Search Results (22)

Powder bed fusion using a laser beam (PBF-LB) offers a suitable alternative to manufacturing Ti65 with intricate geometries and internal structures in hypersonic aerospace applications. However, issues such as undesirable surface roughness, defect formation, and microstructural inhomogeneity remain critical barriers to its wide application. In this study, a coupled discrete element method–computational fluid dynamics (DEM-CFD) model was utilized to investigate the spreading behavior of Ti65 powder in a multi-layer PBF-LB process. The macro- and microscopic characteristics of the powder beds were systematically analyzed across different layers and regions under various spreading velocities. The results show that the packing density and uniformity of the powder beds in multi-layer PBF-LB of Ti65 powder improves as the number of solidified layers increases. Poor bed quality is observed in the first two layers due to a strong boundary effect, while a stable and denser powder bed emerges from the fourth layer. The presence of a previously solidified region strongly influences its neighboring unsolidified areas, enhancing density in the upstream region and causing looser packing downstream. Additionally, due to the existence of a solidified region, the height of the powder bed progressively decreases along the spreading direction. Full article

The trend of adapting powder bed fusion (PBF) for product manufacturing continues to grow as this process is highly capable of producing functional 3D components with micro-scale precision. The powder bed’s properties (e.g., powder packing, material properties, flowability, etc.) and thermal energy deposition heavily influence the build quality in the PBF process. The packing density in the powder bed dictates the bulk powder behavior and in-process performance and, therefore, significantly impacts the mechanical and physical properties of the printed components. Numerical modeling of the powder bed process helps to understand the powder spreading process and predict experimental outcomes. A two-dimensional powder bed was developed in this work using the LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) package to better understand the effect of bimodal and unimodal particle size distribution on powder bed packing. A cloud-based pouring of powders with varying volume fractions and different initialization velocities was adopted, where a blade-type recoater was used to spread the powders. The packing fraction was investigated for both bimodal and unimodal systems. The simulation results showed that the average packing fraction for bimodal and unimodal systems was 76.53% and 71.56%, respectively. A particle-size distribution-based spatially varying powder agglomeration was observed in the simulated powder bed. Powder segregation was also studied in this work, and it appeared less likely in the unimodal system compared to the bimodal system with a higher percentage of bigger particles. Full article

The powder spreading process is a fundamental element within the laser powder bed fusion (PBF-LP) framework given its pivotal role in configuring the powder bed. This configuration significantly influences subsequent processing steps and ultimately determines the quality of the final manufactured part. This research paper presents a comprehensive analysis of the impacts of varying spreading speeds, which are enabled by different roller configurations, on powder distribution in PBF-LP. By utilizing extensive Discrete Element Method (DEM) modelling, we systematically examine how spreading speed affects vital parameters within the spreading process, including packing density, mass fraction, and actual layer thickness. Our exploration of various roller configurations has revealed that increasing spreading speed generally decreases packing density and layer thickness for non-rotating, counter-rotating, and forward-rotating rollers with low clockwise rotational speeds (sub-rolling) due to powder dragging. However, a forward-rotating roller with a high clockwise rotational speed (super-rolling) balances momentum transfer, enhancing packing density and layer thickness while increasing surface roughness. This configuration significantly improves the uniformity and density of the powder bed, providing a technique to accelerate the spreading process while maintaining and not reducing packing density. Furthermore, this configuration offers crucial insights into optimizing additive manufacturing processes by considering the complex relationships between spreading speed, roller configuration, and powder spreading quality. Full article

Powder deposition of even and homogeneous layers is a major aspect of every powder bed fusion process. Powder sieving is commonly performed to powder batches outside of the PBF machine, prior to the part manufacturing stage. In this work, sieving is examined as a method of powder deposition rather than a method to solely filter out agglomerates and oversized particles. Initially, a DEM powder model that has been validated experimentally is implemented, and the sieving process is modelled. The sieving process is optimized in order to maximize mass flow, duration of its linear stage and total mass sieved during linearity. For this, a Taguchi design of experiments with subsequent analysis of variance is deployed, proving that the larger the initial powder loaded in the sieve, the larger the sieve stimulation necessary, both in terms of oscillating frequency and amplitude. The sieve’s aperture shape is also evaluated, proving that the more sides the canonical polygon has, the less the mass flow per aperture for the same maximum passing particle size. Then, the quality of the layer produced via controlled sieving is examined via certain layer quality criteria, such as the surface roughness, layer thickness deviation, surface coverage ratio and packing density. The findings prove that controlled sieving can outperform powder deposition via a non-vibrated doctor blade recoater, both in terms of layer surface quality and duration of layer deposition, as proven by surface skewness and kurtosis evaluation. Full article

