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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.

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.

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.

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.

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.

The present study investigates the anisotropic microstructure, nanomechanical and corrosion behavior of Ti–13Nb–13Zr biomedical alloys, which were fabricated using the direct energy deposition (DED) method. The microstructure of the as-deposited material was studied using a field-emission scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). We found anisotropic mechanical behavior using nanoindentation from strain rate sensitivity and creep tests. For the maximum load of 50 mN, the x-y plane (normal to the building direction) shows better indentation hardness and lower strain rate sensitivity value (0.014) compared to the x-z plane (0.022) (parallel to the building direction). The difference in the indentation hardness was mainly attributed to the smaller equiaxed prior-β grains and finer α’ martensitic laths on the x-y plane. In terms of creep behavior, the x-y planes show better creep strength than the x-z plane. Meanwhile, both planes show a very high creep exponent, which signifies a similar creep mechanism, i.e., dislocation based. Moreover, we further found the anisotropic corrosion behavior using electrochemical tests. Corrosion results reveal that the x-y plane is more corrosion-resistant than the x-z plane. In summary, the x-y plane of the direct energy deposited Ti–13Nb–13Zr alloy possesses better strength and corrosion resistance due to its finer microstructure.

In this study, FeCrCoNiMo0.5W0.75 HEAs functional gradient materials were prepared by the direct energy deposition (DED) technique, and the phase transition, microstructure and mechanical properties of the materials along the building direction were investigated. The material realizes a transition from a single FCC phase to an FCC + TCP phase from the bottom to the top. The bottom and middle of the material are typical dendritic (DR)-interdendritic (ID) structures, and at the top, due to the precipitation of the eutectic structure σ phase and μ phase, the material transforms into a hypoeutectic structure of FCC + eutectic. According to the EBSD results, the interior of the material is mainly columnar crystals that grow vertically to the molten pool. This unidirectional columnar growth makes the material have a strong texture in the direction. In addition, a large degree of grain refinement is exhibited from the bottom to the top, with the grain size reduced from 19 μm to 6.5 μm. According to the TEM results, the density of dislocations is much higher near the phase and grain boundaries than in other regions, and dislocation entanglement is formed by the continuous accumulation of loose dislocations. The micro-hardness of the material increased along the construction direction up to 892.5HV0.5, and the material has good compressive strength up to 2041 ± 45 MPa. The material has excellent wear resistance and high-temperature wear resistance, forming a continuous oxide layer at 800 °C, which greatly reduces the friction coefficient and wear rate.

This study explores cellular structures in TiC/B4CCoCrFeMnNi high-entropy composites (HECs) fabricated by direct energy deposition (DED) additive manufacturing process, investigating the role of TiC and B4C nano-paticles in enhancing mechanical properties. Despite larger dislocation cell structures and thinner boundaries in TiC/B4CCoCrFeMnNi HECs compared to CoCrFeMnNi high-entropy alloy (HEA), they exhibit significantly higher hardness and strength, challenging traditional strength-size relationships. Additionally, we examine the behavior of ceramic nano-particles (TiC and B4C) with high melting points relative to matrix CoCrFeMnNi HEA. Rapid scanning prevents full nano-particle melting, leading to distinct element distribution of cell structure. These findings provide insights for selecting suitable nanoceramic particles in HEC development via metal additive manufacturing.

The fatigue crack propagation (FCP) behavior of L-PBF (laser-powder bed fusion) and DED (direct energy deposition) Ti–6Al–4V (Ti64) specimens with different crack directions (CDs) were studied in air and 3.5% NaCl solution under controlled potential, and the results were compared to that of CM (conventional manufacturing) Ti64 specimen. Among the specimens tested, L-PBF Ti64 specimen showed the lowest resistance to FCP, followed by DED and CM Ti64 specimens. The effect of CD with respect to building direction (BD) was negligible on the FCP behavior of L-PBF and DED Ti64 specimens. The micrographic and fractographic analyses suggested that refined microstructure was responsible for the FCP behavior of L-PBF and DED Ti64 specimens. L-PBF and DED Ti64 specimens were susceptible to EAFCP (environment-assisted FCP) in 3.5% NaCl solution, while the sensitivity was not as significant as that of CM counterpart. The sensitivity to EAFCP of L-PBF and DED Ti64 specimens was related to crack bifurcation, rather than intrinsic environmental degradation in Cl− bearing environment.

