Search

This paper presents a novel application of a three-dimensional smoothed particle hydrodynamics model to simulate directed energy deposition (DED) additive manufacturing processes. A proposed workflow comprises a random powder generator to introduce individual powder particles into the SPH core simulation. The DED workflow simulation is successfully demonstrated for two real DED setups with significantly difference of individual powder/melt-pool size ratios and different materials. The simulation results are in good agreement with experimental data in terms of geometrical dimensions of deposited material and melt-pool surface temperature. Detail analyses on the results revealed transient internal characteristics of the melt-pool which otherwise nearly impossible to be observed from experimental data. These include the concave shape of the melt-pool surface, bifurcations and circulations of metal liquid flow, and spatial–temporal temperature distributions in the melt-pool which also vary with respect to scan parameters. These findings could provide better understanding on the DED processes that are difficult to measure and help achieve better quality of the printed products. [ABSTRACT FROM AUTHOR]

One of the metallic (additive manufacturing) AM processes is directed energy deposition (DED), which utilizes a machine tool or robotic system for motion control. A laser heat source is used to melt the powder and substrate at the same time after the powder is fed through a powder feeder. Each layer of beads is deposited side by side, and then the layers are stacked over one another. During this process, parts are subjected to intense thermal cycles before reaching room temperature. This rapid heating and cooling, and subsequent expansion and contraction, leads to the generation of tensile and compressive residual stresses within the part. The accumulation of these thermal residual stresses has a detrimental effect on the final product quality. If the residual stresses exceed the yield strength of the material, this will lead to the non-uniform plastic deformation of the substrate as well as cracks, warping, and buckling. One of the influential factors on the amount and gradients of the residual stresses is the deposition or scanning pattern. Therefore, the depositions of the beads in each layer necessitate a careful analysis of the thermal history related to the scanning pattern in order to find the best path for bead deposition. It is desirable to minimize residual stresses and distortions. The purpose of this study was to investigate the thermo-mechanical characteristics for different scanning patterns for laser cladding-based additive manufacturing processes in three types of geometries. This study considered one-way, zigzag, spiral, and raster-angled pattern scans for various component configurations. The fabrication geometries are cross-type, a rectangular surface with a hole, and U-shape. These geometries account for different types of convection-conduction heat diffusion within the parts. The thermo-mechanical responses of the parts to different scanning patterns were assessed using an unsteady finite volume method with a one-way coupling with a finite element structural solver. The scanning patterns were derived from tool path geometry imported from commercial additive manufacturing software (APlus). According to the results, a high conduction zone during the last scan causes a non-uniform cooling rate while the latest scanning area experiences tensile stress. According to the study of different scanning patterns, geometry plays a role in determining which pattern performs best. Cross-type fabrication exhibits the best mechanical response to different scanning patterns. More research needs to be conducted to assess the influences of the geometry in tandem with scanning patterns, and unique AM tool paths may need to be introduced. [ABSTRACT FROM AUTHOR]

In this study, a thin-wall build of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) was additively manufactured by multilayer direct energy deposition process. The effect of heat treatment on the microstructure, phase transformation and mechanical properties was analyzed. The microstructure near the substrate shows a feature of coarse columnar dendritic FCC phases and tiny lamellar eutectic structure distributing in the interdendritic region, while, near the middle region of thin-wall build, the microstructure consists of lamellar eutectic structure. The subsequent heat treatment has a significant effect on the microstructure evolution and mechanical properties. Plenty of short bulk FCC phases emerge during the heat treatment process. When the heat treatment temperature (HTT) reaches 1100 °C, the short bulk FCC phase transforms into BCC phase. The eutectic structure firstly refines and then coarsens with the increase in HTT from 800 to 1300 °C. The tensile strength obtains a maximum value when HTT = 1100 °C at which the eutectic structure has the finest average width. Our results supported some help to understand the microstructure diversity, as well as the effect of heat treatment, in the laser additive manufactured AlCoCrFeNi2.1 EHEA. [ABSTRACT FROM AUTHOR]

This paper describes an Artificial Intelligence based approach to analyze data collected during the manufacturing of metal parts through Direct Energy Deposition (DED) process. A dedicated monitoring system has been integrated into the DED machine with the aim of gathering data while the manufacturing is running. In particular, a camera and a bi-chromatic pyrometer have been added to the optical chain: images and temperatures of the melted area are stored synchronously - as well as the machine axis positions and process parameters. Images represent the process signature, for example the frame brightness has been proved to be related to the local energy or spikes visible in the picture are indicator of process stability. Temperatures, on the other hand, are key in such manufacturing processes as they can trigger residual stresses or distortions in the final parts. In the proposed approach both signals have been considered to pursue a robust and complete solution. A number of tests have been conducted by varying tool path strategies and built parts have been geometrically evaluated. An AI based classifier has been trained starting from this dataset and validated consequently: it receives the signals coming from the monitoring system and provides an indication about the expected quality of the deposited track. In particular, it classifies a track as "good" if no material under/over-deposition is estimated and labels it as "bad" in the opposite situation. The benefits of this solution have been assessed with regard to Inconel 718 parts. Finally, it has been tested on a real use case consisting of deposition of materials on turbine blade tips for repairing actions. [ABSTRACT FROM AUTHOR]

Industrial development continues to present challenges for manufacturers. One of them is additive manufacturing (AM) with metallic materials. One promising solution is wire arc additive manufacturing (WAAM). Currently, WAAM is a more promising tool for developers, firstly due to the simplicity of its realization and secondly for its cost-effectiveness. Building materials are represented by welding wires, so the deposition rate is favorable. A pulse power source is commonly used in this scheme of realization. Much less attention has been paid to the optimization of the power source working regime, i.e., welding mode. Indeed, the power determines the whole process of WAAM. Therefore, in the present work, an attempt has been made to perform a scientifically based design for the optimal welding mode. The austenitic welding wire was chosen to eliminate phase-transition effects in the solid state of the deposited metal. As a result of the investigation, the advantages of the designed welding mode for WAAM application are made clear. It was shown that the predominant effect on penetration depth possesses pulse current and its input is 49%, while other parameters, i.e., pause current, pulse on time, and frequency, have a less valuable impact. The Taguchi optimization algorithm allowed the development of a specific welding mode for providing better formation of the welds, more grain fined microstructure, and thus improved properties of the modeled wall. Successful efforts have been made to optimize welding modes for WAAM applications. This study is important for manufacturers as well as engineers and scientists. [ABSTRACT FROM AUTHOR]

