Laser Powder Bed Fusion Technology Research Articles

Influence of heat treatments on low-power-LPBFed CuCrZr for nuclear fusion applications

In this study, the processability of CuCrZr alloy with additive manufacturing (AM) technology and the performance achievable with Direct Age Hardening treatments for nuclear fusion applications were investigated. This copper alloy is one of the most interesting for the field: it is easier to manufacture through Laser-based additive manufacturing technology and mechanically superior compared to pure copper, and it ensures values of thermal conductivity high enough to be considered a valid substitute for pure copper in many applications.The investigation on CuCrZr alloy was carried out in order to examine the influence of Direct Age Hardening (DAH) treatments on physical and mechanical properties. Laser Powder Bed Fusion technology was used to produce samples with CuCrZr alloy. The additive manufacturing process involved a machine provided with a 370 W IR laser and a preliminary process optimization was carried out to find the printing parameters that assured the highest density (99.15 %), which confirmed the processability of CuCrZr alloy also with low IR laser power. Then, three different DAH treatments were tested and the performance of DAHed material was compared to that of the alloy in as-built conditions. Precipitation phenomena were investigated with DSC analyses, revealing the effectiveness of the treatment already after 1 h. A deep microstructural investigation revealed a fine cellular structure formed during solidification and the presence of nanometric precipitates starting from the as-built condition. The presence of microstructural defects was also investigated. Mechanical performance and thermal conductivity were tested, too: the as-built samples showed limited properties, while very promising results for the use of additively manufactured CuCrZr components have been obtained after the DAHs. The ultimate tensile strength (UTS) and yield strength (YS) doubled the as-built values after 1 h treatment at 550 °C. The thermal conductivity reached three times the initial condition (from 100 W/mK to 300 W/mK).

Frequency- and Temperature-Dependent Uncertainties in Hysteresis Measurements of a 3D-Printed FeSi wt6.5% Material.

Additive manufacturing of soft magnetic materials is a promising technology for creating topologically optimized electrical machines. High-performance electrical machines can be made from high-silicon-content FeSi alloys. Fe-6.5wt%Si material has exceptional magnetic properties; however, manufacturing this steel with the classical cold rolling methodology is not possible due to the brittleness of this material. Laser powder bed fusion technology (L-PBF) offers a solution to this problem. Finding the optimal printing parameters is a challenging task. Nevertheless, it is crucial to resolve the brittleness of the created materials so they can be used in commercial applications. The temperature dependence of magnetic hysteresis properties of Fe-6.5wt%Si materials is presented in this paper. The magnetic hysteresis properties were examined from 20 °C to 120 °C. The hysteresis measurements were made by a precision current generator-based hysteresis measurement tool, which uses fast Fourier transformation-based filtering techniques to increase the accuracy of the measurements. The details of the applied scalar hysteresis sensor and the measurement uncertainties were discussed first in the paper; then, three characteristic points of the static hysteresis curve of the ten L-PBF-manufactured identical toroidal cores were investigated and compared at different temperatures. These measurements show that, despite the volumetric ratio of the porosities being below 0.5%, the mean crack length in the samples is not significant for the examined samples. These small defects can cause a significant 5% decrement in some characteristic values of the examined hysteresis curve.

Sound Characteristics and Mechanical Properties of Metal Powder Chamber Structures Composite Materials Formed by Laser Powder Bed Fusion

Granular damping technology is a widely used method in aerospace and other industries to reduce vibration and noise. However, the technique still faces challenges such as secondary processing, additional structure, single structure, and residual stress. This article introduces a new composite material, the metal powder chamber structure (MPCS), formed through the laser powder bed fusion technology. The article explores the effects of factors like arrangement mode, volume fraction, and powder chamber diameter on the sound and mechanical properties of MPCS. The study shows that MPCS improves the sound insulation effect of the material and defies the mass law of sound insulation. The sample 4B40 using a body‐centered cubic arrangement has a sound insulation coefficient of 52 dB. The sound absorption efficiency curve presents a double peak, and the sample 6F60 exhibits the highest sound absorption efficiency of 0.76. MPCS changes the deformation stage of the material stress–strain curve, and different MPCS also alters the compression deformation mode of the composite material. By studying the effects of MPCS on sound and mechanical properties, it is hoped to provide a better and more sustainable solution for vibration and noise reduction.