The advantages of heterostructured materials as structural materials include superior mechanical properties and the ability to tailor the strength-ductility combination via microstructure customization. To maximize heterostructure effects, this study combined direct energy deposition and ultrasonic nanocrystalline surface modification processes to create a CoCrFeMnNi equiatomic high-entropy alloy with multi-layered microstructures. The fabricated CoCrFeMnNi high-entropy alloy has a novel microstructure composed of multiple layers of repetitive microstructures with heterogeneity and demonstrates a remarkable synergetic strengthening effect in comparison to conventional heterogeneous materials. The outstanding mechanical properties derived from various hard and soft layer interfaces, as well as the effects of each layer and interface, were quantitatively analyzed using grain-scale digital image correlation technology. By combining the direct energy deposition and ultrasonic nanocrystalline surface modification processes, this study presents a method for fabricating a new class of heterostructured materials with multi-layered microstructure that exhibit deformation heterogeneity and grain size heterogeneity. The multi-layered microstructure with multiple heterogeneous boundaries breaks the conventional wisdom regarding heterostructured materials having only one or two heterogeneous interfaces.

Environment-assisted fracture (EAF) behavior of direct energy deposition (DED) Ti–6Al–4V (Ti64) specimen was investigated using a slow strain rate test (SSRT) method in air and 3.5% NaCl solution under controlled potentials, where the susceptibility to EAF was described by the reduction in tensile elongation (RTE) with exposure to aggressive environment. It was found that RTE value of DED Ti64 specimen was approximately 4 times greater than that of conventional manufacturing (CM) counterpart. The fractographic analysis on DED Ti64 specimen tested in 3.5% NaCl solution suggested that crack-like discontinuity was instantly formed from corrosion damages by merging into band-like lack of fusion (LOF) near the surface. Since LOFs were developed perpendicular to build direction (BD), the RTE value of DED Ti64 specimen with tensile direction (TD) perpendicular to BD was approximately 4 times lower than those with TD parallel to BD. Excellent correlation between the area fraction of LOF and the RTE was observed, indicating that LOFs were responsible for high susceptibility to EAF of DED Ti64 specimen in Cl− bearing environment.

This study investigates the wear resistance of an Fe–12Mn–5Cr–1Ni-0.4C (high-manganese steel) produced by direct energy deposition (DED) and spheroidal graphite cast iron. The high-manganese steel was deposited on the spheroidal graphite cast iron substrate. Near the deposit/substrate interface, the graphite phases of the cast iron are completely solutionized owing to the low carbon content of the high-manganese steel. In addition, the steel was deposited with a dense microstructure without interfacial cracks owing to the strong austenite stabilization effect. The wear behavior for various wear loads and sliding speeds was studied using ball-on-disk tribology tests with counterpart balls (KS STB2 bearing steel). The results show that the wear rates of the deposited high-manganese steel and the spheroidal graphite cast iron depended more on the wear load than on the sliding speed. At a low wear load of 20 N or less, the spheroidal graphite cast iron showed a higher wear rate than the deposited high-manganese steel owing to the self-lubricating effect of graphite. When the wear load condition was 50 N, the high-manganese steel had a higher wear resistance than the cast iron owing to the work-hardening effect. Therefore, it is expected that high-manganese steels, produced by DED, with high wear resistance under a high wear load will be effective for repairing spheroidal graphite cast iron products.

A comparative study of the microstructure and mechanical properties (tensile and high-cycle-fatigue) of Incoloy 901 repair welds produced via direct-energy-deposition (DED) and conventional tungsten-inert-gas (TIG) welding was conducted. The initial microstructure of the cast Incoloy 901 substrate exhibited a γ-matrix (an average grain size of ∼235 μm) and spherical γ′ particles (a size of

Epitaxial growth of dendrites often results in a strong texture, which is a common phenomenon in a laser additive manufacturing process. In this study, pulsed lasers with flat-top and Gaussian intensity profiles were used to modulate the molten pool morphology and the solidification texture with a unidirectional scanning strategy. The melt pool is planar for the flat-top mode and it turns arc-shaped for the Gaussian mode. Long columnar grains are uniformly distributed and a strong fiber texture with a weak cube texture is obtained for the flat-top mode sample due to a uniform heat flux through many deposition layers. In contrast, large grains and fine grains are alternately arranged for Gaussian mode sample. The large grains exhibit a strong rotated cubic texture with a V-pattern in the overlapping area of the melt pool due to side-branching from the curved melt pool boundary; while the fine grains exhibit a weak fiber texture in the center of melt pool with a less restriction of the other two crystallographic axes perpendicular to the build direction. After heat treatment, the intensity of the textures of both samples is reduced. More recrystallized grains with twin boundaries are found under Gaussian mode due to the accumulated residual strain. This work manifests a promising method for texture customization by manipulating the heat flux strategy for laser additive manufacturing.