Magnetism and magnetic levitation has found significant interest within the field of micromanipulation of objects. Additive manufacturing (AM), which is the computer-controlled process for creating 3D objects through the deposition of materials, has also been relevant within the academic environment. Despite the research conducted individually within the two fields, there has been minimal overlapping research. The non-contact nature of magnetic micromanipulator levitation systems makes it a prime candidate within AM environments. The feasibility of integrating magnetic micromanipulator levitation system, which includes two concentric coils embedded within a high permeability material and carrying currents in opposite directions, for additive manufacturing applications is presented in this article. The working principle, the optimization and relevant design decisions pertaining to the micromanipulator levitation system are discussed. The optimized dimensions of the system allow for 920 turns in the inner coil and 800 turns in the outer coil resulting in a N i n n e r c o i l : N o u t e r c o i l ratio of 1.15. Use of principles of free levitation, which is production of levitation and restoration forces with the coils, to levitate non-magnetic conductive materials with compatibility and applications within the AM environment are discussed. The Magnetomotive Force (MMF) ratio of the coils are adjusted by incorporation of an resistor in parallel to the outer coil to facilitate sufficient levitation forces in the axial axis while producing satisfactory restoration forces in the lateral axes resulting in the levitation of an aluminum disc with a levitation height of 4.5 mm. An additional payload of up to 15.2 g (59% of mass of levitated disc) was added to a levitated aluminum disk of 26 g showing the system capability coping with payload variations, which is crucial in AM process to gradually deploy masses. The final envisioned system is expected to have positional stability within the tolerance range of a few μm. The system performance is verified through the use of simulations (ANSYS Maxwell) and experimental analyses. A novel method of using the ratio of conductivity (σ) of the material to density (ρ) of the material to determine the compatibility of the levitation ability of non-magnetic materials with magnetic levitation application is also formulated. The key advantage of this method is that it does not rely on experimental analyses to determine the levitation ability of materials. [ABSTRACT FROM AUTHOR]

Direct energy deposition (DED) is an additive manufacturing method that allows repairing the broken parts and building the meter-scale samples. However, the printing of large parts is associated with huge residual stresses and martensite phase formation, which can change the geometry of final samples or initiate the crack. The last factor is especially important for titanium alloys. In this work, we investigated the effect of DED thermal history on the obtained structural and mechanical properties of Ti-6Al-4V using a thermocouple. It was demonstrated that printing with long pauses leads to α′ phase formation, which embrittles the material. Continuous printing with small pauses between tracks leads to the formation of the dual α+β structure. The effect of the texture on the material properties is also discussed. As a result of the study, the specific DED process parameters allow the same mechanical characteristics for as-built titanium alloy and the alloy after heat treatment. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has been a vital element of smart manufacturing. The high energy intensity or environmental sustainability issue of AM, however, has posed a great challenge to the future massive application, particularly laser-based direct energy deposition (L-DED). This study aims to determine the optimal processing parameters for energy-saving without compromising the geometrical appearance. A quantification model for energy efficiency at the process level was established, with two energy efficiency indicators of AM process. Then, a meta-heuristic Mayfly algorithm, augmented with Bayesian technique and mutation strategies, was proposed to improve hyperparameters in a typical machine learning model (XGBoost). Based on the full factorial L-DED experiments, this study compared the improved XGBoost with four types of XGBoost derivatives via four algorithm evaluation metrics. Non-dominated sorting genetic algorithm II was adopted to optimize the processing parameters subject to the constraints of geometrical appearance. Results indicated that the proposed algorithm outperformed other XGBoost derivatives in terms of prediction accuracy and convergence rate. The energy efficiency could be improved by 76.35 J/g or 6.78 % on average while ensuring the geometry of the deposited layers. This study could help enhance energy-efficient additive manufacturing via proper processing parameters selection and facilitate the sustainability in AM domain. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing processes pose a daunting challenge in defining optimal process parameters that yield porosity defect-free, dense parts. This is particularly true in refractory metals, where high melting temperatures limit process parameter windows. This present study investigates a dimensionless number analysis that has been derived through the Buckingham-PI theorem and demonstrates a robust correlation between process parameters and the density of the fabricated components. The introduction of this dimensionless number enables the initial estimation of process parameters without extensive modeling or experimentation. Additionally, a universal scaling law is proposed to enhance the translation of predicting process parameters for achieving an optimal density in as-built parts between different processing techniques. A combination of this proposed dimensionless number and scaling law offers process maps for tungsten and molybdenum with previously unknown process parameters. The universality of the proposed dimensionless number also demonstrates transferability, enabling the prediction of process parameters both for laser powder bed fusion and directed energy deposition systems. • Introduces a dimensionless number to efficiently define optimal parameters used in additive manufacturing • Demonstrates the applicability and transferability of the proposed dimensionless number for accurate prediction of process parameters in both laser powder bed fusion (LPBF) and directed energy deposition (DED) systems • Simplifies the estimation of optimal process parameters, reducing the need for extensive experimental or modeling efforts • By utilizing the proposed dimensionless number and scaling law, the study is capable to unveil process maps for materials, revealing process parameters that were previously unknown. [ABSTRACT FROM AUTHOR]

Metallic additive manufacturing is expeditiously gaining attention in advanced industries for manufacturing intricate structures for customized applications. However, the inadequate surface quality has inspired the inception of metallic coatings through additive manufacturing methods. This work presents a brief review of the different genres of metallic coatings adapted by industries through additive manufacturing technologies. The methodologies are classified according to the type of allied energies used in the process, such as direct energy deposition, binder jetting, powder bed fusion, hot spray coatings, sheet lamination, etc. Each method is described in detail and supported by relevant literature. The paper also includes the needs, applications, and challenges involved in each process.

Additive manufacturing techniques are replacing conventional subtractive machining processes; however, the surface quality and defects have been a key roadblock to expanding AM’s uses. This paper describes experimental investigations in the high-speed dry machining and additive manufacturing (AM) of titanium alloy (Ti6Al4V), discussing the effect of machining and AM conditions on the surface characteristics due to the micro-deformation layer. Analysis of the machined surfaces shows the deposition of microparticles at a high cutting speed of 170 m/min at moderate feed rates. The predominant thermal softening effect at a high cutting speed causes restructuring of the micro-deformation layer. Thus, the machined surface shows fewer alterations and a correspondingly lower surface roughness. A high cutting speed also favors the induction of high residual stresses that are compressive. Shallow grooves are seen throughout the surface along the feed spacing with a higher depth of cut of 0.8 mm. An increase in the cutting speed from 170 m/min to 190 m/min leads to a 61% increase in the surface finish owing to a rise in machining temperature leading to thermal softening, and subsequent restructuring of the machined surface layer occurs. For the feed rate, the surface finish values decrease gradually as the feed rate increases, and the worst finish of 1.37 µm is attained at a feed rate of 0.875 mm/rev. This study also compares different AM processes for Ti6Al4V based on the defects and their effects on mechanical properties, such as tensile and fatigue strength. It was observed that the ultimate tensile strength and the yield strength were approximately 20% more in SLM and direct energy deposition as compared to electron beam melting. The mechanism of these effects is also explained by elaborating on the influence of grain size, phase, and other microstructural behaviors on the final mechanical properties of the produced part.

