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Diamond-like carbon (DLC) films on titanium alloy Ti6Al4V substrates were tested with nanoindentation and surface roughness to look at the hardness and roughness of the coating and substrate systems as well as their mechanical properties. The powdered titanium alloy Ti6Al4V used in the substrate specimen was produced using laser powder bed fusion, an additive manufacturing process. In this study, we investigated the influence of substrates on the nanoindentation and surface roughness of the DLC film layer with an estimated 2. 2 1 μ m thickness on Ti6Al4V substrates. The findings of the nanoindentation show that the reaction to the impact was more flexible than expected. Maximum load, residual nanoindentation depth, hardness, and modulus may influence mechanical properties. The DLC-film Ti6Al4V substrate materials' top surface roughness is measured. As a result of the increased load-carrying ability of DLC/Ti6Al4V, Ti6Al4V is a superior choice for substrate materials for DLC films, A DLC coating, measuring 2. 2 1 μ m in thickness, was applied to a Ti6Al4V substrate utilizing a 5-min chromium deposition process. The biocompatibility of the substrates plays a crucial role in determining the DLC films capacity to prolong the lifespan of bone implants. [ABSTRACT FROM AUTHOR]

Attaining high relative density (RD) is of paramount importance for any new alloy system manufactured through the laser powder bed fusion (L-PBF) process. However, the conventional design of experiment (DOE) methods poses a significant challenge due to the large number of process parameters involved. This study explores the data-driven machine-learning (ML) approach to confine the search for the optimized process parameters to the most significant process parameters. The relevant datasets were obtained from existing literature spanning across the last decade on 11 different alloy systems. The collected datasets were divided into 80:20 for training and testing. In this work, a detailed framework is presented to identify the most appropriate ML model to represent the complexities and nonlinearities in the data accurately. Among the employed models, the gradient boosting–particle swarm optimization (GB-PSO) exhibited the highest predictive performance, with mean absolute error (MAE) and coefficient of determination (R2) values of 0.20 and 0.99 for training and 0.73 and 0.95 for testing, respectively. The Shapley additive explanations (SHAP) analysis was utilized to comprehend the global and local significance of material properties and machine process parameters. The reduced experimental design from the data-driven ML framework is used to validate the predictions from the trained hybrid GB-PSO model. Validation for achieving the highest RD is carried out on the Inconel 718 alloy system deposited in-house. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) combined with liquid silicon infiltration (LSI) holds promise for fabricating intricate SiSiC components. However, its suitability for producing SiC components without free silicon, crucial for acidic or alkaline resistance, remains uncertain. In this study, SiC components were fabricated through successive processes of LPBF, polycarbosilane impregnation (PI), carbonization, LSI, and acid etching using granulated and nongranulated SiC powders. Their properties were compared systematically. The results showed that PI treatment significantly improved the performance of samples made from non-granulated SiC; the bulk density and compressive strength after pyrolysis increased by 33 % and 325 %, respectively, and the bending strength after LSI increased by 26.2 %. These samples also exhibited a higher strength retention after acid etching. In contrast, PI treatment did not benefit the granulated SiC samples. Further analysis suggested that these differences stem from the distinct particle shapes and surface microstructures of granulated and nongranulated SiC, highlighting the need for process optimisation tailored to different SiC raw materials. [ABSTRACT FROM AUTHOR]

Scan strategy plays a key role in the densification of laser powder bed fusion (LPBF) processed materials. Still, it garnered less attention from researchers worldwide doing parameter optimization who focus more on quantitative parameters like laser power and scan speed. The repeatability of the LPBF process is also not studied widely, despite being a vital factor in furthering its industrial application. Keeping these gaps in mind, this study investigates the effects of various scan strategies on the densification behavior during LPBF processing of AlSi10Mg. Multiple cubic samples are manufactured using different scan strategies and their relative density analyzed. For each scan strategy, the values of laser power, scan speed and scan spacing were changed as well to provide a comprehensive picture. It was observed that the relative density of the samples increased as more lateral motion was added to the laser path, increasing the lateral overlapping of the tracks. The optical microscopic studies were conducted as well on the polished samples to understand the pore characteristics and microstructural effects of scan strategy variation, which showed that increased lateral motion not only reduced the porosity but altered pore geometry and other characteristics as well. Finally, using the optimized process parameters and scan strategy, multiple samples are manufactured and relative density was calculated to check the repeatability of the process. It was seen that the LPBF process is a highly non-repeatable process as the mean density observed was 99.5126% with mean absolute deviation of 0.1946% and standard deviation of 0.2376%. [ABSTRACT FROM AUTHOR]

In metal-based additive manufacturing processes, such as laser powder bed fusion (LPBF), the powder utilization is often less than 50%. Considering the cost efficiency, powder reuse is needed for an economical and sustainable LPBF process. As intermetallic compounds, LPBF-fabricated NiTi alloys are characterized with phase transformation behaviors, mechanical properties and functions that are very sensitive to possible changes in powder characteristics caused through reuse, but the exact effects are still poorly understood. Here, the LPBF process has been repeated ten times using the virgin powder supplement method. Results show that the oxygen content of NiTi powders rises from 370 to 752.3 ppm with the enhancement of the reuse cycle number. Powder oxidation enhances the laser absorptivity of the powder bed, leading to an increase in surface roughness and porosity of NiTi parts. Compared to the specimens made from virgin powders, the mechanical property and shape memory function of specimens made from reused powders are degraded, mainly attributed to the oxygen impurity and deteriorated forming quality. This study allows making better decisions with regard to powder reuse in the development of performance-critical NiTi parts fabricated through LPBF. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF), an additive manufacturing technology, is extensively applied in various fields. In the building process, one or more laser beams scan and melt the powder previously deposited on the build platform, following a prescribed scanning path to achieve the designed three-dimensional geometry. After the current powder layer is selectively melted and solidified, another layer of powder is spread, and the laser scanning continues. Such repetitive operations exhibit inherent rapid heating and cooling characteristics, resulting in uneven microstructures and the accumulation of internal stresses for the produced parts. For the most widely used Ti–6Al–4V, this LPBF characteristic forms fine needle-like α′ martensite and small amounts of beta phase. There is a phase potential difference between the α′ and the β phases, which constitutes a corrosive galvanic battery, and the corrosion reaction preferentially occurs at the phase interface of the α′ and the β phases. However, as a metastable structure, the thermodynamic stability of the α′ phase is lower than that of the β phase, which makes the α′ phase preferentially corroded. Moreover, the V element enrichment in the β phase imparts stability, exerting a significant inhibitory effect on the corrosion and dissolution of the Ti–6Al–4V alloy. This is evident in the denser and more stable passive film formed on the β phase compared with that on the α′ or α phase, accompanied by a corresponding increase in corrosion resistance. To better meet different service conditions, it is imperative to regulate its microstructure and alleviate residual stresses through heat treatment as a heat-treatable α + β type titanium alloy. However, the optimal heat treatment conditions for LPBF Ti–6Al–4V are being determined. We aim to provide a comprehensive overview of the current literature, focusing on the perspective that the properties of a material are inherently influenced by its microstructure. Specifically, the correlation between microstructure and corrosion resistance in LPBF-produced Ti–6Al–4V before and after heat treatment is explored. The influence of post-heat treatment on the microstructure and corrosion behavior of LPBF-produced Ti–6Al–4V is also discussed. Results reveal that appropriate heat treatment can facilitate the decomposition of fine needle-like α′ martensite and the formation of β phases, enhancing the corrosion resistance of LPBF-produced Ti–6Al–4V. However, excessive heat treatment will increase the grain size of the LPBF Ti–6Al–4V and deteriorate the corrosion resistance. Finally, conclusions are drawn, which is expected to bring some support to researchers.