Developing thermal storage materials is crucial for the efficient recovery of thermal energy. Salt-based phase-change materials have been widely studied. Despite their high thermal storage density and low cost, they still face issues such as low thermal conductivity and easy leaks. Therefore, a new type of NaCl-Al₂O₃@SiC@Al₂O₃ macrocapsule was developed to address these drawbacks, and it exhibited excellent rapid heat storage and release capabilities and was extremely stable, significantly reducing the risk of leakage at high temperatures for industrial waste heat recovery and in concentrated solar power systems above 800 °C. Thermal storage macrocapsules consisted of a double-layer encapsulation of silicon carbide and alumina and a self-standing core of NaCl-Al₂O_3. After enduring over 1000 h at a high temperature of 850 °C, the encapsulated phase-change material exhibited an extremely low weight loss rate of less than 5% compared with NaCl@Al₂O₃ and NaCl-Al₂O₃@Al₂O₃ macrocapsules, for which the weight loss rate was reduced by 25% and 10%, respectively, proving their excellent leakage prevention. The SiC powder layer, serving as an intermediate coating, further prevented leakage, while the use of Al₂O₃ ceramics for encapsulation enhanced the overall mechanical strength. It was innovatively discovered that the Al₂O₃ particles formed a network structure around the molten NaCl, playing an important role in maintaining the shape and preventing leakage of the composite thermal storage phase-change material. Furthermore, the addition of Al₂O₃ significantly enhanced the rapid heat storage and release rate of NaCl-Al₂O₃ compared to pure NaCl. This encapsulated phase-change material demonstrated outstanding durability and rapid heat storage and release performance, offering an innovative approach to the application of salt phase-change materials in the field of high temperature rapid heat storage and release and encapsulating NaCl as a high-temperature thermal storage material in a packed bed system. Compared with conventional salt-based phase-change materials, the developed product is expected to significantly improve the reliability and thermal efficiency of thermal storage systems. Full article

The powder bed packing density of metal powders plays a crucial role in additive manufacturing as it directly affects the defect and mechanical properties of the fabricated parts. Powder bed packing density is related to powder flowability and spreadability. In this study, we introduced a new method to improve powder flowability and spreadability, where Haynes 230 powder with exceptional flowability was successfully produced using an in situ micro-oxidation gas atomization process. Compared to conventional gas atomization, the powder exhibited improved flowability and spreadability, measuring at 11.8 s/50 g. Additionally, the angle of repose was reduced by 25%, resulting in a powder bed packing density of 5.67 g/cm³, corresponding to 63.7% of the theoretical density. Notably, the oxygen content in the powder was only 180 ppm, as confirmed by XRD testing, and no oxide peaks were detected. Furthermore, the depth of the oxide layer on the particle surface increased by less than 20 nm. As a result, the in situ micro-oxidation process reduces the number of pores and cracks in the Haynes 230 alloy formed specimens and improves the relative density of the built specimens. This study highlights the potential of in situ micro-oxidation gas atomization as a promising method for producing powders with high flowability and spreadability for laser powder bed fusion (LPBF) processes. Full article

The powder bed fusion–laser beam (PBF-LB) process, a method of additive manufacturing (AM), was used to print duplex stainless steel (DSS) using commercial-grade 2507 powders. While conventionally processed DSS has a two-phase microstructure consisting of 50% austenite and 50% ferrite, the PBF-LB-printed 2507 alloy was nearly 100% ferrite. Optimal processing conditions that minimized porosity were determined to be 290 W laser power and 1000 mm/s scan speed, and grain size, texture, and phases were characterized as a function of laser power and scan speed. Grain size increased with increasing laser power but decreased with increasing scan speed. A <100> texture diminished with increasing scan speed from 1000 mm/s to 1400 mm/s. No austenite phase was detected. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) characterization revealed nanoscale chromium nitride precipitates in the ferritic matrix (incoherent hexagonal close-packed (HCP) precipitates at grain boundaries and coherent body-centered cubic (BCC) precipitates within the grains) and a high density of tangled dislocations. Tensile tests of as-printed alloys showed a yield strength of 570 MPa, an ultimate tensile strength of 756 MPa, and an elongation to failure of 10%. The tensile properties were analyzed based on the observed microstructure considering grain size, nanoscale precipitates, and the high density of dislocations. Full article