The reconstruction of the geometry of weld-deposited materials plays an important role in the control of the torch path in GMAW. This technique, which is classified as a direct energy deposition technology, is experiencing a new emergence due to its use in welding and additive manufacturing. Usually, the torch path is determined by computerised fabrication tools, but these software tools do not consider the geometrical changes along the case during the process. The aim of this work is to adaptively define the trajectories between layers by analysing the geometry and symmetry of previously deposited layers. The novelty of this work is the integration of a profiling laser coupled to the production system, which scans the deposited layers. Once the layer is scanned, the geometry of the deposited bead can be reconstructed and the symmetry in the geometry and a continuous trajectory can be determined. A wall was fabricated under demanding deposition conditions, and a surface quality of around 100 microns and mechanical properties in line with those previously reported in the literature are observed.

Predicting the temperature field during the direct energy deposition (DED) process is vital for the microstructure control and property tuning of fabricated metals. The widely used data-driven machine learning method for accurate temperature prediction, however, is impractical and computation-intensive due to its sole reliance on large datasets; also being a black-box model in nature, it lacks interpretability. We propose a physics informed neural network (PINN) model, which adopts a novel physics-data hybrid method by embedding the heat transfer law into the loss function of the neural network, to model the temperature field in both single-layer and multi-layer DED. The results show that the PINN-based models with additional extrapolation ability can accurately predict temperatures with a mean relative error of 4.83%, and achieve identical prediction accuracy with only 20% of the labeled data required for training the data-driven deep neural network. The proposed model is more explainable in terms of the physics of the DED process and is also applicable for the DED of different metals. [ABSTRACT FROM AUTHOR]

In this paper, the refurbishing of worn-out brake discs by coating with powder via direct energy deposition (DED) is evaluated. A medium carbon steel powder was used to coat cast-iron discs. Deposition of this steel was carried out directly on the disc surface or, alternatively, after a previous deposition of a buffer layer made of stainless steel. It was seen that the use of a buffer layer ensured a good coating adhesion, despite the formation of cast microstructures at the interfaces between the disc and the two different coatings (buffer and outer layer). Coated discs were tested against two different Cu-free commercial friction materials to evaluate their tribological properties. Very similar friction coefficients, specific wear rates, and total emissions were measured for both friction materials sliding against the coated disc. These tribological data are slightly higher with respect to those obtained in the case of an uncoated disc, suggesting that improvement of the top coating composition and surface finishing is necessary in order to achieve better performances. [ABSTRACT FROM AUTHOR]

In this study, a process-to-property linear regression model was developed to predict the yield and ultimate tensile strengths of as printed Ti-6Al-4V from electron beam additive manufacturing (EBAM). A total of 8 printing conditions such as bead width, wire feed rate, deposition speed were utilized to predict the material properties in three different notional parts produced over a period of several months. It was found that as the precision and variety of processing conditions collected during print improved between prints, so did the predictive ability of the model. In the final print, the model predicted the yield and ultimate strengths of 72 specimens with an R2 correlation of 0.8 and 0.6 for the horizontal and vertical test specimens, respectively. Although the current model indirectly accounted for thermal fluctuations, further improvements to the model's ability to predict material strength are expected with the addition of thermal data captured in subsequent notional parts. [ABSTRACT FROM AUTHOR]

Metallic additive manufacturing processes have been significantly developed since their inception with modern systems capable of manufacturing components for structural applications. However, successful processing through these methods requires extensive experimentation before optimised parameters can be found. In laser-based processes, such as direct energy deposition, it is common for single track beads to be deposited and subjected to analysis, yielding information on how the input parameters influence characteristics such as the output's adhesion to the substrate. These characteristics are often determined using specialised software, from images obtained by cross-section cutting the line beads. The proposed approach was based on a Python algorithm, using the scikit-image library and optical microscopy imaging from produced 18Ni300 Maraging steel on H13 tool steel, and it computes the relevant properties of DED-produced line beads, such as the track height, width, penetration, wettability angles, cross-section areas above and below the substrate and dilution proportion. 18Ni300 Maraging steel depositions were optimised with a laser power of 1550 W , feeding rate of 12 g min − 1 , scanning speed of 12 mm   s − 1 , shielding gas flow rate of 25 L min − 1 and carrier gas flow rate of 4 L min − 1 for a laser spot diameter of 2.1 mm . Out of the cross-sectioned beads, their respective height, width and penetration were calculated with 2.71 % , 4.01 % and 9.35 % errors; the dilution proportion was computed with 14.15 % error, the area above the substrate with 5.27 % error and the area below the substrate with 17.93 % error. The average computational time for the processing of one image was 12.7 s. The developed approach was purely segmentational and could potentially benefit from machine-learning implementations. [ABSTRACT FROM AUTHOR]

The final mechanical and physical properties should be predicted in tandem with the bead geometry characteristics for effective additive manufacturing (AM) solutions for processes such as directed energy deposition. Experimental approaches to investigate the final geometry and the mechanical properties are costly, and simulation solutions are time-consuming. Alternative artificial intelligent (AI) systems are explored as they are a powerful approach to predict such properties. In the present study, the geometrical properties as well as the mechanical properties (residual stress and hardness) for single bead clads are investigated. Experimental data is used to calibrate multi-physics finite element models, and both data sets are used to seed the AI models. The adaptive neuro-fuzzy inference system (ANFIS) and a feed-forward back-propagation artificial neural network (ANN) system are utilized to explore their effectiveness in the 1D (discrete values), 2D (bead cross-sections), and 3D (complete bead) domains. The prediction results are evaluated using the mean relative error measure. The ANFIS predictions are more precise than those from the ANN for the 1D and 2D domains, but the ANN had less error for the 3D scenario. These models are capable of predicting the geometrical and the mechanical properties values very well, including capturing the mechanical properties in transient regions; however, this research should be extended for multi-bead scenarios before a conclusive "best approach" strategy can be determined. [ABSTRACT FROM AUTHOR]

