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Influence of particle morphology and size distribution on the powder flowability and laser powder bed fusion manufacturability of Ti-6Al-4V alloy
摘要： Laser powder bed fusion (LPBF) additive manufacturing technology is sensitive to variations in powder particle morphology and size distribution. However, the absence of a clear link between the powder characteristics and the LPBF performances complicates the development, selection and quality control of LPBF powder feedstock. In this work, three Ti-6Al-4V powder lots produced by two different techniques, namely, plasma atomization and gas atomization, were selected and characterized. Following the micro-computed tomography analysis of the powder particles’ morphology, size and density, the flowability of these powder lots was concurrently evaluated using Hall and Gustavsson flowmeters and an FT4 powder rheometer. Using established rheology-based criteria, a figure of merit was proposed to quantify the overall powder suitability for the LPBF process. Next, the same three powder lots were used to 3D-print and post-process a series of testing specimens with different layer thicknesses and build orientations, in order to establish a correlation between the powder characteristics and the geometric and mechanical properties of a final product. This study demonstrates that the use of highly spherical powders with a limited amount of fine particles promotes their flowability and yields LPBF components with improved mechanical and geometric characteristics.
关键词： sphericity,powder flowability,particle size distribution,Laser powder bed fusion,layer thickness,Ti-6Al-4V
更新于2025-09-12 10:27:22
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Model-based feedforward control of laser powder bed fusion additive manufacturing
摘要： Control of laser power to improve part quality is critical for fabrication of complex components via Laser Powder Bed Fusion (LPBF) additive manufacturing (AM) processes. If the laser power is too low, it will result in a small melt pool and lack of fusion; on the other hand, if the laser power is too high, it will result in keyhole and material evaporation. This paper examines a model-based feed-forward control for laser power in LPBF to improve build quality by avoiding the onset of keyhole formation or reducing over-melting. First, an analytical, control-oriented model on the dynamics of melt-pool cross-sectional area in scanning a multi-track part was developed, and then a nonlinear inverse-dynamics controller was designed to adjust laser power such that the melt-pool cross-sectional area can be regulated to a constant set point during the build process. The resulting control trajectory on laser power from the simulated closed-loop controller was then implemented in a LPBF process as a feed-forward (FF) controller for laser power. Multiple bead-on-plate samples of Inconel 625, with different number of tracks and track lengths, were then built on an EOSINT M 280 AM system to evaluate the performance of the resulting FF-Analytic controller. Experimental results demonstrated that the proposed FF-Analytic control of laser power was able to avoid the onset of keyhole formation that occurred under a constant laser power for certain samples. Furthermore, the proposed FF-Analytic control was demonstrated to have significantly reduced over-melting at the returning ends of the laser scan path in scanning a multi-track part compared to applying a constant laser power, albeit with some over-compensation due to modeling imperfection. Overall, the proposed FF-Analytic control of laser power had 23% ? 40% lower average error rate than applying a constant laser power in regulating the melt-pool cross-sectional area to a constant reference value, in terms of measurements of cross-sections at track ends.
关键词： keyhole,control-oriented model,powder bed fusion,feed-forward control,multi-track
更新于2025-09-12 10:27:22
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Construction of Cellular Substructure in Laser Powder Bed Fusion
摘要： Cellular substructure has been widely observed in the sample fabricated by laser powder bed fusion, while its growth direction and the crystallographic orientation have seldom been studied. This research tries to build a general model to construct the substructure from its two-dimensional morphology. All the three Bunge Euler angles to specify a unique growth direction are determined, and the crystallographic orientation corresponding to the growth direction is also obtained. Based on the crystallographic orientation, the substructure in the single track of austenitic stainless steel 316L is distinguished between the cell-like dendrite and the cell. It is found that, with the increase of scanning velocity, the substructure transits from cell-like dendrite to cell. When the power is 200 W, the critical growth rate of the transition in the single track can be around 0.31 ms?1.