Crack-free Al–Zn–Mg–Cu alloy, processed by laser powder bed fusion, displays a characteristic microstructure comprising fine equiaxed grains (EGs) and coarse columnar grains (CGs). Notably, the CGs show a high hardness compared to EGs due to the high density of in-situ precipitates. Analysis of mechanical properties takes into account the precipitates in the grain and hierarchical differences in grain morphologies near the melt pool boundary. Strengthening mechanisms are elucidated through synergistic hetero-deformation-induced strengthening, where multi-modal-sized EGs induce significant strain gradients within EG regions. Our findings demonstrate the potential to enhance strength of Al–Zn–Mg–Cu-based alloy in as-built state through architecting microstructures.

The multi-material components formed by laser powder bed fusion (LPBF) have shown potential in advanced equipment due to their superior performance. The uneven distribution of immiscible in the molten pool is a challenge for the performance of multi-material components. In this study, a thermo-fluidic particle scale numerical model coupled with a ray-tracing method is established to understand the formation of the immiscible CuCrZr/316L multi-material. The impact of process parameters on the distribution of CuCrZr and 316L is investigated. Results reveal that the experimental and simulation results agree well with a maximum molten pool width and depth difference of 7%. The recoil pressure and Marangoni convection contribute to the mixing of 316L and CuCrZr. As the scanning speed decreases or the scanning power increases, a longer molten pool lifetime is obtained, which increases the immiscible CuCrZr/316L mixing. A large number of CuCrZr islands are formed inside the molten pool at high energy density with improved homogeneity. This work can provide fundamental insights into understanding the distribution of immiscible metal material in the multi-materials LPBF process.

Characterization of defects in large 3D printed metals is critical but challenging. This study reports on the X-ray micro-computed tomography (micro-CT) examination of porosities in large-volume 3D-printed and heat-treated titanium (Ti–6Al–4V) alloys, together with their tensile properties and failure mechanisms. Titanium alloy powders were analyzed using scanning electron microscopy (SEM). Laser powder bed fusion (L-PBF) was used to print titanium alloy specimens vertically and horizontally, followed by stress-relieved heat treatment. Micro-CT imaging was performed on printed specimens of 10 × 20 mm3 (diameter × length) to determine their porosities, pore locations and size distributions using an industrial micro-CT system and relevant imaging software. Tensile testing of the processed specimens was conducted to determine their mechanical properties. Optical microscopy and SEM were used to examine the tension-induced failure mechanisms. The results show that porosities, pore sizes and locations were influenced by the build direction, resulting in different mechanical properties. Horizontal printing achieved higher tensile modulus, strength, ductility, resilience and toughness than vertical printing. Heat treatment did not change porosities in horizontally built specimens, but slightly reduced porosities for vertically built ones by 10%. This led to most mechanical properties nearly unchanged for the horizontally printed specimens but remarkably increased yield and tensile strength, and resilience, for the vertically printed ones. All tension-induced fractured surfaces contained pores, possible indicators of failure origins, which should be diminished in advanced processes for higher mechanical reliability.

Laser powder bed fusion (LPBF) Invar 36 alloy has attracted plenty of attention in cryogenic components or precision instruments due to its low coefficient of thermal expansion in a wide range of temperature. However, the LPBF Invar 36 has a significant anisotropic mechanical property due to the unique columnar grain morphology and pore feature. In this study, the influence of scanning speed on the anisotropic tensile properties were investigated, and the melt pool dynamics were analyzed by the numerical simulation. In this respect, tensile tests of specimens parallel and perpendicular to the building direction with a scanning speed from 200 to 1400 mm/s of LPBF Invar 36 alloy were conducted, and the microstructural influential factors on the anisotropic tensile properties were analyzed. Results show that as the volumetric energy density (VED) increases, the inhomogeneity of grain morphology decreases, while the pore feature changes from the lack-of-fusion (LOF) pore perpendicular to the building direction to the bubble-shaped spherical pore, which is resulted from the collapse of the key-holes. In this case, the grain orientation and size, as well as the dislocation density in the vicinity of pores are influenced by the pore morphology due to different thermal history. On the whole, the combined morphology of dislocation and stress concentration affected by the pore morphology are the main reason of the increased level of anisotropy in tensile properties.

β-type Ti–Nb alloys are promising materials for load-bearing implant applications with improved mechanical biofunctionality and biocompatibility. In this work, the electrochemical and tribo-electrochemical behaviour of laser powder bed fusion (LPBF) produced β-type Ti–42Nb alloy processed via Gaussian and top hat laser was investigated and compared with commercial grade β-type Ti–45Nb and α+β-type Ti–6Al–4V ELI. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization experiments were performed in phosphate-buffered saline (PBS) for corrosion behaviour. Tribocorrosion behaviour was studied under open circuit potential (OCP) conditions in PBS by using a reciprocating pin-on-disk tribometer. The passivation nature of the LPBF alloys is more decisive than the microstructural particularities for electrochemical behaviour. The overall corrosion response is similar due to the protective nature of the passive films formed on Ti alloys. Ti–6Al–4V ELI exhibits the best corrosion performance among all tested alloys with lower corrosion and passivation current density values. However, LPBF-produced alloys exhibit less reactive surfaces with better passive film properties compared to Ti–45Nb. In addition, EIS results revealed that passive film resistance values are higher for LPBF-produced alloys than conventionally produced Ti–45Nb. LPBF-produced alloys exhibit better tribo-electrochemical behaviour compared to Ti–45Nb. The differences in volume loss are mainly attributed to the microhardness of the alloys and the volume loss is dominated by mechanical wear. The alloys produced with LPBF show promising corrosion and tribocorrosion performance to be a potential candidate for load-bearing implant applications.