Hot stamping uses boron (B) steel to simultaneously form parts at high temperatures while cooling the parts in a mold, which is advantageous because of the ability to freeze the forms. However, compared to conventional cold forming, this technique requires additional facilities that include heating devices and additional time for cooling after forming at high temperatures. Additionally, because of the high strengths of hot stamping parts, shear process operations after molding tend to be difficult to perform as a continuous operation via press processing; thus, most operations depend on separate laser processing, which results in lower productivity and increased manufacturing costs. This limitation continues to be the most significant problem with this technology, therefore, restricting its commercialization because of increased mold manufacturing costs and durability problems. This study investigated a low-cost, high-functionality shear mold manufacturing method for 1.5 GPa grade hot-stamped components using heterogeneous metal additive manufacturing. After the concentrated stress in steel during the shearing processes was analyzed using a multi-physical analysis, metal additive manufacturing was used to fabricate the shear mold. Its life was evaluated through trial molding and compared with that for conventional technology. Finally, the commercialization potential of the newly developed method was assessed. [ABSTRACT FROM AUTHOR]

Hybrid additive and subtractive machining combines the flexibility of additive manufacturing (AM) with the high precision and geometrical accuracy of computer numerical control (CNC) machining. Of the many metal AM strategies blown powder direct energy deposition (DED) is the method most commonly chosen for incorporation into hybrid additive and subtractive platforms. Due to the necessity for coolant during machining operations, these platforms are usually not sealed environments meaning the deposition of reactive metals such as titanium to acceptable standards is not possible due to oxygen absorption from the surrounding environment. The research presented focuses on the investigation of the effect of a series of shielding methods in the geometry and microstructure of the materials deposited in a hybrid-manufacturing platform. The ultimate objective is to select the method with the biggest potential to enable the deposition of reactive materials with the aim of successfully depositing low oxygen content titanium, enabling the creation of Ti-6Al-4V at grade 5 and grade 23. To achieve this, bath and bag shielding strategies were compared with the standard through nozzle shielding when depositing in 15-5 PH stainless steel, Inconel 718 and Ti-6Al-4V. Based on the results of the post machining analysis the oxygen content of a multi-layer titanium sample was found to be 0.079%, lower than the maximum limit for grade 23 Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

Effects of annealing condition and crack orientation on fatigue crack propagation (FCP) behavior of DED (direct energy deposition)-processed Ti–6Al–4V (Ti64) specimens were studied. It was found that the FCP resistance of Ti64 increased significantly with annealing, particularly above β transus temperature, due to the microstructural coarsening inducing less damage accumulation at the tip of crack. The FCP behavior of as-built and as-annealed DED Ti64 specimens was isotropic with crack direction either parallel or perpendicular to building direction. The detailed micrographic and fractographic analyses on FCP-tested specimens suggested that the presence of largely elongated β grain boundaries did not affect the advance of crack. [ABSTRACT FROM AUTHOR]

Additive manufacturing of structural metallic components is an emerging technology. The DED-arc (direct energy deposition) process combines efficiency with high degrees of freedom and predictable quality. Compared to powder-based processes, the surface is relatively coarse as a result of high heat input and larger molten zones. In industrial applications, the post-treatment of surfaces of DED-arc components cannot be guaranteed for economic reasons or due to geometric constraints. Hence, the surface topography must be evaluated and quality levels need to be defined. Unfortunately, established surface parameters and their determination cannot be directly transferred to DED-arc components and further research on this topic is needed. This article demonstrates surface topography features of representative DED-arc components. Furthermore, waviness profiles were established by applying an alternative cutoff wavelength to better represent the DED-arc surface characteristics. Based on these waviness profiles, 2-dimensional height parameters were calculated. The waviness parameters were determined for four DED-arc specimens made from high strength wire electrodes. The manufacturing parameters were varied in terms of different energy input and interpass temperature, resulting in varying deposition rates and surface qualities. The waviness parameters correlated with manufacturing parameters. A mixed deterministic and random nature of the surface topography was verified.

Direct energy deposition (DED) is an efficient manufacturing process for the fabrication of complex parts and repair of worn-out turbine blades. In DED, all the injected powder is not going to melt and solidify due to spattering, reflection, ejection, effect of inert gas, and turbulence around the melt pool. In this study, through numerical simulation, the effect of powder size and inert gas flow under coaxial nozzle was analyzed. The number of particle participation in the melt pool by the effect of inert gas and the size of powder particles were analyzed. The powder particle sizes considered for the study were 50–60, 60–70, 70–80, 80–90, 90–100, and 45–90 µm. Argon and helium gases were used as carrier gas and shielding gas, respectively. According to gas–solid multiphase simulation, the convergence distance of the powder flow and powder participation focal point was analyzed through numerical simulation. The simulated results showed that using argon gas as a carrier gas produced high powder efficiency compared to helium gas. The focal point is forming at 11.86 mm, approximately 12 mm from the nozzle exit, which occurred for 60–70-µm particle size. The powder particle participation efficiency obtained was 64.1% using argon gas as carrier gas.

In this study, one-dimensional beads and three-dimensional cubes of 1.2709 maraging steel were printed using a laser additive manufacturing (AM) technology. The direct energy deposition (DED) was firstly employed to evaluate the optimal conditions of the single-bead deposition. High-energy (> 64.9 J/mm2) and low-energy (< 64.9 J/mm2) groups of beads were deposited according to a full factorial design of experiment (DOE) and analyzed regarding the optimal aspect ratio between 3 and 5. The low-energy DED was evaluated as the optimal one regarding the required morphology with large process window. The effect of DED process parameters on density/porosity, microstructure, and residual stresses of the cubic specimens was then analyzed. It was found that by reducing the laser energy and print overlap, it is possible to drastically reduce the residual stresses as well as by increasing the powder density. Scanning strategies do not have a strong influence on residual stresses but affect the porosity. Moreover, the porosity is increased with increasing laser energy and print overlap. The best compromise between porosity, residual stresses, and productivity was obtained with a surface energy of 35 J/mm2, a 30% overlap, and a bidirectional-rotation scanning strategy. The presented work highlights the essential experimental data for an upcoming DED of large parts and their characterization suitable for industrial injection molding applications. [ABSTRACT FROM AUTHOR]

Wire‐and‐arc additive manufacturing (WAAM) is an innovative technology that involves deposition of subsequent layers of molten materials. Due to the high deposition rates, this technology is suitable for the production of large‐scale complex structures. Further enhancement in the productivity can be achieved by an interlayer cooling strategy that reduces idle time between depositions. However, the effect of the interlayer cooling on microstructure and mechanical properties has to be addressed. In this view, the present work compares microstructural features and mechanical properties of WAAM‐produced plates of austenitic AISI 304 L, focusing on the effect of both active interlayer air cooling and possible anisotropy induced by the additive process. Microstructural and mechanical characterization was conducted on samples extracted along the longitudinal, transverse, and diagonal directions to the deposition layers of WAAM plates, processed with and without interlayer active cooling. Results showed no remarkable influence of cooling conditions on the microstructure and mechanical properties of WAAM plates, which are indeed affected by the anisotropy induced by the additive process. The observed anisotropy in the elastic modulus, independent from different cooling conditions, was related to the crystallographic texture consequent to the highly oriented microstructure typically induced by the process. [ABSTRACT FROM AUTHOR]

