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T A Palmer - One of the best experts on this subject based on the ideXlab platform.
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microtexture in additively manufactured ti 6al 4v fabricated using Directed Energy Deposition
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Daudi Waryoba, J S Keist, C Ranger, T A PalmerAbstract:Abstract The additive manufacturing (AM) of α + β titanium alloys using electron beam (EB) and laser Directed Energy Deposition (DED) processes has been widely characterized in both the as-deposited and post processed conditions. Fine basket weave α lath structures are commonly observed in both the as-deposited and post processed hot isostatically pressed (HIP) conditions for both laser and EB DED processes, but more in-depth knowledge of the crystallographic texturing and variant selection of the α laths growing from the primary β-grains across the height of EB DED Ti-6Al-4V structures is not well established. At locations near the substrate in both conditions, microtexturing is weak, but EB DED builds exhibit a strong microtexture and pronounced variant selection with increasing build height. On the other hand, the laser DED builds displayed weak texturing and no prominent variant selection across all heights. With the addition of HIP post processing, there was no change in microtexturing of the coarsened α laths for both the laser and EB structures, and the same variant selection observed in the as-deposited EB DED builds was present.
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correlating microstructure and superelasticity of Directed Energy Deposition additive manufactured ni rich niti alloys
Journal of Alloys and Compounds, 2018Co-Authors: Reginald F Hamilton, Beth A Bimber, T A PalmerAbstract:Abstract Laser-based Directed Energy Deposition (LDED) additive manufacturing of Ni-rich NiTi shape memory alloys was shown to produce inhomogeneous precipitate morphologies and characteristic grain structures consisting of columnar grains coexisting with equiaxed and subgrain structures. Post-processing solutionizing and aging heat treatments impacted microstructure and martensitic phase transformation (MT) responses underpinning superelastic shape memory responses. A solution treatment of 950 °C for 24 h was found to produce a uniform composition of the B2 austenite parent phase without affecting the coexistence of columnar and equiaxed substructures. Aging the solution treated material brought about a spatially uniform Ni4Ti3 precipitate morphology. Due to the uniform morphology, an underlying austenite-martensite interface motion accompanies the compressive stress-induced MT (SIMT). Reversible interface motion underpinned the compressive superelastic response for the solutionized and aged condition. On the other hand, strain concentrations existed at different spatial locations in the as built condition as well as when the as built material was aged. The stark contrasts in the SIMT exposed precipitate morphology as a controlling factor in tailoring the superelastic response of Ni-rich NiTi SMAs fabricated by LDED.
Richard P. Martukanitz - One of the best experts on this subject based on the ideXlab platform.
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thermal and microstructural analysis of laser based Directed Energy Deposition for ti 6al 4v and inconel 625 deposits
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Joshua Z Park, J S Keist, Sanjay Joshi, Richard P. MartukanitzAbstract:Abstract Accurate temperature measurements based on careful experimentation and microstructural analysis were conducted for Ti-6Al-4V and Inconel 625 alloys deposited using the laser-based Directed Energy Deposition process. In the case of the Ti-6Al-4V alloy, thermal measurements were made in the first layer during the first and four subsequent deposits to ascertain microstructural evolution during the heating and cooling cycles. Four Energy densities were utilized during Deposition of the Inconel 625 alloy to alter cooling rates and determine the impact of processing conditions on solidification morphology. The precise experimental measurements enabled a comprehensive analysis of the solid state reactions for Ti-6Al-4V, and the solidification phenomena to be elucidated for Inconel 625. The results for the Ti-6Al-4V alloy indicated that the measured thermal response could be used to anticipate initial microstructure based on cooling rates from the β-transus, and subsequent thermal cycles could be utilized to define potential transformations between α, α′, and β. Analysis of the measured thermal cycles from the liquid through solidification for the Inconel 625 alloy showed that processing parameters could be linked to factors governing the solidification process and microstructural features. Using these relationships, an accurate processing map for laser-based Directed Energy Deposition for Inconel 625 was constructed to enable the identification of solidification morphology and microstructural scale based on critical processing parameters.