Adiabatic shearing represents a prevalent mode of deformation failure in metals when subjected to impact loading. In this work, dynamic shearing interruption tests considering various shear displacements (i.e., shear strains) were conducted on of the CoCrFeNi high-entropy alloy (HEA) produced by laser powder bed fusion (LPBF) to analyze the microstructural evolution during adiabatic shearing. From the results, it was observed that the columnar grains in the shear region only distorted to different degrees at the lower levels of shear strain. Then, it was also found that the increase in shear strain caused severe distortion and refinement of the columnar grains, ultimately leading to adiabatic shearing band (ASB) at a critical shear strain threshold. During inhomogeneous deformation at high strain rate, the ASB formation was predicated on enough plastic deformation work. The interconnection between microstructural softening mechanisms and macroscopic mechanical behavior during ASB evolution and fracture was also highlighted. The nano-sized equiaxed recrystallized grains within the ASB were formed by rotational dynamic recrystallization (RDRX) rather than migratory recrystallization. Moreover, a large number of nano-twins were formed in these nano-sized recrystallized grains to motivate the mechanism of slip within nano-twins, thus accommodating the continuous plastic deformation. These results are the main reasons for the outstanding resistance to shear deformation of CoCrFeNi HEA produced by LPBF.

The fabrication of high quality copper alloys using laser powder bed fusion (LPBF) technology remains challenging due to their low laser absorption and high thermal conductivity. LPBF often involves intrinsic defects, such as rough surface and internal pores, which largely deteriorate the performance of as-built copper alloy components. Here we studied the effect of scanning speed on the evolution of surface morphologies and internal pores of LPBF-fabricated CuSn10 alloy. The melt flow behaviors were studied by both experiments and in situ observations where combined a high-speed camera with an infrared thermal imager. With increasing the scanning speed, the morphology of melt track evolves from a continuous track to a discontinuous one, whereas the internal defects change from a great number of spherical pores to many irregular pores. A higher scanning speed decreases the peak temperature of the melt pool and causes less overlaps between neighboring melt tracks, thus deteriorating wetting behaviors. It is expected that the obtained results are beneficial for guiding the additive manufacturing of copper alloy parts with high metallurgical quality and thus promoting their industrial applications.

Porous β-Ti composites hold large promise for lightweight components due to their exceptional strength-ductility synergy. However, their microstructural behavior under both impact and compressive conditions have received limited attention. This study investigates the compressive and impact behavior of porous β-type Ti–25Nb (at.%) composites fabricated using laser powder bed fusion (LPBF). The composites feature a rhombic dodecahedron (RD) lattice structure and incorporate a central solid cylinder with varying diameters. Microstructural characterizations and finite element simulations were employed to analyze mechanical properties and stress distribution. Incorporation of 3 mm radius cylinders (TIII ∼45% porosity) significantly enhances compressive yield stress (88 ± 10 MPa), impact yield stress (153 ± 10 MPa), and impact energy absorption (41.2 J/cm³) while maintaining material plasticity. Compressive and impact loading initiate a martensitic transformation from β to α″ phase, strengthening the alloy through refined α″ formation with a finer grain size than β phase. Notably, a β→ α″ transformation and grain refinement occur in the node region that connects the solid cylinder and lattices, which undergoes significant deformation during impact. This observation suggests the impact resistance of porous β-Ti composites can be enhanced through tailored microstructures and strategic structural design.

Laser powder bed fusion (LPBF) Al–Li alloy technology demonstrates adaptability to the development requirements of structural complexity and functional integration, making it a promising area of research in additive manufacturing for the aerospace, defense industry, and other fields. However, challenges such as microstructure anisotropy and metallurgical defects inevitably arise during the LPBF process of lightweight alloys, significantly impeding further enhancements in their formability properties. Some improvement measures offer a viable solution to enhance the microstructure, mitigate metallurgical defects, and optimize residual stress distribution in additive structures, thereby enabling high–performance Al–Li alloy production by LPBF. This paper first introduces the fundamental principle of LPBF and discusses the process of parameter optimization for LPBF Al–Li alloys. It then describes the typical microstructures and common metallurgical defects of LPBF Al–Li alloys, along with examining the evolution process of microstructures and formation mechanism of metallurgical defects. Specifically, it focuses on discussing the influence of Li element on solidification structure. On this basis, it presents the mechanical properties and anisotropy of mechanical properties for LPBF Al–Li alloys. Afterward, a comprehensive review is provided of the current research status regarding LPBF improvement measures, including powder alloying, heat treatment, and other technologies. Emphasis is placed on improvements in microstructure anisotropy and reductions in metallurgical defects through these improvement measures. Finally, this article summarizes the research progress made in LPBF Al–Li alloys and its improvement measures while also prospecting future research work.

Abstract Laser powder bed fusion (LPBF) is an additive manufacturing technology with high practical value. In order to improve the quality of the fabricated parts, process monitoring has become a crucial solution, offering the potential to ensure manufacturing stability and repeatability. However, a cardinal challenge involves discerning a precise correlation between process characteristics and potential defects. This paper elucidates the integration of an off-axis vision monitoring mechanism via a high-speed camera focused on capturing the single-track melting phenomenon. An innovative image processing method was devised to segment the plume and spatters, while Kalman filter was employed for multi-object tracking of the spatters. The features of both the plume and spatters were extracted, and their relationship with molten states was investigated. Finally, the PSO-XGBoost algorithm was utilized to identify five molten states, achieving an accuracy of 92.16%. The novelty of this approach resides in its unique combination of plume characteristics, spatter features, and computationally efficient machine learning models, which collectively address the challenge of limited field of view prevalent in real production scenarios, thereby enhancing process monitoring efficacy. Relative to existing methodologies, the proposed PSO-XGBoost approach offers heightened accuracy, convenience, and appropriateness for the monitoring of the LPBF process. This work provides an effective and novel approach to monitor the LPBF process and evaluate the part fabrication quality for complex and changeable working conditions.