This work investigated the effect of Fe/Mn ratio on the microstructure and mechanical properties of non-equimolar Fe_80−xMn_xCo₁₀Cr₁₀ (x = 30% and 50%) high-entropy alloys (HEAs) fabricated by laser powder bed fusion (LPBF) additive manufacturing. Process optimization was conducted to achieve fully dense Fe₃₀Mn₅₀Co₁₀Cr₁₀ and Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEAs using a volumetric energy density of 105.82 J·mm⁻³. The LPBF-printed Fe₃₀Mn₅₀Co₁₀Cr₁₀ HEA exhibited a single face-centered cubic (FCC) phase, while the Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA featured a hexagonal close-packed (HCP) phase within the FCC matrix. Notably, the fraction of HCP phase in the Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEAs increased from 0.94 to 28.10%, with the deformation strain ranging from 0 to 20%. The single-phase Fe₃₀Mn₅₀Co₁₀Cr₁₀ HEA demonstrated a remarkable combination of high yield strength (580.65 MPa) and elongation (32.5%), which surpassed those achieved in the FeMnCoCr HEA system. Comparatively, the dual-phase Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA exhibited inferior yield strength (487.60 MPa) and elongation (22.3%). However, it displayed superior ultimate tensile strength (744.90 MPa) compared to that in the Fe₃₀Mn₅₀Co₁₀Cr₁₀ HEA (687.70 MPa). The presence of FCC/HCP interfaces obtained in the Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA resulted in stress concentration and crack expansion, thereby leading to reduced ductility but enhanced resistance against grain slip deformation. Consequently, these interfaces facilitated an earlier attainment of yield limit point and contributed to increased ultimate tensile strength in the Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA. These findings provide valuable insights into the microstructure evolution and mechanical behavior of LPBF-printed metastable FeMnCoCr HEAs. Full article

Diamond/SiC (Dia/SiC) composites possess excellent properties, such as high thermal conductivity and low thermal expansion coefficient. In addition, they are suitable as electronic packaging materials. This study mainly optimized the diamond particle size packing and liquid-phase silicon infiltration processes and investigated a method to prevent the adhesion of the product to molten silicon. Based on the Dinger–Funk particle stacking theory, a multiscale diamond ratio optimization model was established, and the volume ratio of diamond particles with sizes of D20, D50, and D90 was optimized as 1:3:6. The method of pressureless silicon infiltration and the formulas of the composites were investigated. The influences of bedding powder on phase composition and microstructure were studied using X-ray diffraction and scanning electron microscopy, and the optimal parameters were obtained. The porosity of the preform was controlled by regulating the feeding amount through constant volume molding. Dia/SiC-8 exhibited the highest density of 2.73 g/cm³ and the lowest porosity of 0.6%. To avoid adhesion between the sample and buried powder with the bedding silicon powder, a mixed powder of α-Si₃N₄ and silicon was used as the buried powder and the related mechanisms of action were discussed. Full article

Powder-bed-based additive manufacturing processes (PBAM) are sensitive to variations in powder feedstock characteristics, and yet the link between the powder properties and process performance is still not well established, which complicates the powder selection, quality control, and process improvement processes. An accurate assessment of the powder characteristics and behavior during recoating is important and must include the flow and packing properties of the powders, which are dependent on the application conditions. To fulfill the need for suitable powder testing techniques, a novel apparatus is developed to reproduce the generic PBAM powder spreading procedure and allow the measurements of the powder bed density, surface uniformity, and spreading forces as functions of the powder characteristics and spreading conditions, including the spreading speed and the type of spreading mechanism. This equipment could be used for research and development purposes as well as for the quality control of the PBAM powder feedstock, as showcased in this paper using a gas-atomized Ti-6Al-4V powder (D10 = 25.3 µm, D50 = 35.8 µm and D90 = 46.4 µm) spread using a rigid blade by varying the recoating speed from 100 to 500 mm/s and the layer thickness from 30 to 100 µm. Full article

Powder bed fusion (PBF), a subset of additive manufacturing methods, is well known for its promise in the production of fully functional artefacts with high densities. The quality of the powder bed, commonly referred to as powder spreading, is a crucial determinant of the final quality of the produced artefact in the PBF process. Therefore, it is critical that we examine the factors that impact the powder spreading, notably the powder bed quality. This study utilised a newly developed testing apparatus, designed specifically for examining the quality of powder beds. The objective was to analyse the influence of various factors, including the recoater shape, recoater gap size, and the different powder flow properties, on the powder bed relative packing fraction. Additionally, the study aimed to assess the variation in the particle size and shape across the build plate. The results indicated that all of the variables examined had an impact on the relative packing fraction, as well as the size and shape variations observed across the build plate. Full article