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Partitioning of laser Energy during Directed Energy Deposition
Additive manufacturing, 2017Co-Authors: Frederick Lia, Joshua Park, Jay F. Tressler, Richard P. MartukanitzAbstract:Abstract An Energy balance that describes the transfer of Energy is proposed for the laser-based Directed Energy Deposition process. The partitioning of laser Energy was experimentally measured and accurately validated using a special process calorimeter for Ti-6Al-4V and Inconel 625™ alloys. The total Energy provided by the laser was partitioned as: the Energy directly absorbed by the substrate, the Energy absorbed by the powder stream and deposited onto the substrate, the Energy reflected from the substrate surface, and the Energy reflected or absorbed and lost from the powder stream. Titanium alloy Ti-6Al-4V showed higher overall or bulk absorption than the Inconel 625™ alloy. Processing with powder resulted in lower laser Energy absorption within the substrate than without powder, due to the “shadowing” effect of the powder stream within the beam and loss of Energy representing unfused powder. During processing at a laser power of approximately 1 kW the total Energy absorbed during the Deposition process was found to be 42% for the Ti-6Al-4V alloy and 37% for the Inconel 625™ alloy. Under these conditions 14% of the total Energy was lost by the Ti-6Al-4V unfused powder; whereas only 11% was lost by the Inconel 625™ powder.
J S Keist - One of the best experts on this subject based on the ideXlab platform.
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microtexture in additively manufactured ti 6al 4v fabricated using Directed Energy Deposition
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Daudi Waryoba, J S Keist, C Ranger, T A PalmerAbstract:Abstract The additive manufacturing (AM) of α + β titanium alloys using electron beam (EB) and laser Directed Energy Deposition (DED) processes has been widely characterized in both the as-deposited and post processed conditions. Fine basket weave α lath structures are commonly observed in both the as-deposited and post processed hot isostatically pressed (HIP) conditions for both laser and EB DED processes, but more in-depth knowledge of the crystallographic texturing and variant selection of the α laths growing from the primary β-grains across the height of EB DED Ti-6Al-4V structures is not well established. At locations near the substrate in both conditions, microtexturing is weak, but EB DED builds exhibit a strong microtexture and pronounced variant selection with increasing build height. On the other hand, the laser DED builds displayed weak texturing and no prominent variant selection across all heights. With the addition of HIP post processing, there was no change in microtexturing of the coarsened α laths for both the laser and EB structures, and the same variant selection observed in the as-deposited EB DED builds was present.
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thermal and microstructural analysis of laser based Directed Energy Deposition for ti 6al 4v and inconel 625 deposits
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Joshua Z Park, J S Keist, Sanjay Joshi, Richard P. MartukanitzAbstract:Abstract Accurate temperature measurements based on careful experimentation and microstructural analysis were conducted for Ti-6Al-4V and Inconel 625 alloys deposited using the laser-based Directed Energy Deposition process. In the case of the Ti-6Al-4V alloy, thermal measurements were made in the first layer during the first and four subsequent deposits to ascertain microstructural evolution during the heating and cooling cycles. Four Energy densities were utilized during Deposition of the Inconel 625 alloy to alter cooling rates and determine the impact of processing conditions on solidification morphology. The precise experimental measurements enabled a comprehensive analysis of the solid state reactions for Ti-6Al-4V, and the solidification phenomena to be elucidated for Inconel 625. The results for the Ti-6Al-4V alloy indicated that the measured thermal response could be used to anticipate initial microstructure based on cooling rates from the β-transus, and subsequent thermal cycles could be utilized to define potential transformations between α, α′, and β. Analysis of the measured thermal cycles from the liquid through solidification for the Inconel 625 alloy showed that processing parameters could be linked to factors governing the solidification process and microstructural features. Using these relationships, an accurate processing map for laser-based Directed Energy Deposition for Inconel 625 was constructed to enable the identification of solidification morphology and microstructural scale based on critical processing parameters.
Panagiotis Michaleris - One of the best experts on this subject based on the ideXlab platform.