This study investigates the effect of changing the chemical composition during ultrasonic atomization (UA) and laser powder bed fusion (LPBF) of low‐alloy steel. UA is used to produce a spherical powder with d50 equal to 49 μm. During UA, the chemical composition of the material changes, which is associated with selective evaporation of Mn from 1.42% to 0.35% and B from 0.0012% to <0.0001%. Thermodynamic calculations confirm that during atomization, mostly Mn and Fe evaporate. To achieve a high density of 3D printed parts, in situ remelting in LPBF is applied. A microstructure consisting of fine grains of tempered martensite and bainite in crystallized meltpools is observed. The selected high‐quality LPBF samples are austenitized in the temperature range of 900–1200 °C for 20 min and quenched in oil. The samples are characterized by light and scanning electron microscopy, as well as Vickers hardness. Changes in chemical composition result in a decrease in the hardenability of the material, and quenching only at 1200 °C produces a martensitic microstructure. LPBF samples show a hardness higher than that of the postheat‐treated sample, but still significantly lower than that of the as‐delivery condition, which is related to the change in chemical composition. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) fuses metallic powder using a high-energy laser beam, forming parts layer by layer. This technique offers flexibility and design freedom in metal additive manufacturing (MAM). However, achieving the desired surface quality remains challenging and impacts functionality and reliability. L-PBF process parameters significantly influence surface roughness. Identifying the most critical factors among numerous parameters is essential for improving quality. This study examines the effects of key process parameters on the surface roughness of AlSi10Mg, a widely used aluminum alloy in high-tech industries, fabricated by L-PBF. Part orientation, laser power, scanning speed, and layer thickness were identified as crucial parameters via cause-and-effect analysis. To systematically examine their effects, the Taguchi method was employed within the framework of the design of experiment (DoE). Experimental results and statistical analysis revealed that laser power, scanning speed, and layer thickness significantly influence surface roughness parameters: arithmetic mean (Ra) and root mean square (Rq). Main effect plots and energy density analyses confirmed their impact on surface quality. Microscopic investigations identified surface flaws such as spattering, balling, and porosity contributing to poor quality. Given the complex interplay between parameters and surface quality, accurately predicting their effects is challenging. To address this, machine learning models, specifically random forest regression (RFR) and support vector regression (SVR), were used to predict the effects on surface roughness. The RFR model's R2 values for predicting Ra and Rq are 97% and 85%, while the SVR model's predictions are 85% and 66%, respectively. Evaluation metrics demonstrated that the RFR model outperformed SVR in predicting surface roughness. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is a metal additive manufacturing (AM) process where a part is created layer-by-layer through the melting and solidification of powder layers. The main challenge in LPBF is quality assurance. An estimation of powder rheology/flowability, as a quality-impacting factor, is therefore necessary prior to printing. To predict powder flowability based on morphological features without cost- and time-inefficient experiments, this study explores using machine learning algorithms (ML). It focuses on a sample set of standard and off-size Ti6Al4V (Ti64) powders, aiming to (1) assess ML regressors and equation fitting for flowability prediction, using the small original dataset and (2) overcome data limitations' impact on regression through data augmentation techniques. Results showed conventional ML regressors like support vector regression (SVR) sufficed for dynamic flowability prediction. Still, more complex targets such as shear flowability and hall flowability required innovative approaches like genetic programming (equation fitting) and synthetic minority over-sampling (SMOTE), respectively, as proposed in this work. [ABSTRACT FROM AUTHOR]

Tungsten and its alloys have a high atomic number, high melting temperature, and high thermal conductivity, which make them fairly appropriate for use in nuclear applications in an extremely harsh radioactive environment. In recent years, there has been growing research interest in using additive manufacturing techniques to produce tungsten components with complex structures. However, the critical bottleneck for tungsten engineering manufacturing is the high melting temperature and high ductile-to-brittle transition temperature. In this study, laser powder bed fusion has been studied to produce bulk pure tungsten. And finite element analysis was used to simulate the temperature and stress field during laser irradiation. The as-printed surface as well as transverse sections were observed by optical microscopy and scanning electron microscopy to quantitatively study processing defects. The simulated temperature field suggests small-sized powder is beneficial for homogenous melting and provides guidelines for the selection of laser energy density. The experimental results show that ultra-dense tungsten bulk has been successfully obtained within a volumetric energy density of 200–391 J/mm3. The obtained relative density can be as high as 99.98%. By quantitative analysis of the pores and surface cracks, the relationships of cracks and pores with laser volumetric energy density have been phenomenologically established. The results are beneficial for controlling defects and surface quality in future engineering applications of tungsten components by additive manufacturing. [ABSTRACT FROM AUTHOR]

Additive manufacturing has been playing a significant role in the manufacturing of components with complex geometries for aerospace applications recently. Comprehensive nondestructive testing techniques (NDT) are vital for the successful quality evaluation of critical components in this domain. Appropriate selection of the NDT scheme is essential for the qualification of such components. Major NDT techniques are designed based on the interaction of electromagnetic radiation and the response of the sound or heat energy transmission or reflection from the test object. The common defects noticed in the components made through additive manufacturing (AM) routes are pores, clusters of porosities, micro-cracks, lack of fusion and layer delamination. Considering the morphology and the complications in the geometry of aerospace components, many conventional NDT techniques are unsuitable for the inspection of AM components. Detection of unfused powder in the AM components by conventional radiography is difficult due to the low radiation attenuation coefficient gradient between the unfused and fused metallic regions. Also, the detection of defects in the radiography technique depends entirely on the beam path. Multiple radiography images with different beam angles and film combinations are essential to get the maximum information on the defects by conventional radiography techniques. In this aspect, computed tomography, a noncontact NDT technique provides a better solution for determining embedded defects such as lack of fusion and layer separation due to presence of unfused powder in the AM components. The present study compares the capability of computed tomography and 2D digital radiography for the identification of lack of fusion defects in stainless steel SS316L specimens fabricated through the Laser powder bed fusion AM route. [ABSTRACT FROM AUTHOR]

Shape Memory Alloys (SMA) are materials used to design smart structures with intrinsic functional properties and improved efficiency. This is a key aspect of aerospace industry and makes SMA good candidates in this field. One of the most widespread SMA is the equiatomic NiTi alloy which, however, has the strong limitation of poor machinability, so only simple shapes can be obtained. Additive Manufacturing processes allow to overcome this limit and to design complex shapes. Compared to other metallic materials, the optimization of the process for NiTi alloy is complicated because, beside mechanical properties and presence of defects, considerable attention needs to be dedicated to the material functionality. The high temperatures involved in the additive process significantly affect the material properties due to possible evaporation of Ni and formation of precipitates that enable a shift of the phase transformation temperatures. This paper is focused on the optimization of the process parameters of the NiTi alloy printed through the Laser Powder Bed Fusion (L-PBF) to ensure optimal pseudo-elastic behaviour, which is essential for the design of structural dampers. This was accomplished starting from simple structures and then designing a damper that couples the pseudoelasticity of NiTi with load support capacity. The L-PBF is a powder-bed technique that selectively melts layers of micrometric metal powder. A pseudoelastic NiTi powder with 50.8 at. % of Ni content was selected and characterized through scanning electron microscope (SEM) and observations connected to an Energy Dispersive X-ray Spectroscopy (EDX) probe. After that, some cubic samples were manufactured, with the dimension of 3 × 3 × 15 mm3. A set of different laser powers and scanning speeds were used to find the set of process parameters that optimize the functional properties of the printed parts. Near fully dense specimens with density higher than 99.5 % were selected for further investigations. Differential scanning calorimetry (DSC) and mechanical tests were performed on as-built and heat-treated samples. Quasi-static mechanical tests were accomplished in compression mode, at different strains, up to 8 %. It was observed that the residual strain for cyclic loading at 4 % is lower than 1 %, so good recovery of the deformation was shown. Moreover, numerical analyses that mimic the pseudoelastic behaviour in compression tests were implemented. Finally, the best set of parameters was selected on the basis of the material's ability to recover deformations and its loss factor. • Optimization of process parameters for functional behaviour of SMA. • Design of damping structure using pseudoelastic effect of Nitinol. • Internal defects observation of manufactured specimens. • Compression tests on as built and thermal treated specimens with strain up to 8 %. • Numerical simulation of compression tests with experimental correlation. [ABSTRACT FROM AUTHOR]

