Direct Energy Deposition Method Research Articles

Improvement of layer fabrication efficiency and dilution rate for nickel based super alloy by multibeam directed-energy-deposition with blue diode lasers

A bead of nickel based super alloy was deposited on an SS304 substrate by a multibeam directed energy deposition method using a blue diode laser. Previously, the fabrication of nickel based super alloy using a blue diode laser had not been performed. Therefore, the laser output power and sweep speed were varied to investigate the effects of these variables on the bead. The results showed that laser output power and sweep speed affected the bead height, width, fabrication efficiency, and dilution rate in the fabrication of nickel based super alloy beads. In addition, we were able to produce a lower dilution than previously reported.

Achieving low-porosity AlSi10Mg cladding layers for the additive repair of aluminum alloy parts by directed energy deposition

Directed Energy Deposition (DED) has broad application prospects for repairing damaged aluminum alloy parts such as piston aero-engine casing. However, due to the low laser absorptivity and the complex thermal cycle process, it is challenging to obtain aluminum alloy cladding layers with high-quality morphology and low-porosity by DED method. In this work, a series of individual stages of DED process are studied during single-tracks overlapping and layers stacking. Correspondingly, the within layer scanning strategy, inter-layer stacking strategy, and process parameters are examined carefully. Using the proposed DED processing flow that combines substrate preheating with intermittent process, the deposited layers without balling and collapse are successfully achieved. Furtherly, the bi-directional scanning strategy for single-tracks overlapping within layer is proposed to compensate the thickness nonuniformity caused by heat accumulation. The inter defects identified as “lack of fusion” and “gas pores” are observed in the cladding layers with uniform surface. By analyzing the pore formation mechanism and considering the energy distribution and re-melting, the multi-layer offset stacking strategy is proposed to inhibit the porosity to 0.25 %. Combined with the optimized process parameters, the porosity is reduced up to 0.09 %, ensuring the density of the DED deposition coating. This work provides new pathway and direct guidance for fabricating high-quality AlSi10Mg cladding layers during the DED repairing of valuable aluminum alloy parts.

Manufacturing of Ni-Co-Fe-Cr-Al-Ti High-Entropy Alloy Using Directed Energy Deposition and Evaluation of Its Microstructure, Tensile Strength, and Microhardness.

High-entropy alloys (HEAs) have drawn significant attention due to their unique design and superior mechanical properties. Comprising 5-35 at% of five or more elements with similar atomic radii, HEAs exhibit high configurational entropy, resulting in single-phase solid solutions rather than intermetallic compounds. Additive manufacturing (AM), particularly direct energy deposition (DED), is effective for producing HEAs due to its rapid cooling rates, which ensure uniform microstructures and minimize defects. These alloys typically form face-centered cubic (FCC) or body-centered cubic (BCC) structures, contributing to their exceptional strength, hardness, and mechanical performance across various temperatures. However, FCC-structured HEAs often have low yield strengths, posing a challenge for structural applications. In this study, a Ni-Co-Fe-Cr-Al-Ti HEA was manufactured using the DED method. This study proposes that the addition of aluminum and titanium creates a γ + γ' phase structure within a multicomponent FCC-HEA matrix, enhancing the thermal stability and coarsening the resistance and strength. The γ' phase with an ordered FCC structure significantly improves the mechanical properties. Analysis confirmed the presence of the γ + γ' structure and demonstrated the alloy's high tensile strength and microhardness. This approach underscores the potential of AM techniques in advancing HEA production for high-performance applications.

A novel ultrasonic rolling assisted direct energy deposition method with semi-solid thixo-forming characteristics for AA6061

In order to overcome the defects during the process of additive manufacturing for AA6061, a novel ultrasonic rolling assisted direct energy deposition method with semi-solid thixo-forming characteristics was proposed in this study, which used cold deformed AA6061 wire as raw material, and a corresponding process platform was established. The results showed that under the conditions of laser heating temperature of 750 ℃ and heating plate temperature of 200 ℃, the sample could achieve continuous multi-pass deposition while retaining some of the cold-drawn plastic deformation energy. When the vertical deformation rate was 0.153 and the ultrasonic amplitude was 20 μm, the microstructure of deposition sample after semi-solid heat-treat exhibited typical equiaxed grain characteristics, corresponding to average grain diameter of 95.6 μm and shape coefficient of 1.263. Thin-walled samples with different shapes were formed to verify the capability of process platform. The inference of the formation mechanism of semi-solid microstructure was revealed at last: the introduction of ultrasonic rolling supplemented the plastic deformation energy, and semi-solid heat-treat provided temperature and time for the incubation of equiaxed grains, both of which were crucial for the formation of the semi-solid microstructure.

