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.

Effect of ultrasonic micro-forging on the microstructure and properties of GH4169 superalloy deposited by laser direct energy deposition

Nickel-based superalloys prepared by laser direct energy deposition (DED) still suffer from microstructure, elemental segregation, and unstable strength, which cannot meet the service requirements and severely limit the application and development of DED-prepared superalloy parts. In this paper, GH4169 specimens with high density and free of defects were prepared by ultrasonic micro-forging assisted laser direct energy deposition (UMT-DED) method. The effects of UMT on the dendritic structure, elemental segregation, and precipitation phases of the alloys prepared by UMT-DED, as well as the densities, hardness, and tensile properties at room and high temperatures were investigated. The contribution of the strengthening mechanism to the yield strength was estimated. The grain refinement mechanism and the deformation mechanism of the Laves phase in GH4169 were discussed. The results show that UMT achieves grain refinement by forming fine crystal strips between the layers. The proportion of fine grain areas increased from 5.9 % to 33.3 %. The plastic deformation introduced by UMT provides external work for dislocation movement to break and fracture part of the Laves phase during plastic deformation, with dislocation cutting of the Laves phase being the main deformation mechanism. The residual stresses was transformed into residual compressive stress. The tensile strength, yield strength, and elongation of the specimens at 25 °C were increased by 4.23 %, 6.42 %, and 23.67 % respectively.

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.

Toward developing remanufactured Ti6Al4V alloys with high fatigue crack growth resistance by in-situ cooling during laser remanufacturing

The fatigue performance of remanufactured titanium alloy blade components has garnered significant attention in recent years. The repaired titanium alloy components using the direct energy deposition (DED) method exhibit structural differences, leading to an inhomogeneous microstructure that directly impacts the service life of the remanufactured component. The work presented here aimed to investigate novel approaches for enhancing the resistance to crack propagation and to gain a deeper insight into the fatigue crack propagation characteristics of the Ti6Al4V remanufactured interface with an inhomogeneous microstructure. The research focused on analyzing the microstructure evolution and fracture properties of remanufactured components using in-situ cooling. The results indicate that in-situ cooling has the potential to decrease the anisotropy of the repaired zone (RZ) and enhance the resistance to crack propagation in the heat-affected zone (HAZ) and base metal (BM). The high cooling rate associated with the in-situ cooling can elevate the presence of high-angle grain boundaries (HAGBs) in the RZ, diminish the phase transformation between the HAZ and BM, and decrease the size of the secondary α phase. The research contributes to a deeper comprehension of fatigue crack propagation in remanufactured components and provides a pathway for the improvement of fatigue performance of remanufactured titanium alloy.

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.

Thermal, Microstructural, and Mechanical Analysis of Complex Lattice Structures Produced by Direct Energy Deposition.

Lattice structures have gained attention in engineering due to their lightweight properties. However, the complex geometry of lattice structures and the high melting temperature of metals present significant manufacturing challenges for the large-scale fabrication of these structures. Direct Energy Deposition (DED) methods, such as the Wire Arc Additive Manufacturing (WAAM) technique, appear to be an interesting solution for overcoming these limitations. This study provides a detailed analysis of the manufacturing process of carbon steel lattice structures with auxetic geometry. The study includes thermal analysis using infrared thermography, microstructural characterization through metallography, and mechanical evaluation via hardness and mechanical testing. The findings reveal the significant impact of heat input, thermal cycles, and deposition sequence on the morphology and mechanical properties of the lattice structures. Fast thermal cycles are related to areas with higher hardness values, smaller strut diameters, and porous formations, which shows that controlling heat input and heat dissipation is crucial for optimizing the properties of lattice structures produced using WAAM.

Metastable core-shell precipitation strengthened high-entropy alloys fabricated by direct energy deposition with multi-stage terrace-like slip wave toughening

This study investigates the development of novel high-entropy alloys (HEAs) with enhanced mechanical properties through an innovative fabrication method of direct energy deposition (DED). The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism, a novel approach to improving both strength and ductility simultaneously. Mechanical testing reveals that the developed HEAs exhibit superior mechanical properties, including high yield strength, ultimate tensile strength, and exceptional ductility. The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features. This toughening mechanism involves the sequential activation of slip systems, facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material. The terrace-like pattern of these slip waves enhances the material's ability to deform plastically, providing a significant toughening effect while maintaining high strength levels. Furthermore, the study delves into the fundamental interactions between the microstructural elements and the deformation mechanisms. It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly, delay the onset of necking, and prevent premature failure. This synergistic interaction between the microstructural features and the slip wave toughening mechanism is central to the remarkable balance of strength and ductility achieved in the HEAs. The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.

