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

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

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

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

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

In laser‐based direct energy deposition (DED‐LB) additive manufacturing (AM), wire or powder materials are melted by a high‐power laser beam. Process‐specific characteristics enable robust in situ fabrication of compositionally graded materials, e.g., through an adaption of powder mass flow from independent hoppers. Based on the high flexibility of this approach, pathways toward multimaterial AM have been unlocked. Obviously, such characteristics enable high‐throughput alloy development. However, rapid alloy development demands substantial characterization efforts to assess phase and microstructural evolution. So far, property analysis is considered as the limiting factor for these high‐throughput approaches. Herein, the use of high‐brilliance X‐Ray analysis and subsequent micropillar compression testing are introduced to tackle these challenges. As a proof of concept, their application to a compositionally graded material made from AISI 316L stainless steel and a CoCrMo alloy is presented. The results obtained reveal that X‐Ray analysis can be exploited to evaluate process robustness, chemical characteristics, and phase composition within the gradient regions. Moreover, the use of micropillar compression testing provides spatially resolved insights into the mechanical properties of the gradient regions. The combination of both characterization techniques eventually opens pathways toward a robust and time‐efficient alloy development using powder‐fed DED‐LB (DED‐LB/P). [ABSTRACT FROM AUTHOR]

In this study, the effects of the laser power (2000 W, 2250 W, 2500 W), scanning speed (0.6, 0.8, 1 m/min), and powder feed rate (10, 12.5, 15 g/min) on material structures and their mechanical properties were investigated in the production of 316L stainless steels through Direct Energy Deposition (DED). In addition, changes in the microstructure caused by the re-melting process were also investigated. Optimized process parameters were modeled using the CFD software (FLOW 3D V3.0). In order to see the effects on the density and mechanical properties, the sample production was repeated as a build and by applying the re-melting process between the layers. When the energy density and powder feed rate are considered together, it has been determined that the deposition rate increases in direct proportion to the energy density and tends to decrease inversely with the powder feed rate. When the experimental and analysis results of the single clad height are compared, it is seen that the values obtained are very approximate. It has been observed that the most important parameters affecting the formation of porosity are the energy density and powder feed density. Re-melting slightly affects the microstructure of the material and causes grain growth. Changes in the impact strength of the re-melted samples were observed depending on the energy density. [ABSTRACT FROM AUTHOR]

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.

This study investigated the corrosion behavior of AISI 316L produced by direct energy deposition (DED). Microstructural and chemical analysis showed a homogeneous distribution of Si and Si–Mn inclusions of 0.5–1 µm and the Cr and Mo enrichment within interdendritic areas. Scanning Kelvin probe analysis of additively manufactured stainless steel highlighted a regular "striped‐like" surface potential feature with a potential gradient of 30 mV for a mean value of 0.320 ± 0.017 V versus standard hydrogen electrode. It can be related to the presence of the residual stress in the oxide film and the complex thermal history due to the fabrication process. A cyclic corrosion test simulating atmospheric conditions revealed the same corrosion properties for stainless steel fabricated by DED compared to cold rolled one. Various surface preparations of 316L were also exposed for corrosion tests. It was found that the "as‐received" and "brushed" surfaces exhibited poorer corrosion resistance due to the presence of an as‐build defective layer. However, prior passivation of brushed surface, machining, or mechanical grinding down to P1200 improve significantly the corrosion resistance. [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. [ABSTRACT FROM AUTHOR]

In this study, the effects of the laser power (2000 W, 2250 W, 2500 W), scanning speed (0.6, 0.8, 1 m/min), and powder feed rate (10, 12.5, 15 g/min) on material structures and their mechanical properties were investigated in the production of 316L stainless steels through Direct Energy Deposition (DED). In addition, changes in the microstructure caused by the re-melting process were also investigated. Optimized process parameters were modeled using the CFD software (FLOW 3D V3.0). In order to see the effects on the density and mechanical properties, the sample production was repeated as a build and by applying the re-melting process between the layers. When the energy density and powder feed rate are considered together, it has been determined that the deposition rate increases in direct proportion to the energy density and tends to decrease inversely with the powder feed rate. When the experimental and analysis results of the single clad height are compared, it is seen that the values obtained are very approximate. It has been observed that the most important parameters affecting the formation of porosity are the energy density and powder feed density. Re-melting slightly affects the microstructure of the material and causes grain growth. Changes in the impact strength of the re-melted samples were observed depending on the energy density.