Influence of scale effect on surface morphology in laser powder bed fusion technology

ABSTRACT Laser powder bed fusion (LPBF) of multi-scaled structures is a prominent direction pursued by innovative designs and engineering applications. However, understanding the impact of scale effect on the effectiveness of actual structures is a pressing challenge. This work investigates the influence of structure scale on surface morphology and mechanical property by fabricating tensile samples with gauge diameters ranging from 0.2 mm to 5.0 mm. For the hatching scanning strategy, the surface roughness drastically reduces by ∼51% as the diameter increases. This appears to be the coupling results of heat accumulation, molten pool morphology at the end of single-track, overlap between multi-tracks within a layer, and successive rotational buildup between layers. Moreover, decreasing the diameter substantially reduces the tensile strength. Fortunately, a hatching-contour scanning strategy is proposed to eliminate the scale effect of surface morphology and strength. These efforts provide essential guidance for the broader application of multi-scaled structures.

Microstructures and precipitation behaviors of a hypoeutectic high-entropy alloy prepared by laser powder bed fusion

The trade-off between strength and ductility remains a significant challenge for high-entropy alloys (HEAs). The layer-by-layer printing manner inherent in the laser powder bed fusion (L-PBF) leads to distinctive microstructures in alloys, in turn yielding unexpected performances that are promising for resolving this contradiction. At present, the influence of L-PBF technology on the microstructures and mechanical properties of near-eutectic HEAs has yet to be explored. In the present work, a metastable AlCo0.4CrFeNi2.7 hypoeutectic HEA with an extraordinary strength-ductility combination was successfully fabricated using L-PBF. The precipitation behaviors and mechanical properties of the alloy were further modulated through annealing. The results reveal that the high cooling rates inherent in L-PBF promote the formation of a “pseudoeutectic” structure featuring the face-centered-cubic (FCC) + body-centered-cubic (BCC) dual-phase nanolamellae. Furthermore, after annealing at 600–750 °C, the L12 and B2 precipitates are generated in the FCC lamellae, accompanied by a coarsening of the original Cr-rich precipitates (BCC) in the BCC lamellae. The as-printed sample exhibits remarkable mechanical properties, posing a yield strength of 1007 MPa, an ultimate strength of 1249 MPa, and a total elongation of ∼25.1 %. After annealing at 750 °C, the tensile yield strength and ultimate strength are further increased to 1201 MPa and 1512 MPa, respectively, while the elongation is maintained at ∼15.1 %. The analysis results demonstrate that the high strength originates from the hard BCC lamellae and nanolamellar interfaces, while the good ductility stems from the soft FCC lamellae and coordinated deformation of the dual-phase nanolamellae. Furthermore, the strength increase is further substantiated through the introduction of annealing-induced nanoprecipitates, thereby contributing to additional precipitation strengthening.

EBSD investigation of microstructure and microtexture evolution on additively manufactured TiC-Fe based cermets—Influence of multiple laser scanning

Sustainable TiC-Fe-based cermets have been fabricated by adopting an Additive Manufacturing route based on laser powder bed fusion technology (L-PBF). The objective is to produce crack-free cermet components by employing novel multiple laser scanning techniques with variations in laser process parameters. Electron backscatter diffraction analysis (EBSD) was used to study the microstructure and microtexture evolution with variations in laser process parameters. The investigation revealed that adjusting the preheating scan speed (PHS) and melting scan speed (MS) influenced the growth and nucleation of TiC phases. Lowering these speeds resulted in grain coarsening, while higher scan speeds led to grain refinement with larger sub-grain boundaries. Moreover, a high scanning speed increases the degree of dislocation density and internal stress in the fabricated cermet parts. Notably, it is revealed that decreasing the laser scan speed enhanced the proportion of high-angle grain boundaries in the cermet components, signifying an increase in material ductility.