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Towards computational modeling of temperature field evolution in Directed Energy Deposition processes
Volume 2: Control and Optimization of Connected and Automated Ground Vehicles; Dynamic Systems and Control Education; Dynamics and Control of Renewabl, 2018Co-Authors: Qian Wang, Panagiotis MichalerisAbstract:In modeling and simulating thermo-mechanical behavior in a Directed Energy Deposition process, it often needs to compute the temperature field evolved in the Deposition process since thermal history in the Deposition process would affect part geometry as well as microstructure, material properties, residual stress, and distortion of the final part. This paper presents an analytical computation of temperature field evolved in a Directed Energy Deposition process, using a single-bead wall as an illustrating example. Essentially, the temperature field is computed by superposition of the temperature fields generated by the laser source as well as induced from each of the past beads, where the transient solution to a moving heat source in a semi-infinite body is applied to describe each individual temperature field. For better characterization of cooling effect (temperature contribution from a past bead), a pair of positive and negative virtual heat sources is assigned for each past bead. In addition, mirrored heat sources through a reflexion technique are introduced to define the adiabatic boundaries of the part being built and to account for the substrate thickness. In the end, three Depositions of Ti-6AL-4V walls with different geometries and inter-layer dwell times on an Optomec® laser engineered net shaping (LENS) system are used to validate the proposed analytical computation, where predicted temperatures at several locations of the Depositions show reasonable agreement with the in situ temperature measurements, with the average prediction error less than 15%. The proposed analytical computation for temperature field in Directed Energy Deposition could be potentially used in model-based feedback control for thermal history in the Deposition, which could affect microstructure evolution and other properties of the final part.
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An Analytical Computation of Temperature Field Evolved in Directed Energy Deposition
Journal of Manufacturing Science and Engineering-transactions of The Asme, 2018Co-Authors: Qian Wang, Panagiotis MichalerisAbstract:This paper presents an analytical computation of temperature field evolved in a Directed Energy Deposition process, using single-bead walls as illustrating examples. Essentially, the temperature field evolution during the Deposition of a wall is computed by super-position of the temperature field generated by the laser source depositing the current bead and that induced from each of the past beads (layers). First, the transient solution to a point heat source in a semi-infinite body is applied to describe each individual temperature field. Then, to better describe temperature contribution from a past bead, a pair of virtual heat sources with positive and negative powers is assigned for each past bead to compute the temperature field under cooling. In addition, mirrored heat sources through a reflexion technique are introduced to define adiabatic boundaries of the part and to account for substrate thickness. In the end, three Depositions of Ti-6AL-4V walls with different geometries and interlayer dwell times on an Optomec® laser engineering net shaping (LENS) system are used to validate the proposed analytical computation, where predicted temperatures at several locations of the substrate show reasonable agreement with the in situ temperature measurements with prediction error rate ranging from 12% to 27%. Furthermore, temperature distributions predicted by the proposed model are compared to finite element simulations. The proposed analytical computation for temperature field could be potentially used in model-based feedback control for thermal history in the Deposition, which could affect microstructure evolution and other properties of the final part.
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Measurement of forced surface convection in Directed Energy Deposition additive manufacturing
Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2015Co-Authors: Jarred C. Heigel, Panagiotis Michaleris, Todd PalmerAbstract:The accurate modeling of thermal gradients and distortion generated by Directed Energy Deposition additive manufacturing requires a thorough understanding of the underlying physical processes. One area that has the potential to significantly affect the accuracy of thermomechanical simulations is the complex forced convection created by the inert gas jets that are used to deliver metal powder to the melt pool and to shield the laser optics and the molten material. These jets act on part surfaces with higher temperatures than those in similar processes such as welding and consequently have a greater impact on the prevailing heat transfer mechanisms. A methodology is presented here which uses hot-film sensors and constant voltage anemometry to measure the forced convection generated during additive manufacturing processes. This methodology is then demonstrated by characterizing the convection generated by a Precitec® YC50 Deposition head under conditions commonly encountered in additive manufacturing. Surfac...
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Thermo-mechanical model development and validation of Directed Energy Deposition additive manufacturing of Ti-6Al-4V
Additive Manufacturing, 2015Co-Authors: Jarred C. Heigel, Panagiotis Michaleris, E. E. ReutzelAbstract:A thermo-mechanical model of Directed Energy Deposition additive manufacturing of Ti-6Al-4V is developed using measurements of the surface convection generated by gasses flowing during the Deposition. In Directed Energy Deposition, material is injected into a melt pool that is traversed to fill in a cross-section of a part, building it layer-by-layer. This creates large thermal gradients that generate plastic deformation and residual stresses. Finite element analysis (FEA) is often used to study these phenomena using simple assumptions of the surface convection. This work proposes that a detailed knowledge of the surface heat transfer is required to produce more accurate FEA results. The surface convection generated by the Deposition process is measured and implemented in the thermo-mechanical model. Three Depositions with different geometries and dwell times are used to validate the model using in situ measurements of the temperature and deflection as well as post-process measurements of the residual stress. An additional model is developed using the assumption of free convection on all surfaces. The results show that a measurement-based convection model is required to produce accurate simulation results.