Additive manufacturing processes are currently studied in many research areas. Indeed, to qualify additively manufactured metallic parts, it is important to understand how process and postprocessing treatments influence the microstructure and mechanical properties of the parts. However, it is also essential to understand how the process parameters impact bead geometry. In this paper, various first-order parameters were studied, and beads were measured to identify correlations between input parameters (laser power P, scanning speed V and powder feed rate F) and geometrical outputs of Ti-6Al-4V beads (height, dilution, width) manufactured with the laser metal powder deposition process. Several results of linear or multiple linear regressions were analyzed to quantify the quality of the prediction of bead geometry. The results show that the emerged and diluted heights are correlated with the laser power/powder feed rate ratio (LEPF), energy density (ED) and powder density (PD). Additionally, the dilution rate seems to be better predicted when expressed as a function of P, V and F. Bead width regressions gave accurate predictions with low errors. These equations could be used to predict the bead geometry from input parameters or to predict input parameters as a function of the needed geometric properties. [ABSTRACT FROM AUTHOR]

In this study, the wear resistance of AISI M2 high-speed tool steel produced using direct energy deposition (DED) was investigated in detail. Wear behavior was studied under different wear loads and sliding speeds using ball-on-disk tribology tests with two different counterpart balls (bearing steel and ZrO2). The wear test results revealed that there was almost no wear damage in the M2 alloy when a bearing steel counterpart ball was used. When a ZrO2 ball was used as the counterpart, a measurable, but small, amount of wear weight loss of M2 was observed. It was found that M2 alloy fabricated by DED has excellent wear resistance, greater than fully carburized conventional steel and high wear resistance steel produced by DED. The formation of a lubricious tribo-oxide film on the worn DED M2 surface is likely the reason for its excellent wear performance. The total wear weight losses of only ~1.5 mg was observed for the M2 produced by the DED, both in the as-DEDed and heat treated states against ZrO2 balls, under the wear loading conditions of 50 N wear load, 100 mm/s sliding speed and total sliding distance of 500 m. In comparison to the other wear-resistance materials, the wear weight loss of the M2 produced by the DED was more than 6 times smaller than the fully carburized structural steel and 1.5–4 times smaller than high wear resistance steel produced by the DED. Thus, DED of the M2 alloy offers a great potential for the production of wear-resistance hard-facing of tribological components. [ABSTRACT FROM AUTHOR]

In additive manufacturing (AM), the surface roughness of the deposited parts remains significantly higher than the admissible range for most applications. Additionally, the surface topography of AM parts exhibits waviness profiles between tracks and layers. Therefore, post-processing is indispensable to improve surface quality. Laser-aided machining and polishing can be effective surface improvement processes that can be used due to their availability as the primary energy sources in many metal AM processes. While the initial roughness and waviness of the surface of most AM parts are very high, to achieve dimensional accuracy and minimize roughness, a high input energy density is required during machining and polishing processes although such high energy density may induce process defects and escalate the phenomenon of wavelength asperities. In this paper, we propose a systematic approach to eliminate waviness and reduce surface roughness with the combination of laser-aided machining, macro-polishing, and micro-polishing processes. While machining reduces the initial waviness, low energy density during polishing can minimize this further. The average roughness ( R a = 1.11 μ m) achieved in this study with optimized process parameters for both machining and polishing demonstrates a greater than 97% reduction in roughness when compared to the as-built part. [ABSTRACT FROM AUTHOR]

In order to achieve the microstructure homogeneity at a lower temperature and improve the mechanical properties, a novel post heat treatment was introduced to Inconel 718 fabricated by laser direct energy deposition (LDED), by means of δ aging treatment + solution treatment. The microstructure analysis shows that the fully precipitation of δ phase in LDED Inconel 718 superalloy can “cut” the long strip Laves phase into small pieces. According with the δ phase solution treated at 1020 °C for 30 min, only tiny particle Laves phase was remained. The equilibrium volume fraction of Laves phase after δ phase solution treatment is about 1%, which is much lower than that of the as-deposited sample or the sample only solution treated at 1020 °C. Due to the solution strengthening and precipitation of γ″ phase during aging treatment, the tensile strength of δ aging + δ solution + double aging treated samples was 10.27% higher than that of directed solution + double aging treated samples, as well as a 31.38% and 52.71% increases in elongation and the reduction of area during tensile tests.

The tool-path problem has been extensively studied in manufacturing technologies, as it has a considerable impact on production time. Additive manufacturing is one of these technologies; it takes time to fabricate parts, so the selection of optimal tool-paths is critical. This research analyzes the tool-path problem in the direct energy deposition technology; it introduces the main processes, and analyzes the characteristics of tool-path problem. It explains the approaches applied in the literature to solve the problem; as these are mainly geometric approximations, they are far from optimal. Based on this analysis, this paper introduces a mathematical framework for direct energy deposition and a novel problem called sequence strategy generation. Finally, it solves the problem using a benchmark for several different parts. The results reveal that the approach can be applied to parts with different characteristics, and the solution to the sequence strategy problem can be used to generate tool-paths.

The primary goal of this study is to create a magnetic levitation system for additive manufacturing (AM) applications. The emphasis of this research is placed on Laser Directed Energy Deposition via Powder Feeding (LDED-PF). The primary benefit of using a magnetic levitation system for AM applications is that the levitated geometry is expected to be a portion of the final part manufactured, thus eliminating the need for a substrate and reducing the post-processing operation requirement. Two novel levitation systems were designed, optimized, and manufactured. The design, optimization, and analysis were first conducted in the simulation environment using ANSYS Maxwell and then tested with experiments. The newly developed systems depicted a much-improved performance compared to the first prototype developed in a previous article written by the authors. The newly developed systems had an increase in levitation height, the surface area for powder deposition activities, the time available for AM operations, and the ability to support additional mass within the limits of allowable inputs. The compatibility of the levitation system with AM applications was also verified by testing the impact of powder deposition and the ability of the levitated disc to support added mass as a function of time with minimal loss in performance. This article also highlights the development of a novel feedback PID controller for the levitation system. To improve the overall performance of the controller, a feedforward controller was added in conjunction with the PID controller. Finally, the levitation system was shown to highlight control over levitation height and maintain constant levitation height with the addition of an added mass using the feedback controller.

