Powder Bed Fusion Process Research Articles

Origin of the enhanced pseudo-elasticity of additively manufactured Fe-17Mn-5Si-4Ni-10Cr-(V, C) shape memory alloy fabricated by laser powder bed fusion

This study investigated the origin of the enhanced pseudo-elasticity of additively manufactured vanadium carbide-containing Fe-based shape memory alloys. The aged samples with two different starting microstructures, as-built and solution-treated, showed completely different final microstructures following identical aging treatments. The sample aged directly from the as-built microstructure exhibited typical solidification structures, molten pools, and cellular structures with fine grain sizes inherited from the laser powder bed fusion process with a high cooling rate. In contrast, the sample aged following solution treatment revealed fully recrystallized grain structures with relatively larger grain sizes than the former. Despite having the same type of carbides, the directly aged sample had finer and denser precipitates than the sample aged following solution treatment. Additionally, compared to the sample aged following solution treatment, the directly aged sample exhibited a larger pseudo-elastic recovery strain. The precipitation behavior may have had a negligible impact on the pseudo-elastic behavior because the increase in the pseudo-elastic recovery strain following aging treatment was not significant for either sample. Besides, thermodynamic calculations predicted that the stability of the face-centered cubic (fcc)-γ phase would be increased by local elemental segregation at cell boundaries. Cell boundaries with high fcc-γ phase stability can act as sites that can apply back stress on the deformation-induced hcp-ε phase, thus promoting reverse motion of the Shockley partial dislocations or deformation-induced hcp-ε phase. Furthermore, the smaller grain size enhanced the stability of the fcc-γ phase.

Volume energy density and laser power: key determinants in SLS-processed PA12 mechanical properties

AbstractAdditive manufacturing (AM) represents a significant breakthrough in the field of engineering, revolutionizing the way products and components are designed and manufactured. Among the various methods used to employ polymer materials in AM, powder bed fusion (PBF) processes, specifically selective laser sintering (SLS), stand out as one of the most widely utilized approaches. This method offers substantial advantages over other AM techniques for treating polymers. However, SLS is inherently based on complex underlying physical mechanisms and phenomena and it involves a significant number of process parameters, making a comprehensive and extensive study of the process necessary. In the present article, we conduct an experimental study to examine the impact of two pivotal process parameters in SLS: volumetric energy density (VED) and nominal laser power (LP), on the mechanical properties of Polyamide 12 (PA12). The assessment of the material’s mechanical behavior was conducted by measuring its tensile, compressive, and flexural properties, adhering to the respective ASTM standards. Additionally, we employed appropriate statistical tests, including the Coefficient of Variation (CV) to estimate the process’s repeatability and consistency, and Fisher’s least significant difference (LSD) method to determine significant differences between mean property values for different process parameters. The results revealed the impact of volumetric energy density (VED) and nominal laser power (LP) on each mechanical property and mechanical index. Furthermore, the study identifies general rules and trends related to the efficiency and feasible thresholds of the process. Finally, we provide an interpretation of the results based on the fundamental physical mechanisms, also supported by the respective XRD and microscopy images.

Simulation of 316L Stainless Steel Produced the Laser Powder Bed Fusion Process.

Additive manufacturing is increasingly being used in the production of parts of simple as well as complex shapes designed for various areas of industry. Prevention of errors in the production process is currently enabled using simulation tools that have the function of predicting possible errors and, at the same time, providing a set of information about the behaviour of the material in the metal additive manufacturing process. This paper discusses the simulation processes of 316L stainless steel produced using the laser powder bed fusion (L-PBF) process. Simulation of the printing process in the Simufact Additive simulation program made it possible to predict possible deformations and errors that could occur in the process of producing test samples. After analysing the final distortion already with compensation, the simulation values of maximum deviation -0.01 mm and minimum -0.13 mm were achieved.

Prediction of Ni-based alloy microstructure in wire arc additive manufacturing from cellular automata model

Wire Arc Additive manufacturing (WAAM) process is a class of directed energy deposition processes with wire feedstock. The process enables a higher build rate than the powder-based additive process and integrates multiple custom wire feedstock to induce spatial variation of microstructure and composition. The lower speed employed in WAAM reduces the cooling rate and resultant residual stress compared to the powder bed fusion process. The systematic epitaxy across the layer creates a directional/columnar microstructure for Ni-superalloy. Here, we report cellular automata model development to predict the microstructure evolution with surface and bulk nuclei for single track and multiple layers. The cellular automata model was developed to account for secondary element addition, predict segregation, local melting, and latent heat release, as well as predict crystallographic texture/Euler angles from orientation information. We experimentally validated the layer-level microstructure and texture from SEM and EBSD, respectively, and found agreement with the CA model developed.