Comparative analysis of mechanical properties enhancement in SCM440 through similar and dissimilar material deposition using directed energy deposition method

The Directed Energy Deposition (DED) method, which utilizes metal powder and a high-powder laser directed at specific locations on a substrate, is employed across various fields for repairing and refurbishing existing parts. In this study, two types of multi-materials were fabricated by depositing materials similar in alloy composition, and dissimilar, respectively, on an SCM440 substrate using the DED method. Unlike similar material, depositing the dissimilar material resulted in a recrystallized fine microstructure in the interlayer region, which enhanced the tensile properties of the multi-layer specimens. The yield strength, tensile strength, and elongation of the multi-layer specimen with similar material were 562 MPa, 787 MPa, and 14%, respectively, while those of the specimen with dissimilar material were significantly higher at 934 MPa, 1016 MPa, and 30%. These results demonstrate that using dissimilar materials, rather than identical or similar compositions, can improve the tensile properties when repairing and refurbishing parts made of SCM440 material.

Performance evaluation of GH3536/GH4169 functionally graded materials with linear gradient changes fabricated through direct energy deposition

This study employs the direct energy deposition method to fabricate functionally graded materials (FGMs) using GH3536 and GH4169 alloys. The approach achieves a seamless linear gradient transition in the FGMs, progressing from GH3536 alloy to GH4169 alloy. Additionally, the impact of a solid solution twin-aging process on the properties of the FGMs was investigated. The findings reveal that variations in the powder content of GH3536/GH4169 alloy exhibit minimal impact on the microstructure of the deposited FGMs, with columnar crystals predominantly growing along the <001> direction. The direct energy deposition process induces an exceptionally high temperature gradient and cooling rate, preventing the timely precipitation of the second strengthening phase (γ", γ', δ), as well as M6C and M23C6 in the FGMs. Furthermore, the formation of the Laves phase (Ni2Nb, Cr2Mo) diminishes the overall performance of the FGMs. In correspondence with the linear variation of GH3536/GH4169 alloy powder content, the hardness of each layer within the deposited FGMs exhibits an initial increase followed by a subsequent decrease. Following the solution aging treatment, complete dissolution of the Laves phase and δ phase occurs, leading to the formation of a secondary chain phase (M23C6) along the grain boundaries. Simultaneously, needle and granular δ phases disperse within the grain structure, contributing to enhanced performance in the FGMs and ensuring uniform hardness throughout.

Repairing weld for directly solidified Ni-based superalloy substrates using directed energy deposition of Inconel 625

Although the maintenance, repair, and operation of gas turbine systems are important issues in enhancing the operation of power units, advanced welding repair processes have limitations in depositing directionally solidified Ni-based superalloy components. To overcome this problem, in this study, a directed energy deposition method was applied to repair directionally solidified components using an Inconel 625 alloy. The rapid cooling rate and small laser beam diameter during directed energy deposition minimized the heat-affected zone and duration in the mushy zone, resulting in crack inhibition at the interface. The first laser scan partially melted the substrate and formed a mixing zone with a chemical composition gradient. By combining the chemical compositional gradient and dislocation accumulation due to repetitive solidification, that is, with the melting cycles of directed energy deposition, the thermal stability decreased, resulting in recrystallization and grain growth in the mixing zone. Consequently, the crack-free continuous interface of the partially repaired components did not induce tensile fracture near the interface. Although the mechanical properties of the IN625 deposit layer were degraded by severe heat treatment of the substrate, the results demonstrated that energy deposition with post-heat treatment is an effective approach in repairing Ni-based superalloy components without cracks and inclusion initiation.