Composite materials made from aluminum foam are increasingly used in aerospace and automotive industries due to their low density, high energy absorption capacity, and corrosion resistance. Additive manufacturing processes offer several advantages over conventional manufacturing methods, such as the ability to produce significantly more geometrically complex components without the need for expensive tooling. Direct Energy Deposition processes like Wire Arc Additive Manufacturing (WAAM) enable the additive production of near-net-shape components at high build rates. This paper presents a technology for producing aluminum foam structures using WAAM. This paper's focus is on the development of welding wires that are mixed with a foaming agent (TiH 2 ) and produce a foamed weld metal as well as their processing using MIG welding technology., Competing Interests: The authors declare no conflicts of interest.

The direct energy deposition (DED) process utilizes laser energy to melt metal powders and deposit them on the substrate layer to manufacture complex metal parts. This study was applied as a remanufacturing and repair process to fix used parts, which reduced unnecessary waste in the manufacturing industry. However, there could be defects generated during the repair, such as porosity or bumpy morphological defects. Traditionally the operator would use a design of experiment (DOE) or simulation method to understand the printing parameters' influence on the printed part. There are several influential factors: laser power, scanning speed, powder feeding rate, and standoff distance. Each DED machine has a different setup in practice, which results in some uncertainties for the printing results. For example, the nozzle diameter and laser type could be varied in different DED machines. Thus, it was hypothesized that a repair could be more effective if the printing process could be monitored in real time. In this study, a structured light system (SLS) was used to capture the printing process's layer-wise information. The SLS system is capable of performing 3D surface scanning with a high resolution of 10 μm. It can provide the information to determine how much material needs to be deposited and monitor the layer-wide surface topography for each layer in real-time. Once a defect was found in situ, the DED machine (hybrid machine) would change the tool and remove the flawed layer. After the repair, the nondestructive approach computed tomography (CT) was applied to examine its interior features. In this research, a DED machine using 316L stainless steel was used to perform the repairing process to demonstrate its effectiveness. The lab-built SLS system was used to capture each layer's information, and CT data was provided for the quality evaluation. The novel manufacturing approach could improve the DED repair quality, reduce the repair time, and promote repair automation. In the future, it has a great potential to be used in the manufacturing industry to repair used parts and avoid the extra cost involved in buying a new part. [ABSTRACT FROM AUTHOR]

Direct energy deposition has been established as one of the methods for additive manufacturing metallic parts. The combination of direct energy deposition capabilities with traditional machining centre capabilities has enabled over the past few years the creation of hybrid manufacturing cells that are able to additively manufacture and finish machine components under one platform. This article investigates the production of geometries using a hybrid, additive and subtractive approach. The parameters for depositing stainless steel 316L are initially investigated followed by an assessment of machinability of the additively manufactured material. Finally, the quality of the deposited and machined material was thoroughly examined with a series of destructive and non-destructive methods. [ABSTRACT FROM AUTHOR]

Residual stresses and deformation in additive manufactured (AM) are two main barriers which hinder its extensive application seriously. In recent years, pulsed laser additive manufacturing has been widely examined for its advantages such as lower finer microstructure, more excellent mechanical properties, and heat accumulation in comparison with continuous-wave laser additive manufacturing. Few researches about residual stress of pulsed laser additive manufacturing, however, have been studied, and the development law of stain and residual stress is not clear. In this work, a three-dimensional (3D) transient uncoupled thermo-elastic-plastic model for pulsed-wave laser additive manufacturing procedure is carried through to examine the residual stress distribution and thermal history in 316L laser cladding. Excellent acceptance between the experimental measurements and the numerical results is obtained. It is discovered that pulsed-wave laser additive that manufactures attributes melt pools with periodic shape changes, the thermal stress evolution process moves like heartbeat periodically, and the residual stress distribution in laser cladding direction is similar to zigzag inhomogeneity. Furthermore, the influence of laser pulse parameters on residual stress distribution has been studied, and the results indicated that decreasing constant duty cycle and laser pulse length reduces the size and stress gradient of maximum stress' region for x-direction tensile stresses. It provides operation parameters' optimization choice with guidance to control or reduce residual stress. [ABSTRACT FROM AUTHOR]

Laser-directed energy deposition (L-DED) is a type of additive manufacturing (AM) technology that allows the manufacture of complex geometry components in a layer-by-layer way and can be considered an emerging manufacturing technique. The process efficiency and properties of produced parts are closely linked to its parameters, i.e., laser power, deposition speed, material flow rate and, inert gas flows. These operational parameters usually are different depending on the machine and material employed. The best combination of process parameters is fundamental to obtain the best characteristics together with process sustainability for each manufactured component. At the present work, an L-DED head and a powder feeding system are combined in a particular machine to deposit Inconel 625 on a substrate made of AISI 304 stainless steel. A combination of analytical studies, CFD simulations, and experimental tests was carried out, finding a process setting that offers a higher concentration of particles, quality depositions, and optimal cooling rates, reducing gas and material consumption during the process. After some in-situ tests, the best results were employed to fabricate thin wall structures and solid components. The specimens were characterized by laser confocal microscopy, roughness, and Vickers microhardness measurements, finding exciting results with a significant reduction in gas consumption and metal powder usage. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are composed of 5–35 at% of five or more elements, have high configurational entropy, do not form intermetallic compounds, and have a single-phase face-centered cubic structure or body-centered cubic structure. In particular, refractory HEAs (RHEAs), based on refractory materials with excellent mechanical properties at high temperatures, have high strength and hardness at room temperature and excellent mechanical properties at low and high temperatures. In this study, the Ti-Nb-Cr-V-Ni-Al RHEAs were deposited using direct energy deposition (DED). In the microstructure of Ti-Nb-Cr-V-Ni-Al, the sigma, BCC A2, and Ti2Ni phases appeared to be different from the BCC A2, BCC B2, and Laves phases predicted in the phase diagram. This microstructure was similar to that of the casted Ti-Nb-Cr-V-Ni-Al and had a constructed fine grain size. It was found that the growth of these microstructures was due to the DED process, which has a fast solidification rate. The fine grain size caused high hardness, and the microhardness of the Ti-Nb-Cr-V-Ni-Al was measured to be about 900 HV. In addition, in order to analyze the thermal properties of Ti-Nb-Cr-V-Ni-Al composed of the refractory material, the heat-affected zone (HAZ) was analyzed through a preheating test. The HAZ was decreased, owing to the high thermal diffusivity of Ti-Nb-Cr-V-Ni-Al.