Exploring How LPBF process parameters impact the interface characteristics of LPBF Inconel 718 deposited on Inconel 718 wrought substrates

This work investigates the interface properties of LPBF Inconel 718 deposited on Inconel 718 wrought substrates fabricated using the laser powder bed fusion (LPBF) technique. The as-printed (S1, S2, S3, and S4) samples were characterized using optical microscopy (OM),scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and micro-hardness techniques.The samples showed the development of a melted interface zone (MIZ) at the wrought substrate-deposition interface for all processing conditions. The developed interface showed a dendritic grain structure, signifying the remelting of the wrought substrate followed by rapid solidification. The MIZ thickness increased with an increase in laser power and scan speed (28.5 % increase in the MIZ thickness with a ∼ 12 % increase in normalized enthalpy). The assessment of the MIZ showed a high-quality interface. However, with an increase in scanning speed, the density of the MIZ decreases owing to increased porosity and lack-of-fusion (LOF) defects. The S1 condition (250 W and 850 mm/s) resulted in a highly dense part with no visible porosity, LOF defects, and a high relative density (∼99.9 %) in the MIZ region. The S4 condition showed the presence of large porosities and LOF defects at the deposition-MIZ interface, signifying an inferior bond between the deposition and substrate. The microstructural characterization of the LPBF-processed and MIZ region showed an increase in the primary dendritic arm spacing (PDAS) with increasing laser power due to a reduced cooling rate. The micro-hardness characterization of the sample shows a decrease in the hardness of the MIZ attributed to the dissolution of strengthening phases due to remelting. The present work outcome demonstrates the effectiveness of the proposed methodology for manufacturing high-quality parts using LPBF technology.

Laser additive manufacturing of hierarchical multifunctional chiral metamaterial with distinguished damage-resistance and low-frequency broadband sound-absorption capabilities

Traditional materials or advanced artificially engineered metamaterials are incapable of effectively addressing the simultaneous challenges of impact energy hazards and low-frequency noise. There is an urgent need for multifunctional materials that can address this multi-physics field coupling problem. Herein, a hierarchical multifunctional chiral metamaterial (HMCM) is proposed for damage-resistance and low-frequency broadband sound-absorption capabilities fabricated by means of laser powder bed fusion technology. Cavity resonators with internally extended tubes with hierarchical chiral configuration were selected as primary units. The damage-resistance performance of the HMCM was investigated systematically through experimental, numerical, and theoretical methods. Crashworthiness design and optimization on the multifunctional chiral metamaterial were implemented to explore the effect of geometrical parameters including distance ratio and wall thickness distribution on crushing resistance. It was determined that specific configurations in these parameters significantly enhance mechanism for dissipating energy of the HMCM. Furthermore, the designed metamaterial has been experimentally, numerically, and theoretically proven to possess quasi-perfect broadband sound absorption in the target range of 425 Hz to 553 Hz with an average sound absorption coefficient exceeding 0.9. Overall, this work not only offers a promising solution for designing multifunctional metamaterials but also highlights the potential of additive manufacturing techniques in the development of such sophisticated materials.

Mesoscale Simulation of Laser Powder Bed Fusion with an Increased Layer Thickness for AlSi10Mg Alloy

Low performance is considered one of the main drawbacks of laser powder bed fusion (LPBF) technology. In the present work, the effect of the AlSi10Mg powder layer thickness on the laser melting process was investigated to improve the LPBF building rate. A high-fidelity simulation of the melt pool formation was performed for different thicknesses of the powder bed using the Kintech Simulation Software for Additive Manufacturing (KiSSAM, version cd8e01d) developed by the authors. The powder bed after the recoating operation was obtained by the discrete element method. The laser energy deposition on the powder particles and the substrate was simulated by ray tracing. For the validation of the model, an experimental analysis of single tracks was performed on two types of substrates. The first substrate was manufactured directly with LPBF technology, while the second was cast. The simulation was carried out for various combinations of process parameters, predominantly with a high energy input, which provided a sufficient remelting depth. The calculations revealed the unstable keyhole mode appearance associated with the low absorptivity of the aluminum alloy at a scanning speed of 300 mm/s for all levels of the laser power (325–375 W). The results allowed formulating the criteria for the lack of fusion emerging during LPBF with an increased layer thickness. This work is expected to provide a scientific basis for the analysis of the maximum layer thickness via simulation to increase the performance of the technology.