Influence of thermal conductivity on evolution of grain morphology during laser-based directed energy deposition of CoCrxFeNi high entropy alloys

A model CoCrxFeNi high entropy alloy system was chosen to investigate the effect of thermal conductivity on the evolution of spatial orientation of columnar grain morphology during laser directed energy deposition. The thermal conductivity of the alloy was varied by tuning the chromium content in CoCrxFeNi alloys. CoCrxFeNi alloys with chromium content ranging between 0 and 24 at% were produced under identical processing conditions of laser direct energy deposition method. Electron back scattered diffraction images of the cross-sections revealed that the spatial orientation of grain morphology transitioned from zigzag columnar grains from layer-to-layer to near-continuous columnar grains across multiple layers with increased content of chromium in CoCrxFeNi. A multi-scale multi-physics finite element based thermo-kinetic model with consideration to multi-track multi-layer nature of the laser direct energy deposition technique was adopted to correlate the process thermo-kinetics with the evolution of microstructure. The computation calculations revealed that the decrease in thermal conductivity from 36 W/m.K (CoFeNi) to 26 W/m.K (CoCr24FeNi) at the melting point reduced the cooling rate from 3.3 ×104 °C/s to 1.3 ×104 °C/s in CoFeNi and CoCr24FeNi alloys, respectively. This subsequently evolved into increased degree of remelting of previously deposited layers and caused the direction of resultant thermal gradient to reorient towards the build direction. Such reorientation in resultant thermal gradient contributed to transition of spatial orientation of grain morphology from columnar zigzag microstructures from layer-to-layer to near continuous columnar grains across multiple layers. The present observation was verified compared with other reported metallic systems exhibiting zigzag and continuous columnar grains, and a unified mechanism underlining the role of thermal conductivity on microstructure evolution was proposed.

Predicting rapid growth behavior in solidified eutectic ceramic composites using infrared thermal imaging and thermal field simulation during laser directed energy deposition

Cylindrical Al2O3/GdAlO3 binary in situ oxide eutectic ceramic composite, with a glossy surface and high relative density, has been fabricated using the laser directed energy deposition method (LDED) with optimized process parameters. In a novel and innovative approach, infrared thermal imaging and the finite element method (FEM) have been combined for the first time to capture the temperature field distribution across different regions of the molten pool during the LDED processing of the binary oxide eutectic ceramic composite, thereby synergistically obtaining the solidification characteristics. With an increase in the scanning rate, the temperature gradient within the molten pool decreases from 3.38 × 105 K/m to 1.62 × 105 K/m, while it shows minimal variation with fluctuations of the laser power. Under the conditions of high temperature gradients and rapid non-equilibrium solidification characteristic of LDED, the Al2O3/GdAlO3 (GAP) binary eutectic ceramic composites, which exhibit typical high melting entropy and faceted/non-faceted growth modes, exhibit complex and variable microstructure morphology. A combination of regular/irregular models, including JH (Jackson-Hunt), MK (Magnin-Kurz), GK (Guzik-Kopyciński) and TMK (Trivedi-Magnin-Kurz), is employed to investigate and predict the growth and transformation of microstructures. The JH and TMK models fairly predict the rod-like regular eutectic microstructure inside the colony and lamellar regular eutectic within adjacent layers, respectively. The “Chinese-script” irregular microstructure at the interface between the colony and the layers is consistent with the MK and GK models. The as-deposited eutectic ceramic composite presents ultra-fine microstructures, clear and strongly bonded phase interfaces with low strain energy, contributing to its microstructure stability after high temperature heat treatment at 1773 K for 200 h, and achieving a minimum microstructure coarsening rate of 0.0005 μm/h.