In this study, the effect of preheating a AISI 304 steel substrate to 300 °C, compared to a room-temperature substrate, just before direct energy deposition (DED) additive manufacturing of a AISI 316 L steel deposit in terms of absorptivity of the laser beam, heat transfer, microstructure, hardness and residual stress. The samples were thermally isolated using an alumina cup. Using direct energy deposition for 20 and 40 layers of steel, it was found absorptivities of 18% and 16%, respectively, in room temperature (RT) experiments. At high temperatures (HT, 300 °C) the net absorptivity is almost zero because of convective and radiative cooling. The estimated heat transfer coefficients are approximately 1.0 and 0.4 Wm−2K−1, for RT and HT respectively. The microstructure and hardness obtained under each condition (RT or HT) for 20 or 40 layers, were quite similar. The microstructures were composed of austenitic grains with a Vickers hardness values ranging from 170 to 220 HV. The measured residual stresses were quite low for additive manufacturing of austenitic stainless steel, ranging from 11 to −22 MPa for RT and from 37 to −17 MPa for HT.

In wire arc additive manufacturing, residual displacements represent a common challenge. Simulations act as a tool for predicting this deformation, consequently reducing scrap rates. This paper aims to present the use of the inherent strain simulation for rapid and quantitatively satisfactory displacement predictions in the wire arc additive manufacturing process. The inherent strain method inserts layer-wise a strain tensor into the part. The inherent strain tensor results from the thermal expansion and contraction cycles. In this work, the activation of elements to model the material deposition has been investigated by simulating a reactivation area representing the remelting and annealing of the previously deposited material. Accordingly, three activation models were calibrated on the basis of experiments and validated based on two very different structures. While the conventional activation model proves unfeasible, the second activation model of partial removal of the stress and strain history in the previously deposited material is able to reproduce the displacement field with respect to the modeling limitations of the inherent strain model. Furthermore, the penetration depth for this annealing effect is a displacement-sensitive parameter and can be estimated semi-analytically. For industrial purposes, the simulated and experimental displacements of the validation bodies were in good agreement, implying that the predicted displacement can be considered in design processes and welding trajectory planning.

This paper deals with the fabrication of porous materials using direct energy deposition, which is a versatile 3D printing technique for metals. To manufacture a porous material, a mixture consisting of AlSi12 powder and a foaming agent (ZrH2) is sprayed onto an aluminum substrate and subsequently fused with the substrate using a high-power laser beam. We examined the effects of the main process parameters, namely the laser power, scanning speed and foaming agent ratio, on the total porosity, average pore size and number of pores of the final product. The results showed that the use of an excessive amount of foaming agent or energy decreases the porosity. In addition, a statistical analysis as well as the optimization of the main process parameters to ensure high porosity was conducted using the response surface method. Based on the central composite design method, the foaming agent ratio was found to have the greatest effect on the porosity, and a porous material with a maximum porosity of 24.83% could be fabricated using the optimal combination of the main process parameters. Finally, a mathematical model was derived to predict the relationship between these parameters and the porosity.

This work investigates the viability of fabricating Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-CTM) using laser-based and powder-fed directed energy deposition. To determine an appropriate ageing strategy, heat treatments were conducted at 440 °C and 480 °C over different periods of time and their effectiveness were determined through hardness testing. After identifying an optimal ageing treatment, tensile properties were investigated on the samples in the as-built and aged conditions. The microstructure, hardness and tensile properties of the as-built sample was found to resemble that of a conventionally-manufactured and solution-treated alloy. However, as compared to conventionally-manufactured Ti-3Al-8V-6Cr-4Mo-4Zr subjected to the same ageing temperature, the ageing process was much quicker with the DED-processed alloy because of its high dislocation density. Furthermore, the latter can also achieve much higher strength while also having comparable ductility. To achieve a similar ageing response and tensile behavior, conventionally-manufactured Ti-3Al-8V-6Cr-4Mo-4Zr would require cold-working prior to ageing. Carbon additions were also investigated to further accelerate the ageing response and to refine the β grain size. While the ageing response was much quicker and a much harder alloy can be produced, the carbon amount added was insufficient for β grain refinement, which resulted in reduced ductility without a change in strength.

