recycling,separation,and reuse of unmelted high-value powder are imperative.Despite the availability of numerous separation methods,identifying a suitable approach for every multi-material combination to achieve the required separation efficiency remains a formidable challenge.Therefore,to address the recycling dilemma at its root,it is essential to optimize powder spreading technology and eliminate cross-contamination at the source.Given the current technological maturity level,it remains difficult to simultaneously achieve high building efficiency,low system complexity,and superior powder spreading quality.Thus,decisions regarding equipment fabrication,technology selection,and process parameter optimization must be tailored to specific application requirements. To date,MM-LPBF powder spreading technology has achieved a certain level of overall maturity,with four promising technical development pathways:blade-based powder spreading,electrostatic powder spreading,gas aspirating-dispensing powder spreading,and ultrasonic vibration-assisted powder spreading.Blade-based powder spreading extends single-material spreading technology by integrating additional powder feed cylinders to enable multi-material configurations,and auxiliary devices are subsequently employed to remove unmelted powder,thereby achieving multi-material deposition within the same layer.Electrostatic powder spreading technology is derived from the electrophotography principle-an established and widely utilized technology in daily laser printing applications-which leverages electrostatic forces to adsorb powder particles for precise deposition,with Fig.10(a)illustrating a schematic of the electrophotographic printing process and Fig.10(b)presenting a schematic of the electrostatic powder spreading principle specifically for MM-LPBF systems.Gas aspirating-dispensing powder spreading technology,developed by Aerosint,is an aerodynamically driven approach that utilizes controlled tubular aspirator arrays to selectively attract and release powder particles,forming predefined single-material powder patterns,and multi-material spreading can be realized by increasing the number of powder feeding devices,with this technology already validated in industrial applications.Ultrasonic vibration-assisted powder spreading employs computer-controlled piezoelectric transducers to generate ultrasonic vibrations that disrupt the powder dome structures at the container orifice,after which the powder falls onto the build platform under gravity[the system schematic is depicted in Fig.13(a)],and this method enables high-precision powder control,while an array of multiple powder containers facilitates multi-material spreading within the same layer. In the LPBF process,the flow field is typically utilized to remove process by-products such as spatter.However,the scenario becomes more complex in MM-LPBF due to the Coanda effect:when inert gas enters the build chamber,the airflow tends to adhere to the powder bed surface,resulting in relatively high flow velocities.Excessive flow rates may exceed the powder entrainment threshold,compromising powder bed integrity,deteriorating print quality,or inducing powder cross-contamination.Under such circumstances,flow field simulation and structural design are required to mitigate this effect.Furthermore,to ensure the efficacy of non-contact spreading technologies(e.g.,ultrasonic vibration-assisted powder spreading),the flow field must be effectively coordinated with the spreading system.For instance,during powder spreading operations,the gas flow rate should be reduced or the fan should be shut down entirely.Although integrating a powder bed monitoring system increases system complexity and reduces build efficiency,in-situ monitoring is indispensable for enhancing the overall powder spreading quality in MM-LPBF.Current research on powder bed quality monitoring primarily focuses on four methods:1)Grayscale analysis or other image processing techniques applied to powder bed optical images captured by industrial cameras;2)Three-dimensional topography reconstruction of the powder bed using fringe projection technology;3)Monitoring via sensors integrated into the spreading device;4)Powder bed scanning utilizing contact image sensor(CIS)units. Conclusions and Prospects This paper reviews the research progress in powder spreading technologies for MM-LPBF,while analyzing auxiliary technologies and the specific challenges inherent to multi-material powder spreading compared with single-material counterparts.Although critical issues remain to be better addressed-including the trade-offs among powder spreading precision,system complexity,and build efficiency;powder cross-contamination and recycling challenges;and the advancement of auxiliary technologies(notably flow field simulation,structural design,and control,as well as powder bed monitoring and defect detection)—MM-LPBF powder spreading technology has generally attained a certain level of maturity.Four promising technical development pathways have emerged:blade-based powder spreading,electrostatic powder spreading,gas aspirating-dispensing powder spreading,and ultrasonic vibration-assisted powder spreading.Significant progress has been achieved in each of these directions,with commercial companies already launching related equipment.MM-LPBF technology enables the fabrication of highly complex components with multi-functional integration and robust environmental adaptability,offering distinct advantages in manufacturing efficiency and cost-effectiveness.In the foreseeable future,MM-LPBF is poised to achieve broader development and application in high-value industries such as aerospace,automotive manufacturing,consumer electronics,biomedicine,and jewelry.