A diffusion-leakage model coupled with dose point kernels (DPK) for dosimetry of diffusing alpha-emitters radiation therapy (DaRT).

Diffusing alpha-emitters radiation therapy (DaRT) is a novel brachytherapy technique that leverages the diffusive flow of 224Ra progeny within the tumor volume over the course of the treatment. Cell killing is achieved by the emitted alpha particles that have a short range in tissue and high linear energy transfer. The current proposed absorbed dose calculation method for DaRT is based on a diffusion-leakage (DL) model that neglects absorbed dose from beta particles. This work aimed to couple the DL model with dose point kernels (DPKs) to account for dose from beta particles as well as to consider the non-local deposition of energy. The DaRT seed was modeled using COMSOL multiphysics and the DL model was implemented to extract the spatial information of the diffusing daughters. Using Monte-Carlo (MC) methods, DPKs were generated for 212Pb, 212Bi, and their progenies since they were considered to be the dominant beta emitters in the 224Ra radioactive decay chain. A convolution operation was performed between the integrated number densities of the diffusing daughters and DPKs to calculate the total absorbed dose over a 30-day treatment period. Both high-diffusion and low-diffusion cases were considered. The calculated DPKs showed non-negligible energy deposition over several millimeters from the source location. An absorbed dose>10Gy was deposited within a 1.8mm radial distance for the low diffusion case and a 2.2mm radial distance for the high diffusion case. When the DPK method was compared with the local energy deposition method that solely considered dose from alpha particles, differences above 1Gy were found within 1.3 and 1.8mm radial distances from the surface of the source for the low diffusion and high diffusion cases, respectively. The proposed method enhances the accuracy of the dose calculation method used for the DaRT technique.

Absorbed Dose-Response Relationship in Patients with Gastroenteropancreatic Neuroendocrine Tumors Treated with [177Lu]Lu-DOTATATE: One Step Closer to Personalized Medicine.

[177Lu]Lu-DOTATATE has been approved for progressive and inoperable gastroenteropancreatic neuroendocrine tumors (GEP-NETs) that overexpress somatostatin receptors. The absorbed doses by limiting organs and tumors can be quantified by serial postinfusion scintigraphy measurements of the γ-emissions from 177Lu. The objective of this work was to explore how postinfusion [177Lu]Lu-DOTATATE dosimetry could influence clinical management by predicting treatment efficacy (tumor shrinkage and survival) and toxicity. Methods: Patients with GEP-NETs treated with [177Lu]Lu-DOTATATE between 2016 and 2022 and who underwent dosimetry were included. Absorbed doses were calculated for healthy organs (liver, kidneys, bone marrow, and spleen) and tumors using PLANET Dose and the local energy deposition method based on serial posttreatment SPECT/CT. Up to 5 lesions per site were selected and measured on images collected at baseline and 3 mo after treatment end (measurement masked to the somatostatin receptor imaging uptake). For toxicity assessment, laboratory parameters were regularly monitored. Clinical data, including time to death or progression, were collected from the patients' health records. Correlations between absorbed doses by organs and toxicity and between absorbed doses by lesions and tumor volume variation were studied using regression models. Results: In total, 35 dosimetric studies were performed in patients with mostly grade 2 (77%) tumors and metastases in liver (89%), lymph nodes (77%), and bone (34%), and 146 lesions were analyzed: 1-9 lesions per patient, mostly liver metastases (65%) and lymph nodes (25%). The median total absorbed dose by tumors was 94.4 Gy. The absorbed doses by tumors significantly decreased between cycles. The absorbed dose by tumors was significantly associated with tumor volume variation (P < 0.001) 3 mo after treatment end, and it was a significant prognostic factor for survival. Toxicity analysis showed a correlation between the decrease of hematologic parameters such as lymphocytes or platelet concentrations and the absorbed doses by the spleen or bone marrow. The mean absorbed dose by the kidneys was not correlated with nephrotoxicity during the studied period. Conclusion: In patients treated with [177Lu]Lu-DOTATATE for GEP-NETs, tumor and healthy organ dosimetry can predict survival and toxicities, thus influencing clinical management.

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.

