Search Results (67)

Due to the high potential of shot peening to improve the surface quality of additively manufactured components, in this work, the influence on surface morphology and, thus, the surface topography and selected properties of the surface and subsurface regions of additively manufactured parts is analysed. For this, cubic specimens made of stainless steel 316L and AlSi10Mg were manufactured via powder bed fusion laser beam metal (PBF-LB/M), and subsequently, their “as-built” surfaces were shot peened. Shot peening was conducted with stainless steel or ceramic beads using pressures of 3 and 5 bar. The resulting morphologies were analysed regarding topography, microstructure and mechanical properties (hardness and cyclic deformation behaviour) in the subsurface region and the residual stresses. The results demonstrate a strong plastic deformation due to shot peening, resulting in a decreased surface roughness as well as an increased hardness and compressive residual stresses near the surface. These effects were generally more pronounced after using higher peening pressure and/or ceramic beads. Note that two sets of PBF-LB/M parameters were used to produce the AlSi10Mg specimens. The investigation of these specimens reveals an interrelation between the parameters used in shot peening and PBF-LB/M on the resulting surface morphology. Full article

Laser beam powder bed fusion of metals (PBF-LB/M, or simply L-PBF) has emerged as one of the most competitive additive manufacturing technologies for producing complex metallic components with high precision, design freedom, and minimal material waste. Among the various categories of additive manufacturing processes, L-PBF stands out, paving the way for the execution of part designs with geometries previously considered unfeasible. Despite offering several advantages, parts with overhang features require the use of support structures to provide dimensional stability of the part. Support structures achieve this by resisting residual stresses generated during processing and assisting heat dissipation. Although the scientific community acknowledges the role of support structures in the success of L-PBF manufacturing, they have remained relatively underexplored in the literature. In this context, the present work investigated the impact of laser power and scanning speed on the dimensioning, integrity and tensile strength of single-walled block type support structures manufactured in AISI 316L stainless steel. The method proposed in this work is divided in two stages: processing parameter exploration, and mechanical characterization. The results indicated that support structures become more robust and resistant as laser power increases, and the opposite effect is observed with an increment in scanning speed. In addition, defects were detected at the interfaces between the bulk and support regions, which were crucial for the failure of the tensile test specimens. For a layer thickness corresponding to 0.060 mm, it was verified that the combination of laser power and scanning speed of 150 W and 500 mm/s resulted in the highest tensile resistance while respecting the dimensional deviation requirement. Full article

The study investigates the influence of microstructures on fatigue behavior and failure mechanisms of the α-β titanium alloy Ti6246, fabricated via Powder Bed Fusion-Laser Beam (PBF-LB). In particular, the investigation assesses the effect of two post-processing heat treatments, namely α-β annealing at 875 °C (AN875) and solution treatment at 825 °C followed by aging at 500 °C (STA825), on the alloy’s rotating and bending fatigue behavior. The results indicate that the STA825 condition provides superior fatigue resistance (+25%) compared to AN875, due to the presence of a finer bilamellar microstructure, characterized by thinner primary α lamellae (α_p) and a more homogeneous distribution of secondary α lamellae (α_s) within the β matrix. Additionally, an investigation conducted using the Kitagawa–Takahashi (KT) approach and the El-Haddad model, based on the relationship between the fatigue limit and defect sensitivity, revealed improved crack propagation resistance from pre-existing defects (ΔK_th) for the STA825 condition compared to AN875. Notably, the presence of fine α_s after aging for STA825 is effective in delaying crack nucleation and propagation at early stages, while refined α_p contributes to hindering macrocrack growth. The fatigue behavior of the STA825-treated Ti6246 alloy was even superior to that of the PBF-LB-processed Ti64, representing a viable alternative for the production of high-performance components in the automotive and aerospace sectors. Full article

