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Additive Manufacturing marks a transformative advancement in space exploration, where customization and efficient resource use are paramount. Metal additive manufacturing, specifically using the directed energy deposition process with wire feedstock, addresses the limitations of polymer-based Fused Filament Fabrication, which has been the primary focus of space missions until now. Metal additive manufacturing produces stronger metallic components and optimizes material usage, which is essential for prolonged space missions. Moreover, employing lasers as the heat source in additive manufacturing provides high precision, control, and reduced electromagnetic interference, which is crucial for operating in microgravity and electronic-sensitive environments. This review focuses on laser-based metal additive manufacturing in space exploration, highlighting the pivotal role of numerical simulations in case of limited access to experiments in space. These simulations are vital, cost-effective tools for predicting component quality, enhancing reliability, and optimizing manufacturing parameters in space-based additive manufacturing. By addressing the unique challenges of space additive manufacturing, metal additive manufacturing technologies promise to revolutionize space missions, reducing development costs and time while fulfilling stringent requirements. • Surveyed the state-of-the-art laser metal additive manufacturing in space. • Highlighted pivotal role of numerical simulations in study. • Outlined future directions in this emerging field. [ABSTRACT FROM AUTHOR]

This work aims to evaluate the behavior of AISI 308L stainless steel, applied in additive manufacturing by direct energy deposition (DED) with the GTA (TIG) process, to find the limits of using this material as a manufacturing technique. The AISI 308L is an austenitic steel with extensive applications across various industrial sectors, particularly in the chemical, food, and biomedical industries. Due to its resistance to ductile–brittle transition, it is widely utilized in cryogenic temperature working conditions. The welding equipment and the test specimen were instrumented for analysis of welding process parameters and evaluation of heat transfer in the material as a function of pulse frequency (0 Hz—conventional GTA, 100 Hz, 1 kHz, and 10 kHz) to determine its influence on ferrite morphology and printability in each test specimen. Under these conditions, the sample was characterized by optical and scanning electron microscopy (SEM) and backscattered electron diffraction (EBSD) to evaluate the direction of solidification by the deposited layer. The results showed that a pulse frequency of 100 Hz reduced the volumetric fraction of ferrite and exhibited the best printability. Furthermore, samples prepared using the pulse frequency showed higher printability values than samples without pulsation, and samples with 10 kHz showed an increase in the formation of acicular ferrite. [ABSTRACT FROM AUTHOR]

Fabrication of Mg alloys using the additive manufacturing process is quite challenging owing to high oxidation and volatile nature at high temperatures. The present study investigates the effect of wire feed speed (WFS) and travel speed (TS) on single tracks of AZ31 Mg alloy fabricated using the cold metal transfer wire arc additive Manufacturing (CMT-WAAM) process. The WFS and TS of CMT-WAAM are optimized to achieve better deposition quality. An increase in WFS increased the width, height, penetration depth, and heat-affected zone of single tracks. In addition, increasing TS decreased the deposited tracks' contact angle and height. The average grain size at the interface zone, center and top portion of single tracks are 35, 42, and 60 μm. The x-ray diffraction results show only the presence of primary phase α-Mg; interestingly, the β-Mg17Al12 and η-Al8Mn5 secondary phases are identified by SEM + EDS and TEM images. The microhardness increased from the substrate to the top section of single tracks due to the increased volume fraction of secondary-phase particles. Based on the best-chosen process parameters obtained from single-track deposition, a multilayer AZ31 Mg thin wall is deposited. The UTS, YS, and % EL of the deposited thin wall in travel direction (TD) are 222 MPa, 102 MPa, and 18%, while in build direction are 202 MPa, 110 MPa, and 14%, respectively. The tensile strength and elongation % of TD and BD samples exhibited comparable properties and were higher than cast AZ31 Mg alloy. [ABSTRACT FROM AUTHOR]

Cracks have consistently been a significant challenge limiting the development of additive manufactured nickel-based superalloys. It is essential to investigate the location of cracks and their forming mechanism. This study extensively examines the impact of solidification process, microstructural evolution, and stress concentration on crack initiation during direct energy deposition (DED). The results emphasize that the crack formation is significantly related to large-angle grain boundaries, rapid cooling rates. Cracks caused by large-angle grain boundaries and a fast-cooling rate predominantly appear near the edge of the deposited samples. Liquation cracks are more likely to form near the top of the deposited sample, due to the presence of eutectics. The secondary dendritic arm and the carbides in the interdendritic regions can obstruct liquid flow during the final stage of solidification, which results in the formation of solidification cracks and voids. This work paves the way to avoid cracks in nickel-based superalloys fabricated by DED, thereby enhancing the performance of superalloys. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM), specifically Directed Energy Deposition (DED)-Arc, holds great potential for the fabrication of individually designed components. In the construction industry, the demand for tailored steel nodes is increasing, particularly for large-scale structures, where high-strength steel deployment can significantly reduce material consumption and production time. However, the thermal material deposition process has a strong impact on the technical properties of high-strength steel. Parameters like heat input, interpass temperature (IPT), and cooling strategies modulate cooling times and peak temperatures in thermal cycles, which are crucial for estimating mechanical properties indispensable for safety certification. The development of digital twins or digital shadows emerges as the primary approach for quality assurance and certification, deploying real-time monitoring of manufacturing parameters such as voltage, current, wire feed, thermal history, and bead shapes. This data can be correlated with specific regions in the fabricated part to draw quality inferences. To interpret this data effectively, an understanding of the influence of these process parameters on resultant properties is indispensable. Given that the resulting microstructure strongly depends on the thermal history in AM parts, temperature monitoring during DED-Arc using thermography emerges as a promising method. This article aims at providing fundamental knowledge about phase transformations of a high strength steel feedstock under repeated reheating and gaining comprehensive knowledge about microstructural evolution during DED-Arc Additive Manufacturing. This is done by the analysis of time-temperature profiles, resulting microstructure and mechanical properties, linking it to CCT diagrams. A novel approach for describing the degree of tempering in different regions of the samples by deploying tempering parameters for anisothermal heat treatments is presented. By using this approach, an estimation about the resulting microstructure and hence the mechanical properties can be drawn.