Research on microstructure and mechanical properties of Ti–6Al–4V ELI fabricated by hybrid directed energy deposition with in-situ rolling and annealing

To achieve superior damage tolerance and fatigue properties, it is desirable for the microstructure of Ti-6Al-4V ELI (Extra Low Interstitial) titanium alloy to consist of equiaxed grains with a homogeneous lamellar structure. However, traditional forging and single additive manufacturing techniques require extreme processes such as quasi β heat treatment and hot isostatic pressing. In this paper, a hybrid directed energy deposition method that integrates in-situ rolling with simple annealing is proposed to simultaneously achieve these microstructures. The results indicate that the initial microstructures produced by hybrid directed energy deposition consist of fine equiaxed prior-β grains, inconspicuous interpass bright bands, randomly oriented lamellar structure and numerous small substructures at the TEM scale. Due to the plastic deformation caused by in-situ rolling, the primary β grains underwent significant refinement with a reduction in grain diameter from over 2000 μm to 113.8 μm. Besides, the unique microstructures and thickness of α laths are influenced by coarsening and dissolution mechanisms that are controlled by diffusion during phase transformation. Furthermore, a uniform microstructure without bright bands and excellent comprehensive properties can be achieved through heating at 880 °C for 2 h and natural cooling. These findings validate that hybrid directed energy deposition coupled with simple annealing present a novel and cost-effective approach for the direct manufacturing of uniform titanium alloy forgings.

Research Trends in the Directed Energy Deposition Method of Heterogeneous Materials

Metal Additive Manufacturing (AM) or 3D printing garners attention for economically producing components with superior strength, durability, and corrosion resistance. The microstructure, influenced by factors like heat input, scanning speed, and layer thickness, shapes metal materials intricately in 3D printing.Unlike traditional manufacturing with separate fabrication and post-processing, Multi Materials AM (MM-AM) streamlines the construction of composite structures in a single step using a single machine. Although initial MM-AM, especially inpolymer 3D printing, was simpler, the shift to metal-based MM-AM presents challenges. The distinctive bonding style in MM-AM facilitates robust connections between different metals, minimizing stress concentration and simplifying the joining of diverse metals. Challenges like intermetallic compound formation, residual stress, and material-specific issues leading to cracks persist. Ongoing research focuses on metallurgy, process optimization,and computational simulation to overcome these hurdles. This review delves into current research trends in multi-material AM, identifying pathways for technological advancements. It discusses the application of Directed Energy Deposition (DED)in stacking austenitic and ferritic metals for nuclear power plant cooling system piping's gradient-form safe-ends. The study emphasizes advanced manufacturing techniques for developing functionally graded materials and dissimilar metal joints, highlighting the transformative potential of additive manufacturing across industries.

Tensile deformation behavior of triple heterogeneous microstructure comprising fine equiaxed/coarse equiaxed/columnar grains in AlCu/AlMgSc bimetal fabricated via dual-wire arc direct energy deposition

In this study, an AlCu/AlMgSc bimetallic alloy is prepared using a dual-wire arc direct energy deposition method and a triple heterogeneous microstructure (fine/coarse equiaxed grains/columnar grains) is constructed. Additionally, a quantitative comparative analysis of the deformation behavior of triple and dual heterogeneous microstructures during interrupted tensile testing is conducted, with emphasis on the effects of grain morphology and size on the tensile deformation mechanisms in the heterogeneous microstructure. Compared with the AlCu alloy with a double heterogeneous microstructure (equiaxed/columnar grain), the AlCu/AlMgSc bimetallic alloy exhibits a higher ultimate tensile strength of 301.4 ± 7.9 MPa, a yield strength of 181.3 ± 1.4 MPa, and an elongation of 9.7 % ± 1.3 %, which correspond to increases by 19.4 %, 21.2 %, and 24.4 %, respectively. Interrupted tensile testing is performed and a quasi-in-situ approach is employed to investigate the plastic deformation mechanisms of the triple heterogeneous microstructure during tensile deformation. The density of geometrically necessary dislocations (GNDs) in the fine equiaxed grains and the rate of GND accumulation during deformation, surpassed those observed in coarse equiaxed and columnar grains. Furthermore, in micrometer-sized equiaxed grains, the ability to accumulate GNDs decreases as the equiaxed grain size increases, and the equiaxed grains exhibit a higher capacity to accumulate GNDs compared with columnar grains. The triple heterogeneous microstructure provides a more favorable environment for trapping GNDs, thus resulting in enhanced strength and plastic deformation capabilities. This study offers guidance for the formulation and engineering application of heterogeneous microstructure alloys with diverse grain morphologies and multiple length scales. Additionally, novel approaches are introduced to enhance the strength and ductility of Al alloys.