Mandibular reconstruction is a major biomechanical challenge because it requires simultaneous restoration of anatomical form and structural stability under dynamic masticatory loading. While the structural degradation and poor conformity inherent to manually bent systems are overcome by patient-specific mandibular reconstruction plates (PSMRPs) fabricated via laser powder bed fusion (LPBF), clinical longevity remains constrained by manufacturing-induced defects and fatigue failure. In this critical review, the foundational engineering science governing LPBF-fabricated titanium alloy PSMRPs is examined, and an integrated paradigm spanning manufacturing science, computational biomechanics, structural optimization, and experimental validation is established. The process–structure–property relationships in LPBF are systematically evaluated, with specific detail given to how porosity morphology, residual stress, microstructural anisotropy, and surface integrity are dictated by volumetric energy density and complex thermal histories, ultimately governing fatigue crack initiation under cyclic loading. Moving from material to system-level mechanics, assembly failure modes are analyzed, while the biomechanical performance of locking versus non-locking fixation is compared. The role of finite element analysis alongside advanced structural optimization strategies is critically evaluated, and the mitigation of stress concentrations and stress shielding through size, shape, and topology optimization is demonstrated. Furthermore, state-of-the-art experimental validation methodologies are scrutinized, with emphasis placed on full-field strain characterization via digital image correlation and biomimetic cyclic fatigue testing. Finally, future translational frontiers are outlined, including artificial intelligence-driven generative design and mechanobiological simulations of long-term osseous remodeling. Collectively, the evidence suggests that the mastery of the interplay between additive manufacturing parameters and multi-scale biomechanics is paramount to the engineering of predictable, optimized cranio-maxillofacial patient-specific implants.

Micronozzle-controlled laser powder bed fusion (LPBF) enables innovative fabrication of multi-material structures, but also introduces a unique powder bed spreading mechanism and requires a technique for real-time in-situ monitoring of powder bed topography during process control. Existing thickness monitoring methods, such as those employing laser displacement sensors and high-resolution balances, are limited by lengthy measurement cycles and high instrumentation costs. This work develops a new pathway based on 4 K imaging and supervised machine learning for powder bed thickness prediction and 3D topography reconstruction, which can be flexibly integrated onto a multi-material LPBF system. The results highlight the high accuracy of the powder bed thickness prediction using the developed multi-feature support vector regression (SVR) fitting. The prediction error remains within approximately 3.31 & micro;m, with an average error of 1-2 & micro;m (maximum absolute percentage error is 9.2%). The reconstructed topography exhibits excellent agreement with the measurements obtained by the laser displacement sensor. In the reconstruction of defected powder beds, the SVR-predicted errors in defect location and width are less than 1 & micro;m. The defect depth errors are below 5 & micro;m, typically remaining around 1 & micro;m. Compared with traditional laser sensor approaches, the developed method is a rapid and cost-effective tool for inline characterisation of powder bed thickness, reducing data acquisition time to 2 s. Importantly, the pathway can be further integrated into various additive manufacturing systems, and benefits the development of highresolution closed-loop strategies for improving powder bed uniformity.

Multi-material additive manufacturing enables the integration of dissimilar materials within a single component, yet achieving a compositionally gradient interface within individual layers remains challenging. This study presents a novel approach using a self-developed ultrasonic nozzle system for programmable, high-precision powder deposition. Using an interdigitated interface design with a layer-wise offset arrangement between 316L stainless steel and IN718 superalloy, we demonstrate that the alternating powder layout, together with intense melt-pool stirring during laser powder bed fusion, promotes thorough material intermixing and creates similar to 1 mm wide compositionally gradient interface. The interface exhibits continuous transitions in grain growth, elemental distribution, and microhardness, confirming the formation of a continuous gradient between materials. Notably, the width of the gradient interface is tailorable through deposition control. This work demonstrates the feasibility of fabricating compositionally gradient interfaces via designed layer-wise powder deposition, providing a controllable approach for manufacturing functionally gradient components.

Laser powder bed fusion (LPBF) has garnered considerable attention for its capacity to fabricate near-net-shaped complex components, particularly in lightweight high-strength Al alloys. The rapid solidification conditions inherent to LPBF can theoretically engineer unique microstructure to surpass mechanical property limits. However, the practical performance of many high-strength age-hardenable Al alloys (such as 2XXX, 6XXX and 7XXX series) processed by LPBF remains non-competitive owing to their high susceptibility to cracking. Herein, we demonstrate a design strategy to synergistically regulate solidification and precipitation behaviors through a minor addition of LaB6 particles (1.0 wt%), enabling the fabrication of crack-free high-strength Al-Cu alloys. We show that LaB6 addition promotes significant grain refinement during solidification and facilitates the formation of dense multiscale precipitates during subsequent aging. This microstructural modification simultaneously improves LPBF processability and enhances alloy strength. We further reveal that the introduced LaB6 particles dissolve within the melt pool and reprecipitate during cooling. The reprecipitated LaB6 particles act as effective heterogeneous nucleation sites for alpha-Al, while residual La solutes suppress the growth of theta-Al2Cu phase under non-equilibrium solidification. Additionally, LaB6 promotes the precipitation of a high density of submicron T-Al20Cu2Mn3 dispersoids and nanoscale theta '-Al2Cu precipitates during solid-state phase transformation. These synergistic effects of crack elimination, grain refinement and nanoscale precipitation result in mechanical properties with a yield strength of 271 +/- 1.8 MPa, an ultimate tensile strength of 341 +/- 6.1 MPa and an elongation of 6.5 +/- 0.8%. The dual roles of LaB6 provide a new strategy for designing multifunctional regulators fabricated by LPBF.