Production and characterization of lattice samples with solid shell in 17-4 PH stainless steel by Laser Powder Bed Fusion technology

In this work, 17-4 PH stainless steel square-based lattice structures with solid shell were manufactured by Laser Powder Bed Fusion. Face Centered Cubic unit cell was chosen as lattice cell geometry. The main aim of this work was to study the role of the shell in the mechanical behavior under compression load and to identify any critical issue due to the connection of the shell with lattice part. This is a relevant topic since often lattice structure are integrated with solid walls and the study of the relative behavior can support the understating of the performance of complex components. The manufactured samples were tested in as-built and heat-treated condition. In detail, solution and aging treatment was performed as a conventional route for 17-4PH steel. In particular, microhardness and compressive tests were performed, and the mechanical behavior and the fracture mechanisms of the samples were investigated. Furthermore, the defects, the geometry of the struts and the connection with the solid part were analyzed.The detachment of the shell from the lattice did not occur. In fact, the solid part followed the deformation of the structure. The microstructural evolution after heat treatment was found to be responsible for an increase in hardness, strength and deformation for the investigated structures.

Investigating the surface roughness of 3D printed metal parts in case of thin 20 µm build layer thickness

In the case of the laser powder bed fusion technology of metals, the surface quality often does not meet the requirements for use. In addition, the surface can be characterized by different values on different surfaces of the part, depending on the preparation of the workpiece and the technology. The parameters affecting the surface roughness and their effect are also explored in the case of different raw materials and technological settings. In this research, the knowledge was expanded in the case of one of the thinnest layer thicknesses under various conditions. The effect of the angle of orientation during the preparation for the upskin and downskin surfaces of the component, in different directions on the surface of the components were determined in the case of titanium and stainless steel raw materials. In addition, the roughness-reducing effect of the shot peening process was also investigated.Graphical abstract

Achieving superelastic shape recoverability in smart flexible CuAlMn metamaterials via 3D printing

Despite the remarkable advancements in the additive manufacturing of metamaterials, tradeoffs remain between functionality and mechanical performance owning to static configuration, which limits their application, particularly in areas that require efficient multifunctionality. In this paper, we present a novel approach for fabricating multifunctional smart flexible metal metamaterials using laser powder bed fusion technology. This approach enables the reversible recovery superelastic strain exceeding 20 % with a 100 % recovery rate—ten times higher than that observed in the printed alloy. This is achieved by utilising an innovative metamaterial structural design and a novel shape memory alloy powder. To achieve the aforementioned purpose, the metamaterial unit cells were initially designed to ensure flexible deformation ability with a Poisson's ratio of zero. Then, we prepared a novel shape memory alloy composition of Cu-18at%Al-l0at%Mn-0.3 at%Si, which exhibited excellent printability and adaptability within the laser powder bed fusion additive manufacturing process. Additionally, the printed SMA exhibited superelasticity, one-way and two-way shape memory effect under varying parameters. Furthermore, the combination of multifunctionality into the flexible CuAlMn metamaterials was achieved by manipulating process parameters. Remarkably, the printed metamaterial demonstrates exceptional flexibility deformation, and presents superelasticity or shape memory effect, ensuring the recovery of its original shape after experiencing deformation. This work not only demonstrates the vast potential of utilising additive manufacturing technology for fabricating functional and adaptable metal metamaterials but also presents an innovative approach for creating smart metal metamaterial.

Thermally stable strong texture in additively manufactured cobalt-based superalloys

Cobalt-based γ'-strengthened superalloy exhibits tremendous potential in numerous fields, such as power generation equipment and the aerospace industry. The characteristics of laser powder bed fusion technology have aligned well with the demands for superalloy's strong texture or single crystal microstructure. However, the post-heat treatment processes often disrupt the initial microstructure of the as-printed parts due to unavoidable recrystallization. In this study, we obtained a strong <101> texture in an as-printed Co-5Al-14V (at.%) ternary cobalt-based superalloy, which is difficult to achieve in nickel-based superalloys. Intriguingly, this <101> texture remains thermally stable even after aging treatment at a near γ' solvus temperature. Hence, a <101> textured microstructure with an evenly distributed γ'(L12) precipitates was attained, which benefits the improvement of high-temperature creep resistance. The unique microstructure characteristics revealed in this work can be beneficial for the development of cobalt-based superalloys and shed light on the microstructural engineering of other LPBF-manufactured superalloys.