Direct Energy Deposition (DED), as one common type of additive manufacturing, is capable of fabricating metallic components close to net-shape with complex geometry. Surface mechanical attrition treatment (SMAT) is an advanced surface treatment technology which is able to yield a nanostructured surface layer characterized by compressive residual stresses and work hardening, thereby improving the fatigue performances of metallic specimens. In the present study, stainless steel 316L specimens were fabricated by DED and subsequently surface treated by SMAT. Both uniaxial tensile tests and uniaxial tension-compression low-cycle fatigue tests were conducted for as-built and SMAT processed specimens. The microstructure of both conditions was characterized by roughness and hardness measurements, scanning electron microscopy and transmission electron microscopy. After SMAT, nanocrystallites and microtwins were found in the top surface layer. These microstructural features contribute to superior properties of the treated surfaces. Finally, it can be concluded that the mechanical performance of additively manufactured steel under static and fatigue loading can be improved by the SMAT process.

A direct energy deposition (DED) process using wires is considered an additive manufacturing technology that can produce large components at an affordable cost. However, the high deposition rate of the DED process is usually accompanied by poor surface quality and inherent printing defects. These imperfections can have a detrimental effect on fatigue endurance and corrosion fatigue resistance. The aim of this study was to evaluate the critical effect of phase transition and printing defects on the corrosion fatigue behavior of 316L stainless steel produced by a wire laser additive manufacturing (WLAM) process. For comparison, a standard AISI 316L stainless steel with a regular austenitic microstructure was studied as a counterpart alloy. The structural assessment of printing defects was performed using a three-dimensional non-destructive method in the form of X-ray microtomography (CT) analysis. The microstructure was evaluated by optical and scanning electron microscopy, while general electrochemical characteristics and corrosion performance were assessed by cyclic potentiodynamic polarization (CCP) analysis and immersion tests. The fatigue endurance in air and in a simulated corrosive environment was examined using a rotating fatigue setup. The obtained results clearly demonstrate the inferior corrosion fatigue endurance of the 316L alloy produced by the WLAM process compared to its AISI counterpart alloy. This was mainly related to the drawbacks of WLAM alloys in terms of having a duplex microstructure (austenitic matrix and secondary delta-ferrite phase), reduced passivity, and a significantly increased amount of intralayer porosity that acts as a stress intensifier of fatigue cracking.

Combined manufacturing of direct energy deposition (DED) and laser shock peening (LSP) exhibits great potentials in repairing titanium alloy components and improving their mechanical properties. In this study, a DEDed repaired sample was fabricated by depositing TA15 powders on a forged TC17 plate, and subjected to a following LSP treatment. The effects of LSP on microstructures, residual stress, and tensile properties of DEDed samples were evaluated. After LSP, a high-level compressive residual stress state (maximum =−596 MPa) and microstructure refinement were induced in the treated surface. The average α phase area decreased from 1.88 μm2 to 0.73 μm2, and much more low angle grain boundaries were induced after LSP. Meanwhile, the corresponding ultimate tensile strength (UTS) was improved by 12.46%.

Direct energy deposition (DED) is a highly applicable additive manufacturing (AM) method and, therefore, widely employed in industrial repair-based applications to fabricate defect-free and high degree precision components. To obtain high-quality products by using DED, it is necessary to understand the influence of the process parameters on the product quality. The optimization of such processing parameters provides several advantages such as minimization of the loss of material and time. However, the optimization of the complex relationship between the process parameters-geometry-properties of the fabricated sample is difficult to realize and requires significant experimentation. Herein, a computational model based on artificial neural networks was developed to optimize process parameters for DED-processed Ti-6Al-4V alloy. The model was developed to estimate the density and build height (the actual build height realized after fabrication) of the sample as a function of power, scan speed, powder feed rate, and layer thickness. The optimum model with high-accuracy predictions was employed to construct the process maps for the DED-processed Ti-6Al-4V. The relative importance indices of process parameters on the build height and density were investigated. Further, the effect of power and scan speed on the microstructure of Ti-6Al-4V alloy was discussed. Finally, based on the obtained results, the optimum fabrication conditions for the DED-processed Ti-6Al-4V alloy were determined. [ABSTRACT FROM AUTHOR]

Microstructural characteristics of additively manufactured Ti-6Al-4V specimens are analyzed in this study. Laser Engineered Net Shaping technology, a direct energy deposition additive manufacturing process, is used to fabricate specimens. Effects of process parameters including machine head laser power, head write speed, layer height, hatch spacing, and powder flow rate on the morphological features of the material are investigated. A first batch of samples is built with a combination of parameters leading to full density metal parts across each layer and near-zero defects likewise more conventional process techniques (i.e. wrought and casting). A second batch of samples is built with a set of processing parameters aimed to induce defects within the parts like voids and porosity. Samples from both batches were stress-relieved in order to remove internal residual stresses generated by the additive manufacturing process. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to characterize the microstructure of all samples. Tensile properties were measured after the stress-relief heat treatment. It was found that Laser Engineered Net Shaping technology parts are strongly sensitive to variations of building process parameters. Different structure morphologies were observed for different incident energies and cooling rates due to the combination of laser power and head write speed. The grain size distribution and shape are influenced by the powder flow rate resulting in either equiaxed or columnar grain microstructures with the development of material defects such as pores, gas entrapment and lack of fusion. Non-porous specimens revealed comparable tensile and ductility properties with the wrought counterpart; however, porous specimens were found to have a reduced strength and ductility. [ABSTRACT FROM AUTHOR]

As a promising additive manufacturing method, direct energy deposition has been widely used to fabricate complex thin-walled parts. However, some defects such as uneven layer surface and excessive build-ups always occur in this process. In this study, a high-fidelity model adopting a novel laser/powder source is developed to simulate the detailed multi-layer deposition process. With layer surfaces being tracked in real-time, laser source model incorporates local incidence angle and defocusing amount to adjust absorbed energy and beam radius on the track surfaces. The powder catchment efficiency varies with the defocusing amount timely. The simulations demonstrate that build-ups are mainly induced by unstable linear powder feed rate and worsen due to laser/powder defocusing and accumulated heat. The layer surface unevenness results from powder positive defocusing, while molten pool dynamics, laser positive defocusing and accumulated heat plays a supplementary role. Eliminating methods are proposed based on the simulations and validated by experiments. [ABSTRACT FROM AUTHOR]