Change in Mechanical Properties of Laser Powder Bed Fused AlSi7Mg Alloy during Long-Term Exposure at Warm Operating Temperatures.

Al-Si-Mg alloys are most commonly used to produce parts by laser powder bed fusion for several industrial applications. A lot of papers have already focused on the effects induced by conventional heat treatments on the microstructure and mechanical properties of AlSi10Mg alloys, rather than on AlSi7Mg. Nobody has investigated thermal stability during long-term direct and artificial aging heat treatments of AlSi7Mg. This study investigates the changes in mechanical properties induced by long-term exposure (512 h) at 150 and 175 °C (the operating temperature of AlSi7Mg) after (i) the laser powder bed fusion process performed on a pre-heated build platform (150 °C), and (ii) heat treatments to the solution at 505 °C per 0.5 and 4 h. Thermal stability was evaluated through both Vickers microhardness measurements to obtain the aging profiles, and tensile tests to evaluate the mechanical properties in specific conditions. An optical microscope was used to investigate the microstructure. It was found that aging at 175 °C confers the same effects induced by a secondary aging heat treatment on as-built samples and, simultaneously, the worst effects on the solution heat treated AlSi7Mg alloy after long-term exposure. The AlSi7Mg DA at both 150 °C and 175 °C showed the same Vickers microhardness (~95 HV0.5), UTS (~300 MPa), and YS (~200 MPa) values for the longest exposure times because the fine and cellular α-Al matrix confers higher stiffness and strength despite the over-aged conditions. On the other hand, the coarsening effects that affected the precipitates during aging at 175 °C, as well as the formation of the precipitate-free zones along the grain boundaries, justified the highest detrimental effects induced on the SHTed samples.

Dynamic Compressive Properties and Failure Mechanism of the Laser Powder Bed Fusion of Submicro-LaB6 Reinforced Ti-Based Composites.

In this study, lanthanum hexaboride (LaB6) particle-reinforced titanium matrix composites (PRTMCs, TC4/LaB6) were successfully manufactured using the laser powder bed fusion (LPBF) process. Thereafter, the effect of the mass fraction of LaB6 on the microstructure and the dynamic compressive properties was investigated. The results show that the addition of LaB6 leads to significant grain refinement. Moreover, the general trend of grain size reveals a concave bend as the fraction increases from 0.2% to 1.0%. Furthermore, the texture intensity of prior β grains and α grains was found to be weakened in the composites. It was also observed that the TC4/LaB6 have higher quasi-static and dynamic compressive strengths but lower fracture strain when compared with the as-built TC4. The sample with 0.5 wt.% LaB6 was found to have the best strength-toughness synergy among the three groups of composites due to having the smallest grain size. Furthermore, the fracture mode of TC4/LaB6 was found to change from the fracture under the combined action of brittle and ductility to the cleavage fracture. This study was able to provide a theoretical basis for an in-depth understanding of the compressive properties of additive manufacturing of PRTMCs under high-speed loading conditions.

Unique Yttria Nanoparticle Strengthening in an Inconel 718 Superalloy Fabricated by Additive Manufacturing

AbstractOxide dispersion strengthened (ODS) nickel (Ni)‐based superalloys are advanced materials known for their outstanding tensile and creep performance at temperatures exceeding 1000 °C. Nevertheless, their conventional synthesis presents a longstanding challenge in cost‐effectively producing intricate components for critical applications. In this work, electrostatic self‐assembly (ESA) of powders with the laser powder bed fusion (LPBF) process are successfully combined to produce yttria ODS Inconel 718 (IN718) alloy for the first time. This approach demonstrates a significant contribution of yttria to the strength of IN718 after the solid solution heat treatment, as evidenced by ≈50% improvement in room temperature yield strength with a 0.5 wt.% yttria addition. The addition of yttria by this process leads to a heterogeneous microstructure. This heterogeneous microstructure comprises two distinct grain areas with varying amounts of yttria nanoparticles and dislocation storage. The results show that the yield strength increase can be predicted by the combination of both Y2O3 dispersion strengthening and dislocation strengthening mechanisms. These findings offer an effective approach to tailor heterogeneous microstructures, unlocking new opportunities for cost‐effectively producing high‐performance ODS Ni‐based superalloy products with excellent mechanical properties.

