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

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

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

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

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

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

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

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

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

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%.

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

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

The paper presents a Finite Element Modelling (FEM) of the turning process on the Nickel superalloy IN718 produced by the Direct Energy Deposition (DED) to predict the residual stress. The material behaviour was implemented by a customized user-routine to take into account the anisotropy of the material due to the DED process. The residual stresses were experimentally measured on the surface and beneath the machined surface and the data collected were used to validate the FEM model. [ABSTRACT FROM AUTHOR]

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

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

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

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

Metal additive manufacturing (MAM) is an emerging technology to produce complex end-use metallic parts. To adopt MAM for manufacturing numerous engineering parts used in critical applications, a thorough understanding of the relationship between the complex thermal cycles in MAM and the unique heterogeneous microstructures of MAM parts need to be established. This review article provides a comprehensive overview of the evolution of heterogeneous microstructures in MAM parts, including melt pool boundaries, heterogeneous grain structure, sub-grain cellular structure, matrix supersaturation, segregation, phase transformation, oxides formation, and texture. The evolution of residual stresses and the anisotropy in MAM parts and the post-MAM heat treatment effects on the microstructural evolution are also discussed. This review covers the microstructural aspects of most engineering materials in particular steels, high entropy alloys, aluminum alloys, titanium alloys, nickel-base superalloys, and copper alloys, with a primary focus on the parts manufactured using selective laser melting, direct energy deposition, and electron beam melting processes. [ABSTRACT FROM AUTHOR]

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.

The application of maraging steels such as 18Ni300 alloy is noteworthy for mould industries, applying repair purposes through direct energy deposition process. This objective requires microstructural characterizations and the evaluation of mechanical behaviour such as hardness. The state of substrate material, including the heat-affected zone (HAZ) and the interface between the HAZ and deposited layer, is essential, the formation of hard phases and abrupt transitions. Thus, the influence of the number of deposited layers or the pre-heating condition appears noteworthy. In the current study, microscopy observations did not reveal the presence of any crack in the cross-sections of deposited 18Ni300 alloy powder on AISI 1045 sheet steel; however, pores were observed in deposited layers. Besides, microscopic analyses revealed the achievement of a smooth HAZ in the deposited layers composed of three-layered depositions or that received preheating, confirmed by hardness measurements as well. Dilution effect ensured a metallurgical bonding between depositions and substrate, strongly affected by preheating. The HAZ microstructure, mainly martensitic transformation, distribution of chemical composition, epitaxial growth at the interface, and the size of crystals and grains were affected by preheating or the number of layers. Moreover, the heat propagation and/or dissipation across the deposited layers influenced the dendrite morphology and the texture of grains. The preheating condition provoked the formation of cellular/equiaxed dendrites that was highlighted in the three-layered deposition, increase in dendrite interspace growth.

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

In this study, we developed an effective and rapid process for nanoscale ink printing, direct laser interference ink printing (DLIIP), which involves the photothermal reaction of a copper-based metal–organic decomposition ink. A periodically lined copper pattern with a width of 500 nm was printed on a 240 μm-wide line at a fabrication speed of 17 mm/s under an ambient environment and without any pre- or post-processing steps. This pattern had a resistivity of 3.5 μΩ∙cm, and it was found to exhibit a low oxidation state that was twice as high as that of bulk copper. These results demonstrate the feasibility of DLIIP for nanoscale copper printing with fine electrical characteristics.

Laminated metal composites are a promising design since the hybrid design enables superior and tailorable material properties compared with bulk material. The article introduces for the first time, laminated metal composites consisting of multiple bilayers of alternating layers of ductile and high-strength steel processed by wire arc additive manufacturing (WAAM). The layup of the laminated metal composites is built up by alternating deposits made of ductile steel and high-strength steel type wires. Governing parameters in the fabrication process affecting the material properties, such as dilution, are discussed. Enhanced material properties of the laminated metal composites fabricated by WAAM are investigated under static tensile, impact and tension-tension high-cycle-fatigue loading and compared to the relating homogenous weld metal. Potential reasons for the retardation of crack propagation in laminated metal composites fabricated by WAAM compared to findings in roll-bonded laminated metal composites are discussed. WAAM is conducted by a collaborative robot providing a high level of flexibility in respect to geometry and scalability. Tailorability of material properties through WAAM-fabricated laminated metal composites adds an important layer of flexibility which has not been explored yet.