Repair offers significant time—cost savings and durability by reusing existing parts efficiently. Prior to implementation of repaired parts, it is crucial to clarify mechanical properties and deformation mechanisms to ensure proper performance. In this study, a repair deposition was performed on the groove of wrought stainless steel 316L using the same material powder. The repaired sample exhibited an excellent combination of ductility and strength (T.EL: 58%, YS: 407 MPa, UTS: 673 MPa) compared to the wrought counterpart. With heterogeneity in microstructure, the hetero-deformation-induced strengthening of the repaired sample resulted in a synergy of strength-ductility combinations.

In the present study, a functionally graded metal-ceramic composite structure comprising SS410, Al 2 O 3 , and SiC particles with varying composition, structure and properties in a single deposit was successfully fabricated using direct energy deposition (DED). The composition varied from 90 % SS410 with 10 % (xAl 2 O 3 + ySiC) to 10 % SS410 with 90 % (xAl 2 O 3 + ySiC), where x = 70 % and y = 30 % in a five-layered FGM design. The microstructure, phase evolution and mechanical properties of the components with different composition gradients were characterized by microscopy, energy dispersive spectroscopy, wavelength dispersive spectroscopy, X-ray diffraction and micro hardness. The investigation revealed that complex phases such as C 0.12 Fe 0.79 Si 0.09 , M 7 C 3 , Fe 3 C, and Fe 3 Si formed as a result of the interaction between SiC and SS410 during the cladding process. Microstructural analysis showed a transition from columnar dendrites at the bottom zone of the cladding to a typical cellular structure and carbide particle agglomerates in the middle zone, with finer grains at the top zone. This gradation in microstructure correlated with an increase in microhardness ranging from 299 HV at the bottom to 966 HV at the top. This enhancement in hardness is primarily attributed to solid solution strengthening from C and Si originating from the decomposition of SiC and the precipitation of intermetallic phases. [ABSTRACT FROM AUTHOR]

Repair offers significant time—cost savings and durability by reusing existing parts efficiently. Prior to implementation of repaired parts, it is crucial to clarify mechanical properties and deformation mechanisms to ensure proper performance. In this study, a repair deposition was performed on the groove of wrought stainless steel 316L using the same material powder. The repaired sample exhibited an excellent combination of ductility and strength (T.EL: 58%, YS: 407 MPa, UTS: 673 MPa) compared to the wrought counterpart. With heterogeneity in microstructure, the hetero-deformation-induced strengthening of the repaired sample resulted in a synergy of strength-ductility combinations. [ABSTRACT FROM AUTHOR]

AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA), with its distinctive heterogeneous structure, not only overcomes the drawback of insufficient strength of FCC single-phase high-entropy alloys (HEAs), but also overcomes the drawback of insufficient ductility of BCC single-phase HEAs, making it a promising candidate for engineering application. In addition, EHEAs possessing excellent castability are considered to be suitable for additive manufacturing (AM). The AlCoCrFeNi2.1 EHEA prepared by direct energy deposition (DED) exhibits a dual-phase structure consisting of FCC(L12) and BCC(B2) phases. With the increase of deposition height, its morphology transforms from columnar and dendrite structures to lamellar structure. Furthermore, the tensile strength and yield strength of the DED-ed EHEA samples increase, while the ductility decreases with the increase of deposition height. Especially, the middle region of the DED-ed samples achieves a good strength-ductility balance. The lamellar structure composed of soft FCC(L12) phase and hard BCC(B2) phase produces a hetero deformation induced (HDI) hardening, which improves the strength of the samples and promotes plastic deformation. The FCC(L12)/BCC(B2) phase interfaces not only hinder the movement of a large number of dislocations and cause dislocation pile-up, but also allow some dislocations to slip across, which helps to plastic co-deformation of two phases in the EHEA samples. This work provides useful guidance for the performance improvement of EHEAs using laser additive manufacturing.

In recent years, efforts have been focused on the development of metal additive manufacturing (AM) processes to address the growing trend of miniaturization in industries such as aerospace and electronics. Thus, new technologies have been developed based on a downscaled approach using direct energy deposition (DED) processes, now referred to as μ-DED. In this context, the development of a downscaled DED prototype based on gas metal arc (GMA) working with micrometric wires (μ-GMA) has the potential to unify the positive characteristics of GMA-based DED, increasing the complexity of the design and resolution of the produced parts. Therefore, this work focuses on developing a μ-GMA prototype and assessing its technical feasibility. This paper describes the development of the μ-GMA prototype, characterizes the metallic transfer mode, and statistically analyzes the effect of deposition parameters on bead width and height. Additionally, microstructural analysis, Vickers microhardness, and reduced Young's modulus tests were performed. The μ-GMA prototype demonstrated the capability to deposit beads with an approximate width of 1 mm, nearly 5 times thinner than standard GMA-based DED deposition, with a build rate of 30 cm3/h, which is lower than GMA-based DED but higher than other μ-DED processes. Furthermore, the mechanical properties of the μ-GMA depositions are comparable to regular GMA-based DED parts.

