Laser Melting Research Articles

Investigating the Effects of Boron Nitride on Mechanical Properties of CoCrFeNiMn Composites

High‐entropy alloys (HEAs) are gaining attention for their exceptional properties but achieving precision and surface quality in powder metallurgy (PM) can be challenging. This study investigates the mechanical properties of CoCrFeNiMn HEAs produced through the flake powder metallurgy (FPM) technique and laser powder bed fusion (LPBF) preservative industrial, which established outstanding antiwear properties. To assess the enhancement of mechanical behavior and wear resistance by incorporating boron nitride (BN) into CoCrFeNiMn composites is fabricated via FPM. By incorporating BN into the composites, the mechanical behavior is significantly enhanced, leading to improved resistance against wear. Furthermore, the study delivers comprehensions into the serration behavior microstructure and shear localization in a high‐strain‐rate‐deformed CoCrFeMnNi entropy‐high alloy produces through metallurgy in powder. The serration behavior of the CoCrFeMnNi HEA is discussed concerning strain rate and temperature. Accordingly, the study employs the LPBF technique to fabricate the CoCrFeMnNi alloy from the prepared flakes. Microstructural characterization using scanning electron microscopy and X‐ray diffraction techniques to explore phase distribution, grain size, and possible segregation in the CoCrFeMnNi alloy produced through FPM‐LPBF is performed. In this particular investigation, a gradient microstructure is achieved through fusion in a laser‐powder bed of CoCrFeMnNi HEA onto highly deformed equal‐atomic HEA sheets. The resulting combination of partially recrystallized regions, exhibiting elevated yield strength, and fully recrystallized regions, demonstrates enhanced strain hardenability and elongation, and yields superior mechanical properties. The results obtained from the FPM‐LPBF CoCrFeMnNi alloy will be compared with those of conventionally processed CoCrFeMnNi to highlight the advantages and improvements achieved through the proposed method. The study findings reveal that the fundamental understanding of HEAs’ behavior under LPBF with FPM affords valuable insights into optimizing the processing parameters and achieving superior mechanical attributes.

Effect of Structural Configurations on Mechanical and Shape Recovery Properties of NiTi Triply Periodic Minimal Surface Porous Structures

Based on the advantages of triply periodic minimal surface (TPMS) porous structures, extensive research on NiTi shape memory alloy TPMS scaffolds has been conducted. However, the current reports about TPMS porous structures highly rely on the implicit equation, which limited the design flexibility. In this work, novel shell-based TPMS structures were designed and fabricated by laser powder bed fusion. The comparisons of manufacturability, mechanical properties, and shape recovery responses between traditional solid-based and novel shell-based TPMS structures were evaluated. Results indicated that the shell-based TPMS porous structures possessed larger Young’s moduli and higher compressive strengths. Specifically, Diamond shell structure possessed the highest Young’s moduli of 605.8±24.5 MPa, while Gyroid shell structure possessed the highest compressive strength of 43.90±3.32 MPa. In addition, because of the larger specific surface area, higher critical stress to induce martensite transformation, and lower austenite finish temperature, the Diamond shell porous structure exhibited much higher shape recovery performance (only 0.1% residual strain left at pre-strains of 6%) than other porous structures. These results substantially uncover the effects of structural topology on the mechanical properties and shape recovery responses of NiTi shape memory alloy scaffolds, and confirm the effectiveness of this novel structural design method. This research can provide guidance for the structural design application of NiTi porous scaffolds in bone implants.

Effect of gradually decreasing laser power on the microstructure and properties of laser melting deposited Inconel 718Plus alloy thin-wall

