A Comparison of the Thermo-Fluid Properties of Ti-6Al-4V Melt Pools Formed by Laser and Electron-Beam Powder-Bed Fusion Processes

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
M Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Numerical Model ◽  
Cooling Rate ◽  
Liquid Velocity ◽  
Full Density ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
Fluid Properties ◽  
Simulation Results

Abstract Powder-bed fusion (PBF) process is a subdivision of additive manufacturing (AM) technology where a heat source at a controlled speed selectively fuses regions of a powder-bed material to form three-dimensional (3D) parts in a layer-by-layer fashion. Two of the most commercialized and powerful PBF methods for fabricating full-density metallic parts are the laser PBF (L-PBF) and electron beam PBF (E-PBF) processes. In this study, a multiphysics-based 3D numerical model is developed to compare the thermo-fluid properties of Ti-6Al-4V melt pools formed by the L-PBF and E-PBF processes. The temperature-dependent properties of Ti-6Al-4V alloy and the parameters for the laser and electron beams are incorporated in the model as the user-defined functions (UDFs). The melt-pool geometry and its thermo-fluid behavior are investigated using the finite volume (FV) method, and results for the variations of temperature, thermo-physical properties, velocity, geometry of the melt pool, and cooling rate in the two processes are compared under similar irradiation conditions. For an irradiance level of 26 J/mm3 and a beam interaction time of 1.212 ms, simulation results show that the L-PBF process gives a faster cooling rate (1. 5 K/μs) than that in the E-PBF process (0.74 K/μs). The magnitude of liquid velocity in the melt pool is also higher in L-PBF than that in E-PBF. The numerical model is validated by comparing the simulation results for the melt-pool geometry with the PBF experimental results and comparing the numerical melt-front position with the analytical solution for the classical Stephan problem of melting of a phase-change material (PCM).

scholarly journals Comparison of Phase Characteristics and Residual Stresses in Ti-6Al-4V Alloy Manufactured by Laser Powder Bed Fusion (L-PBF) and Electron Beam Powder Bed Fusion (EB-PBF) Techniques

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 796
Author(s):  
Aya Takase ◽  
Takuya Ishimoto ◽  
Naotaka Morita ◽  
Naoko Ikeo ◽  
Takayoshi Nakano
Keyword(s):  
Electron Beam ◽  
Residual Stresses ◽  
Cooling Rate ◽  
Process Parameters ◽  
Phase Evolution ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Solidification Temperature ◽  
Powder Bed ◽  
Β Phase

Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters.

scholarly journals Laser Powder Bed Fusion of an Al-Mg-Sc-Zr Alloy: Manufacturing, Peak Hardening Response and Thermal Stability at Peak Hardness

Metals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 57
Author(s):  
Bharat Mehta ◽  
Arvid Svanberg ◽  
Lars Nyborg
Keyword(s):  
Thermal Stability ◽  
Al Alloys ◽  
Peak Hardness ◽  
Full Density ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
Different Temperatures ◽  
Zr Alloy

This study shows a rapid and systematic approach towards identifying full density and peak hardness for an Al-Mg-Sc-Zr alloy commonly known as Scalmalloy®. The alloy is tailored for the laser powder bed fusion process and has been shown to be printable with >99.8% relative density. The microstructure suggests Al grain refinement in melt pool boundaries, associated with formation of primary Al3(Sc,Zr) particles during solidification. Peak hardening response was identified by heat treatment tests at 573,598 and 623 K between 0 and 10 h. A peak hardness of 172 HV0.3 at 598 K for 4 h was identified. The mechanical properties were also tested with yield and ultimate strengths of 287 MPa and 364 MPa in as-printed and 468 MPa and 517 MPa in peak hardened conditions, respectively, which is consistent with the literature. Such an approach is considered apt when qualifying new materials in industrial laser powder bed fusion systems. The second part of the study discusses the thermal stability of such alloys post-peak-hardening. One set of samples was peak hardened at the conditions identified before and underwent secondary ageing at three different temperatures of 423,473 and 523 K between 0 and 120 h to understand thermal stability and benchmark against conventional Al alloys. The secondary heat treatments performed at lower temperatures revealed lower deterioration of hardness over ageing times as compared to the datasheets for conventional Al alloys and Scalmalloy®, thus suggesting that longer ageing times are needed.

scholarly journals Powder bed fusion modelling based on Discontinuous Galerkin formulation

2021 ◽  
Author(s):  
Larbi Arbaoui ◽  
Pierre Schrooyen ◽  
Nicolas Poletz ◽  
Koen Hillewaert
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Discontinuous Galerkin ◽  
Solid Phase ◽  
High Order ◽  
Heat Of Fusion ◽  
Element Formulation ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool

Microscopic defects may occur during powder-bed fusion processes which originate from molten pool instabilities. To investigate this issue, a numerical model focusing on the interaction between laser and powder, melt pool formation and thermodynamics effects is on development. The approach used in the model assumes an incompressible Newtonian flow based on an enthalpy-porosity method for solid/liquid metal transition. The jump conditions at the liquid-solid interface for the energy equation are included through the modification of the enthalpy which incorporates the latent heat of fusion. A Carman-Kozeny porosity method is implemented in the momentum equation to penalize the flow in the solid phase. Molten flows are driven by natural and thermocapillary convection which are modelled using Boussinesq approximation and Marangoni free-surface stresses respectively. This numerical model is implemented within a Discontinuous Galerkin (DG) finite element formulation which ensures high order convergence on unstructured mesh [1]. In this work, a sharp interface method is integrated into the three dimensional high-order DG code Argo [2] to capture the free surface of the melt pool. This method allows to keep the high-order of convergence of the DG scheme even near the interface not conforming with the mesh. This is essential to capture the thermo-hydrodynamics phenomena during powder-bed fusion with accuracy. Current effort is dedicated to improve the model accounting for physical phenomena such as surface tension and vaporization. The main purpose is to investigate the occurrence of discontinuities in fused powder tracks depending on material properties and process parameters.

scholarly journals In Situ Thermography During Laser Powder Bed Fusion of a Nickel Superalloy 625 Artifact with Various Overhangs and Supports

2021 ◽  
Vol 126 ◽  
Author(s):  
Benjamin Molnar ◽  
Jarred C. Heigel ◽  
Eric Whitenton
Keyword(s):  
Cooling Rate ◽  
High Speed ◽  
Nickel Superalloy ◽  
Powder Bed Fusion ◽  
Support Structures ◽  
Radiance Temperature ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool

This document provides details on the experiment and associated measurement files available fordownload in the dataset “In Situ Thermography During Laser Powder Bed Fusion of a Nickel Superalloy 625 Artifact with Various Overhangs and Supports.” The measurements were acquired during the fabrication of a small nickel superalloy 625 (IN625) artifact using a commercial laser powder bed fusion (LPBF) system. The artifact consists of two half-arch features with increasing slopes for overhangs. These overhangs range from 5° from vertical to 85° from vertical in increments of 10°. The artifact geometry and process are controlled to ensure consistent processing along the overhang geometry. This control enables the effect of overhang geometry and support structures to be isolated from effects of inter-layer scan strategy variations. The measurements include high-speed thermography of each layer, from which radiance temperature, cooling rate, and melt pool length are calculated.

Thermofluid Properties of Ti-6Al-4V Melt Pool in Powder-Bed Electron Beam Additive Manufacturing

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
M Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Heat Source ◽  
Thermal Behavior ◽  
Source Parameters ◽  
Three Dimensional ◽  
Full Density ◽  
Layer By Layer ◽  
Powder Bed ◽  
Melt Pool

Electron beam additive manufacturing (EBAM) is a powder-bed fusion additive manufacturing (AM) technology that can make full density metallic components using a layer-by-layer fabrication method. To build each layer, the EBAM process includes powder spreading, preheating, melting, and solidification. The quality of the build part, process reliability, and energy efficiency depends typically on the thermal behavior, material properties, and heat source parameters involved in the EBAM process. Therefore, characterizing those properties and understanding the correlations among the process parameters are essential to evaluate the performance of the EBAM process. In this study, a three-dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder was developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt pool dynamics and its thermal behavior were investigated numerically, and results for temperature profile, melt pool geometry, cooling rate and variation in density, thermal conductivity, specific heat capacity, and enthalpy were obtained for several sets of electron beam specifications. Validation of the model was performed by comparing the simulation results with the experimental results for the size of the melt pool.

Thermal Analysis of Electron Beam Additive Manufacturing Using Ti-6Al-4V Powder-Bed

2017 ◽  
Author(s):  
M. Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Three Dimensional ◽  
Vital Role ◽  
Full Density ◽  
Rate Variation ◽  
Layer By Layer ◽  
Powder Bed ◽  
Part Quality ◽  
Melt Pool

Electron Beam Additive Manufacturing (EBAM) is one of the emerging additive manufacturing (AM) technologies that is uniquely capable of making full density metallic components using layer-by-layer fabrication method. To build each layer, the process includes powder spreading, pre-heating, melting, and solidification. The thermal and material properties involved in the EBAM process play a vital role to determine the part quality, reliability, and energy efficiency. Therefore, characterizing the properties and understanding the correlations among the process parameters are incumbent to evaluate the performance of the EBAM process. In this study, a three dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder has been developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt-pool dynamics and its thermal behavior have been investigated numerically using a CFD solver and results for temperature profile, cooling rate, variation in density, thermal conductivity, specific heat capacity, and enthalpy have been obtained for a particular set of electron beam specifications.

scholarly journals Finite Element Modeling of Melt Pool Dynamics in Laser Powder Bed Fusion of 316L Stainless Steel