High-strength metastable β-titanium alloys like Ti-5553 (Ti–5Al–5Mo–5V–3Cr) are frequently used in highly loaded aerospace components. Such aerospace parts tend to be expensive to traditionally manufacture due to current industry process limitations such as inflexibility for complex geometries, costs related to tooling for large forgings, extended lead times, poor machinability and high material waste. These challenges are leading to increased interest in exploring alternative manufacturing routes. This work investigates the use of additive manufacturing to deposit cost-effective and machinable Ti-64 (Ti–6Al–4V) alloy onto a forged Ti-5553 alloy substrate. The microstructure evolution, microhardness and tensile properties have been investigated for both the as-deposited as well as for stress relief heat-treated conditions. The results confirmed the formation of coarse columnar β grains with a fine basketweave α structure. The heat affected zones (HAZs) developed in the Ti-5553 substrate material from the cyclic thermal fluxes introduced from the melt-pool were characterized by a gradient microstructure of dissolving constituent phases with nearing proximity to the fusion zone. Tensile testing in the as-deposited condition was characterised with a UTS of 884 MPa and a ductility of 15%. Tensile samples extracted across the substrate-deposit interface all failed in the WAAM Ti-64 material and demonstrated comparatively greater strength but poorer ductility. A band of tensile residual stresses was imparted along the substrate, but was adequately stress relieved after heat-treatment at 600 °C. The heat-treatment led to the formation of more homogeneous α-phase laths throughout the HAZ of the Ti-5553 material and provided overall improvements to the strength and ductility.

This paper provides a critical overview of experimental and computational studies conducted on additive manufacturing (AM) or 3D printing using bimetallic alloys. The review acknowledges the complexity introduced by mechanical interactions and significant interface anisotropies in multi-material AM, making the mechanisms of phase change and microstructure evolution more intricate. Various computational models, such as density functional theory (DFT), phase field, and finite element models, employed in the study of 3D printed bimetallic materials are discussed. The paper highlights the importance of future research in developing quantitative predictions that can simulate and forecast microstructure formation during the AM process. By incorporating computational modeling, this review underlines the potential for overcoming challenges associated with the intricate interactions between different materials in multi-material AM (MMAM). [ABSTRACT FROM AUTHOR]

In the present study, a systematic comparison of additively manufactured CoCrNi medium entropy alloy having face-centered-cubic (FCC) structure with standard FCC materials 316L austenitic stainless steel was carried out. The effect of energy density (71 J/mm2) on microstructural heterogeneity and crystallographic orientation of planes parallel to the build direction (X–Z) and perpendicular to the build direction (X–Y) was recorded. Scanning electron microscopy, x-ray diffraction and electron backscattered diffraction techniques were used to reveal the surface and structural features. The effect of repetitive heating associated with layer-by-layer deposition of the X–Z axis was reflected as the favorable formation of the (1 1 1) plane at the expense of the (2 2 0) plane. The low angle grain boundaries at the X–Z axis have been decreased by ~ 27% compared to the X–Y axis for CoCrNi, while a ~ 17% reduction was recorded for 316L austenitic stainless steel. Furthermore, the decreasing trends in nanomechanical properties and wear resistance were observed, with a low number of low angle grain boundaries at the X–Z axis, by employing a nanoindenter. Significant microcracks in CoCrNi medium entropy alloy manifest the brittle fracture mode, whereas 316L alloy denotes the mixed type of failure mode. [ABSTRACT FROM AUTHOR]

Humping is a common defect in direct energy deposition processes that reduces the geometric integrity of printed products. The available literature on humping detection is deemed reactive, as they focus on detecting late-stage melt pool spatial abnormalities. Therefore, this work introduces a novel, proactive indicator designed to detect early-stage spatiotemporal abnormalities. Specifically, the proposed indicator monitors the variability of instantaneous melt pool solidification-front speed (VIMPS). The solidification front dynamics quantify the intensity of cyclic melt pool elongation induced by early-stage humping. VIMPS tracks the solidification front dynamics based on the variance in the melt pool infrared radiations. Qualitative and quantitive analysis of the collected infrared data confirms VIMPS's utility in reflecting the intricate humping-induced dynamics and defects. Experimental results proved VIMPS' proactivity. By capturing early spatiotemporal abnormalities, VIMPS predicted humping by up to 10 s before any significant geometric defects. In contrast, current spatial abnormality-based methods failed to detect humping until 20 s after significant geometric defects had occurred. VIMPS' proactive detection capabilities enable effective direct energy deposition control, boosting the process's productivity and quality. [ABSTRACT FROM AUTHOR]