Laser melting deposition (LMD) technology offers a novel method for fabricating superalloy thin-walled parts because of its significant advantage of rapidly producing near-net-shape moldings. However, the coarse columnar crystals in these deposited thin-walled parts resulted in poor mechanical properties, which significantly limited its wide application. To address this problem, a layer-by-layer decreasing laser power deposition strategy (LT) is proposed in this study, which can increase the cooling rate of the molten pool by reducing the thermal cycling. Results indicate that the thin walls of Inconel 718Plus alloy deposited by the LT strategy exhibit dendrites at heights of 4.5 mm (bottom region), 16.5 mm (middle region) and 28.5 mm (top region). The Laves phase at the bottom of the LT alloy thin-wall was randomly distributed granular, which gradually transformed into granular, short-chain and its mixed structures with increasing height. Formation of long-chain Laves phases was hindered by the connection of dendrites. The densely distributed granular Laves phase in the LT strategy alloy thin wall could effectively transfer and dispersed the stress and hindered the crack initiation and extended. Compared to the bottom region, the yield strength of the LT alloy thin-wall in the middle and top region increased by 6.7 % and 12.6 %, and the tensile strength increased by 10.7 % and 16.2 %. In conclusion, the alloy thin-walls fabricated by the LT strategy exhibit superior strength and more balanced mechanical properties.

Mode selective damping behavior of additively manufactured beam structures

AbstractAdditive manufacturing, with its inherent process-related degrees of freedom, offers significant potential for manufacturing high-performance parts. This allows effects to be integrated that enable completely new solution mechanisms for existing conflicting objectives, which means that the degrees of design freedom make it possible to optimize the application-specific behavior of a part. In addition to the thermal or electrical properties, the dynamic behavior of a part can also be optimized, for example. This article focuses on the integration of the particle damping effect, which can contribute significantly to increased part damping. Unfused powder inside the part leads to energy dissipation through impact and friction mechanisms. However, the particle damping effect is not yet fully explored, lacking essential knowledge for application in product design. Therefore, test specimens with particle dampers, manufactured using laser powder bed fusion by laser beam from 1.2709 tool steel, are investigated, with variations in the position and size of the particle-filled cavities. To determine damping, the samples are freely supported and excited with an impulse. The damping ratio is calculated based on the recorded decay behavior. The results show an increase in damping ratio of up to a factor of 70, with the extent of improvement strongly dependent on the cavity’s volume and, crucially, its position relative to the part’s mode shape. A linear relationship between the damping ratio and the displacement of the volume of the cavities of the beams is shown.

Electro-discharge machining using copper-coated additively-manufactured AlSi10Mg electrodes

Customized fabrication of electrodes for electro-discharge machining (EDM) is considered as a useful emerging application of metal additive manufacturing technologies for building complex shaped tools in a short period of time. This approach of producing electrodes not only effectively addresses the design flexibility and complexity issues of the tools but also enables the use of various materials so as to ingrain the desired properties in them. The current study explores the production of laser powder bed fusion (LPBF) AlSi10Mg tools for machining of titanium alloy. Moreover, it explicitly assesses the machining performance of additively manufactured electrodes when the tools are subjected to a thin layer of copper coating. Three types of acidic baths are used for electroless coating of tools. The machining performance of the tools in terms of material removal rate, tool wear rate, surface crack density, surface roughness, white layer thickness, and microhardness of the white layer is compared for different electroless copper coating processes. It is observed that the coated tools significantly enhance material removal rate; however, uncoated LPBF tools exhibit superior surface morphology and surface roughness.

Two-staged attention-based identification of the porosity with the composite features of spatters during the laser powder bed fusion

Porosity is one of the most serious defects in laser powder bed fusion (LPBF). Reducing porosity is essential to improve the mechanical properties of parts in high-end applications. It is found that the spatter dynamic status is closely related to the porosity, giving an idea to identify. In this study, we propose a novel approach for in-situ identification of porosity in the LPBF with spatter features. To achieve efficient and accurate detection, segmentation, and motion tracking of spatters from captured high-speed images during the LPBF process, YOLO and DeepSORT algorithms are employed. Subsequently, a two-staged attention-based recurrent neural network (TARNN) method is proposed to realize the classification of porosity. The input to TARNN consists of both static and dynamic spatter features extracted from every 10 consecutive frames. Leveraging the RNN architecture enables us to effectively exploit temporal information. Moreover, we introduce an attention-aware linear layer and an attention-based RNN to enhance the extraction of representative features related to porosity characteristics. Through the analysis of the attention mechanism, we can explicitly assess the importance ranking of input features, providing a deeper understanding of spatter features. Experimental results demonstrate the superior performance of the proposed TARNN, with an accuracy of 99.50 % at an inference time of 6.5 milliseconds. The proposed method offers a promising avenue for advancing the understanding and characterization of porosity using spatter features in the LPBF process.