Horizontal gradient interfaces within each building layer are required for spatial multi-material structures by laser powder bed fusion (LPBF), but remain underdeveloped due to limitations in equipment capabilities, process design, and conceptual frameworks. We demonstrate a micronozzle-controlled powder bed layout strategy, inspired by Continuously Variable Transmission (CVT) mechanics, to fabricate heterogeneous gradient interfaces by docking thickness gradients of two dissimilar powder layers. This approach, for the first time worldwide, enables flexible composition adjustment without powder pre-mixing between the model materials 316L and IN718, even within each similar to 100 mu m-thick powder layer, while allowing programmable vertical spatial arrangement of the two materials within the layer. Stacking in-layer gradient powder beds in three different sequences produces CVT-type interface architectures, termed CVT_IN/SS, CVT_SS/IN and CVT_IN/SS/SS/IN. The NO-pre-mixing gradient strategy reduces material cross-contamination and allows for selectable melt/solidification dynamics happened between the powder bed and the laser beam. The strong interdependence among thermal field, solidification kinetics, and material docking sequence achieves the highest cooling rate of 1.9 & times; 10(6) K/s across the CVT_SS/IN interface, in which each sloping 316L powder layer is deposited above a corresponding IN718 powder layer slope, leading to refined and smooth material transitions and grain-size gradients compared to CVT_IN/SS and CVT_IN/SS/SS/IN interface. Such that, the CVT_SS/IN-type powder layouts allow dynamic control of interfacial composition and, in turn, enhance interfacial structural integrity and mechanical continuity, as evidenced by a reduced mean absolute error in interface mechanical continuity down to 0.036 +/- 0.02 GPa. Importantly, the CVT-inspired powder deposition strategy establishes a scalable pathway for site-specific material tailoring and functional gradient design, achievable even within each precise layer of multi-material LPBF.

This study employs an innovative gas–liquid in-situ reaction approach combined with laser powder bed fusion (LPBF) technology to fabricate pure titanium matrix functionally graded composite materials (FGMs) under a progressively decreasing nitrogen (N2) atmosphere. Consequently, the TiN reinforcement was successfully synthesized within a pure Ti matrix, leading to the fabrication of TiN-reinforced titanium matrix FGMs with well-defined gradient features and minimal defects. Furthermore, the continuous decrease in N2 concentration along the LPBF construction direction leads to a corresponding reduction in both the volume fraction and particle width of in-situ formed TiN reinforcement. As a result, a continuously graded microstructure evolves, characterized by the progressive refinement of the α′-Ti phase and prior β grain from the top to the bottom of the fabricated FGMs. This graded microstructure, in turn, gives rise to smooth gradients in microhardness and wear resistance, which stem from the synergistic effects of nitrogen solid solution strengthening, the variation in content and size of TiN reinforcement, and the refinement strengthening of the matrix grain.

In this study, we investigate the evolution of deformation microstructures in a NiCoCr0.5V0.5 alloy with varying grain sizes, specifically fully-recrystallized ultrafine-grained (UFG) and the coarse-grained (CG) samples, at temperatures of 298 K and 77 K, respectively. Microstructural analyses conducted using transmission electron microscopy (TEM) revealed that, during the initial stage of plastic deformation, dislocations glide via 1/2<110> dislocations dissociated into 1/6<112> Shockley partials on {111} planes, analogous to the typical low stacking-fault-energy (SFE) alloys. The measured partial separations yielded an SFE of 31 +/- 5 mJ/m(2), comparable to that of the CrMnFeCoNi (Cantor alloy). As strain increases, SF (298 K) and twinning (77 K) emerge as additional deformation mechanisms in the UFG alloy. In contrast, the CG alloy deforms through a combination of dislocation glide, SF, and twinning at 298 K, and dislocation glide, SF, twinning, and shear banding at 77 K. Additionally, the dislocation patterns exhibit a strong dependence on grain size, with dislocation tangles observed in the UFG and planar slip bands in the CG alloy. The identification of these characteristic deformation microstructures is advantageous for achieving enhanced mechanical properties in alloys, which holds significant scientific and technological implications.