Closed-loop control is desirable in direct energy deposition (DED) to stabilize the process and improve the fabrication quality. Most existing DED controllers require system identifications by experiments to obtain plant models or layer-dependent adaptive control rules, and such processes are cumbersome and time-consuming. This paper proposes a novel data-driven adaptive control strategy to adjust laser voltage with the melt pool size feedback. A multitasking controller architecture is developed to incorporate an autotuning unit that optimizes controller parameters based on the DED process data automatically. Experimental validations show improvements in the geometric accuracy and melt pool consistency of controlled samples. The main advantage of the proposed controller is that it can adapt to DED processes with different part shapes, materials, tool paths, and process parameters without tweaking. System identification is not required even when process conditions are changed, which reduces the controller implementation time and cost for end-users. [ABSTRACT FROM AUTHOR]

The effect of deposition pattern on the temperature and global distortion of Direct Metal Tooling (DMT) based Additive Manufactured (AM) is investigated through the experimental results of laser deposited SUS316. DMT is one of the Directed Energy Deposition (DED) processes. In situ temperature measurements were used to monitor the temperature of the substrates and global distortion patterns were analyzed using CMM (coordinate Measuring Machine) after the deposition. Six different patterns combining long raster and short raster patterns were considered for the case studies. The results showed that the deposition pattern affects the temperature gradient and that the peak temperature of each layer can increase or decrease according to the sequence of the deposition pattern. Also, the pattern of the first layer had a dominant influence on the longitudinal bending deflection that occurs. Based on these results, appropriate tool path schedule can be utilized to control not only the distortion but also the peak temperature of the DMT-based AM parts. [ABSTRACT FROM AUTHOR]

Soft magnetic alloys produced by additive manufacturing (AM) typically exhibit inferior magnetic properties compared to conventionally processed counterparts. The present study shows that the saturation magnetization and coercivity of the equiatomic ternary CoFeNi complex concentrated alloy (CCA), processed using the laser engineered net shaping (LENS) additive manufacturing (AM) technique, is identical to that of conventionally cast and thermo-mechanically processed samples. Further, the LENS processed alloy exhibits higher yield strength and marginally lower ductility compared to conventionally processed alloys. LENS processed CoFeNi exhibited an excellent combination of soft magnetic and mechanical properties, relevant, e.g., to high speed electrical machines. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Direct energy deposition (DED) is a three-dimensional (3D) deposition technique that uses metallic powder; it is a multi-bead, multi-layered deposition technique. This study investigates the dependence of the defects of the 3D deposition and the process parameters of the DED technique as well as deposition characteristics and the hardness properties of the deposited material. In this study, high-thermal-conductivity steel (HTCS-150) was deposited onto a JIS SKD61 substrate. In single bead deposition experiments, the height and width of the single bead became bigger with increasing the laser power. The powder feeding rate affected only the height, which increased as the powder feeding rate rose. The scanning speed inversely affected the height, unlike the powder feeding rate. The multi-layered deposition was characterized by pores, a lack of fusion, pores formed by evaporated gas, and pores formed by non-molten metal inside the deposited material. The porosity was quantitatively measured in cross-sections of the depositions, revealing that the lack of fusion tended to increase as the laser power decreased; however, the powder feeding rate and overlap width increased. The pores formed by evaporated gas and non-molten metal tended to increase with rising the laser power and powder feeding rate; however, the overlap width decreased. Finally, measurement of the hardness of the deposited material at 25?, 300°C, and 600°C revealed that it had a higher hardness than the conventional annealed SKD61. [ABSTRACT FROM AUTHOR]

Miniaturization of bearing rollers used in autos and robots will require a manufacturing system that combines a deposition method that can fabricate thin jigs without defects and a non-destructive inspection method that can detect cracks on such jigs. Here, we are developing a system that uses directed energy deposition (DED), which is a 3D-printing (additive manufacturing, AM) process, to fabricate thin jigs, and then uses laser ultrasonics (LU) to inspect the jigs. Here, deposited layers having a 0.4 × 0.6mm² cross-section were fabricated using DED, and then non-destructively inspected using LU. However, using LU on such a small area has three problems: the effect of overlapping of the excitation and detection laser beams, difficulty in separating the multiple types of waves due to the simultaneous generation, and complexity of the acoustic field. Therefore, first, the acoustic field was examined using the finite element method (FEM), and then LU was used to inspect a small area of the deposited layer using complex discrete wavelet transform. Results show successfully detection of spontaneously occurring cracks, thus confirming the effectiveness of LU for non-destructive inspection of a thin jig. [ABSTRACT FROM AUTHOR]

The influence of modern additive manufacturing methods, especially from the direct energy deposition (DED) processes to the coat-like finished components, is crucial under present industrial circumstances. DED induces several traits like enhanced mechanical, thermal properties in shorter lead time, which extend their adaptation for diverse applications including aerospace and automobile industries. Among the several DED processes, laser cladding has been a prospect that explores various capabilities of improving the wear resistance of cobalt-chromium (Co-Cr)-based alloys. Rather than fabricating the complete component using expensive alloys, laser cladding has paved an approach to deposit particles possessing superior qualities over the conventional material. This research work attempts to evaluate the surface integrity of SS420 when cladded with Stellite 6. The vertical face milling is executed on the cladded component surface to facilitate either low-plasticity burnishing (LPB) or cryogenic burnishing (CB) as sequential post-treatment processes. The effects of these post-treatments on the surface and subsurface microhardness, surface topography and residual stress profiles are elaborated. Increased surface and subsurface microhardness, as well as improved residual stress profiles, are observed with CB over LPB-processed specimen samples. [ABSTRACT FROM AUTHOR]