Laser direct energy deposition (DED) has some accompanying issues, such as existence of micropores, elemental segregation at grain boundaries, intergranular corrosion, etc. Therefore, the current work aims for a reduction in clad defects and enhancement in surface properties for laser direct deposition of Inconel 625 by implementing ultrasonic vibration. The acoustic streaming and cavitation effect induced by ultrasonic vibration results in the breaking of columnar grains, along with grain refinement and better elemental distribution in the matrix during the solidification process. The investigation is carried out for deposition using a 240 W Yb-fiber laser under the application of ultrasonic vibration with a variable amplitude of 6–13 μm (frequency: 33–28 kHz). A relatively higher vibration amplitude was found more efficient in converting long columnar grains into finer and uniformly distributed equiaxed grains, with a significant reduction in micropores. Further, it resulted in a shorter molten pool lifetime because of the generation of more nucleation centers, leading to better cooling. The above effects resulted in higher microhardness of the deposited layer. Further, the wear and corrosion resistance showed an improvement with the application of vibration, which may be due to the finer equiaxed grains, less porosity, and better elemental distribution at a higher vibration amplitude. [ABSTRACT FROM AUTHOR]

Aluminum matrix composites (AMCs) have garnered significant attention across various industrial sectors owing to their remarkable properties compared to conventional engineering materials. These include low density, high strength-to-weight ratio, excellent corrosion resistance, enhanced wear resistance, and favorable high-temperature properties. These materials find extensive applications in the military, automotive, and aerospace industries. AMCs are manufactured using diverse processing techniques, tailored to their specific classifications. Over three decades of intensive research have yielded numerous scientific revelations regarding the internal and extrinsic influences of ceramic reinforcement on the mechanical, thermomechanical, tribological, and physical characteristics of AMCs. In recent times, AMCs have witnessed a surge in usage across high-tech structural and functional domains, encompassing sports and recreation, automotive, aerospace, defense, and thermal management applications. Notably, studies on particle-reinforced cast AMCs originated in India during the 1970s, attained industrial maturity in developed nations, and are now progressively penetrating the mainstream materials arena. This study provides a comprehensive understanding of AMC material systems, encompassing processing, microstructure, characteristics, and applications, with the latest advancements in the field. [ABSTRACT FROM AUTHOR]

In this study, we investigated the displacement behavior of SUS316L stainless steel under five consecutive direct energy depositions through experiments and the use of the ANSYS commercial finite element method software. We explored the effects of displacement after cooling the five deposited layers and examined the relationship between different curvatures and laser parameters, including laser power and laser feed rate. In this research, a complete crosssectional profile was obtained through experiments. Subsequently, simulations were conducted using laser powers of 300, 400, and 500 W, along with laser feed rates of 3, 5, and 7 mm/s, employing a thermal-solid coupling model. The results indicated that the optimal preheating temperature during the deposition process was around 150 °C, leading to a more stable displacement difference. The influence of curvature on displacement was relatively consistent along the neutral axis, allowing for the prediction of large displacement amounts along a straightline path. Through simulation, it could be understood that when utilizing direct energy deposition to deposit SUS316L, considering the displacement conditions during the deposition process, it was preferable to use a low laser power and a high deposition rate. [ABSTRACT FROM AUTHOR]

The repair of airfoil blades is an enabling technology to extend the operational life of gas turbine engines. Directed energy deposition (DED) additive manufacturing (AM) provides the ability to add material by melting blown powder using a directed energy source. Seventeen Ti‐6Al‐4V airfoil blades were repaired using DED AM and analyzed to determine what effect the repair will have on the blade performance in high cycle vibration fatigue testing. Volumetric computed tomography (CT) was used to quantify the pores from the AM process. The blades were then subjected to vibrational bending fatigue, used to simulate turbine engine loading conditions, until failure. Only three blades failed in the repaired sections. The identified pore sizes and fatigue stress distribution in the blade were used to suggest that understanding the impact of internal and near surface level pores arising from the AM repair is critical towards the implementation of AM repair in aerospace components under fatigue loading. Highlights: Investigates directed energy deposition additive manufacturing repair for engine rotors.Examines defects in additive repairs using CT scans and image processing techniques.Studies the prediction of bending fatigue life based on porosity size and location. [ABSTRACT FROM AUTHOR]

Novel ternary titanium alloys with a bainitic microstructure have been designed specifically for additive manufacturing (AM). The Ti-xCu-yFe alloys take advantage of constitutional supercooling to suppress the growth of large columnar grains usually associated with AM Ti alloys. In the as-built condition the bainitic microstructure consists of a refined α-phase within a matrix of β-phase. The intermetallic phase, Ti2Cu, forms predominantly on the interface of the α- and β-phase and within the β matrix. The high strength of these materials is attributed to the refined α-phase and Ti2Cu particles as well as significant solid solution hardening. This work demonstrates a viable way to fabricate structural components with unique and excellent properties using low-cost elemental powders with AM.

Wire-arc direct energy deposition was used in this study to manufacture a standing pressure vessel made of stainless steel. Considering the thickness of the additively manufactured sections, the fabricated part was divided into two major components: the shell and the head. The shell with a nominal wall thickness of 5 mm was manufactured using a single-pass technique, while the relatively thicker head, with a maximum thickness of 30 mm, was fabricated using a multi pass approach. The transition from the shell to the 15–30 mm thick head was done by variating wall thickness, enabled by additive manufacturing. After additive manufacturing, the full-scale component was tested up to the maximum internal water pressure of 111 bar (defined per the vessel’s industrial application). Further, to evaluate the mechanical properties of the additively manufactured steel and the effects of pressure loads on it, quasi-static tensile and fatigue tests were conducted on coupons prepared from the material in two conditions: as-built (without any preload) and preloaded (after the pressure test) extracted from various sections. Finally, metallurgical characterization was performed to establish a correlation between the microstructural features and the mechanical performance. The results showed that it is possible to manufacture high-performance and quality pressure vessels using the wire-arc direct energy deposition method.