Characterisation and prediction of mechanical properties in laser powder bed fusion-printed parts: a comparative analysis using machine learning

ABSTRACT This study investigates the effects of process parameters including scanning strategy, build orientation, and hatching distance on the mechanical properties of AlSi10Mg parts produced by Laser Powder Bed Fusion (L-PBF). The experiment varied these parameters within defined ranges and used statistical analysis to evaluate their impact on tensile strength and ductility. Results showed that scanning strategy had the greatest influence, followed by hatching distance, while build orientation affected anisotropic properties. Microstructural analysis showed clear correlation between process conditions and mechanical strength, thereby showing the underlying mechanisms that govern material behavior. Moreover, Machine learning models, including Random Forest Regression (RFR), Support Vector Regression (SVR), and Artificial Neural Networks (ANNs), were applied to predict tensile strength and ductility characteristics. RFR and SVR outperformed ANNs, showing high predictive accuracy with limited datasets. These findings emphasize the importance of optimizing L-PBF process parameters to minimize anisotropy and achieve consistent mechanical properties in produced parts.

Microstructure and Electrochemical Corrosion Behavior of Inconel 718 Alloy Fabricated by Selective Laser Melting

Microstructure and Electrochemical Corrosion Behavior of Inconel 718 Alloy Fabricated by Selective Laser Melting

3D Printed Metallic Pillar Nanomechanical Resonators Decorated with TiO2 Nanotubes for Highly Sensitive Environmental Applications

AbstractMicro and nanomechanical devices offer enhanced sensing capabilities for detecting biological and chemical small molecules. However, miniaturization necessitates advanced fabrication processes and complex measurement systems, hindering routine sensor analysis. While alternative methods like 3D printing show promise, challenges such as low device resolution persist due to intrinsic damping of polymer inks. In this study, an array of micrometric pillar resonators is fabricated in Ti6Al4 V alloy using additive manufacturing based on laser powder bed fusion technology. These metallic nanomechanical resonators exhibit a very high quality factor with minimal difference between air and vacuum measurements due to low intrinsic damping. Furthermore, titania nanotubes grown on the pillars via anodic oxidation heighten sensitivity for molecular dye degradation evaluation. Leveraging the weak coupling phenomenon among the pillars in the array, these devices facilitate large‐scale parallelized measurements, here demonstrated with real‐time analysis of dye degradation process. This approach to creating mass sensing devices via metallic additive manufacturing can usher in a new generation of highly performing resonating sensor arrays, offering a cost‐effective and efficient alternative to traditional silicon microfabrication methods.

Compressive Mechanical and Heat Conduction Properties of AlSi10Mg Gradient Metamaterials Fabricated via Laser Powder Bed Fusion

Metamaterials are defined as artificially designed micro-architectures with unusual physical properties, including optical, electromagnetic, mechanical, and thermal characteristics. This study investigates the compressive mechanical and heat transfer properties of AlSi10Mg gradient metamaterials fabricated by Laser Powder Bed Fusion (LPBF). The morphology of the AlSi10Mg metamaterials was examined using an ultrahigh-resolution microscope. Quasi-static uniaxial compression tests were conducted at room temperature, with deformation behavior captured through camera recordings. The findings indicate that the proposed gradient metamaterial exhibits superior compressive strength properties and energy absorption capacity. The Gradient-SplitP structure demonstrated better compressive performance compared to other strut-based structures, including Gradient-Gyroid and Gradient-Lidinoid structures. With an apparent density of 0.796, the Gradient-SplitP structure exhibited an outstanding energy absorption capacity, reaching an impressive 23.57 MJ/m3. In addition, heat conductivity tests were performed to assess the thermal resistance of these structures with different cell configurations. The gradient metamaterials exhibited higher thermal resistance and lower thermal conductivity. Consequently, the designed gradient metamaterials can be considered valuable in various applications, such as thermal management, load-bearing, and energy absorption components.