Influence of scanning strategy on magnetic properties of 630 stainless steel fabricated by directed energy deposition method

We investigated how the scanning strategy (SS) influences the magnetic properties of ferromagnetic metal specimens additively manufactured using 630 stainless steel powder and a directed energy deposition machine. The magnetization curves were measured by using B and H coils and a magnetic flux meter. The specific saturation magnetization, coercivity, and specific magnetic susceptibility were calculated from the magnetization curves obtained. Moreover, the martensite fraction, magnetization structure, and martensite structure were measured and visualized using X-ray diffraction, the Bitter method, and electron backscatter diffraction, respectively. The magnetic properties and martensite fraction depended on the SS, and magnetic poles were generated in each sub-block structure. Furthermore, a numerical analysis using a magnetic micromechanics model indicated that the variation in the martensite structure due to the SS produced differences in the magnetic properties.

Effect of heat treatment on microstructure and wear properties of laser additively manufactured 316 L stainless steel/Co-Cr-W alloy part using directed energy deposition method

The directed energy deposition additive manufacturing was applied to fabricate hard Co-Cr-W layers on the 316 L stainless steel substrate. The effect of different heat treatment cycles was investigated. The primary microstructure of deposited layers contained a cobalt matrix with interdendritic eutectic carbides mainly M7C3, M23C6, and M6C. Most of the primary carbides were dissolved in the matrix after the solution treatment at 1250 °C for 1 h. The aging treatment promoted the precipitation of (W/Co)6C carbides. The hard carbides caused the third-body wear and increased the wear volume loss of specimens. The solution & double aging treatment provided the optimum combination of hardness and wear resistance due to the best distribution of W/Co carbide. The wear volume loss after heat treatment was decreased from about 6.6 mm3 to 2.8 mm3 compared to the as-deposited specimen. The proposed solution & double aging heat treatment improved wear resistance by 50%.

Simultaneously enhanced tensile strength and ductility of nano-Y2O3-reinforced TiAl alloy prepared by directed energy deposition

The effect of Y2O3 nanoparticles on microstructure and high-temperature mechanical properties of Ti–48Al–2Cr–2Nb alloy prepared by directed energy deposition was investigated. Cracks in the TiAl alloy sample were eliminated by a new directed energy deposition method with a preheating unit. The results indicated that the microstructure of TiAl alloy without Y2O3 nanoparticles addition was composed primarily of (α2/γ) lamellar colony. While the equiaxed γ phase was generated within the (α2/γ) lamellar colony and on the colony boundaries, and the microstructure exhibited a duplex structure due to the 0.5 wt% nano-Y2O3 addition, and the grain size was decreased from 183 μm to 25 μm. The ultimate tensile strength and fracture elongation tested at 750 °C were enhanced simultaneously from 615.1 to 805.7 MPa and from 5.56% to 7.40%, respectively, by 0.5 wt% Y2O3 nanoparticles addition. Finally, the strengthening mechanism and microstructure refinement mechanism were discussed in detail. This investigation provides a valuable reference for TiAl alloy fabrication and widespread engineering applications.

Development of High-precision, High-efficiency, High-quality Molding System by Directed Energy Deposition Method

Development of High-precision, High-efficiency, High-quality Molding System by Directed Energy Deposition Method

Rotating bending fatigue behaviour and quasi‐static tensile properties of Wire Arc Additively Manufactured 308L stainless steel

AbstractWire Arc Additive Manufacturing (WAAM) is a direct energy deposition method used to manufacture steel components by using an electric arc as a heat source to melt a metal wire and deposit it layer by layer. In this study, monotonic tensile tests, standardized Charpy impact tests, and rotating bending fatigue tests are executed to characterize the mechanical properties of WAAM 308L stainless steel using specimens extracted from additively manufactured plates. In particular, monotonic tensile properties are investigated in three directions: that is 0, 90, and 45 degrees with respect to the plane of deposition, whereas the fatigue strength is quantified for one direction only, i.e. 90 degrees since this is deemed to be the weakest.The mechanical characterization highlights that WAAM 308L SS shows an anisotropic behaviour, an enhanced strain‐rate sensitivity, and an overall reduced yield strength as compared to the base material 308L. The anisotropic material behaviour is explained by the microstructure morphology since the austenite grains form anisotropic columnar zones due to an uneven heat profile during production. During the fatigue tests, the relatively high strain rate sensitivity causes susceptibility to self‐heating at relatively low loading frequencies, i.e. below 100Hz.