Directed Energy Deposition‐Arc Repair Al6.5Cu2Ni0.3Ti0.5Zr0.25V Alloy: Microstructure Evolution and Strengthening Mechanism

Casting Al6.5Cu2Ni0.3Ti0.5Zr0.25V alloy is applied to aircraft engine components, but the casting defects are difficult to avoid. In this research, the local defects of casting heat‐resistant Al6.5Cu2Ni0.3Ti0.5Zr0.25V alloy parts are repaired by the arc‐directed energy deposition method. To examine the mechanism of the microstructure in the repaired zone of the heat treatment condition on the high‐temperature characteristics, the microstructure evolution of the repaired zone before and after heat treatment is analyzed. The results indicate that stratification exists in the sedimentary layer, however, the overall grain distribution is relatively uniform. After heat treatment, the microstructure of the repaired zone is changed, Cu element distribution becomes uniform and dendrite segregation disappears; simultaneously, the grain in the repaired zone mainly exists as high angle grain boundaries, which improves the fracture resistance ability of the material. At 350 °C, the average tensile strength, yield strength and elongation are 120.0 MPa, 98.6 MPa and 12.9%, respectively, the tensile strength reaches 94.1% of the matrix. Dimples abound on the fracture's exterior, and the fracture form of the repaired zone is microporous aggregate fracture. δ‐Al3CuNi and γ‐Al7Cu4Ni enhance the grain boundary strength, and θ′‐Al2Cu diffuses from the α‐Al matrix during aging, which is the main reason for the excellent high‐temperature performance of the repaired zone.

Effect of welding mode on selected properties of additively manufactured AA5087 aluminium alloy parts

Wire and arc additive manufacturing (WAAM) is a popular direct energy deposition (DED) method for producing large-scale metallic components. The main advantages of the technique are a high deposition rate and low cost. Furthermore, the utilization of the WAAM is prevalent in the aerospace industry. The AA5087 aluminium alloy with 4.5 wt.% of magnesium has been investigated because of its excellent properties. The present research deals with the study of thermal cycles and fields developed in the alloy during additive manufacturing with two different Cold metal transfer (CMT) modes, namely conventional (CMT) and cycle-step (CMT-CS). The welding system was equipped with a Fronius TransPulse Synergic 3200 CMT power source, a Fanuc Arc Mate 1000iC 6-axes robot with an R 30iA control unit, a welding torch, and a 1-axis positioner. The AA5087 aluminium alloy welding wire with a diameter of 1.2 mm was deposited onto the AA5083 aluminium alloy plate with dimensions of 70 mm x 200 mm x 3 mm during the experiment. The thermal cycles were documented using an Ahlborn Almemo 5690-2 measuring station equipped with K-type thermocouples. The thermal fields were monitored with a FLIR E95 thermography camera. The results showed the evident influence of arc mode on the temperatures developed in manufactured aluminium alloy parts during the process of WAAM.

Difference of properties after heat treatment between GH4169 and GH3536 alloys fabricated by direct energy deposition

In this study, thin-walled parts of GH4169 and GH3536 superalloys were prepared using the direct energy deposition (DED) method, respectively. The results revealed that solution aging treatment was effective in eliminating the boundary of the molten pool and refining the grain structure to some extent. Subsequently, the Laves phase redissolved in the γ matrix, releasing Nb element. This was followed by the formation of γ′, γ″, and δ phases, which effectively improved the yield strength and tensile strength of the GH4169 alloy after high temperature heat treatment. In the case of the GH3536 alloy, heat treatment caused a change in microstructure from columnar crystals to larger equiaxed crystals. Additionally, chain carbides precipitated at the grain boundaries, which increased the elongation after fracture but decreased the yield strength and tensile strength to some extent. Following solid solution aging treatment, the ultimate tensile strength of GH4169 deposited parts exhibited a 27.7% increase in the deposition direction and a 15.6% increase in the laser scanning direction. Conversely, the tensile strength of GH3536 showed minimal variations, but the elongation in both directions experienced notable improvements, rising by 22% and 20.7%, respectively. Solution aging treatment further eliminated the mechanical anisotropy of the two superalloys due to the inhomogeneity of microstructure and grains, as well as the existence of molten pool boundaries and grain boundary segregation. Furthermore, the microstructure and mechanical properties of GH3536 alloy were found to be better than those of GH4169 alloy, both before and after aging.

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.

Investigations into the interfacial characteristics of Inconel 718/stainless steel 316L fabricated by multi-material Laser Powder Bed Fusion.

The numerous advantages of Additive manufacturing (AM) are being utilized to print multi-material components for different applications. Although the AM method of laser powder bed fusion (LPBF) can print more complex and dimensionally accurate parts than the directed energy deposition (DED) method, printing multi-material components is challenging for LPBF. This study demonstrates an attempt at bimetallic 3D printing of stainless steel 316L and Inconel 718 by multi-material laser powder bed fusion and its characterization. A continuous wave (CW) fiber laser was used for the LPBF process and laser parameters for the bimetallic components were optimized. Microstructural studies were carried out with optical microscopy and scanning electron microscope (SEM) to investigate the interfacial characteristics for different numbers of interlayers. The thickness of the interfacial region was around 50-100 μm. Vickers microhardness (HV) and nanoindentation were performed at various locations around the fusion zone resulting in an average micro and nano hardness of 303 HV and 4.622 GPa respectively.