Fatigue Scattering Analytics and Prediction of SS 316L Fabricated by Laser Powder Bed Fusion

Abstract Laser powder bed fusion (LPBF) is an enabling process manufacture of complex metal components. However, LPBF is prone to generate geometrical defects (e.g., porosity, lack of fusion), which causes a significant fatigue scattering. However, LPBF fatigue scattering data and analysis in the literature are not only sparse and limited to tension-compression mode but also inconsistent. This article presents a robust high-frequency fatigue testing method to construct stress-cycle curves of SS 316L to understand the scattering nature and predict the scattering pattern. A series of bending fatigue tests are performed at different stress amplitudes. Two different runout criteria are used to investigate fatigue life, fatigue limits, and scattering. The endurance limit reaches around 300 MPa for the defect size distribution at the selected process space. The defect size-based fatigue limit model is found to underestimate the endurance limit by about 30 MPa when comparing with the experimental data. Fatigue scattering is further calculated by using 95% prediction intervals, showing that low fatigue scattering is present at high stresses while a large variation of fatigue life occurs at stresses near the knee point.

Development of laser felling modes of gas-thermal coating

The use of copper and its alloys to create parts for metallurgical equipment is associated with an increase in abrasive wear and high-temperature corrosion. In this regard, there is a need to apply a protective coating. In particular, to prevent wear and premature chipping of the metal of copper tuyeres, the surface is hardened with a coating of zirconium dioxide stabilized with yttria oxide by thermal spraying in an air atmosphere. Due to the difference in the coefficient of thermal expansion of copper (at T = 300 K: 16.7 µm/m оС and at T = 750 K: 19.7 µm/m оС) and its low resistance to gas corrosion, the application of zirconium oxide (produced by a preapplied intermediate layer that plays a role in matching the coefficient of thermal expansion (CTE) between the copper base and the ceramic coating. In addition, the intermediate layer protects copper from gas corrosion. In this case, The use of copper and its alloys to create parts for metallurgical equipment is associated with an increase in abrasive wear and high-temperature corrosion. In this regard, there is a need to apply a protective coating. In particular, to prevent wear and premature chipping of the metal of copper tuyeres, the surface is hardened with a coating of zirconium dioxide stabilized with yttria oxide by thermal spraying in an air atmosphere. Due to the difference in the coefficient of thermal expansion of copper (at T = 300 K: 16.7 pm/m °G and at T = 750 K: 19.7 pm/m оG) and its low resistance to gas corrosion, the application of zirconium oxide (produced by a pre-applied intermediate layer that plays a role in matching the coefficient of thermal expansion (CTE) between the copper base and the ceramic coating. In addition, the intermediate layer protects copper from gas corrosion. In this case, nickel-based alloys were used as intermediate layers. The use of nickel as the basis of intermediate layers is due to the fact that copper and nickel form a continuous series of solid solutions, such as cupronickel or monel metal-like structures. This, in turn, assumes a smooth transition of thermophysical properties from copper to nickel alloy. To ensure increased adhesion of the transition layer to copper by increasing the area of mutual contact between copper and the sublayer (dagger penetration) and significantly increasing the homogeneity of the material of the intermediate layer made of a nickel alloy, laser melting of the intermediate sublayer (Ni–B–Si system) was used on a laser complex based on laser LS-5 with a power of 5 kW with a KUKA KR-60HA robot in an argon atmosphere. To test the modes, experiments were carried out on copper samples of a flat shape and a body of rotation. The optimal parameters for the process of melting flat samples were: processing speed 33 mm/s, power from 400 to 3900 W, focal length from 200 to 230 mm, pitch between tracks: 0.25, 0.5 and 1 mm. The optimal parameters for the process of melting rotating samples were: laser radiation power 400–450 W, processing step 0.125; 0.5, focal length from 200 to 210 mm.

Two-Staged Technology for CoCr Stent Production by SLM

Additive manufacturing of porous materials with a specific macrostructure and tunable mechanical properties is a state-of-the-art area of material science. Additive technologies are widely used in industry due to numerous advantages, including automation, reproducibility, and freedom of design. Selective laser melting (SLM) is one of the advanced techniques among 3D fabrication methods. It is widely used to produce various medical implants and devices including stents. It should be noticed that there is a lack of information on its application in stent production. The paper presents the technological aspects of CoCr stent SLM fabrication, including design of stents and development of regimes for their manufacturing. Physical, chemical, and technological properties of CoCr powder were initially determined. Parametric design of mesh stent models was adopted. A two-stage approach was developed to ensure dimensional accuracy and quality of stents. The first stage involves a development of the single-track fusion process. The second stage includes the stent manufacturing according to determined technological regimes. The single-track fusion process was simulated to assign laser synthesis parameters for stent fabrication. Melting bath temperature and laser regimes providing such conditions were determined. Twenty-seven SLM manufacturing regimes were realized. Dependence of single-tracks width and height on the laser power, exposition time, and point distance was revealed. The qualitative characteristics of tracks imitating the geometry of the stent struts as well as favorable and unfavorable fusion regimes were determined. The results of surface roughness regulating of the stents’ structural elements by various methods were analyzed. Thus, this two-staged approach can be considered as a fundamental approach for CoCr stent SLM fabrication.