2021 ◽  
Author(s):  
Juan Trejos-Taborda ◽  
Luis Reyes-Osorio ◽  
Carlos Garza ◽  
Patricia del Carmen Zambrano-Robledo ◽  
Omar Eduardo Lopez-Botello
Keyword(s):  
Numerical Model ◽  
Relative Error ◽  
Laser Scanning ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
History Of ◽  
Dynamics Stability

Abstract In Laser Powder Bed Fusion (LPBF), melt pool dynamics stability determines the overall quality of a manufactured component. In this work, a numerical model of the LPBF process was developed in order to study and fully understand the behavior of the melt pool dynamics. The numerical model takes into account most of the manufacturing parameters, thermophysical properties, an enhanced thermal conductivity approach and a volumetric heat source in order to precisely mimic LPBF. This research assumes that the energy emitted by the laser interacts with the metal powder with an absorptivity gradient through the layer thickness in order to calculate the thermal history of the process and the evolution of the melt pool dimensions. The obtained results determined that melt pool dimensions follow a thermal pattern, which is caused by the laser scanning strategy of the LPBF process. A new effective width criterion was proposed in the present research in order to accurately relate both calculated and measured dimensions of the melt pool, reducing the relative error of the model and obtaining data scattering with a standard deviation of ±7.21 µm and a relative error of 2.92%.

Heat Transfer and Melt-Pool Evolution During Powder-Bed Fusion of Ti-6Al-4V Parts Under Various Laser Irradiation Conditions

2020 ◽  
Author(s):  
M. Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Laser Irradiation ◽  
Laser System ◽  
Maximum Temperature ◽  
Rate Variation ◽  
Powder Bed Fusion ◽  
Cross Sectional ◽  
Powder Bed ◽  
Melt Pool ◽  
Simulation Results ◽  
Functional Components

Abstract Laser Powder-bed Fusion (L-PBF) is a promising additive manufacturing (AM) process that is capable of speedily fabricating functional components typically used for aerospace, automotive, microelectronics, and biomedical applications. In this study, a 3-D computational fluid dynamics model with Ti-6Al-4V powder-bed is developed incorporating a moving conical volumetric heat source and thermophysical properties of Ti-6Al-4V alloy to conduct the simulations of the L-PBF process. The melt-pool dynamics and its thermal behavior are investigated numerically and results for temperature profile, cooling rate, variation in density, thermal conductivity, specific heat capacity, and enthalpy are obtained for different laser irradiation conditions. Simulation results show that the maximum temperature, dimensions, and liquid lifetime of the melt pool increase with the increase of the laser power and decrease of the scanning speed. A custom ytterbium fiber laser system is applied to perform laser melting experiments with a solid Ti-6Al-4V specimen. The microstructures of the cross-sectional areas are examined by a scanning electron microscope to observe the melt-pool dimensions and the heat-affected zones. Finally, the simulation results for melt-pool geometry are compared with the experimental results to validate the numerical model for the L-PBF process.

scholarly journals Multi-Scale Modeling of Residual Stresses Evolution in Laser Powder Bed Fusion of Inconel 625

2021 ◽  
Vol 6 (1) ◽  
pp. 2
Author(s):  
Mohamed Balbaa ◽  
Mohamed Elbestawi
Keyword(s):  
Residual Stresses ◽  
Cooling Rate ◽  
Process Parameters ◽  
Laser Exposure ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Linear Temperature ◽  
Powder Bed ◽  
Multi Scale ◽  
Melt Pool

Laser powder bed fusion exhibits many advantages for manufacturing complex geometries from hard to machine alloys such as IN625. However, a major drawback is the formation of high tensile residual stresses, and the complex relationship between the process parameters and the residual stresses has not been fully investigated. The current study presents multi-scale models to examine the variation of process parameters on melt pool dimensions, cyclic temperature evolutions, cooling rate, and cyclic stress generation and how they affect the stress end state. In addition, the effect of the same energy density, which is often overlooked, on the generated residual stresses is investigated. Multi-level validation is performed based on melt pool dimensions, temperature measurements with a two-color pyrometer, and finally, in-depth residual stress measurement. The results show that scan speed has the strongest effect on residual stresses, followed by laser power and hatch spacing. The results are explained in light of the non-linear temperature evolution, temperature gradient, and cooling rate during laser exposure, cooling time, and the rate during recoating time.

Grain Morphology and Texture Development in a Co-Cr-Mo Alloy Fabricated by Powder Bed Fusion with an Electron Beam

2019 ◽  
Author(s):  
Yufan Zhao ◽  
Yuichiro Koizumi ◽  
Kenta Aoyagi ◽  
Daixiu Wei ◽  
Kenta Yamanaka ◽  
...  
Keyword(s):  
Electron Beam ◽  
Grain Morphology ◽  
Texture Development ◽  
Powder Bed Fusion ◽  
Powder Bed
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