In this work, we address the task of monitoring Powder Bed Fusion–Laser Beam processes for metal powders (PBF-LB/M). Two main contributions with practical merit are presented. First, we consider the comparison between a large deep neural network (VGG-19) and a small model consisting of, among others, four convolutional layers. Our study shows that the small model can compete favorably with the big model, which takes advantage of transfer learning techniques. Secondly, we present a filtering method using a semantic segmentation approach to preselect a region for the classification algorithm. The region is selected based on post-exposure images, and preselection can be easily adopted for any machine independently of the software used for the translation of process input files. To consider the task, a master dataset with over 260,000 samples was prepared, and a detailed process of preparing the training datasets was described. The study demonstrates that the classification time can be reduced by a factor of 4.51 while still maintaining the model’s necessary performance to detect errors in a PBF-LB process. Full article

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

Ti and Ti alloys are being widely used as bone tissue repair materials. Progress on mechanical properties and bio-functionality is required for their applications due to the large difference in elastic modulus between bone and Ti implants and the fact that the Ti materials themselves are biologically inert. In this work, a low-modulus, β-phase Ti-15Mo alloy based on a triply periodical minimal surfaces (TPMS) structure was fabricated using a Powder Bed Fusion-Laser Beam (PBF-LB) under optimized printing parameters into implant samples with controllable porous structures. The selection of TPMS, lattice unit cell size, and relative density was based on a combination of mechanical properties and cytocompatibility. Surface modifications were used to further impart antibacterial, antioxidant, and osteogenesis properties to the implants. Broad-spectrum antibacterial Ag, antioxidant tannic acid (TA), and highly stable fluorinated hydroxyapatite ((F)HA) were applied as an advanced coating on a microporous TiO₂ surface modification layer formed by micro-arc oxidation. Ultimately, porous Ti-15Mo implant samples with a biofunctional coating were obtained with Young’s modulus 15–50 GPa, a yield strength of approximately 100 MPa, and good cytocompatibility, hemocompatibility, and bactericidal effects. This study provides a systematic scheme for the preparation and surface modification of β Ti alloy implants for subsequent studies. Full article

The boiling point of metals is dependent on the ambient pressure. Therefore, in laser-based fusion welding and additive manufacturing processes, the resulting process regime, ranging from heat conduction welding to the keyhole mode, is also influenced by the process pressure. While laser welding deliberately uses reduced process pressures to achieve the keyhole mode with a lower laser power input as well as a more stable keyhole, there are no positive findings on the laser powder bed fusion process (PBF-LB/M) under vacuum conditions so far. Furthermore, the literature suggests that the process window is significantly reduced, particularly in the high vacuum regime. However, this work demonstrates that components made of the ferritic steel 22NiMoCr3-7 can be successfully manufactured at low process pressures of ${2 \times 10}^{-2} \mathrm{mbar}$ using a double-scanning strategy. The strategy consists of a first scan with a defocused laser beam, where the powder is preheated and partially sintered, followed by a second scan with a slightly defocused laser beam, in which the material within a single layer is completely melted. To test this manufacturing strategy, 16 test cubes were manufactured to determine the achievable relative densities and tensile specimens were produced to assess the mechanical properties. Metallographic analysis of the test cubes revealed that relative densities of up to 98.48 ± 1.43% were achieved in the test series with 16 different process parameters. The tensile strength determined ranged from 722 to 724 MPa. Additionally, a benchmark part with complex geometric features was successfully manufactured in a high vacuum atmosphere without the need for a complex parameterization of individual part zones in the scanning strategy. Full article

The powder bed fusion of metals using a laser beam (PBF-LB/M) is an additive manufacturing process for the direct production of metal parts using powder as a starting material. The PBF-LB/M process consists of two main steps: the application of a new powder layer and the melting of the cross-sections of the parts in each layer. Laser exposure usually takes up a lot of time during a build process; however, the application of powder layers, also taking up a considerable amount of time, offers potential to shorten production times. In this work, a powder test rig that mimics the real flow conditions of a PBF-LB/M system is used to measure the quality of X3NiCoMoTi18-9-5 powder layers applied at different recoater speeds by determining the powder surface roughness. The same recoating settings are then used on a real PBF-LB/M system to produce samples and investigate their densities as a function of recoater speed. The results show that the recoater speed influences the surface of the applied powder bed and has an effect on the density of the manufactured samples. However, this influence decreases if only samples with a high relative density are considered. Full article