Abstract Successful additive manufacturing involves the optimisation of numerous process parameters that significantly influence product quality and manufacturing success. One commonly used criteria based on a collection of parameters is the global energy distribution (GED). This parameter encapsulates the energy input onto the surface of a build, and is a function of the laser power, laser scanning speed and laser spot size. This study uses machine learning to develop a model for predicting manufacturing layer height and grain size based on GED constituent process parameters. For both layer height and grain size, an artificial neural network (ANN) reduced error over the data set compared with multi linear regression. Layer height predictions using ANN achieved an R2 of 0.97 and a root mean square error (RMSE) of 0.03 mm, while grain size predictions resulted in an R2 of 0.85 and an RMSE of 9.68 μm. Grain refinement was observed when reducing laser power and increasing laser scanning speed. This observation was successfully replicated in another α + β Ti alloy. The findings and developed models show why reproducibility is difficult when solely considering GED, as each of the constituent parameters influence these individual responses to varying magnitudes.

Most metallic structural materials possess an intrinsic inverse relationship between strength and ductility. Heterostructured materials are expected to address this issue. Through composition regulation, TC4/TC4+2.5Ni layered heterostructures with exceptional strength and ductility were fabricated by direct laser deposition (DLD), exhibiting a significant increase in strength compared to that of TC4 while retaining excellent ductility. The mechanism of strength–ductility synergy was investigated under different alternating interlayer design conditions. The addition of nickel refined the microstructure of TC4, promoting the transformation of coarse columnar grains into nearly equiaxed grains. The DLD-fabricated TC4/TC4+2.5Ni layered heterostructure comprised alternating regions of columnar and near-equiaxed grains. By appropriately adjusting the thickness of alternating components (three to four DLD-deposited layers), a significant compositional and microstructural heterogeneity was achieved, resulting in a synergistic effect on strength and ductility in TC4-TC42.5Ni layered heterostructures. Moreover, strength–ductility synergy was achieved under the combined effect of hetero-deformation-induced stress, crack deflection near the component interface, and inhibition of strain localization by alternating soft and hard regions. This study provides a theoretical foundation and key evidence for designing DLD-deposited heterostructured titanium alloys with improved strength–ductility synergy, offering novel insights and contributions to improving the performance of titanium alloys.

Magnesium and its alloys remain perilous in the framework of light weighting and advanced devices structure such as rockets and satellites. However, the utilization of Magnesium (Mg) is increasing every year, revealing growing demands in manufacturing industries. Manufacturing of Mg components is challenging because of their HCP crystal structure and limited ductility. In this context, additive manufacturing (AM) provides the flexibility to manufacture complex shape components with excellent dimensional stability. It also provides a new possibility for utilizing novel component structures that increase the applications for Mg alloy. This review herein pursues to holistically explore the additive manufacturing of Mg alloy with a synopsis of processes used and microstructure, mechanical properties, corrosion behaviour and postprocessing of AMed Mg alloy. The challenges and future scope of AMed Mg alloys are critically explored.

Direct energy deposition (DED) is a widely used manufacturing process for the production of high-performance metallic components. The process involves depositing a molten metal onto a substrate, which solidifies rapidly to form a clad layer. In this study, the effect of the DED-cladded material of SS316 on a Duplex SS was investigated using Barkhausen noise (BN) analyzer, and the BN signals was measured before and after the cladding process. The method is demonstrated to be effective in detecting microstructural changes, identifying defects, and evaluating the residual stress of the cladded material. The peak and RMS values of both cases exhibit an upward trend when the magnetizing frequency and magnetic field intensity are increased. There is a lower BN response appeared in the duplex SS compared to the cladded material, which gave direct information of the smaller grain size present in the duplex SS. The hysteresis loop characteristics, namely the average permeability, and remanence, showed an inverse relationship with respect to the low-frequency range. However, coercivity is directly proportional to all frequency ranges of the magnetizing waveform, whether it is a sine or triangular wave. The coercivity of the cladded material showed higher than the duplex SS, which is due to having a lower hardness level in the cladded material. Also, a parametric simulation is done to analyze the temperature distribution and heat affected zone (HAZ) at the interface of the deposited material and substrate. The results showed that at the higher value of the laser power, more HAZ appeared; however, as increasing the scanning speed, the HAZ values showed less at the constant value of laser power. The study provides valuable insights into the magnetic properties of cladded materials and their substrates, which can be used to evaluate material quality, hardness, and other mechanical properties. [ABSTRACT FROM AUTHOR]