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. [ABSTRACT FROM AUTHOR]

Manufacturing of components through additive manufacturing has become increasingly popular over the last years. Direct energy deposition (DED) is one of the methods gaining popularity due to the high throughput of the methods compared to powder bed fusion methods. For the establishment of DED as a viable option for manufacturing mission critical components, the material characteristics and the mechanical properties of the deposited material must be thoroughly understood. This research focuses on the investigation of the mechanical properties of 15-5PH stainless steel manufactured with direct energy deposition and the effect of heat treatment on the characteristics of the components that were manufactured. The effect of the orientation of the build relevant to the test orientation was examined with relevant tests while a benchmark against wrought 15-5PH was also examined. Finally, the characteristics of the bond between an AM coupon and a base material were investigated. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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

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.

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]

Abstract In the present study, we investigated the feasibility of fabricating multi-layered materials (MLMs) composed of austenitic stainless steel (316L) and ferritic steel (P21) using one of the additive manufacturing technologies, direct energy deposition (DED). With DED, an intermediate buffer layer is introduced between a bottom (P21) and a top (316L) layer. The relative compositions (wt%) of the three layers are 0:100, 50:50, and 100:0. Microstructure and mechanical properties were characterized via optical microscopy, electron backscatter diffraction (EBSD), Vickers microhardness, and miniaturized tensile testing in conjunction with digital image correlation (DIC). Finite element simulations were also conducted to obtain the local stress and strain states in the MLMs to elucidate the bulk plastic deformation behavior. The main finding was that the intermediate buffer layer, when processed with a mixture of P21 and 316L alloys, exhibited superior mechanical properties such as continuous yielding, a low yield to tensile strength, and a high work-hardening rate. The macroscopic deformation behavior was related to the initial microstructure that consisted of a small fraction of retained austenite and fine α′ martensite. During a compression test to study the bulk deformation behavior, MLMs with an intermediate buffer layer exhibited a relatively superior load-carrying capacity compared with MLMs without an intermediate buffer layer. Highlights • MLMs which were composed of 316L and P21 were fabricated by DED technique. • Microstructure and mechanical properties were characterized using OM, EBSD, Vickers microhardness, and tensile test. • The intermediate buffer layer exhibits superior mechanical properties such as a low YS/TS, and a high work-hardening rate. • MLM with the intermediate buffer layer exhibited a relatively superior load-carrying capacity. [ABSTRACT FROM AUTHOR]

• The microstructure evolution process of 316L stainless steel formed by direct energy deposition (DED) was revealed. • The effect of microstructure on mechanical properties was studied. • The machinability of 316L stainless steel formed by DED was studied and the control mechanism of that was revealed. • The process method of additive/subtractive hybrid manufacturing (ASHM) was put forward. • The ability and advantage of ASHM in surface quality and dimensional precision were verified. Additive/subtractive hybrid manufacturing (ASHM) technology is mostly based on direct energy deposition technology and achieves the direct forming of functional components by the timely use of alternating deposition and milling. This technology combines the high efficiency and material utilization of additive manufacturing (AM) with the high dimensional accuracy and surface quality of subtractive manufacturing (SM). In this work, the AM forming was utilized to rapidly generate the basic configuration of a 316L stainless steel components and the SM milling achieved its machined surface, aiming to study the forming mechanism and their effects on machinability. The rapid cooling rate in the direct energy deposition process contributed to grain refinement and precipitation of ferrite, which resulted in the improvement of hardness and tensile strength. There was no obvious linear relationship between work hardening and cutting speed or feed per tooth because the work hardening was affected by a combination of shear strain strengthening effect and thermal softening effect. The fine grains and more molten pool boundaries in the stainless steel by AM process leaded to the larger depth of work hardening during SM process. Finally, a variety of stainless steel components exhibited the good surface quality and dimensional accuracy by ASHM process. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of laser power and scanning speed on the surface roughness, clad morphology, microstructure, texture, and hardness of single layers of 316 L SS during direct energy deposition (DED) was investigated in this study. A columnar to equiaxed transition was observed in the deposited clads. Cellular, dendritic, columnar, and planar substructures were observed in the equiaxed region of the clad that was near to the free surface. In the interior region of the clad, grains were columnar in nature and was observed to grow at different angles with respect to the build direction (BD) depending on the interaction angle with the substrate. At intermediate laser power and scanning speeds, 〈001〉 || BD and 〈001〉 || scan direction (SD) orientations were observed. When the laser power was at the lower level, <001> || transverse direction (TD) orientations were obtained. When the laser power was at the higher level, a uniform mixture of austenite and martensite was obtained in the clad. The compositional shift in the deposited bead was responsible for the formation of the martensite phase. When the scanning speed was at lower level, 〈111〉 || SD and 〈110〉 || BD orientations were observed. When the scanning speed was at higher level, <001> || BD orientations were observed. A hardness in the range of 187± 13 Hv was obtained for all the samples except for the sample that was built at high laser power. • The effect ofprocess parameterson the microstructure of single-layer 316L SS fabricated by DED was investigated • A columnar-to-equiaxed transition in the morphology ofgrains was observed in the deposited clads • A uniform mixture of austenite and martensite and possibly some ferrite was formed atrelatively high laser power • <001> || TD orientations were obtained at a relatively low level of laser power • <111> || SD and<110> || BD orientations were observed at a relatively low level of scanning speed [ABSTRACT FROM AUTHOR]