Powder Bed Fusion–Laser Beam (PBF-LB) is a leading technique in metal additive manufacturing, yet it continues to face challenges related to residual stresses and distortions. The inherent strain method has emerged as a valuable predictive tool, offering early assessments of part behaviour due to its simplicity and manageable computational demands. However, accurately defining the inherent strain tensor, which is critical for these models, remains a challenge. This study provides a comprehensive analysis of the local meso-scale model definition and inherent strain calculation procedure in the PBF-LB process using a multi-scale modelling approach. The primary objective is to guide the definition of local high-fidelity thermo-mechanical models. This research investigates the contributions of thermal, plastic, and activation strains (strains due to Finite Element (FE) activation) to the inherent strain tensor, demonstrating the significant impact of activation strains. A sensitivity analysis identified an optimal control volume size to ensure minimal boundary effects. An optimised local high-fidelity model is proposed to efficiently calculate inherent strain tensor, significantly reducing computational costs without compromising accuracy. The method was validated by applying it to a complex SBA actuator geometry, which showed good agreement between predicted and experimental distortions. The consistency of the proposed method with empirically derived tensors further reinforces its potential to improve predictive capabilities in the PBF-LB process, ultimately enhancing part quality. Full article

Powder bed fusion–laser beam (PBF-LB) additive manufacturing enables the production of intricate, lightweight metal components aligned with Industry 4.0 and sustainable principles. However, residual stresses and distortions challenge the dimensional accuracy and reliability of parts. Inherent strain methods (ISMs) provide a computationally efficient approach to predicting these issues but often overlook transient thermal histories, limiting their accuracy. This paper introduces an enhanced inherent strain method (EISM) for PBF-LB, integrating macro-scale temperature histories into the inherent strain framework. By incorporating temperature-dependent adjustments to the precomputed inherent strain tensor, EISM improves the prediction of residual stresses and distortions, addressing the limitations of the original ISM. Validation was conducted on two Ti-6Al-4V geometries—a non-symmetric bridge and a complex structure (steady blowing actuator)—through comparisons with experimental measurements of temperature, distortion, and residual stress. Results demonstrate improved accuracy, particularly in capturing localized thermal and mechanical effects. Sensitivity analyses emphasize the need for adaptive layer lumping and mesh refinement in regions with abrupt stiffness changes, such as shrink lines. While EISM slightly increases computational cost, it remains feasible for industrial-scale applications. This work bridges the gap between simplified inherent strain models and high-fidelity simulations, offering a robust tool for simulation-driven optimisation. Full article

The potential of an optimization process with respect to reduced mass can be used to the full extent by utilizing a high-strength material as it is, among others, strength-dependent. For the additive manufacturing process, Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M), 316L is commonly used. PBF-LB/M/316L has its benefits, like good material properties, such as availability, corrosion resistance, strength, and ductility. Nevertheless, a higher-strength material is required to fully take advantage of the optimization process and achieve a greater reduction in the mass of manufactured parts. The high-strength austenitic stainless steel investigated in this study is Printdur^® HSA. Its main alloying elements are manganese, chromium, molybdenum, carbon, and nitrogen. The steel obtains its high strength properties from the alloyed carbon and nitrogen via solid solution hardening and improving the austenite stability. Therefore, it is defined as (C+N) steel. The datasheet of the powder manufacturer describes a yield strength (R_p0.2; 0.2% offset proof stress) of 915 MPa, an ultimate tensile strength of 1120 MPa, and an elongation at fracture of 30%. These are clear benefits in comparison to PBF-LB/M/316L. Since there are no further investigations made on Printdur^® HSA, a thorough investigation of material behavior, fatigue life, and microstructure is needed. Full article

The laser-beam powder-bed fusion (PBF-LB) method enables the semi-automatic fabrication of complex three-dimensional structures, making it useful for dental prostheses. However, residual stress during fabrication can cause deformation. Herein, we applied the segmented-scan strategy to three-unit fixed dental prostheses (FDPs) and evaluated its effects on residual stress and fit accuracy compared to conventional methods. Three-unit FDPs consisting of two abutments and a pontic were fabricated using a PBF-LB machine with Co-Cr-Mo powder. In the segmented-scan group, pontics and abutments were scanned separately to shorten the scan vector. Fit accuracy was assessed by measuring the gap between the abutment and the FDPs. Residual stress was measured in the X and Y directions at three points using X-ray diffraction, while CT scans were used to count internal microstructures. The residual stress was lower in the X-direction in the segmented-scan group (24.61–217.17 MPa, respectively) than in the control group (187.70–293.71 MPa, respectively). However, no significant differences in fit accuracy were observed (p < 0.05). The segmented-scan strategy reduced residual stress in the X-direction but did not improve the fit accuracy. Applying this strategy to dental prosthetic devices can shorten the scan vector and reduce residual stress. Full article