Most materials conventionally found in nature expand with an increase in temperature. In actual systems and assemblies like precision instruments, this can cause thermal distortions which can be difficult to handle. Materials with a tendency to shrink with an increase in temperature can be used alongside conventional materials to restrict the overall dimensional change of structures. Such structures, also called negative-thermal-expansion materials, could be crucial in applications like electronics, biomedicine, aerospace components, etc., which undergo high changes in temperature. This can be achieved using mechanically engineered materials, also called negative thermal expansion (NTE) mechanical metamaterials. Mechanical metamaterials are mechanically architected materials with novel properties that are rare in naturally occurring materials. NTE metamaterials utilize their artificially engineered architecture to attain the rare property of negative thermal expansion. The emergence of additive manufacturing has enabled the feasible production of their intricate architectures. Industrial processes such as laser powder bed fusion and direct energy deposition, both utilized in metal additive manufacturing, have proven successful in creating complex structures like lattice formations and multimaterial components in the industrial sector, rendering them suitable for manufacturing NTE structures. Nevertheless, this review examines a range of fabrication methods, encompassing both additive and traditional techniques, and explores the diverse materials used in the process. Despite NTE metamaterials being a prominent field of research, a comprehensive review of these architected materials is missing in the literature. This article aims to bridge this gap by providing a state-of-the-art review of these metamaterials, encompassing their design, fabrication, and cutting-edge applications. [ABSTRACT FROM AUTHOR]

This study investigated the influence of Fe content on the microstructure and mechanical properties of Ti–6Al–4V(TC4) + 25Ti alloys prepared by low-energy-density direct energy deposition (DED) technology. With the incorporation of the Fe elements, the α-Ti phases exhibited significant changes in size and morphology, while the numerous β-Ti phases and some triclinic-Ti precipitates were retained. With the refinement of the α-Ti phase, retainment of the β-Ti phase and the presence of triclinic-Ti precipitates, the mechanical properties of DED samples can be significantly improved compared with DED TC4 alloys. The room-temperature mechanical property tests showed that the ultimate tensile strength (UTS) of 3Fe + TC4 + 25Ti achieved 1298.64 ± 5.26 MPa with an elongation of 4.82% ± 0.20%, and the maximum elongation of 1Fe + TC4 + 25Ti reached 10.82% ± 0.82% with a UTS of 1076.95 ± 11.69 MPa. The strengthening mechanism of DED Ti-Al-V-Fe alloys were further discussed, providing new insights into the microstructure control and the composition design of additive manufacturing of Ti alloys. [ABSTRACT FROM AUTHOR]

Laser-based additive manufacturing processes, particularly direct energy deposition (DED), have gained prominence for fabricating complex, functionally graded, or customized parts. DED employs a high-powered heat source to melt metallic powder or wire, enabling precise control of grain structures and the production of high-strength objects. However, common defects, such as a lack of fusion and pores between layers or beads, can compromise the mechanical properties of the printed components. This study focuses on investigating the recurrent causes of pore defects in the powder-fed DED process, with a specific emphasis on the influence of oxidized metal powders. This research explores the impact of intentionally oxidizing metal powders of hot work tool steel H13 by exposing them to regulated humidity and temperature conditions. Scanning electron microscopy images and energy-dispersive X-ray spectroscopy results demonstrate the clumping of powders and the deposition of iron oxides in the oxidized powders at elevated temperatures (70 °C for 72 h). Multi-layered depositions of the oxidized H13 powders on STD61 substrate do not show significant differences in cross sections among specimens, suggesting that oxidation does not visibly form large pores. However, fine pores, detected through CT scanning, are observed in depositions of oxidized powders at higher temperatures. These fine pores, typically less than 250 µm in diameter, are irregularly distributed throughout the deposition, indicating a potential degradation in mechanical properties. The findings highlight the need for careful consideration of oxidation effects in optimizing process parameters for enhanced additive manufacturing quality. [ABSTRACT FROM AUTHOR]

Magnesium and its alloys remain perilous in the framework of light weighting and advanced devices structure such as rockets and satellites. However, the utilization of Magnesium (Mg) is increasing every year, revealing growing demands in manufacturing industries. Manufacturing of Mg components is challenging because of their HCP crystal structure and limited ductility. In this context, additive manufacturing (AM) provides the flexibility to manufacture complex shape components with excellent dimensional stability. It also provides a new possibility for utilizing novel component structures that increase the applications for Mg alloy. This review herein pursues to holistically explore the additive manufacturing of Mg alloy with a synopsis of processes used and microstructure, mechanical properties, corrosion behaviour and postprocessing of AMed Mg alloy. The challenges and future scope of AMed Mg alloys are critically explored. [ABSTRACT FROM AUTHOR]

In this study, the temperature evolutions in the laser direct energy deposition process of Fe-based metallic materials are numerically investigated using the finite element method. The effects of heat input method and the model reduction strategy based on the lumped approach in the simulations were studied numerically. The simulations were carried out following the depositions of single beads, single layers, and multiple layers. The results of the simulations were compared with the temperature evolutions obtained in the experiments as well as the melt pool shapes observed in the experiments. Based on the numerical and experimental results, a numerical modeling strategy is proposed for estimating the temperature distributions in the laser direct energy deposition processes in a time-efficient manner, while maintaining the accuracy of the simulation. The proposed simulation strategy used rough simulation time steps for estimating the overall temperature rise, in addition to using only a few fine simulation time steps for predicting detailed temperature distributions at certain simulation times of interest. The proposed strategy allowed the FE model to reduce calculation time by more than 3.8 times while also accurately simulating the detailed temperature of the region of interest. [ABSTRACT FROM AUTHOR]