Investigation of the 4D Multi-Material 316L/FeNi36 Obtained by Selective Laser Melting

Multi-material can have functional properties, which are not typical for the materials of which they are composed (for instance, shape-changing effect). This can be used in robotics, micromachines, aerospace, and other fields. In this work, the 316L/FeNi36 multi-material produced by selective laser melting was investigated. The results show that the interfacial zone of the multi-material exhibits mixing regions of the two alloys but no defects. The microstructure is constituted by large grains with epitaxial growth, which propagate in a directional manner from the 316L alloy through the interfacial zone to the FeNi36 region. The multi-material sample displays three different zones of chemical composition: the FeNi36 composition zone; the interfacial zone; and the 316L zone. The size of the interfacial zone is approximately 50 µm. The multi-material sample exhibits the presence of three distinct phases: γ-Fe; γ-Fe64Ni36; and α-Fe. The hardness of the FeNi36 zone is approximately 163 HV, followed by an interfacial zone with a hardness of approximately 200 HV and then, the 316L zone with a hardness of approximately 214 HV. Functional tests demonstrate that the shape-changing effect is directly correlated with the variation in the FeNi36 thermal expansion coefficient with temperature. For achieving the most pronounced shape-changing effect, the temperature range of 25–215 °C is more suitable.

4D Printing: Research Focuses and Prospects

As an emerging technology in the field of additive manufacturing, 4D printing is highly disruptive to traditional manufacturing processes. Therefore, it is necessary to systematically summarize the research on 4D printing to promote the development of related industries and academic research. However, there is still an obvious gap in the visual connection between 4D printing theory and application research. We collected 2070 studies from 2013 on 4D printing from the core collection of Web of Science. We used VOSviewer 1.6.20 and CiteSpace software 6.3.3 to visualize the references and keywords to explore focuses and trends in 4D printing using scientometrics. In addition, real-world applications of 4D printing were analyzed based on the literature. The results showed that “tissue engineering applications” is the most prominent focus. In addition, “shape recovery”, “liquid crystal elastomer”, “future trends”, “bone tissue engineering”, “laser powder bed fusion”, “cervical spine”, “4D food printing”, “aesthetic planning” are also major focuses. From 2013 to 2015, focuses such as “shape memory polymers” and “composites” evolved into “fabrication”. From 2015 to 2018, the focus was on “technology” and “tissue engineering”. After 2018, “polylactic acid”, “cellulose”, and “regenerative medicine” became emerging focuses. Second, emerging focuses, such as polylactic acid and smart polymers, have begun to erupt and have become key research trends since 2022. “5D printing”, “stability” and “implants” may become emerging trends in the future. “4D + Food”, “4D + Cultural and Creative”, “4D + Life” and “4D + Clothing” may become future research trends. Third, 4D printing has been widely used in engineering manufacturing, biomedicine, food printing, cultural and creative life, and other fields. Strengthening basic research will greatly expand its applications in these fields and continuously increase the number of applicable fields.

The Effects of Laser Power on the Performance and Microstructure of Inconel 718 Formed by Selective Laser Melting

In this study, the effects of laser power on the microstructure and mechanical properties of Inconel 718 formed by SLM were systematically studied. The results show that with the increase in laser power from 285 W to 360 W, the increase in working temperature in the molten pool promoted the evaporation of gas and the vaporization of the low-melting-point alloy components, and the relative density gradually increased from 99.31% to 99.79%. In addition, with the increase in laser energy density, the microstructure gradually coarsened from columnar dendrites to cellular crystals. The nano-hardness of the material decreased with the increase in laser power. The nano-hardness of four groups of samples from 285 W to 360 W decreased form 3.43 GPa to 2.09 GPa, and the elastic modulus decreased form 205.72 GPa to 199.91 GPa.