Additively Manufactured Zn-2Mg Alloy Porous Scaffolds with Customizable Biodegradable Performance and Enhanced Osteogenic Ability.

The combination of bioactive Zn-2Mg alloy and additively manufactured porous scaffold is expected to achieve customizable biodegradable performance and enhanced bone regeneration. Herein, Zn-2Mg alloy scaffolds with different porosities, including 40% (G-40-2), 60% (G-60-2), and 80% (G-80-2), and different unit sizes, including 1.5mm (G-60-1.5), 2mm (G-60-2), and 2.5mm (G-60-2.5), are manufactured by a triply periodic minimal surface design and a reliable laser powder bed fusion process. With the same unit size, compressive strength (CS) and elastic modulus (EM) of scaffolds substantially decrease with increasing porosities. With the same porosity, CS and EM just slightly decrease with increasing unit sizes. The weight loss after degradation increases with increasing porosities and decreasing unit sizes. In vivo tests indicate that Zn-2Mg alloy scaffolds exhibit satisfactory biocompatibility and osteogenic ability. The osteogenic ability of scaffolds is mainly determined by their physical and chemical characteristics. Scaffolds with lower porosities and smaller unit sizes show better osteogenesis due to their suitable pore size and larger surface area. The results indicate that the biodegradable performance of scaffolds can be accurately regulated on a large scale by structure design and the additively manufactured Zn-2Mg alloy scaffolds have improved osteogenic ability for treating bone defects.

Fabrication of functionalised graphene-PAEK nanocomposites for different manufacturing processes

ABSTRACTAchieving good dispersion of graphene (GNP), in polyetheretherketone (PEEK), is challenging due to the high melt viscosity, solvent resistance and processing temperature of PEEK. In addition, certain manufacturing processes tend to enhance the anisotropy due to GNP orientation within the structure. This study investigated the fabrication of nanocomposite parts through hot compression moulding (C-MOULD) and powder bed fusion (PBF) processes, using powder with GNPs fused to the surface of polymeric particles, through a process called mechanofusion. The method applies mechanical forces of compression, shear and impact to generate a mechanical bond between materials, in this case, O2 functionalised GNP and a developmental polyaryletherketones (PAEK) grade powder. The novelty of this work is in the combination of processes used for manufacturing (material preparation and actual manufacturing processes), which are scalable and efficient in comparison with existing methods (such as solvent mixing or melt-compounding). The mechanofusion GNP-PAEK composite powders were successfully printed for the first time using the EOS P800 system with notable improvements in electrical and mechanical properties. This study highlights that the mechanofusion process could be used as an efficient process for making multifunctional nanocomposite materials and this can be combined with additive manufacturing (AM) processes to produce complex components.

Development and application of a simplified thermo-evaporative multi-track laser powder bed fusion model for Ti6Al4V

Often the parametric analyses of the laser powder bed fusion (LPBF) process are concerned with laser power or scan speed, and other parameters such as scan spacing are paid lesser attention, particularly due to the huge computational power required for their investigation. Hence, in this study a simple and efficient thermo-evaporative model is developed for multi-track LPBF that excluded the solution of melt pool flow dynamics and thus enabled faster and economic simulation of the problem. Material evaporation was added to control the temperature rise up to reasonable levels, which acted only as a heat loss flux on the top boundary. The model has been first validated against the single track results and then applied to multi-track modeling for several different values of scan spacing while other parameters are kept constant. The study showed the potential of the developed thermo-evaporative model in simulating the multi-track problem and conducting a parametric analysis concerning the variation of scan spacing. The results were verified against the experimental results at a higher scan spacing where the computed and experimental porosities were compared qualitatively, and it was observed that the proposed model predicted the lack of melting porosity very well. The temperature field and other thermal characteristics such as thermal gradients and heating/cooling rates were calculated and discussed as well.