The deposition process of a nickel-based cermet coating with a high (60 wt.%) mass content of tungsten carbide was investigated. The results showed preheating the substrate to 500°C prevented the formation of cracks and pores in the coating. This is because preheating reduces the thermal shock between the substrate and the coating, leading to better adhesion and fewer defects. Additionally, synchrotron radiation was used to analyze the phase composition of the resulting composite. It was found that additional heating of the sample to 500°C during surfacing did not cause significant changes in the phase composition of the composite. [ABSTRACT FROM AUTHOR]

Ti6Al4V alloy billets were additively manufactured by direct energy deposition and then equal channel angularly pressed (ECAPed) at 700 °C. The originally prepared α′ martensite microstructure was completely converted to an equiaxed fine grain structure during ECAP processing. The α′ martensite decomposed into α + β dual phase structure. The dislocation density in the deposited and ECAPed samples was measured by X-ray profile analysis in samples of two orientations. The dislocation density estimated in the deposition plane was found to be higher than that estimated perpendicularly. This difference is probably a consequence of the internal stresses generated in the samples during the deposition process. A similar anisotropy in dislocation density and crystallite size was found in the ECAPed samples. Lattice constants were measured for the α′ martensite and α phase of the ECAPed alloy. The crystallite size distribution was found to be moderately different for samples cut parallel and perpendicular to the extrusion direction. [ABSTRACT FROM AUTHOR]

Additive manufacturing can produce complex parts with poor surface quality, requiring post-processing machining. The combination of additive and machining processes has been identified as a potential solution for achieving sustainable and cleaner production. This approach can enable the use of eco-friendly materials such as recycled or biodegradable ones, while reducing waste, energy consumption, and materials usage. Additionally, it can achieve precision and be used for repairing and finishing complex features. However, there is a lack of literature documenting fundamental material deformation and friction behavior in hybrid additive/subtractive manufacturing, which is necessary for optimizing the process efficiency and achieving cleaner production with reduced material usage and energy. This study investigates material deformation behavior in dry and wet hybrid manufacturing through shear stress, shear angle, and friction. The commonly used Johnson-Cook (JC) model may not adequately represent the deformation behavior in these operations. Therefore, a dual-zone thermomechanical model approach is applied modifying the JC model to hybrid manufacturing. The modified JC constitutive equation and analytical models are used in both modeling and parameter identification. This approach reduces the experimental effort significantly as only a few orthogonal cutting tests are needed to identify the material model and friction. The presented work contributes to a better understanding and modeling of hybrid manufacturing processes, aiming to enhance sustainability by minimizing material waste and energy consumption, ensuring product quality and integrity, and facilitating the adoption of sustainable practices. [Display omitted] • Sustainable hybrid additive/subtractive manufacturing of SLM and DED parts is studied. • Fundamentals of material deformation behavior are studied in dry and wet conditions. • Machining of AM and wrought parts are compared using stresses, shear angle, friction. • JC equation and analytical models for sliding friction identification are determined. • Novel study models hybrid manufacturing for aiming sustainability & waste reduction. [ABSTRACT FROM AUTHOR]

A new alloy Ti6Al4V/CrCFs synthesized from powder mixture Ti6Al4V and carbon fibers (CFs) coated of chromium (Cr) during direct energy deposition (DED) was investigated. The microhardness, wear properties, and microstructural characteristics of (Ti,Cr)xCy type carbides are determined. Samples Ti6Al4V/CrCFs were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscope (EDS), respectively. The microhardness of matrix and single carbides (Ti,Cr)xCy of new alloy Ti6Al4V/CrCFs was 450 HV0.01 and 1000 HV0.01, respectively. The (Ti,Cr)xCy synthesized carbides in a sample of the Ti6Al4V/CrCFs alloy grown by the DED method assist to a partial decrease in the coefficient of friction by 1.75 times compared to the Ti6Al4V alloy. This investigation revealed the wear performance of the DEDed specimens Ti6Al4V/CrCFs and their new (Ti,Cr)xCy carbides, which could pave the way for producing components for wear-related applications. [ABSTRACT FROM AUTHOR]

Recent advancements have shown great promise in utilizing wire‐fed direct energy deposition (DED) for building aluminum alloy structures. However, utilizing the wire‐fed DED approach for fabricating metal matrix composite structures remains a significant challenge. Herein, a wire‐based additive manufacturing process is used to successfully produce a 1D boron nitride nanotube (BNNT)‐reinforced aluminum composite with high strength. Al‐BNNT electrode is developed in house. The microstructural changes that occur during layer‐by‐layer deposition are investigated. The grain morphology changes from equiaxed grains in the bottom layer to columnar grains in the top layer. BNNTs act as nuclei to promote the formation of equiaxed grains and interfacial compounds (AlN and AlB2) during solidification. This results in improved strength, with Al‐BNNT composite exhibiting a tensile strength of 47 MPa, 2.3 times higher than its pure Al. Higher strength is attributed to the retention and uniform distribution of BNNT reinforcement in the melt pool, leading to effective load transfer. This study demonstrates the potential of additive manufacturing for producing high‐performance metal matrix composites with novel 1D reinforcements and improved multifunctional properties. [ABSTRACT FROM AUTHOR]