Achieving robust bonding between dissimilar materials is crucial for both vertical and horizontal interfaces in multi-material structures fabricated via layer-by-layer laser powder bed fusion (LPBF). However, horizontal bonding has been less explored than vertical bimetallic interfaces, largely because of the limitations in the available equipment, process strategies, and research concepts. In this study, we propose a practical horizontal dissimilar laser offset strategy, wherein the laser spot is displaced outwards from the interface profile by a certain distance, to improve horizontal bonding in CuSn10/IN718 structures. A laser offset of 75 mu m enhanced metallurgical bonding and reduced microcracks, resulting in a smoother surface. The laser offset area displayed interlocking macro-segregation peninsulas composed of CuSn10 or IN718. The diffusion behaviour between these segregated peninsulas, located at the boundary of the molten pool, was found to be more intense than that at the centre, driven by a steeper temperature gradient at the molten pool boundary (22.61 x106 K.m-1 at the boundary vs 18.03 x106 K.m-1 at the centre, representing a 25.4 % increase). Such material heterogeneity shows microstructural differences, characterised by fine columns, reticulations, and discrete pellets. Consequently, hardness and elastic modulus exhibited a smooth transition across the CuSn10/IN718 interface, which was enabled by the homogeneous material distribution obtained using the laser offset technique. The laser offset strategy provides a convenient laser scanning approach for LPBF and other laser-based multi-material AM processes. This study conducted a detailed analysis of segregation and interlocking at the interface, which may be beneficial for studying other material combinations.

Multi-material laser powder bed fusion (LPBF) innovates design opportunities by integrating multiple materials into predetermined 3D shapes. However, for satisfying the diverse performance/functional layouts, understanding the fundamental role of material building sequences in interfacial bonding is still insufficient. This work prepared multi-material structures of immiscible CuSn10-18Ni300 with an interlayer IN718 vertically, using two reversed building sequences by LPBF, to compare their interfacial segregation and microstructure, resulting mechanical properties, and behind mechanisms. Sequence I printed CuSn10 onto 18Ni300 via IN718; Sequence II printed 18Ni300 onto CuSn10 via IN718. Both sequences produce three shapes of interfacial macrosegregation (shape of beaches, peninsulas, and islands), but following different thermodynamic mechanisms. The microstructure highlights the traces related to those macrosegregation shapes, verifying the mechanism, and interestingly, the cracks are even healed by upper CuSn10 under Sequences I, benefiting interfacial bonding. Besides, a transition of cellular-columnar grains from 18Ni300 to IN718 is observed under both sequences, while less visible molten pool boundaries are seen in CuSn10. Those IN718 columns are either (001) oriented along the building direction under Sequence I, or randomly oriented under Sequence II with reduced temperature gradients. Finally, microhardness evolution and tensile behaviours successfully evaluate the structural reliability under two building sequences. A favourable ductile fracture within the CuSn10 region is produced with strength of 395 +/- 29 MPa and elongation of 16.6 +/- 2.6 % under Sequence I, benefiting from the healed cracks and enhanced interfacial bonding. Conversely, Sequence II causes a brittle fracture within the interlayer with lower tensile properties, due to the remaining cracks and microstrain. Such high microstrain even impacts the detection of clear Kikuchi bands. These results could enrich theoretical bases for selecting building sequences and matched structural designs for manufacturing multi-materials by LPBF.

While laser powder bed fusion (LPBF) has emerged as a transformative approach for fabricating geometrically intricate metal matrix-diamond composites, the interfacial integrity of these components is critically undermined by residual stress originating from rapid thermal cycling and severe thermal expansion mismatch between diamond reinforcements and metallic binders. Existing mitigation strategies-including process parameter optimization, ductile phase incorporation, and graded CTE transition layers-fail to eliminate interfacial microcracks due to inherent limitations in thermal strain compensation. Herein, we propose a phasetransformation-driven stress-relief strategy by engineering a W/Co bilayer coating on diamond particles within a CuSn10 matrix. The tungsten interlayer ensures interfacial integrity through carbide bonding and thermal buffering, while the cobalt overlayer exploits HCP -> FCC phase transformation during LPBF thermal cycling to generate compensatory volumetric expansion, effectively counteracting thermal contraction-induced residual stress. The W-Co coated diamond/CuSn10 composite achieved a bending strength of 159 MPa (90 % higher than Ti-Cu coated counterparts) and a friction coefficient of 0.25, with complete suppression of interfacial cracking under cyclic wear. Multiscale characterization revealed that Co-induced twinning and dynamic recrystallization synergistically enhanced interfacial toughness, while molecular dynamics simulations quantitatively validated the stress-neutralization mechanism through lattice mismatch analysis. This work establishes a transformative "expansion-compensation" paradigm for residual stress regulation in MMCs, advancing the design of crack-resistant diamond composites for high-stress additive manufacturing applications.