Laser based technologies enable major opportunities in performing quite heterogeneous deposition and subtraction processes characterized by very similar process dynamics. Hybrid machines integrating high power and ultra-short laser sources can efficiently exploit such technologies only when they embed a sensing system able to execute in-line inspection of partially manufactured parts. The current work presents an innovative configuration of Direct Energy Deposition hybrid machine equipped with a custom 3D vision system and software that allow: 1) the part shape measurement at every user defined checkpoint; 2) the acquisition of the temperature distribution onto this part surface; 3) the analysis of the data and the defect identification. The system is based on structured light technique and measures the spatial position of thousands of points belonging to the part surface. The measurements performed by a thermal camera are then associated to this point cloud and a dedicated software performs the comparison of the acquired geometry to the CAD model to detect over- or under-deposition areas and analyses the thermal distribution to detect potential defects. Corrective strategies can be generated for the layers that still have to be manufactured in terms of additional deposition or ablation. The benefits of the approach have been evaluated on experimental tests inspired by industrial scenarios. [ABSTRACT FROM AUTHOR]

In this paper, the restoration of damaged Inconel 718 parts has been accomplished through a laser-based Hybrid Technology. The system has been equipped with a Laser Metal Deposition (LMD) head for material deposition and a nanosecond ablation laser scanner for both worn surface preparation and post-deposition surface finishing. The assessment of the repaired metal parts has been performed through a digital microscope and an industrial 3D scanner with regards to specific KPI addressing both the external surface quality and structural integrity of the restoration. The benefits of this approach have been addressed in relation to industrial use case scenarios. [ABSTRACT FROM AUTHOR]

Laser direct energy deposition (DED) is an advanced additive manufacturing technology, which can produce fully dense and functionally graded materials (FGMs) metal parts. Residual stress and distortion are crucial issues in DED process reducing the mechanical strength and the geometrical accuracy of the fabricated components. This work provided a combined approach involving thermo-mechanical model and experimental validation toward two FGM cases fabricated by DED process to reveal the residual stress and distortion distribution. Two fabrication approaches were used: a direct deposition of Cu on SS304L and a structure graded from iron alloy SS316L to nickel alloy In718 to pure Cu based on SS304L substrate. Thermal histories of the substrate and the residual stress on cross-section of the FGM part were measured to calibrate the 3D coupled thermo-mechanical model. The predicted temperature and stress results showed a good agreement with the experimental measurements. The distortion results of both fabricated walls showed an upwards bent trend. Because of the high-temperature gradient induced by the mismatch in the thermal expansion coefficient of different materials, very high distortion was observed at two edge regions of the second printing material of FGM part. From the residual stress standpoint, direct joining Cu on SS304L resulted in extremely high residual stress at the bi-material interface due to mismatch in the thermal expansion coefficient of different materials. By introducing SS316L and In718 buffer layers, defect-free Cu can be successfully deposited on SS304L. This model can be used to predict the stress behavior of products fabricated by DED process and to help with the optimization of design and material chosen of FGMs process. [ABSTRACT FROM AUTHOR]

Directed energy deposition (DED) is an additive manufacturing (AM) process where a laser is used to fuse a metal powder onto a substrate. The powder is deposited in a layer-by-layer fashion, and each deposited track is referred to as the clad. Large thermal gradients that occur during DED can cause changes in the clad geometry as well as deformation of the substrate and final part. Thermal behavior of DED manufactured parts and mitigation of thermal distortion has been addressed in the literature, but these studies mainly focused on material properties while neglecting the effect of thermal distortion on part geometry. One of the mitigation strategies that has been widely tested and accepted is substrate preheating. This study uses analytical and experimental models to observe changes in clad geometry when energy input to the part is varied by adjusting process parameters and preheating the substrate. A method to quantify substrate energy, or the amount of heat energy the substrate holds, is found as well as a relationship between the substrate energy and clad geometry. The geometry of the clad can be controlled by controlling the total energy added to the clad. [ABSTRACT FROM AUTHOR]