3D Chiral Energy-Absorbing Structures with a High Deformation Recovery Ratio Fabricated via Selective Laser Melting of the NiTi Alloy.

Excellent energy-absorbing structures have been highly sought after in engineering applications to improve devices and personal safety. The ideal energy absorption mechanism should exhibit characteristics such as lightweight, high energy absorption capacity, and efficient reusability. To address this demand, a novel three-dimensional (3D) chiral lattice structure with compression-twist coupling deformation is fabricated by combining the left and right chiral units. The proposed structure was fabricated in NiTi shape memory alloys (SMAs) by using laser powder bed fusion technology. The compression experiment result indicates that the shape recovery ratio is as high as 94% even when the compression strain is over 80%. Additionally, the platform strain reaches as high as 66%, offering high-level specific energy absorption, i.e., 213.02 J/g. The obtained results are of great significance for basic research and engineering applications of energy-absorbing structures with high deformation recovery ratios.

Fatigue analysis of as-built and heat-treated severely notched AlSi10Mg alloy specimens made by laser powder bed fusion technology

This study examines L-PBF-fabricated aluminium alloy specimens with smooth and notched geometries, assessing their axial fatigue performance in both as-built and heat-treated conditions. The influence of the performed heat treatment on microstructure, production defects and fatigue properties was investigated on unnotched specimens and specimens with deep U-notch geometry. The experimental results revealed significant impact of heat treatment on the microstructure and internal defects, which resulted in an enhancement of fatigue properties of the specimens. Lastly, the fatigue results revealed a negligible impact of the employed heat treatment on the notch sensitivity of the studied materials.

Regulate the microstructure, tensile properties and fatigue crack growth behavior of an Al–Zn–Mg–Cu alloys fabricated by laser powder bed fusion via post-heat treatment

An Al–Zn–Mg–Cu–Si–Zr–Er alloy was fabricated by laser powder bed fusion technology. A unique cellular structure consisting of α-Al, Mg2Si, and Al2CuMg phases was observed in both as-printed (AP) and direct aging (DA) alloys. Direct aging treatment at 150 °C × 4 h can improve the yield strength and hardness of the alloy, and precipitation strengthening and fine grain strengthening are dominant mechanisms. The strength of the regression re-aging (RRA) heat treated alloy decreased, while the elongation was obviously improved, and the grain boundary was continuous without precipitates free zones. DA could not significantly hinder the fatigue crack growth rate of the as-printed alloy, but the improvement of plasticity, elimination of residual stress, and the effect of precipitates in RRA alloy extend the life of the fatigue crack growth stage, thereby improving the overall fatigue life of the alloy from 1.17 × 105 cycles to 3.93 × 106 cycles.

Functionality and Mechanical Performance of Miniaturized Non-Assembly Pin-Joints Fabricated in Ti6Al4V by Laser Powder Bed Fusion.

In this work, additively manufactured pin-joint specimens are analyzed for their mechanical performance and functionality. The functionality of a pin-joint is its ability to freely rotate. The specimens were produced using laser powder bed fusion technology with the titanium alloy Ti6Al4V. The pin-joints were manufactured using previously optimized process parameters to successfully print miniaturized joints with an angle to the build plate. The focus of this work lies in the influence of joint clearance, and therefore all specimens were manufactured with a variety of clearance values, from 0 µm up to 150 µm, in 10 µm steps. The functionality and performance were analyzed using torsion testing and tensile testing. Furthermore, a metallographic section was conducted to visually inspect the clearances of the additively manufactured pin-joints with different joint clearance values. The results of the torsion and tensile tests complement each other and emphasize a correlation between the joint clearance and the maximal particle size of the powder utilized for manufacturing and the mechanical behavior and functionality of the pin-joints. Non-assembly multibody pin-joints with good functionality were obtained reliably using a joint clearance of 90 µm or higher. Our findings show how and with which properties miniaturized pin-joints that can be integrated into lattice structures can be successfully manufactured on standard laser powder bed fusion machines. The results also indicate the potential and limitations of further miniaturization.