The Inconel 718 superalloy demonstrates the potential to fabricate high-temperature components using additive manufacturing. However, additively manufactured Inconel 718 typically exhibits low strength, necessitating post-heat treatments for precipitate strengthening. This study investigated the microstructures and mechanical properties of the Inconel 718 superalloy fabricated via laser powder bed fusion. The room-temperature and high-temperature tensile properties of the Inconel 718 alloy samples following various post-heat treatments were evaluated. The results indicate that the as-built samples exhibited columnar grains with fine cell structures. Solution treatment resulted in δ phase formation and grain recrystallization. Subsequent double aging led to finely distributed nanoscale γ′ and γ″ particles. These nanoscale particles provided high strength at both room and high temperatures, resulting in a balanced strength and ductility comparable to the wrought counterpart. High-temperature nanoindentation analyses revealed that the double-aging samples exhibited very high hardness and low creep rates at 650 °C. [ABSTRACT FROM AUTHOR]

An integral part of laser powder bed fusion (LPBF) quality control is identifying optimal process parameters tailored to each application, often achieved through time-consuming and costly experiments. Melt pool dynamics further complicate LPBF quality control due to their influence on product quality. Using machine learning and melt pool monitoring data collected with photodiode sensors, the goal of this research was to efficiently customize LPBF process parameters. A novel aspect of this study is the application of standard and off-size powder feedstocks. Ti6Al4V (Ti64) powder was used in three size ranges of 15–53 µm, 15–106 µm, and 45–106 µm to print the samples. This facilitated the development of a process parameters tailoring system capable of handling variations in powder size ranges. Ultimately, per each part, the associated set of light intensity statistical signatures along with the powder size range and the parts' density, surface roughness, and hardness were used as inputs for three regressors of Feed-Forward Neural Network (FFN), Random Forest (RF), and Extreme Gradient Boosting (XGBoost). The laser power, laser velocity, hatch distance, and energy density of the parts were predicted by the regressors. According to the results obtained on unseen samples, RF demonstrated the best performance in the prediction of process parameters. [ABSTRACT FROM AUTHOR]

Crack-free Al–Zn–Mg–Cu alloy, processed by laser powder bed fusion, displays a characteristic microstructure comprising fine equiaxed grains (EGs) and coarse columnar grains (CGs). Notably, the CGs show a high hardness compared to EGs due to the high density of in-situ precipitates. Analysis of mechanical properties takes into account the precipitates in the grain and hierarchical differences in grain morphologies near the melt pool boundary. Strengthening mechanisms are elucidated through synergistic hetero-deformation-induced strengthening, where multi-modal-sized EGs induce significant strain gradients within EG regions. Our findings demonstrate the potential to enhance strength of Al–Zn–Mg–Cu-based alloy in as-built state through architecting microstructures. The Al–Zn–Mg–Cu alloy, fabricated by laser powder bed fusion, exhibiting hierarchical microstructure consisting of hard coarse and soft fine grains shows synergistic in-situ precipitation and hetero-deformation-induced strengthening. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion allows the production of complex geometries and eases the shaping of difficult-to-transform materials, such as near-equiatomic Ti-Ni shape memory alloys. In this study, a numerical model was used to select 11 sets of printing parameters with different volumetric energy densities (VEDs) and build rates (BRs) to produce bulk Ti-50.26at%Ni alloy specimens. The manufactured specimens were studied in terms of their structural integrity, printed density, chemical composition, transformation temperatures, and crystalline phases. At high VEDs and low BRs, a significant decrease in the nickel content was observed. VED = 90 J/mm3 and BR = 10 cm3/h yielded a printed density of 99.94% and an austenite finish temperature of Af = 26.3 °C. The same printing conditions were used to produce 60% porous diamond and gyroid lattice structures. After heat treatment at 500 °C for 30 min, the diamond lattices manifested larger apparent recovery strains (7 vs. 6%), higher compliance (2.9 vs. 3.4 GPa), and similar yield stresses (~48 MPa) compared to their gyroid equivalents. The numerical model predicted that at an equivalent apparent compression strain of 6%, only a ~2% volume fraction of the diamond lattice material underwent plastic deformation as compared to ~20% for its gyroid equivalent. [ABSTRACT FROM AUTHOR]

The additive manufacturing technology powder bed fusion of metal with a laser beam (PBF-LB/M) is industrially established for tool-free production of complex and individualized components and products. While the in-processing is based on a layer-by-layer build-up of material, both upstream and downstream process steps (pre-processing and post-processing) are necessary for demand-oriented production. However, there are increasing concerns in the industry about the efficient and economical implementation and validation of the PBF-LB/M. Individual products for mass personalization pose a particular challenge, as they are subject to sophisticated risk management, especially in highly regulated sectors such as medical technology. Additive manufacturing using PBF-LB/M is a suitable technology but a complex one to master in this environment. A structured system for holistic decision-making concerning technical and economic feasibility, as well as quality and risk-oriented process management, is currently not available. In the context of this research, a framework is proposed that demonstrates the essential steps for the systematic implementation and validation of PBF-LB/M in two structured phases. The intention is to make process-related key performance indicators such as part accuracy, surface finish, mechanical properties, and production efficiency controllable and ensure reliable product manufacturing. The framework is then visualized and evaluated using a practice-oriented case study environment. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is a promising metal additive manufacturing technology for producing functional components. However, there are still a lot of obstacles to overcome before this technology is considered mature and trustworthy for wider industrial applications. One of the biggest obstacles is the difficulty in ensuring the repeatability of process and the reproducibility of products. To tackle this challenge, a prerequisite is to represent and communicate the data from the part realisation process in an unambiguous and rigorous manner. In this paper, a semantically enriched LPBF part data model is developed using a category theory-based modelling approach. Firstly, a set of objects and morphisms are created to construct categories for design, process planning, part build, post-processing, and qualification. Twenty functors are then established to communicate these categories. Finally, an application of the developed model is illustrated via the realisation of an LPBF truncheon. [ABSTRACT FROM AUTHOR]

Defect detection is an essential way to ensure the quality of parts made by laser powder bed fusion (LPBF) and industrial cameras are one of the commonly used tools for defect monitoring. Different lighting environments affect the visibility of defects in the images, and the illumination condition becomes one of the most important factors affecting the defect detection effect of industrial cameras, but the modification of the equipment lighting environment will increase the complexity and cost of monitoring. In this study, only an off-axis CMOS camera monitoring system is used and the lighting facilities are not changed to improve the effect of defect detection under uneven lighting conditions. A dual-input convolutional neural network fusing defect parameter vectors and layerwise images is proposed for real-time online monitoring of defects in the LPBF process using a paraxial CMOS camera monitoring system. The model integrates the image and the parameter information related to defect generation, and can distinguish some defects that are not easily discerned by images alone. To a certain extent, it avoids the problem that the same defects are visually indistinguishable in images caused by uneven light distribution and reflections on metal surfaces. The results indicate that the method has better performance than the method with a single image input, with recognition accuracies above 80.00% for all defect categories. In addition, the method is more suitable for real-time online monitoring scenarios due to its low parameter number, short training time and fast prediction speed compared to classical deep learning algorithms. [ABSTRACT FROM AUTHOR]