Microstructure-induced anisotropic tribological properties of Sc-Zr modified Al–Mg alloy (Scalmalloy®) produced via laser powder bed fusion process

AbstractIn this study, the correlation between the microstructure and tribological performance of Sc and Zr-modified Al–Mg alloy (Scalmalloy®) samples produced via laser powder bed fusion process was evaluated via a dry sliding Pin-on-Disc wear test under different planes, directions, and various normal applied loads. The results revealed a remarkable dependency of wear properties on the as-built microstructure so that different behaviors were observed along the scanning and building planes. The microstructural examination indicated the presence of bi-modal grains and finely shaped equiaxed grains observed in the building and scanning planes, respectively. Increasing the applied loads from 20 to 40 N led to a significant increase in the coefficient of friction (COF) while increasing the load from 40 to 60 N, slightly decreasing the COF for the studied samples. No dependency was found between the COF and the corresponding microstructure at the highest applied load. The anisotropic wear resistance and COF values were predominant at the lowest applied load. Due to tailored as-built microstructural features and different microhardness values, lower wear rates were noticed along the scanning plane for all applied loads. Under the 20 N applied load, however, the worn surface of the scanning plane showed a clearer and smoother surface compared to the building plane surfaces. Ultra-fine equiaxed grains along the scanning plane and columnar grains along the building plane were determined as the main factors creating anisotropic tribological behavior. The outcomes of this study can pave the way toward producing more wear-resistant surfaces and developing components for critical wear applications in as-built conditions with no need for expensive and time-consuming surface treatments.

Solute trapping and non-equilibrium microstructure during rapid solidification of additive manufacturing

Solute transport during rapid and repeated thermal cycle in additive manufacturing (AM) leading to non-equilibrium, non-uniform microstructure remains to be studied. Here, a fully-coupled fluid dynamics and microstructure modelling is developed to rationalise the dynamic solute transport process and elemental segregation in AM, and to gain better understanding of non-equilibrium nature of intercellular solute segregation and cellular structures at sub-grain scale during the melting-solidification of the laser powder bed fusion process. It reveals the solute transport induced by melt convection dilutes the partitioned solute at the solidification front and promotes solute trapping, and elucidates the mechanisms of the subsequent microstructural morphology transitions to ultra-fine cells and then to coarse cells. These suggest solute trapping effect could be made used for reducing crack susceptibility by accelerating the solidification process. The rapid solidification characteristics exhibit promising potential of additive manufacturing for hard-to-print superalloys and aid in alloy design for better printability.

Magneto-active composites with locally tailored stiffness produced by laser powder bed fusion

Additive manufacturing technologies enable the production of complex and bioinspired shapes using magneto-responsive materials, which find diverse applications in soft robotics. Particularly, the development of composites with controlled gradients in mechanical properties offers new prospects for advancements in magneto-active materials. However, achieving such composites with gradients typically involves complex multi-material printing procedures. In this study, a single-step laser powder bed fusion (LPBF) process is proposed that enables precise local adjustments of the mechanical stiffness within magneto-active composites. By utilizing distinct laser parameters in specific regions of a composite containing thermoplastic polyurethane and atomized magnetic powder derived from hard magnetic Nd-Fe-B, the stiffness of the composite can be modified within the range of 2–22 MPa. Various magneto-responsive actuators with locally tailored stiffness are fabricated and their magnetic performance is investigated. The enhanced response exhibited by actuators with locally adjusted mechanical properties in comparison to their homogeneous counterparts with identical geometries is shown. As a demonstration of a biomedical application, a magnetically responsive stent with localized adjustment is presented with the ability to meet specific requirements in terms of geometry and local stiffness based on an individual's anatomy and disease condition. The proposed method presents an approach for creating functionally graded materials using LPBF, not only for magneto-active materials but also for several other structural and functional materials.

Assessment Possibility of Controlling Structure Formation by Changing the Technological Parameters LPBF Process

Abstract—In this paper, the possibility of creating a controlled structure by varying the parameters of laser powder bed fusion (LPBF) process on the example of austenitic stainless steels is studied. Based on the study of the structure of experimental samples, the influence of a combination of various technological parameters that make up the scanning strategy when preparing a 3D-model for the LPBF process on the processes of structure formation is shown. The possibility of forming elements with different structures within one part during its manufacture by the LPBF method by changing the technological parameters of the process that make up the scanning strategy is shown. It is noted that the use of 3D-models identical in the geometry formed, but different in the strategy of scanning with a laser beam directly in the process of laser fusion, leads to the formation of a fundamentally different structure of the created sample, since the formation of the microstructure is strongly influenced by the conditions of metal crystallization, which directly depend on the scanning strategy.