For additive manufactured parts, it is important to measure homogeneity and demonstrate representative parts can be printed faster while maintaining key mechanical properties. In this work, a multiscale characterization of microstructural and mechanical properties was carried out to gain a thorough understanding of a range of powder bed fusion-laser beam (PBF-LB)-manufactured Scalmalloy for future optimization of the processing parameters. The relationship between microstructure, including porosity, grain structure, and precipitates, and mechanical properties, is investigated. The stress-relieved samples were characterized mainly using scanning electron microscopy (SEM) suite, uniaxial tensile tests and nanoindentation. The results show the multiple strengthening mechanisms in Scalmalloy, including solid solution strengthening, grain size, precipitates and dislocations strengthening, demonstrated through a combination of the nanoindentation measurements with microstructural analysis at the local scale. The current work suggests potential mechanisms for further improvement of the strength and ductility in PBF-LB-Scalmalloy. Full article

Additive manufacturing (AM) methods like powder bed fusion–laser beam (PBF-LB) enable complex geometry production. However, understanding and predicting the microstructural properties of AM parts remain challenging due to the inherent non-homogeneity introduced during the manufacturing process. This study demonstrates a novel approach for 3D microstructure representation and virtual testing of non-homogeneous AM materials using 2d electron backscatter diffraction (EBSD) data. By employing the representative volume element (RVE) method, we reconstruct the 3D microstructure from 2D EBSD datasets, effectively capturing the grain morphological characteristics of PBF-LB-produced Hastelloy X. Using validated RVE data, we artificially generate combinations of two grain textures to gain deeper insight into locally affected areas, particularly the stress distribution within the interfaces, as well as global material behavior, exploring non-homogeneity. Computational homogenization (CH) utilizing a crystal elasticity finite element (CEFE) method is used to virtually test and predict directional elastic properties, offering insights into relationships between microstructure evolution and property correlation. The experimentally validated results show a strong correlation, with only 0.5–3.5% correlation error for the selected grain tessellation method. This consistency and reliability of the methodology provide high confidence for additional virtual tests predicting the properties of non-homogeneous, artificially generated combined-grain structures. Full article

The mechanical behavior of the metallic components fabricated by additive manufacturing (AM) technologies can be influenced by adjustments in their microstructure or by using specially engineered geometries. Manipulating the topological features of the component, such as incorporating unit cells, enables the production of lighter metamaterials, such as lattice structures. This study investigates the mechanical behavior of lattice structures created from AlSi10Mg, which were produced using the laser beam powder bed fusion (LB-PBF) process. Specifically, their behavior under pure compressive loading has been numerically and experimentally investigated using ten different configurations. Experimental methods and finite element analysis (FEA) were used to investigate the behavior of body-centered cubic (BCC) lattice structures, specifically examining the effects of tapering the struts by varying their diameters at the endpoints ($d_{\mathrm{end}}$) and midpoints ($d_{\mathrm{mid}}$), as well as altering the height of the joint nodes (h). The unit cells were designed with varying parameters in such a way that $d_{\mathrm{end}}$ is changed at three levels, while $d_{\mathrm{mid}}$ and h are changed at two levels. Significant differences in Young’s modulus, yield strength, and ultimate compressive strength between the various specimen configurations were observed both experimentally and numerically. The FEA underestimated the Young’s modulus corresponding to the configurations with thinner struts in comparison to the higher values found experimentally. Conversely, the FEA overestimated the Young’s modulus of those configurations with larger strut diameters with respect to the experimentally determined values. Additionally, the proposed FE method consistently underestimated the yield strength relative to the experimental values, with notable discrepancies in specific configurations. Full article