Development and research testing of a low thrust on gaseous-propellant rocket engine chamber

The article presents preliminary results of the development and research testing of a rocket engine chamber with a thrust of 100 N operating on fuel components: gaseous oxygen-gaseous hydrogen, designed to be used as the main engine of a small upper stage for launching a payload weighing up to 150 kg into target orbits. The main features of the engine chamber are its fabrication by selective laser melting from 12X18N10T steel powder and its regenerative cooling with gaseous hydrogen. Calculation and experiments confirmed the possibility of regenerative cooling of the chamber in the nominal mode. In addition, the current results of the development of a technique for optical recording of the process of structural material removal from the chamber during tests using different optical filters are presented. It is shown that there is a correlation between the brightness of the obtained frames and the hydrogen flow rate. It is also shown that the afterburning of the removed material particles, in contrast to high thrust engines, occurs mainly in the tail of the jet.

Optimal process parameter determination in selective laser melting via machine learning-guided sequential quadratic programing

Selective Laser Melting (SLM) is a widely used additive manufacturing method with critical processing parameters such as Laser Power, Scanning Speed, Hatch Distance, and Laser Beam Diameter, which significantly impact process quality and mechanical properties of fabricated parts like Relative Density, Hardness, and Surface Roughness. This study investigates an effective approach to modeling the SLM process for predicting and optimizing processing parameters using a combination of Machine Learning (ML) and Sequential Quadratic Programing (SQP). The proposed method aims to predict the mechanical properties of SLM-produced AlSi10Mg parts using Machine Learning techniques and then transform the process into a constrained multiple-objective optimization model employing the SQP algorithm to determine optimal process parameters. Artificial Neural Networks (ANN), Gaussian Process Regression (GPR), and Support Vector Machine (SVM) algorithms are applied to establish correlations between process parameters and mechanical properties, represented as mathematical functions. A cost function is formulated using these functions and minimized using the SQP method. Statistical analysis is implemented to validate the influence of processing parameters on mechanical properties accordingly. The outcomes of the method are verified through additional experiments and analyses using Micro-CT scanning techniques. The results demonstrate that processing parameters have a significant impact on part properties across different scales, with Micro-CT scanning proving instrumental in validating mechanical properties. Overall, this study establishes that multiple objectives can be efficiently optimized through the integration of ML and SQP methods, complemented by a judicious number of experiments.

In-situ laser powder bed fusion: real-time assessment of residual stress through thermal gradient analysis

In-situ laser powder bed fusion: real-time assessment of residual stress through thermal gradient analysis

Generalized SmartScan: An Intelligent LPBF Scan Sequence Optimization Approach for Reduced Residual Stress and Distortion in 3D Part Geometries

Abstract Laser powder bed fusion (LPBF) is an additive manufacturing technique that is gaining popularity for producing metallic parts in various industries. However, parts produced by LPBF are prone to residual stress, deformation, cracks and other quality defects due to uneven temperature distribution during the LPBF process. To address this issue, in prior work, the authors have proposed SmartScan, a method for determining laser scan sequence in LPBF using an intelligent (i.e., model-based and optimization-driven) approach, rather than using heuristics, and applied it to simple 2D geometries. This paper presents a generalized SmartScan methodology that is applicable to arbitrary 3D geometries. This is achieved by: (1) expanding the thermal model and optimization approach used in SmartScan to multiple layers; (2) enabling SmartScan to process shapes with arbitrary contours and infill patterns within each layer; (3) providing the optimization in SmartScan with a balance of exploration and exploitation to make it less myopic; and (4) improving SmartScan’s computational efficiency via model order reduction using singular value decomposition. Sample 3D test artifacts are simulated and printed using SmartScan in comparison with common heuristic scan sequences. Reductions of up to 92% in temperature inhomogeneity, 86% in residual stress, 24% in maximum deformation and 50% in geometric inaccuracy were observed using SmartScan. An approach for using SmartScan for printing complex 3D parts in practice, by integrating it as a plug-in to a commercial slicing software, was also demonstrated experimentally, along with its benefits in significantly improving printed part quality.