关键词： cell,cell-like dendrite,crystallographic orientation,model,laser powder bed fusion,substructure,growth direction
更新于2025-09-12 10:27:22
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Influence of laser post-processing on pore evolution of Ti–6Al–4V alloy by laser powder bed fusion
摘要： In laser powder bed fusion (LPBF) processes, critical defect issues such as porosity limit the quality of the fabricated part. This work investigates the mechanism of pore evolution during the laser post-processing of an LPBF part. A laser beam was utilized to scan the top surface of a Ti–6Al–4V alloy part. The morphologies of the internal layers as well as the distribution of the porosity inside the Ti–6Al–4V sample were experimentally measured and compared using micro-computed tomography (micro-CT). It was found that the void fraction was significantly decreased, from 2.51% to 0.77%, by laser post-processing. A multi-physics coupled finite element model based on the Level-set method was built to analyze the evolution mechanism of the pore. This model simulated the effects of the energy density, Marangoni flow and mass transfer on the pore evolution. Typical processes were studied in detail, and a table summarizing the pore evolution under different post-processing parameters is given.
关键词： Ti–6Al–4V alloy,Laser powder bed fusion,Pore evolution,Additive manufacturing,Level-set method
更新于2025-09-12 10:27:22
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Accurate Determination of Laser Spot Position during Laser Powder Bed Fusion Process Thermography
摘要： High-speed thermography is useful tool for researching the laser powder bed fusion process by providing thermal information in heat affected zone. However, it is not directly possible to ascertain the position of the laser spot with respect to the melt pool, which could provide key information regarding how laser energy is distributed and absorbed. In this paper, we demonstrate a procedure for registering the laser spot position with the melt pool using a bright illumination source co-axially aligned with the laser to project a sharp spot on the build plane. This spot is fixed to the laser position and used as a reference frame for registering the laser spot with the melt pool radiance temperature distribution. Measurement results demonstrate the effect of varying process parameters (laser power and scan speed) on the melt pool thermal field and respective position of the laser spot.
关键词： additive manufacturing,Laser powder bed fusion,thermography
更新于2025-09-12 10:27:22
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Rapid Solidification and Non-equilibrium Phase Constitution in Laser Powder Bed Fusion (LPBF) of AlSi10Mg Alloy: Analysis of Nano-precipitates, Eutectic Phases, and Hardness Evolution
摘要： The non-equilibrium phase evolution during laser powder bed fusion (LPBF) of AlSi10Mg alloy is thoroughly characterized and analyzed by means of advanced electron microscopy and analytical simulation of rapid solidification phenomenon. The evolution of microstructural strengthening agents such as inter-cellular eutectic phase and intra-cellular precipitates is presented in correspondence with the local variation of cellular/dendritic solidification patterns within a typical melt pool. The eutectic phase exhibits two different morphologies: lamellar and fibrous. As with the cell size variation, the overall volume fraction of eutectic phase and the lamella spacing is shown to gradually decrease by moving away from the melt-pool boundary (MPB), i.e., through crossing over from a coarse to a fine cellular zone. The eutectic-free regions within the a-Al cells contain a large number density of nano-sized precipitates that are predominantly Si-rich and are either fully or semi-coherent with the Al matrix. The formation of nano-precipitates is linked to the increased (non-equilibrium) solubility limits of a-Al cells due to the rapid solidification effect. For the first time, we identify such nano-precipitates with non-equilibrium crystal structures and morphologies: ‘‘Spheres’’ and ‘‘Ellipsoids’’ with Face Centered Cubic (FCC), and ‘‘Plates’’ and ‘‘Needles’’ with a Diamond Cubic (DC) superlattice structure that emerges from within the Al matrix. The microstructure in the heat-affected zone (HAZ) right underneath the MPB exhibits an absence of cell boundaries and eutectic phases while consisting primarily of large Si-rich and Mg-rich precipitates. Finally, the local variation of nano-hardness across a solidified melt pool is shown to correlate well with the corresponding profile of microstructural refinement, i.e., exhibiting a minimum at the HAZ and a peak at around the melt-pool centerline. The findings here can significantly advance the state of knowledge for the strengthening behavior in an as-built LPBF-processed AlSi10Mg alloy.