Developing Four Powder Recycling Strategy for Sustainable Additive Manufacturing 3D Printing Process

This paper presents a detailed analysis of four different powder recycling strategies for the metal additive manufacturing process focused on examining the efficacy of recycling Ti6Al4V alloy powder for the Laser-Based Powder Bed Fusion (LBPF) process. The study evaluates four distinct recycling strategies (A, B, C, D) and their impact on powder-saving mechanisms. The experimental methodology involves careful leftover powder sampling, implementation of recycling strategies and print cycle analysis from each recycling strategy. The results show that Strategies C and D exhibit the lowest powder waste, allowing 6 times the reuse of leftover powder and producing 384 parts with minimal powder waste at the end of the process. Strategy B also performs well, enabling 8 cycles and building 512 parts with only a small amount of powder wasted. Conversely, Strategy A yields the highest powder waste despite achieving the same number of cycles and prints. This proposed approach requires a total volume of 224,000 mm3 of powder for each build. This entails using 500g of gas-atomized Ti-6Al-4V powder, with an average particle size D90 of approximately 50 μm. This features a continuous mixing technique, wherein each build combines 50% virgin powder with 50% of the previously collected and sieved powder.

Multi-material additive manufacturing-functionally graded materials by means of laser remelting during laser powder bed fusion

Many processes may be used for manufacturing functionally graded materials. Among them, additive manufacturing seems to be predestined due to near-net shape manufacturing of complex geometries combined with the possibility of applying different materials in one component. By adjusting the powder composition of the starting material layer by layer, a macroscopic and step-like gradient can be achieved. To further improve the step-like gradient, an enhancement of the in-situ mixing degree, which is limited according to the state of the art, is necessary. In this paper, a novel technique for an enhancement of the in-situ material mixing degree in the melt pool by applying laser remelting (LR) is described. The effect of layer-wise LR on the formation of the interface was investigated using pure copper and low-alloy steel in a laser powder bed fusion process. Subsequent cross-sectional selective electron microscopic analyses were carried out. By applying LR, the mixing degree was enhanced, and the reaction zone thickness between the materials was increased. Moreover, an additional copper and iron-based phase was formed in the interface, resulting in a smoother gradient of the chemical composition than the case without LR. The Marangoni convection flow and thermal diffusion are the driving forces for the observed effect.

Optimizing in-situ monitoring for laser powder bed fusion process: Deciphering acoustic emission and sensor sensitivity with explainable machine learning

Optimizing in-situ monitoring for laser powder bed fusion process: Deciphering acoustic emission and sensor sensitivity with explainable machine learning

Understanding grain evolution in laser powder bed fusion process through a real-time coupled Lattice Boltzmann model-Cellular Automaton simulation

Understanding grain evolution in laser powder bed fusion process through a real-time coupled Lattice Boltzmann model-Cellular Automaton simulation

Laser Powder Bed Fusion Process and Structure Data Set for Process Model Validations

Laser Powder Bed Fusion Process and Structure Data Set for Process Model Validations

Defect detection in laser-based powder bed fusion process using machine learning classification methods

The aim of this study is to deploy machine learning (ML) classification methods to detect defective regions in additive manufacturing, colloquially known as 3D printing, particularly for the laser-based powder bed fusion process. A custom-designed test specimen composed of 316L was manufactured using EOS M 290 machine. Multinomial logistic regression (MLR), artificial neural network (ANN), and convolutional neural network (CNN) classification techniques were applied to train the ML models using optical tomography infrared images of each additively manufactured layer of test specimen. Based on the trained MLR, ANN, and CNN classifiers, the ML models predict whether the manufactured layer is standard or defective, yielding five classes. Defective layers were classified into two classes for lack of fusion and two classes for keyhole porosity. The supervised approach yielded impeccable accuracy (>99%) for all three classification methods, however CNN inherited the highest degree of performance with 100% accuracy for independent test dataset unfamiliar to the model for unbiased evaluation. The high performance and low cost of computing observed in this work can have the potential to detect and eliminate defective regions by tuning the processing parameters in real time resulting in significantly decreased costs, lead-time, and waste. The proposed quality control can enable mass adoption of additive manufacturing technologies in a vast number of industries for critical components that are design- and shape- agnostic.