Xinchang Zhang - One of the best experts on this subject based on the ideXlab platform.
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A Review on Metallic Alloys Fabrication Using Elemental Powder Blends by Laser Powder Directed Energy Deposition Process.
Materials, 2020Co-Authors: Yitao Chen, Xinchang Zhang, Mohammad Masud Parvez, Frank W. LiouAbstract:The laser powder Directed Energy Deposition process is a metal additive manufacturing technique, which can fabricate metal parts with high geometric and material flexibility. The unique feature of in-situ powder feeding makes it possible to customize the elemental composition using elemental powder mixture during the fabrication process. Thus, it can be potentially applied to synthesize industrial alloys with low cost, modify alloys with different powder mixtures, and design novel alloys with location-dependent properties using elemental powder blends as feedstocks. This paper provides an overview of using a laser powder Directed Energy Deposition method to fabricate various types of alloys by feeding elemental powder blends. At first, the advantage of laser powder Directed Energy Deposition in manufacturing metal alloys is described in detail. Then, the state-of-the-art research and development in alloys fabricated by laser powder Directed Energy Deposition through a mix of elemental powders in multiple categories is reviewed. Finally, critical technical challenges, mainly in composition control are discussed for future development.
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Characteristics of Inconel 625—copper bimetallic structure fabricated by Directed Energy Deposition
The International Journal of Advanced Manufacturing Technology, 2020Co-Authors: Xinchang Zhang, Tomoya Yamazaki, Austin Sutton, Lan Li, Frank LiouAbstract:Inconel 625 (In625) is preferred under the circumstances where high strength and corrosion resistance at elevated temperatures are required. However, the restricted thermal conductivity constrains the application of In625 in high heat flux cases. The joining of materials with high thermal conductivity to In625 is capable of improving upon this limitation so as to adapt for temperature-sensitive requirements. In this study, a bi-metallic structure was fabricated by joining In625 on Copper 110 (Cu) substrate with Directed Energy Deposition. Material examination indicated no crack and minor porosity were detected through and along the interface of two materials and the following as-deposited In625. Mechanical performances were characterized at both as-deposited and heat-treated conditions. The resultant yield strength and ultimate tensile strength of as-deposited In625 was 670.97 ± 5.43 MPa and 925.36 ± 9.90 MPa, respectively, with a mean maximum elongation of 0.416 mm/mm. Slightly decreases (by ~ 5%) in tensile strength were observed after heat treatment under 500 °C for 24 h with an enhancement in elongation by ~ 6%. Ductile fracture mode was observed on the fracture surfaces of broken tensile specimens. The impact toughness for as-deposited In625 and heat-treated In625 (under 600° for 24 h) was 118.058 ± 2.285 and 112.045 ± 5.755 J, respectively. A significant improvement in the thermal diffusivity of ~ 100% was experimentally measured when comparing the bi-metallic structure to pure In625. The thickness fraction of Cu played a significant role in the measured thermal diffusivity result.
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Fabrication of SS316L-IN625 functionally graded materials by powder-fed Directed Energy Deposition
Science and Technology of Welding and Joining, 2019Co-Authors: Xinchang Zhang, Yitao Chen, Frank W. LiouAbstract:In this work, functionally graded materials of Stainless Steel 316L and Inconel 625 were fabricated using Directed Energy Deposition. Intermediate layers were built in between of SS316L and IN625. ...
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Effect of optimizing particle size on Directed Energy Deposition of Functionally Graded Material with blown Pre-Mixed Multi-Powder
Manufacturing Letters, 2017Co-Authors: Wei Li, Jingwei Zhang, Xinchang Zhang, Frank LiouAbstract:Functionally Graded Material (FGM) is often fabricated by Directed Energy Deposition with pre-mixed multiple powders (PMM-powder). Since the supplied PMM-powder directly affects FGM's composition, investigation on PMM-powder's property is greatly needed. This paper employed experimental method to observe an important problem: PMM-powder separation in fabricating FGM. A novel particle size optimization method was introduced as solution to eliminate the powder separation. Pre-mixed pure Cu and 4047 Al powders were used to do two experiments. The first experiment result disclosed the existence of powder separation. By optimizing the particle size, the PMM-powder separation was effectively solved in the second experiment result.