关键词： hardness evolution,Laser Powder Bed Fusion,non-equilibrium phase evolution,eutectic phases,nano-precipitates,AlSi10Mg
更新于2025-09-12 10:27:22
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Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion
摘要： This article deals with the understanding of the influence of surface topography on fatigue behavior of Ti6Al4V alloy specimens produced by laser powder bed fusion (LPBF). The same laser parameters and scan strategy were used for all specimens, giving a sample density higher than 99.5 %. Two different surface topographies were obtained by using the top and side surfaces of the specimens. The surface topography and morphology were investigated by optical surface profilometry and focus variation microscopy. Four-point bending fatigue test was performed on specimens with top and side surfaces as the highest stressed surface respectively. Machined specimens were used as reference. The features of the fracture surface, such as crack initiation and propagation, were analyzed by focus variation and scanning electron microscopy (SEM). Both, fatigue results and fracture surface investigations, were correlated and discussed in relation to surface topography and microstructure, as well as manufacturing parameters.
关键词： laser powder bed fusion,surface topography,Ti6Al4V alloy,fatigue test,fracture mechanisms
更新于2025-09-12 10:27:22
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Multi-physical analysis of thermo-optical effects for different Selective Laser Melting (SLM) scanning strategies
摘要： In this paper, transient thermo-optical effects in protective windows for selective laser melting are analyzed by means of a multi-physical analysis. The temperature distribution of the window is simulated for different scanning strategies and orders of exposure. Therefore, cubic test specimens are virtually built and the resulting axial and lateral focus shift is analyzed. Furthermore, the impact of the distance between the laser scanner and the protective window is analyzed. The simulations predict that spreading the thermal load on the window both spatially and temporally reduces the focus shift. Consequently, the focus shift is reduced if the window is placed further away from the laser scanner.
关键词： thermal lensing,Selective laser melting,protective window,finite element analysis,laser-powder bed fusion,additive manufacturing
更新于2025-09-12 10:27:22
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Process monitoring of meltpool and spatter for temporal-spatial modeling of laser powder bed fusion process
摘要： L-PBF is an additive manufacturing process which can produce nearly fully dense parts with complex geometry by using laser which follows layer-to-layer scanning on powder material. In-process statistical monitoring techniques are required to detect localize material spatter and control the meltpool. High speed video imaging provides process insights for identifying meltpool and spatter and can be integrated into process monitoring for L-PBF process. We demonstrate the use of high speed camera videos for in-situ monitoring of L-PBF of nickel alloy 625 to detect spatter and over melting regions to improve the process control capability. The quantities that can be measured via in-situ sensing can be referred to as process signatures and can represent the source of information to detect possible defects. The video images are processed for temporal-spatial analysis by using principal component analysis and T2 statistical descriptor for identifying the history of pixel intensity levels through the process monitoring. These results are correlated as over melting and spatter regions.
关键词： Meltpool,Monitoring,Powder bed fusion,Spatter,Laser
更新于2025-09-12 10:27:22
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In-situ characterization of tungsten microcracking in Selective Laser Melting
摘要： Additive Manufacturing is a promising way of processing tungsten, with opportunities to create more complex parts than are possible using other powder metallurgical routes. This may lead to extended applications such as collimators, in fusion reactors, or in other structurally loaded, high temperature environments. The poor thermal shock resistance and ductile-to-brittle transition that occurs in tungsten above room temperature are challenges that hinder production of fully dense and crack free parts. This research employs high speed in-situ monitoring of Selective Laser Melting of single tracks to visualize crack initiation and propagation. The circumstances that lead to cracking are correlated with microstructural morphology and processing conditions.
关键词： In-situ monitoring,Additive Manufacturing,Microcracking,Laser powder bed fusion,Tungsten,Selective Laser Melting
更新于2025-09-12 10:27:22