Predictive modeling of lattice structure design for 316L stainless steel using machine learning in the L-PBF process

Lattice structures in additive manufacturing of 316L stainless steel have gained increasing attention due to their well-suited mechanical properties and lightweight characteristics. Infill structures such as honeycomb, lattice, and gyroid have shown promise in achieving desirable mechanical properties for various applications. However, the design process of these structures is complex and time-consuming. In this study, we propose a machine learning-based approach to optimize the design of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using laser powder bed fusion (L-PBF) technology under different loading conditions. A dataset of simulated lattice structures with varying geometries, wall thickness, distance, and angle using a computational model that simulates the mechanical behavior of infill structures under different loading conditions was generated. The dataset was then used to train a machine learning model to predict the mechanical properties of infill structures based on their design parameters. Using the trained machine learning model, we then performed a design exploration to identify the optimal infill structure geometry for a given set of mechanical requirements and loading conditions. Finally, we fabricated the optimized infill structures using L-PBF technology and conducted a series of mechanical tests to validate their performance under different loading conditions. Overall, our study demonstrates the potential of machine learning-based approaches for efficient and effective designing of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using L-PBF technology under different loading conditions. Furthermore, this approach can be used for dynamic loading studies of infill structures.

Assembling feather-like reentrant structures with multiple mechanical properties fabricated by laser powder bed fusion

A new assembly design method for structural components is proposed. Inspired by the feathers of the grey crane, which have an energy dissipation effect, novel re-entrant scapus component and novel re-entrant double-crank component are proposed. Novel re-entrant structures are formed by assembling honeycomb structure (HS), poisson structure (PS), and chiral structure (CS). Laser powder bed fusion technology (LPBF) is utilized for the manufacturing of bio-inspired structures. And the impact of structural assembly on mechanical performance is comprehensively analyzed through experimental, numerical, and theoretical approaches. Euler theory is employed to predict the influence of bionic components on structural load trends, while explaining the relationship between compression load and deformation. Specifically, the average load capacity of bio-inspired scapus re-entrant structures and double-crank re-entrant structures exceeds that of their original designs by at least 55% and 13.2%, respectively. Moreover, specific energy absorption increases by a minimum of 8.6% and 3.4%, accompanied by improved heat dissipation performance in these structures. Finally, battery pack impact resistance models as well as thermal conductivity models for electric-powered vehicles are presented as examples to validate the potential application prospects of this novel bio-inspired re-entrant structure in engineering.

Interface Analysis between Inconel 625 and Cobalt-Chromium Alloy Fabricated by Powder Bed Fusion Using Pulsed Wave Laser.

A few components used in the aerospace and petrochemical industries serve in corrosive environments at high temperatures. Corrosion-resistant metals or unique processes, such as coating and fusion welding, are required to improve the performance of the parts. We have used laser powder bed fusion (LPBF) technology to deposit a 5 mm thick corrosion-resistant CoCrMo layer on a high-strength IN625 substrate to improve the corrosion resistance of the core parts of a valve. This study found that when the laser volumetric energy density (EV) ≤ 20, the tensile strength increases linearly with the increase in EV, and the slope of the curve is approximately 85°. The larger the slope, the greater the impact of EV on the intensity. When EV > 20, the sample strength reaches the maximum tensile strength. When the EV increases from 0 to 20, the fracture position of the sample shifts from CoCrMo to IN625. When EV ≤ 38, the strain increases linearly with the increase in EV, and the slope of the curve is approximately 67.5°. The sample strain rate reaches the maximum when EV > 38. Therefore, for an optimal sample strength and strain, EV should be greater than 38. This study provides theoretical and technical support for the manufacturing of corrosion-resistant dissimilar metal parts using LPBF technology.