Among the several metal additive manufacturing technologies, direct energy deposition (DED) is an innovative way to fabricate near-net-shaped parts and is also applicable to repairing damaged parts due to the simplicity of the machine. However, materials processed with this process have complex residual stress distribution due to the complex thermal history. Excessive residual stress inside the parts can induce shape distortion and cracks that degrade the performance of the parts. In this study, residual stress generated during the DED process was measured with the neutron diffraction method, and the result was compared with the FEM simulation result. Furthermore, to study the effect of the substrate characteristics on the residual stresses developed during DED, the DED samples were produced on two different substrates having different grain sizes and yield strengths. The neutron diffraction and the FEM simulation results fit well and show that the use of a softer substrate would reduce the residual stresses in the DED parts. Moreover, the substrate characteristics do not affect the tensile properties of the DED part. • Residual stress distribution inside parts built by direct energy deposition(DED) was successfully measured by the neutron diffraction. • It was found that the characteristic of substrates can affect the residual stress inside DED parts. • Substrates with low yield strength can reduce the residual stress as thermal shrinkage of deposited metal can be more compensated by plastic deformation of the substrates. • Substrates with larger grain sizes can reduce the residual stress as the grain growth inside the deposited metal is promoted, providing an additional stress-reducing effect. [ABSTRACT FROM AUTHOR]

Recently, direct energy deposition (DED) has been attracting considerable attention in metal additive manufacturing due to its capability of producing multi-materials and composition gradient materials with a high degree of geometrical design freedom and relatively high productivity compared to powder bed fusion processing. In this study, layered multi-materials of austenitic stainless steel (SS316L) and nickel-based superalloy (IN718) were fabricated using DED processing. The produced multi-materials showed a 500 μm thick composition gradient material zone (CGZ) at the interface between the SS316L/IN718 because of dilution. Further, in the CGZ, closer to the SS316L side, fine cracks containing the brittle Laves and NbC phases are detected. Despite the presence of cracks, the multi-material samples showed higher yield strength and ultimate tensile strength than those calculated by rule-of-mixtures. It is attributed to hetero-deformation-induced hardening by the evolution of geometrically necessary dislocations near the CGZ during tensile deformation. [ABSTRACT FROM AUTHOR]

This investigation focuses on obtaining martensite stainless steel part with uniform mechanical properties along the building direction (BD) by plasma arc direct energy deposition (DED). A tailored 1Cr17Ni2B alloy powder and layer minimum temperature control process were employed. The results revealed that the tensile strengths along BD exhibited a good uniformity with a relative difference less than 1.4 % and the average ultimate tensile strength was 1382 MPa. The high microhardness along the BD also showed a good uniformity, only slightly fluctuated from 542–606 HV 0.3 with a periodic length of one concave fish-scale pattern. Then the part along BD was simplified to overlapped concave fish-scale patterns. The microstructure evolution of fish-scale pattern was studied and the result showed that the concave fish-scale pattern was characterized by intragranular lath martensite and intergranular M 23 (C,B) 6 +α-Fe eutectic structure. Besides, M 2 (C,B) particles were distributed on intergranular α-Fe matrix. The layer minimum temperature control of 200︒C process was employed to ensure the eutectic M 23 (C,B) 6 in a concave fish-scale pattern only partly dissolved during the deposition of the next one layer, not during the subsequent layers. It is helpful to deposite concave fish-scale patterns along the BD with similar volume fraction of eutectic M 23 (C,B) 6 and mechanical properties. This investigation discloses a new method to deposite Fe-Cr-C-B alloy part containing intergranular carbides with uniform mechanical properties and high hardness along the BD. [ABSTRACT FROM AUTHOR]