The article describes phenomena which occur in the transitional area between stainless steel and aluminium bronze in laser deposited functionally graded structures created via direct joining method with the InssTek MX-1000 machine. The results of the research demonstrated absence of cracking achieved after changing of the synthesis scheme with the same materials and the same treatment regimes. The sources of cracking on a border between stainless steel and aluminium bronze layers were defined during the research. The results of microhardness measurement of the deposited multilayer structures demonstrated 266 HV maximum value with 43 GPa Young's modulus of elasticity in the same point of a transitional area. Intermetallics forming, dendritic growth, phase composition and microstructure specific properties of laser deposited stainless steel - aluminium bronze functionally graded materials are also observed and described in the article. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is a rising technology bringing new opportunities for design and cost of manufacturing, compared to standard processes like casting and machining. Among the AM techniques, direct energy deposition (DED) processes are dedicated to manufacture functional metallic parts. Despite of their promising perspectives, the industrial implementation of DED processes is inhibited by the lack of structural health control. Consequently, non-destructive testing (NDT) techniques can be investigated to inspect DED-manufactured parts, in an online or offline manner. To date, most ultrasonic NDT applications to metallic AM concerned the selective laser melting process; existing studies tackling DED processes mainly compare various ultrasonic techniques and do not propose a comprehensive control method for such processes. Current researches in the GeM laboratory focus on a multi-sensor monitoring method dedicated to DED processes, with a structural health control loop included, in order to track defect formation during manufacturing. In this way, this paper aims to be a proof of concept and proposes a comprehensive control method that opens the way to in situ ultrasonic control for DED. In this paper, a control method using the phased array ultrasonic testing (PAUT) technique is particularly illustrated on wire-arc additive manufacturing (WAAM) components, and its applicability to laser metal deposition (LMD) is also demonstrated. A specific attention is given to the calibration method, towards a quantitative prediction of the size of the detected flaws. PAUT predictions are cross-checked thanks to X-ray radiography, which demonstrates that the PAUT method enables to detect and dimension defects from 0.6 to 1 mm for WAAM aluminum alloy parts. Then, an applicable scenario of inspection of a WAAM industrial and large-scale part is presented. Finally, perspectives for in situ and real-time application of the chosen method are given. This paper shows that real-time monitoring of the WAAM process is possible, as the PAUT method can be integrated in the manufacturing environment, provides relevant in situ data, and runs with computing times compatible with real-time applications. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the interfacial strength between a material deposited on a substrate via direct energy deposition (DED) process. Using the DED process, a powder of the hot work tool steel H13 was deposited onto a substrate of SKD61 steel, and shear tests were performed at various temperatures (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C) to investigate the strength of the interface between the deposited material and the substrate. After the shear test, the fractured specimens were also analyzed. As a tested result at room temperature (25 °C), the cracks in the specimen were initiated in the deposited region; however, at high temperatures, the specimens were fractured only in the substrate regions. However, despite the difference in the location of the fracture-containing region, at no test temperature did interfacial cracking or delamination occur between the deposited material and the substrate. Thus, the interface demonstrated high bonding strength. [ABSTRACT FROM AUTHOR]

This study investigated the effect of ultrasonic nanocrystal surface modification (UNSM) on the deteriorated surface of AISI 316L deposited using the direct energy deposition (DED) technology. After UNSM treatment, the coarse DEDed surface was fined, and a regular micro-surface profile was implemented. Compared to the case before UNSM treatment, the waviness and roughness of the surface after UNSM treatment decreased by up to 73.8 % and 86.2 %, respectively, and reduced further as the UNSM interval was decreased. Surface severe plastic deformation (S2PD) was induced in the dendrite structure of the UNSM-treated DEDed sample surface. The microstructure was deformed till a depth of up to 92.13 mm from the surface and was significantly affected by the interval. After UNSM treatment, the hardness improved by up to 71.5 % and gradually decreased from the surface to the inside; the hardness was improved by UNSM up to a maximum depth of 400 μm. Although the UNSM interval condition had a significant effect on the DEDed surface, it barely affected the relationship between the directions of DED deposition and UNSM treatment. This study confirmed that the UNSM technology can effectively improve a DEDed surface. [ABSTRACT FROM AUTHOR]

In the directed energy deposition (DED) process, the scanning speed around sharp corners decreases from the command speed to a capable-curve speed. At a constant powder feed rate, the reduction in the scanning speed causes oversized beads owing to the increased deposition amount per unit time. In this study, the excessive deposition at the corners is controlled by the tailored setting of the corner scanning speed. The proposed control method enables fabrication of an equal-height rectangular corner geometry using the DED process. The bead height along the rectangular corner is controlled to be equal to those of the linear segments. For the sensitivity analysis of the process parameters, the effect of the scanning speed, laser power, and powder feed rate on the bead deposition was investigated experimentally. To generate smooth and equal-height deposition, a corner scanning-speed control algorithm was applied. Results showed that over deposition occurred near the corner section due to the scanning speed drop but after applying the controlled scanning speed, over deposition was decreased. In addition, a three-dimensional thermo-mechanical finite element simulation was performed to investigate the temperature field and induced residual stresses. [ABSTRACT FROM AUTHOR]

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

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