The microstructural features and crystallographic texture of 316L stainless steel prepared by direct energy deposition (DED) are studied. The grain size, morphology, grain boundary, misorientation distribution along different direction and mechanical properties are characterized via detailed electron backscatter diffraction (EBSD) analysis and Vickers microhardness tester. The DED-built 316L stainless steel exhibits equiaxed cellular and elongated morphology. Only a few number of dislocations are accumulated and entangled near small grain boundary. The sample contains mainly large angle grain boundary. 316L stainless steel powder is melted to form a deep and shallow shape measured from the top view. The average grain size is 38.32 µm and 29.79 µm for the top and side view, respectively. Two strong textural components of {001}<100> cube texture and {110}<001> Goss texture are formed perpendicular and parallel to the scanning direction, respectively. The microhardness of DED-built 316L stainless steel achieves a higher average value of 261.74 HV. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) technology using the direct energy deposition (DED) process and wires as feedstock material is commonly used to produce large components at an affordable cost. The wire laser AM (WLAM) process is one type of DED technology that uses welding wire as the raw material and a laser beam as the energy source. The goal of this study was to understand and evaluate the effect of microstructure modifications on the stress corrosion endurance of 15-5 PH stainless steels produced through WLAM, compared to their counterpart wrought alloy AISI 15-5 PH. All the tested alloys were heat treated using a standard age hardening treatment (H-1150M) prior to their examination. The microstructure analysis was performed using optical and electron microscopy (SEM and TEM) and X-ray diffraction analysis. The environmental behavior was characterized through electrochemical examination using potentiodynamic polarization and impedance spectroscopy analysis, while stress corrosion behavior was evaluated by means of slow strain rate testing (SSRT). The corrosion experiments were conducted in a simulated corrosive environment in the form of a 3.5% NaCl solution. The results showed that the microstructure modifications in the WLAM alloy (mainly in terms of austenite content, passivation capability and inherent printing defects) have a significant detrimental effect on stress corrosion resistance. [ABSTRACT FROM AUTHOR]

This study investigates the influence of process parameters on catchment efficiency and geometric characteristics such as track height, track width, and wetting angle for low energy density inputs in the blown powder Laser Metal Deposition (LMD) process for building thin-walled parts or repair volumes. Initially, a pilot study was conducted to examine the process parameters that affect catchment efficiency and geometric characteristics, from which five different process parameters such as (i) Laser power, (ii) Carrier gas flow rate, (iii) Deposition speed, (iv) Stand-off distance, and (v) Powder feed rate were identified as parameters of significance to the study. The impacts of these process parameters on catchment efficiency and geometric characteristics were investigated experimentally, and the data were analyzed using ANOVA and Response Surface Methodology (RSM). An analytical model was developed to predict the catchment efficiency, which was validated through experimentation. A comparison was made between the analytical, empirical, and experimental models for catchment efficiency, and it was found that the error was less than 8% which shows relatively good agreement between the proposed and experimental measurements. Furthermore, an empirical-statistical method was employed to establish the relationship between the chosen process parameters, catchment efficiency, and geometric characteristics to fabricate a single continuous track. Based on these correlations, a process map was constructed to identify the optimal processing conditions to obtain a single continuous track of IN625 powder on SS304 substrate with a higher catchment efficiency. This study achieved a maximum catchment efficiency of 71% for a low-energy density input. [ABSTRACT FROM AUTHOR]

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.

A wide range of additive manufacturing (AM) processing conditions can be rapidly realized within a single specimen via high-speed direct energy deposition laser based (DED-LB), due to a variety of cooling conditions and in-situ powder mixing. Since existing approaches are inefficient in exploring the vast material and process design space in AM, high-speed DED-LB can be employed as a novel technology for high-throughput alloy design tool. However, an evaluation of the process transferability of the high-speed DED-LB process with respect to the currently dominating metal AM technologies, namely laser powder bed fusion (PBF LB/M) and conventional DED-LB, is required. In this study, high-speed DED-LB is applied for the high-throughput sample production, using the nickel alloy IN718 as reference material as well as the AM processes PBF LB/M and DED-LB as reference processes. The resulting microstructures are characterized and compared using optical microscopy and large-area scanning electron microscopy (SEM) analysis combined with energy-dispersive X-ray spectroscopy (EDS). Furthermore, a model for calculation of the volumetric energy density is developed to compare the applied AM processes. The significant influence of the processing conditions on the solidification behavior of the investigated material allows for efficient exploration of the microstructure and phase composition. Specific high-speed DED-LB-process conditions achieved the average solidification cell size and laves phase content as observed in the PBF LB/M- and DED-LB -produced counterparts. The applicability of the high-speed DED-LB process for rapid alloy and process development, i.e., process transferability, is critically evaluated. The results show that high-speed DED-LB can be used to emulate cooling conditions of PBF-LB/M and DED-LB and, therefore, be used as tool for rapid alloy development.

Coarse β-columnar grains are often present in Ti–6Al–4V laser-additive-manufactured samples, resulting in anisotropic and inferior fatigue performance under dynamic loading. Fine-equiaxed grains (FEGs) with a mean grain size of approximately 139 μm were successfully obtained by a novel deposition strategy through coordinated regulation of direct energy deposition technological parameters. Microstructures were transformed from α′ martensite to α'' martensite. As a result, the comprehensive performance was significantly improved. Without the use of an argon atmosphere glovebox and post heat treatment, the tensile strength and elongation in the horizontal direction of the FEGs were 1091 MPa and 4.09%, respectively. The corrosion resistance was 11.71-fold higher than that of the coarse columnar grains (CCGs). Improving the microstructure and performance by optimizing pulsed laser parameters is simple, effective, and conducive to online regulation of the quality of laser additive samples.