The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects. [ABSTRACT FROM AUTHOR]

Direct energy deposition (DED) was used to additively manufacture 22–13-5 austenitic stainless steel (SS), of which the mechanical properties and corrosion resistance are superior to those of SS316L and SS304L. Additionally, in-situ formed oxide-driven strengthening was utilized in this study. The DED-processed austenitic SS matrix nanocomposite (SSMNC) exhibited unique microstructural features of heterogeneous grains and dislocation networks. The nano-sized precipitates existed at the sub-structure boundaries and decorated the dislocation network. The results of the transmission electron microscopy (TEM)-energy loss spectroscopy (EELS) analyses revealed nano-sized precipitates with an average size of 21.1 nm that were identified as (Mn,Cr)-rich oxides. This means that, during the DED process, the oxygen in the powder feedstock transformed into nano-sized oxide particles by rapid solidification. The DED-processed SSMNC revealed a yield strength of 705.4±5.3 MPa, which is higher than those of reported AM-processed stainless steels. In addition, the elongation-to-failure was measured as 41.8±3.5%. This suggests that the DED-processed SSMNC has an excellent combination of strength and ductility at room temperature. The high ductility of the alloy developed in this work was found to be achieved by a twinning-induced plasticity (TWIP) mechanism that operated during the deformation. Based on the above findings, the relationships between the microstructure, mechanical properties, and deformation mechanism are also discussed. • 22–13-5 austenitic stainless steel matrix nanocomposite (SSMNC) was successfully manufactured by direct energy deposition. • DED-processed SSMNC shows heterogenous grain, dislocation networks and in-situ nano-sized (Mn,Cr)-rich oxide. • DED-processed SSMNC reveals ultra-high strength with excellent ductility. [ABSTRACT FROM AUTHOR]

The present study aims to evaluate the stress corrosion behavior of additively manufactured austenitic stainless steel produced by the wire arc additive manufacturing (WAAM) process. This was examined in comparison with its counterpart, wrought alloy, by electrochemical analysis in terms of potentiodynamic polarization and impedance spectroscopy and by slow strain rate testing (SSRT) in a corrosive environment. The microstructure assessment was performed using optical and scanning electron microscopy along with X-ray diffraction analysis. The obtained results indicated that in spite of the inherent differences in microstructure and mechanical properties between the additively manufactured austenitic stainless steel and its counterpart wrought alloy, their electrochemical performance and stress corrosion susceptibility were similar. The corrosion attack in the additively manufactured alloy was mainly concentrated at the interface between the austenitic matrix and the secondary ferritic phase. In the case of the counterpart wrought alloy with a single austenitic phase, the corrosion attack was manifested by uniform pitting evenly scattered at the external surface. Both alloys showed ductile failure in the form of "cap and cone" fractures in post-SSRT experiments in corrosive environment. [ABSTRACT FROM AUTHOR]

The paper is devoted to the direct energy deposition (DED) of functionally graded materials (FGMs) created from stainless steel and aluminum bronze with 10% content of Al and 1% of Fe. The results of the microstructure analysis using scanning electronic microscopy (SEM) demonstrate the existence of a dendritic structure in the specimens. The crystallization rate of the gradient binary Cu-Fe system structures was investigated and calculated using the model of a fast-moving concentrated source with an ellipsoid crystallization front. The width of the secondary elements of the dendrites in the crystallized slab was numerically estimated as 0.2 nm at the center point of the circle heat spot, and the two types of dendrites were predicted in the specimen: the dendrites from 0.2 to approximately 50 nm and from approximately 0.1 to 0.3 μm in width of the secondary elements. The results were found to be in good accordance with the measured experimental values of the dendritic structure geometry parameters. [ABSTRACT FROM AUTHOR]