At present, no consensus has been reached on the generation mechanism of anisotropy in materials fabricated by laser powder bed fusion (LPBF), and most attention has been focused on crystallographic texture. In this paper, an analysis and test were carried out on the hardness, defect distribution, residual stress distribution, and microstructure of WE43 magnesium alloy fabricated by LPBF. The results indicate that LPBF WE43 exhibits obvious anisotropy—the hardness HV of X–Z surface (129.9 HV on average) and that of Y–Z surface (130.7 HV on average) are about 33.5% higher than that of X–Y surface (97.6 HV on average), and the endurable load is smaller in the stacking direction Z compared to the X and Y directions. The factors contributing more to the anisotropy are listed as follows in sequence. Firstly, the defect area of the X–Y projection surface is about 13.2% larger than that of the other two surfaces, so this surface shows greatly reduced mechanical properties due to the exponential relationship between the material strength and the number of defects. Secondly, for laser scanning in each layer/time, the residual stress accumulation in the Z direction is higher than that in the X and Y directions, which may directly reduce the mechanical properties of the material. Finally, more fine grains are distributed in X–Z and Y–Z surfaces when comparing them with those in an X–Y surface, and this fine-grain strengthening mechanism also contributes to the anisotropy. After T5 aging heat treatment (250 °C/16 h), a stronger crystallographic texture is formed in the <0001> direction, with the orientation density index increasing from 10.92 to 21.38, and the anisotropy disappearing. This is mainly caused by the enhancement effect of the texture in the <0001> direction on the mechanical properties in the Z direction cancelling out the weakening effect of the defects in the X–Y surface in the Z direction. [ABSTRACT FROM AUTHOR]

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Additive Manufacturing (AM) appears as a very interesting alternative to conventional production routes for alloys and metals, thanks to the fact that at the end of printing, the final product is obtained directly. The present article looks for the inclusion of duplex stainless steel 2205 (DSS-2205) in the commercial catalog of steels utilized in powder bed fusion (PBF) technologies, specifically applying the selective laser melting (SLM) technique. The main objective is to establish optimal printing parameters that reproduce the closest results to the base material properties. To achieve this, the response surface method was used in the methodology and experimental design, studying the parameters of laser power, scanning speed, and hatching distance. A reference material, machined from a hot-rolled plate, was utilized to compare the results obtained through tensile strength. Lastly, the optimal parameters have been obtained for this stainless steel. Additionally, a study of heat treatments has been developed, aiming to optimize the austenitization process, achieving an improvement in mechanical properties. A steel with mechanical properties practically identical to those of steel produced using conventional techniques has been obtained through SLM. [ABSTRACT FROM AUTHOR]

Concerning the high demand for lightweight and multifunctional properties of engineering structures, the coral skeleton-inspired sheet-based (CSS) structure, which was a novel bio-mimicking coral skeleton wall-septa architecture with a unique ability to resist wave shocks was fabricated using NiTi alloy by laser powder bed fusion (LPBF) technology. The effects of laser energy density (LED) on surface morphologies, microstructures, phase transformation behavior, and mechanical properties of LPBF-fabricated CSS structures were systematically investigated. The results indicated that the size deviation was predominantly governed by powder adhesion and step effect. NiTi CSS structures with LED of 71 J·mm−3 possessed superior compressive modulus (∼100 MPa), ultimate strength (∼13 MPa), and energy absorption efficiency (∼69%). The compression fracture mechanism of the LPBF-fabricated NiTi CSS structures was revealed to be predominantly brittle fracture accompanied by ductile fracture. Furthermore, the Ni4Ti3 nanoprecipitates induced the precipitation strengthening effect, enabling better shape memory response at LED of 71 J·mm−3, with a recoverable strain of 3.63% and recovery ratio of 90.8%, after heating under a pre-strain of 4%. This study highlights the importance of a bionic design strategy for enhancing the mechanical properties of NiTi components and offers the possibility to tailor its functional properties. [ABSTRACT FROM AUTHOR]

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Determining appropriate process parameters in large-scale laser powder bed fusion (LPBF) additive manufacturing pose formidable challenges that necessitate advanced approaches to minimize trial-and-error during experimentation. This work proposed a data-driven approach based on stacking ensemble learning to predict the mechanical properties of Ti6Al4V alloy fabricated by large-scale LPBF for the first time. This method can adapt to the complexity of large-scale LPBF data distribution and exhibits a more generalized predictive capability compared to base models. Specifically, the stacking model utilized artificial neural network (ANN), gradient boosting regressor, kernel ridge regression, and elastic net as base models, with the Lasso model serving as the meta-model. Bayesian optimization and cross-validation were utilized for model optimization and training based on a limited data set, resulting in higher predictive accuracy compared to traditional artificial neural network model. The statistical analysis of the ANN and stacking models indicates that the stacking model exhibits superior performance on the test set, with a coefficient of determination value of 0.944, mean absolute percentage error of 2.51%, and root mean squared error of 27.64, surpassing that of the ANN model. All statistical metrics demonstrate superiority over those obtained from the ANN model. These results confirm that by integrating the base models, the stacking model exhibits superior predictive stability compared to individual base models alone, thereby providing a reliable assessment approach for predicting the mechanical properties of metal parts fabricated by the LPBF process. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF), one of the additive manufacturing methods, has gained an important place in several fields like aviation, space biomedical, etc., due to its advantages, such as producing complex shaped parts with high quality in shorter times. On the contrary, disadvantages such as high surface roughness, low dimensional accuracy, problems in reproducibility, and residual stress may induce difficulties during the production of the part or usage of the final product. To reduce the residual stress on the parts manufactured by the L-PBF technique, methods such as optimizing geometry-related variations and printing process parameters or applying post-processes can be implemented. This study applied different process parameters and geometry-related variations to investigate the residual stress for aluminum 7050-RAM2 (2% ceramic added) alloy prepared by L-PBF. Laser power, scanning speed, re-melting (double scan) as the process parameters and dimensional variations of the sample (surface area), and different print orientations (0°, 45°) as the geometry-related variations were examined. Minor differences in the process parameters and geometry-related variations affected the residual stress significantly. Especially up-skin scan parameters, build orientation, and size of the top surface area may entirely change the residual stress characteristics. [ABSTRACT FROM AUTHOR]

In this study, multi-scale and multi-physics field simulation methods were used to optimize the forming process parameters for FGH96-R alloy manufactured by laser powder bed fusion. The effects of laser power, scanning speed and hatch spacing on the printing quality and grain orientation of blade repair were investigated. When the laser line energy density is lower than 0.117 J/mm or the hatch spacing is greater than 65 μm, there were defects of pores and lack of fusion and this leads to significant stray crystal formation and discontinuous growth of interlayer grains. While the laser line energy density is higher than 0.154 J/mm or the laser line energy density is constant, increasing the laser power and scanning speed, the orientation between the epitaxially grown grains and the substrate is different, and the overall residual stresses in the FGH96-R alloy gradually increase. The process parameters for the formation of crack-free, well-oriented columnar crystal FGH96-R superalloys were obtained by simulation optimization: laser power of 175 W, scanning speed of 1300 mm/s and hatch spacing of 50 µm. The research results have laid the foundation for accurate modeling of additive manufacturing process, temperature field and stress field simulation to guide the optimization of the aero-engine blade repair process. [ABSTRACT FROM AUTHOR]