Laser Powder Direct Energy Deposition (LP-DED) allows for manufacturing of large components while still maintaining internal thin walls for heat exchanger applications. The LP-DED process has been matured for alloys including stainless steels, superalloys, and titanium, but has had very limited research using copper-based alloys, which are important for applications that require high thermal conductivity. This study quantifies the size effects on microstructure, surface metrology, microhardness, and mechanical response to tensile loads for different thicknesses and powder compositions of hot isostatic pressed (HIP) LP-DED Copper-Chromium-Niobium alloy, specifically GRCop-42. To accomplish this, tensile specimens were sectioned from single track build walls in both horizontal and vertical orientations to also investigate possible anisotropic behavior in the part. Results show that microstructure, hardness, surface metrology, and porosity are independent of wall thickness. Uniaxial loading response showed some variations with specimens orientation and size effects. For vertical specimens, thicker specimens showed a 6% higher elongation than thinner specimens. Horizontal specimens showed close to double the elongation when compared to vertical specimens, where thinner specimens had a higher reduction in elongation than thicker specimens. Additionally, removing the surface effects through polishing practically eliminated the anisotropic behavior between horizontal and vertical specimens along with the observed size effects. To demonstrate size effects dependency on the manufacturing process comparison is made between GRCop-42 alloy produced by Laser Powder Bed Fusion (L-PBF) and LP-DED.

In this study, we report a method for the repair of damaged SUS 630 parts by directed energy deposition (DED). Herein, we aim to analyze the variations in the mechanical properties of such parts caused by post-repair heat treatment performed to regain the pre-repair mechanical properties. Before repair, substrates were subjected to solution annealing (SA-wrought) or SA treatment followed by precipitation hardening (SA + PH-wrought). Each substrate was repaired using SUS 630 powder. The repaired region was dominated by BCC-structured ferrite (96.7%). It also contained FCC-structured retained austenite (3.3%). The martensite fraction of the samples treated with SA after repair increased by 3.1%. Although BCC remained dominant after the SA + PH post-repair heat treatment, reverted austenite and a large amount of precipitate were generated along the grain boundaries after sufficient aging time of PH treatment. The repaired region displayed lower hardness than the substrate. However, the post-repair heat treatment increased the hardness. Meanwhile, the tensile test results revealed that the tensile strength decreased from that of the wrought material because of the cracks generated at the interface between the repaired region and substrate. Although the tensile strength was improved by SA and SA + PH post-repair heat treatments, the elongation decreased because of the cracks at the interface and reduction in the FCC content of the repaired part. Although cracks occurred at the interface, tensile characteristics almost similar to those of SA-wrought and SA + PH-wrought were observed owing to SA + PH post-repair heat treatment.

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.

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.

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 promising additive manufacturing technology for large-scale fabrications of high-value components. Grain structure control is challenging but meaningful for achieving desirable mechanical properties. A multi-scale three-dimensional (3D) Finite Volume Method-Cellular Automaton (CA-FVM) model is developed. The grain structure evolution in the transition-mode melting is investigated, and the simulated grain structures show fairly good qualitative and quantitative agreement with the experimental results. The influences of laser power and scanning speed on the formed grain structure are examined. A progressive columnar-to-equiaxed transition (CET) is found. The elongated grain is the primary grain morphology, even with the CET. The effects of high temperature gradient on the development of columnar structure are difficult to overcome. Moreover, nanoparticle reinforcement is numerically investigated as a promising technique to realize the site-specific grain structure control by interfering with the columnar growth. We expect this study to provide a deeper understanding of the DED-produced grain structure and improve confidence in the site-specific structure control.

The family of additive manufacturing techniques has been attracting significant attention of manufacturers and researchers, due to its unrivalled flexibility to fabricate and repair geometrically complex objects. However, material shaping is not sufficient: wide adoption of additive manufacturing can only occur upon the achievement of satisfactory mechanical performance in terms of structural integrity. The present study exploits a wide range of micro-scale experimental techniques to shed light on fatigue failure mechanisms of Laser Metal Deposition IN718 Ni-base superalloy, and to study the effect of shot peening treatment. Thorough microstructural and fractographic analyses revealed the main deformation mechanism associated with twinning during crack propagation, while crack initiation was found to be promoted by both slip system deformation and twinning around microstructural defects, rather than at sample free-surfaces. It was found that precipitates played a major role in determining the deformation mode. It was discovered that in this case-study, shot-peening residual stresses may have a detrimental effect, in view of the presence of the largest defects within a region where tensile residual stress was present. The results presented here improve understanding of failure mechanisms and thus define future directions of development for manufacture optimisation.