Laser powder bed fusion (LPBF) additive manufacturing (AM) has been adopted by various industries as a novel manufacturing technology. Powder spreading is a crucial part of the LPBF AM process that defines the quality of the fabricated objects. In this study, the impacts of various input parameters on the spread of powder density and particle distribution during the powder spreading process are investigated using the DEM (discrete element method) simulation tool. The DEM simulations extend over several powder layers and are used to analyze the powder particle packing density variation in different layers and at different points along the longitudinal spreading direction. Additionally, this research covers experimental measurements of the density of the powder packing and the powder particle size distribution on the construction plate. Full article

Titanium-tantalum (Ti-Ta) alloy has excellent biomechanical properties with high strength and low Young’s modulus, showing great application potential in the biomedical industry. In this study, Ti-Ta alloy samples were prepared by laser powder bed fusion (LPBF) technology with mixed pure 75 wt.% Ti and 25 wt.% Ta powders as the feedstock. The maximum relative density of Ti-Ta samples prepared by LPBF reached 99.9%. It is well-accepted that four nonequilibrium phases, namely, α′, α″ and metastable β phase exist in Ti-Ta alloys. The structure of α′, α″ and β are hexagonal close-packed (HCP), base-centered orthorhombic (BCO) and body-centered cubic (BCC), respectively. X-ray Diffraction (XRD) analysis showed that the α′ phase transformed to the α″ phase with the increase of energy density. The lamellar α′/α″ phases and the α″ twins were generated in the prior β phase. The microstructure and mechanical properties of the Ti-Ta alloy were optimized with different LPBF processing parameters. The samples prepared by LPBF energy density of 381 J/mm³ had a favorable ultimate strength (UTS) of 1076 ± 2 MPa and yield strength of 795 ± 16 MPa. The samples prepared by LPBF energy density of 76 had excellent ductility, with an elongation of 31% at fracture. Full article

Laser powder bed fusion (LPBF) is an additive manufacturing technology that implies using metal powder as a raw material. The powders suitable for this kind of technology must respect some specific characteristics. Controlled gas atomization and post-processing operations can strongly affect the final properties of the powders, and, as a consequence, the characteristics of the bulk components. In fact, a complete characterization of the powders is mandatory to fully determine their properties. Beyond the most used tests, such as the volume particle size distribution (PSD) and flowability, the PSD number, the Hausner ratio and the oxidation level can give additional information otherwise not detectable. The present work concerns the complete characterization of two AlSi10Mg powders: a commercial-grade gas atomized powder and a laboratory-scale gas atomized counterpart. The laboratory-scale gas atomization allows to better manage the amount of the fine particles and the oxidation level. As a consequence, a higher particle packing can be reached with an increase in the final density and tensile strength of the LPBF bulk samples. Full article

Understanding the impact of powder reuse in powder-bed-fusion electron beams (PBF-EB) is key to maintain the processability and yield. Powder oxidation, due to exposure to high temperatures for a prolonged period of time, can lead to a decrease in electrical conductivity of the powder and, hence, electrostatic forces that originate during interaction with the electron beam. The effect of oxidation on physical properties as powder rheological properties, apparent/tap density and charging are studied in this work. The analysis using Scanning Electron Microscopy (SEM) shows thermodynamically stable Al-rich oxide particulates (sized 100–200 nm) covering the surface of the reused powder particles, with an increase of 20% in bulk oxygen in comparison to the virgin powder and, measured by X-ray Photoelectron Spectroscopy (XPS), average oxide thickness of circa 13 nm in the reused powder. On the one hand, reusing the powder positively impacted the flowability studied using the Revolution Powder Analyzer (RPA), in which the avalanche angle was decreased from 37 deg to 30 deg, for virgin and reused powder, respectively. The volume fraction of loose powder was similar for both virgin and reused powder, 57% and 56%, respectively, while the packed volume fraction was measured lower in the reused (57%) than the virgin powder (60%). On the other hand, the charging behavior, studied using the ION Charge Module of the powder, worsened; this almost doubled in the reuse powder (−9.18 V/g) compared to the virgin powder (−5.84 V/g). The observation of ejected particles from the build volume is attributed to the charging behavior and lower packing volume fraction in the reused powder. Full article