Large temperature gradient will produce high residual stress during laser powder bed fusion (LPBF). In metal matrix composites (MMCs), the thermal-induced stress distributes complexly. It is indispensable to study the interfacial stress of MMCs during LPBF process. In this study, a multi-phase finite element model was established to reveal the temperature and stress distributions of TiB2/Al-Si composites fabricated by LPBF. Influences of particulate geometries on the residual stress were also analyzed in the model. The numerical results indicate that the residual stress in the composites was induced by high temperature gradient and coefficient of thermal expansion mismatch simultaneously. TiB2 reinforcing particles suffer large compressive stress perpendicular to the interface. In the matrix, the stress component at the interface is negative and increases rapidly with distance from the particle increases. The interfacial compressive stress lessens the mean tension stress in the nearby regions of the matrix. Maximum von Mises stress is generated at the interface in the matrix, which may cause defects and cracks. High interfacial stress was generated in the vicinity of the vertex of cubic particles and the internal stress large in ellipsoidal particles, indicating that particles with fewer edges and smaller slenderness ratio possess greater thermal shock resistance. [ABSTRACT FROM AUTHOR]

This study investigates the influence of heat treatments on the corrosion behaviour of CuSn10 tin bronze, additively manufactured using Laser Powder Bed Fusion (LPBF). LPBF enables the creation of finely structured, anisotropic microstructures, whose corrosion behaviour is not yet well understood. After production, specimens were heat-treated at 320 °C, 650 °C, and in a two-stage treatment at 800 °C and 400 °C, followed by hardness and microstructure analysis. Corrosion tests were conducted using linear polarisation, salt spray, and immersion tests. The results show that heat treatments at 320 °C and 650 °C have no significant effect on the corrosion rate, while the two-stage treatment shows a slight improvement in corrosion resistance. Differences in microstructure and hardness were observed, with higher treatment temperatures leading to grain growth and tin precipitates. The formation of a passive protective layer was detected after 30 h of OCP measurement. Results from other studies on corrosion behaviour were partially reproducible. Differences could be attributed to varying chemical compositions and manufacturing parameters. These findings contribute to the understanding of the effects of heat treatments on the corrosion resistance of additively manufactured tin bronze and provide important insights for future applications in corrosive environments. [ABSTRACT FROM AUTHOR]

Laser powder bed-fused Ti6Al4V alloy has numerous applications in biomedical and aerospace industries due to its high strength-to-weight ratio. The brittle α′-martensite laths confer both the highest yield and ultimate tensile strengths; however, they result in low elongation. Several post-process heat treatments must be considered to improve both the ductility behavior and the work-hardening of as-built Ti6Al4V alloy, especially for aerospace applications. The present paper aims to evaluate the work-hardening behavior and the ductility of laser powder bed-fused Ti6Al4V alloy heat-treated below (704 and 740 °C) and above (1050 °C) the β-transus temperature. Microstructural analysis was carried out using an optical microscope, while the work-hardening investigations were based on the fundamentals of mechanical metallurgy. The work-hardening rate of annealed Ti6Al4V samples is higher than that observed in the solution-heat-treated alloy. The recrystallized microstructure indeed shows higher work-hardening capacity and lower dynamic recovery. The Considère criterion demonstrates that all analyzed samples reached necking instability conditions, and uniform elongations (>7.8%) increased with heat-treatment temperatures. [ABSTRACT FROM AUTHOR]

This paper presents a study on the thermal and electrical performance of lattice structures designed for a heat exchanger, where the geometry is optimized for enhanced heat management through a numerical simulation scheme based on the response surface method. The goal was to achieve effective heat conduction and convection. Lattice structures were selected for their inherent porosity, enabling efficient heating and cooling cycles. The optimized lattice geometry was fabricated using Laser powder bed fusion (L-PBF) additive manufacturing, with a "green" laser emission wavelength (λ = 515 nm) to improve energy absorption and final product density. Experimental evaluations assessed the thermal and electrical performance of the L-PBF-produced samples, including both workpieces and lattice structures designed for additive manufacturing. Microscopic and microstructural studies were conducted to identify potential manufacturing defects, such as porosities and cracks, resulting from the L-PBF process. Despite some defects persisting in certain lattice structures, the results showed significant improvements in both thermal and electrical properties compared to those obtained using the traditional infrared laser L-PBF process. An enhanced 3D-printed heat exchanger design is proposed, emphasizing lattice-like internal structures. This advancement offers superior control, increased durability, and improved safety for hydrogen storage devices. This research represents a significant contribution to the field of heat exchanger design and additive manufacturing, especially in the context of hydrogen storage technologies. It demonstrates the potential for lattice structures and innovative manufacturing processes to revolutionize the efficiency and safety of thermal systems. [ABSTRACT FROM AUTHOR]

[Display omitted] In response to the critical need for lightweight designs and carbon neutrality, we introduce an innovative additively manufactured ultrafine-grained Al-Mg-Mn-Sc-Zr alloy reinforced with nano-structured planar defects via laser powder bed fusion (L-PBF), developed for complex-shaped parts that demand high strength and superior ductility. Owing to the uneven distribution of the L1 2 -ordered Al 3 (Sc, Zr) nanoparticles, the as-printed alloy demonstrates a hierarchically heterogeneous microstructure featuring a triple-modal grain distribution. Tailored planar defects comprising stacking faults, 9R phase and nanotwins are strategically introduced in the as-printed alloy. Beyond the nano-scaled planar defects and the triple-modal grain distribution, further direct ageing process augments the abundance of nanoprecipitates, collectively boosting the yield strength to 656 MPa, which is higher than almost all L-PBFed Al alloys hitherto reported, and a decent ductility of 7.2 %. This work paves the way for the near net shape forming of high-performance Al alloy components for advanced structural applications. [ABSTRACT FROM AUTHOR]

The application of 2024 aluminum alloy (comprising aluminum, copper, and magnesium) in the aerospace industry is extensive, particularly in the manufacture of seats. However, this alloy faces challenges during laser powder bed fusion (PBF-LB/M) processing, which often leads to solidification and cracking issues. To address these challenges, LaB6 nanoparticles have been investigated as potential grain refiners. This study systematically examined the impact of adding different amounts of LaB6 nanoparticles (ranging from 0.0 to 1.0 wt.%) on the microstructure, phase composition, grain size, and mechanical properties of the composite material. The results demonstrate that the addition of 0.5 wt.% LaB6 significantly reduces the average grain size from 10.3 μm to 9 μm, leading to a significant grain refinement effect. Furthermore, the tensile strength and fracture strain of the LaB6-modified A2024 alloy reach 251 ± 2 MPa and 1.58 ± 0.12%, respectively. These findings indicate that the addition of appropriate amounts of LaB6 nanoparticles can effectively refine the grains of 2024 aluminum alloy, thereby enhancing its mechanical properties. This discovery provides important support for the broader application of 2024 aluminum alloy in the aerospace industry and other high-performance fields. [ABSTRACT FROM AUTHOR]