A Study on the Optimization of 3D Printing Additive Manufacturing by Direct Energy Deposition Method Using High Speed Steel Material

In this study, an additive manufacturing (AM) optimization process experiment was conducted using high-hardness metal powders (AISI M4) that can be used for mold repairs. The process variables applied in the experiment were the laser power, laser head moving speed, and powder feed rate, and the manufacture cross section was analyzed through one-pass manufacturing. The AM efficiency was evaluated for each process with respect to the layer height, dilution ratio, and global energy density. In the case of the layer height, the AM efficiency was good under the condition of the laser output of 500 W. In the case of the dilution ratio, the AM efficiency was good under the conditions of a powder feed rate of 6 g/min and laser head moving speed of 500 mm/min. Finally, the GED values of the process variables applied in this experiment were calculated, and the AM efficiency was excellent at values between 60 and 108 J/mm&lt;sup&gt;2&lt;/sup&gt;.

Laves phase and equiaxed grains formation in directed energy deposited AlCuFeNiTi high entropy alloy

In this study, an equiatomic AlCuFeNiTi high entropy alloy (HEA) was successfully fabricated for the first time using pre-alloyed powder with the directed energy deposition method on a Ti-6Al-4V substrate. The alloy was characterized using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and nanoindentation to provide insight into the relationship between its microstructural and nanoscale mechanical properties. The microstructure has three distinct regions, resulting from variation in the alloy's local elemental and crystallographic composition that influences its mechanical properties. The alloy was found to be multiphase with a mostly ordered Heusler structure (L21) and a small amount of FCC structure with traces of C14 Laves in them. Needle-like and spherical-shaped Cu-rich precipitates were also observed in the dendrites. During the solidification process, evidence of dendritic fragmentation was observed, contributing to the alloy having mostly equiaxed grains rather than the commonly observed columnar grains in previously reported additively manufactured (HEAs). Nanoindentation results showed that the dendrites constitute a hard zone, whereas the inter-dendritic regions typify a continuous soft zone, with the dispersed Laves phase having the highest hardness. The presence of Laves phase inside the grain boundaries and its distribution as small-size grains strengthens the grain boundaries. Results highlight the synthesis of an equiaxed HEA with multiple distinct regions that influence its overall mechanical properties.

Effect of line energy on microstructures and mechanical properties of Co-Cr-Mo alloy single-track fabricated by DED method

The additive material built-up by the directed energy deposition (DED) method is affected by the melting and solidification reaction with the substrate material. This work investigated the effect of line energy on microstructures and mechanical properties of Co-Cr-Mo alloy single-track fabricated by the DED method. The line energy is a function of scanning speed and laser power, which are the main process parameters for the DED method. The Co-Cr-Mo alloy single-track with low line energy has a columnar grain microstructure with a strong (0 0 1)γ texture parallel to the build direction. As the line energy increased, the single-tracks had mixed microstructure, including fine columnar grains and coarse equiaxed grains with random texture. In addition, the secondary dendrite arm spacing of the single-track depends on the line energy due to the rapid cooling rate. The ε-Co phase in Co-Cr-Mo alloy single-track increased with increasing line energy throughout the isothermal γ → ε martensitic transformation. The effect of the ε-Co phase on the mechanical properties of the Co-Cr-Mo alloy single-track is insignificant. The diffusion of alloying elements from the substrate material throughout the fusion zone occurred and influenced the mechanical properties of the Co-Cr-Mo alloy single-track. The elastic modulus and nano hardness decreased with increasing line energy because of the diffusion of alloying elements from the substrate material.