Ceramic-reinforced composite coating with excellent strength and toughness performance, could enhance the impact resistance and wear resistance of parts, which has a perspective application in the tool and die industry. The weight fraction of ceramic particles influences the strength and toughness of the coating. In this study, WC reinforced Fe-based composite coating was fabricated by direct energy deposition (DED) on the surface of H13 steel. The effect of different WC content, between 5 wt% and 50 wt%, on the microstructure was studied. An evaluation method for the strength-toughness property of the composite coatings was proposed. The results showed that the coating with an initial WC content of 40 wt% exhibited the optimal strength-toughness performance. The findings could provide guidance to the parameter determination of the DED process for the composite coating. • WC reinforced Fe-based composite coating is fabricated on H13 steel using DED. • WC particles decomposed in molten pool contribute to solid solution strengthening. • Eutectic carbides contribute to precipitation and grain refinement strengthening. • The composite coating achieves a good strength-toughness value with 40 wt% of WC. [ABSTRACT FROM AUTHOR]

A quasi-continuous-wave laser direct energy deposition (QCW-DED) process was employed to regulate the deposit characteristics, molten pool morphology and microstructure of single-track nickel-based alloy. The variation of the deposit characteristics with laser pulse frequency was investigated through experiment and numerical simulation. The molten pool flow pattern and the dendrite growth mode were described based on the observations of the deposition morphology and microstructure in the cross- and longitudinal-sections. It was concluded that the QCW-generated single-track deposits decreased in width and depth, yet increased solely in height as the pulse frequency increased. A "U" shaped structure composed of substrate materials was observed in the molten pool at the low pulse frequency. The flow in the molten pool of QCW specimens was alternately dominated by the Marangoni force and impact force, whereas the fluid flow in the molten pool formed by continuous wave (CW) was entirely dominated by the Marangoni force. The disappearance of the "U" shaped structure and the rapid remelting effect of the molten pool underlie the epitaxial growth of dendrites at the high pulse frequency. In the CW specimen, disorganized dendrites were produced in the heat flow direction along the molten pool boundary. • QCW and CW specimens exhibit different molten pool shapes. • At low pulse frequency, a "U" shaped structure, comprising substrate materials in the molten pool, is observed. • The flow patterns of the molten pool and the growth modes of the dendrites are revealed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A combination of thermodynamic calculations and in-situ alloying enabled high throughput screening of NiAl-Ta-Cr alloys. • Using induction-assisted directed energy deposition, cracking in NiAl-Ta-Cr specimens could be almost fully eliminated. • In-depth microstructure analysis of graded samples was used to validate calculation results in a high throughput manner. • Eutectic compositions exhibit a nanoscaled structure, which yields a micro hardness of up to 907 HV0.1 for NiAlTa14Cr2.5. The development of new high temperature materials for coatings as well as structural components is an important topic to contribute to a higher efficiency and sustainability of e.g. gas turbine engines. One promising new class of high temperature materials are NiAl-based alloys. Within this study, the microstructure and microhardness of NiAl-Ta-Cr alloys with varying Cr and Ta content were investigated. Graded specimens were fabricated by laser-based directed energy deposition utilizing an in situ alloying approach by mixing elemental Ta and Cr as well as pre-alloyed NiAl powder. Thermodynamic calculations were performed to design the alloy compositions beforehand. Inductive preheating of the substrate was used to counter the challenge of cracking due to the high brittleness. The results show that the cracking decreases with increasing preheating temperature. However, even at 700 °C, the cracking cannot be fully eliminated. Scanning electron microscopy, X-ray diffraction and electron backscatter diffraction revealed the formation of the phases B2-NiAl, A2-Cr and C14-NiAlTa within NiAl-Ta and NiAl-Cr alloys. For NiAl-Ta-Cr compositions, deviations regarding the phase formation between calculation and experiment were observed. Maximum hardness values were achieved within the NiAl-Ta and NiAl-Ta-Cr systems for the eutectic compositions at 14 at.-% Ta with maximum values above 900 HV0.1. [ABSTRACT FROM AUTHOR]

In the process of joining dissimilar materials, the formation of large amounts of intermetallics and the interaction of active materials were reduced. The influence of thermal cycles in the cladding process makes a significant contribution to the formation of the structural-phase composition and mechanical properties of the heterogeneous Ti–Nb–Cu–Fe joint. As the interpass temperature increases, the fusion depth increased, as the rate of diffusion processes. It is shown that the formation of intermetallides such as FexTi, TixCu, FexNb, etc. can be reduced by the variation of the interpass temperature. The best mechanical properties were obtained at an interpass temperature of 10 s, and the ultimate strength was up to 325 MPa. • Dissimilar joint was fabricated by DED via adding an (Nb + bronze) interlayer. • The addition of interlayer (Nb + bronze) can effectively suppress the formation of Ti–Fe IMCs. • The average tensile strength is 335.5 MPa. • The strength of Cp-Ti/316L joint could be improved by using an gradient interlayer. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) enables the rapid fabrication of complex shapes using engineering materials such as austenitic stainless steels and can imbue them with high irradiation resistance for use in reactor components. This is attributed to their refined grain structure and high grain boundary area. In this study, austenitic stainless steels (type 304) fabricated via direct energy deposition (DED) and powder bed fusion (PBF) techniques were irradiated with 5 MeV He ions to an approximate dose of 0.6 dpa at 300°C; subsequently, they were characterized through electron microscopy and the micro tensile testing. The results revealed that austenitic stainless steels manufactured using AM methods exhibited outstanding mechanical performance. The high performance of austenitic stainless steels fabricated through the DED technique can be attributed to their high tensile strength and excellent ductility elongation. This excellent performance is believed to be caused by the low stacking fault energy and the corresponding martensite formation during deformation. In particular, it was found that better mechanical properties were maintained even after helium irradiation, which is an important result obtained from the micro-tensile test. Even a small variation in the chemical composition and sub-microstructure of AM materials could result in improved irradiation tolerances. [ABSTRACT FROM AUTHOR]

This study presents a microstructural model applicable to additively manufactured (AM) austenitic SS 316L components fabricated via a direct energy deposition (DED) process. The model is primarily intended to give an understanding of the effect of microscale and mesoscale features, such as grains and melt pool sizes, on the mechanical properties of manufactured components. Based on experimental observations, initial assumptions for the numerical model regarding grain size and melt pool dimensions were considered. Experimental observations based on miniature-sized 316L stainless steel DED-fabricated samples were carried out to shed light on the deformation mechanism of FCC materials at the grain scale. Furthermore, the dependency of latent strain hardening parameters based on the Bassani–Wu hardening model for a single crystal scale is investigated, where the Voronoi tessellation method and probability theory are utilized for the definition of the grain distribution. A hierarchical polycrystalline modeling methodology based on a representative volume element (RVE) with the realistic impact of grain boundaries was adopted for fracture assessment of the AM parts. To qualify the validity of process–structure–property relationships, cohesive zone damage surfaces were used between melt pool boundaries as the predefined initial cracks and the performance of the model is validated based on the experimental observations.