The non-equilibrium solidification process in the additive manufacturing of titanium alloy leads to special microstructures, and the resulting changes in corrosion behavior are worthy of attention. In this paper, the microstructure and electrochemical corrosion behavior of Ti6Al4V alloys prepared using laser powder bed melting (LPBF) and casting are systematically compared. The results show that the LPBF-processed Ti6Al4V alloy is composed of dominant acicular α′ martensite within columnar prior β phase, and less β disperses have also been discovered, which is significantly different from the α + β dual-phase structure of cast Ti6Al4V alloy. Compared to the as-cast Ti6Al4V alloy, LPBF-processed Ti6Al4V alloy has a thinner and unstable passive film, and exhibits slightly poorer corrosion resistance, which is mainly related to its higher porosity, a large amount of acicular α′ martensite and less β phase compared to as-cast Ti6Al4V alloy. This result proves that suitable methods should be taken to control the relative density and phase composition of LPBF-processed Ti6Al4V alloys before application. [ABSTRACT FROM AUTHOR]

Purpose: Additive manufacturing (AM) of duplex stainless steels (DSS) is still challenging in terms of simultaneously generating structures with high build quality and adequate functional properties. This study aims to investigate comprehensive process-material-property relationships resulting from both laser-directed energy deposition (DED-LB/M) and laser powder bed fusion (PBF-LB/M) of DSS 1.4462 in as-built (AB) and subsequent heat-treated (HT) states. Design/methodology/approach: Cuboid specimens made of DSS 1.4462 were generated using both AM processes. Porosity and microstructure analyses, magnetic-inductive ferrite and Vickers hardness measurements, tensile and Charpy impacts tests, fracture analysis, critical pitting corrosion temperature measurements and Huey tests were performed on specimens in the AB and HT states. Findings: Correlations between the microstructural aspects and the resulting functional properties (mechanical properties and corrosion resistance) were demonstrated and compared. The mechanical properties of DED-LB/M specimens in both material conditions fulfilled the alloy specifications of 1.4462. Owing to the low ductility and toughness of PBF-LB/M specimens in the AB state, a post-process heat treatment was required to exceed the minimum alloy specification limits. Furthermore, the homogenization heat treatment significantly improved the corrosion resistance of DED- and PBF-processed 1.4462. Originality/value: This study fulfills the need to investigate the complex relationships between process characteristics and the resulting material properties of additively manufactured DSS. [ABSTRACT FROM AUTHOR]

Lattice metamaterials based on three-period minimum surface (TPMS) are an effective means to achieve lightweight and high-strength materials which are widely used in various fields such as aerospace and ships. However, its vibration and noise reduction, and damping properties have not been fully studied. Therefore, in this study, the TPMS structures with parameterization were designed by the method of surface migration, and the TPMS structures with high forming quality was manufactured by laser powder bed fusion (LPBF). The mechanical properties and energy absorption characteristics of the beam and TPMS structures were studied and compared by quasi-static compression. The modal shapes of the beam lattice structures and TPMS structures were obtained by the free modal analysis, and the damping properties of two structures were obtained by modal tests. For the two structures after heat treatment with the same porosity of 70%, the yield strength of the beam lattice structure reaches 40.76 MPa, elastic modulus is 20.38 GPa, the energy absorption value is 32.23 MJ·m-3, the damping ratio is 0.52%. The yield strength, elastic modulus, energy absorption value, and damping ratio of the TPMS structure are 50.74 MPa, 25.37 GPa, 47.34 MJ·m-3, and 0.99%, respectively. The results show that TPMS structures exhibit more excellent mechanical properties and energy absorption, better damping performance, and obvious advantages in structural load and vibration and noise reduction compared with the beam lattice structures under the same porosity. [ABSTRACT FROM AUTHOR]

The laser-beam powder bed fusion process for metals, commonly abbreviated as PBF-LB/M, is a widely used process for the additive manufacturing of parts. Numerical simulations are useful to identify optimal process parameters for different materials and to obtain detailed insights into process dynamics. The present work uses a single-phase incompressible Smoothed Particle Hydrodynamics (SPH) scheme to model PBF-LB/M which was found to reduce the required computational time and significantly stabilize the partially violent flow in the melt pool in comparison to a weakly compressible SPH approach. The laser-material interaction is realistically modelled by means of a ray tracing method. An approach to model the effective thermal coductivity of the powder bed is proposed. Excellent agreement between the simulation results and experimental X-ray analyses of the transition from conduction melting mode to keyhole mode including geometric properties of the vapor depression zone was found. These results prove the usability of SPH as a high precision simulation tool for PBF-LB/M. [ABSTRACT FROM AUTHOR]

Laser Powder Bed Fusion (L-PBF) has immense potential for the production of complex, lightweight, and high-performance components. The traditional optimization of process parameters is costly and time-intensive, due to reliance on experimental approaches. Current numerical analyses often model single-line scans, while it is necessary to model multiple fully scanned layers to optimize for bulk material quality. Here, we introduce a novel approach utilizing discrete element simulations with a ray tracing-modeled laser heat source. Our approach significantly reduces the cost and time consumption compared to conventional optimization methods. GPU acceleration enables efficient simulation of multiple layers, resulting in parameters optimized for bulk material. In a case study, parameters were optimized for AlSi10Mg in just 5 days, a process that would have taken over 8 months without GPU acceleration. Experimental validation affirms the quality of the optimized process parameters, achieving an optical density of 99.91%. Optimization using the accelerated simulation yielded an optimized parameter set within 5 days. This resulted in a part with an optical density of 99.91%. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) is an ultra-high temperature ceramic with a melting temperature above 3000 °C and a broad range of high temperature applications. Given the high melting and sintering temperatures of pure ZrC, producing near-net shape and fully dense parts remains challenging with conventional techniques. In this study, we investigate the fundamental laser-material interactions of ZrC under laser powder bed fusion (LPBF) additive manufacturing (AM) conditions. Normalized enthalpy, a scaling law term that is used in welding and AM literature for detailing laser-material interactions in metallic alloys, was calculated to determine the predictive capabilities of melt pool features in ZrC. The melt pool quality of laser irradiated ZrC was used to compare LPBF relevant laser parameter combinations of laser power, scan speed, and beam diameter. Laser build parameters that resulted in desirable melt pool morphologies were applied to the fabrication of ZrC coupons using LPBF AM. A custom LPBF system was used to determine hatch spacing and layer height parameters that resulted in a fabricated sample with a density of 85% as measured by Archimedes and a Vicker's microhardness of 20.9 ± 1.9 GPa. This investigation reveals the laser-material interactions of ZrC under AM relevant conditions and is the first step towards LPBF fabrication of ZrC parts. [ABSTRACT FROM AUTHOR]