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17 pages, 10260 KiB

Open AccessArticle

Microstructure and Mechanical Properties of P21-STS316L Functionally Graded Material Manufactured by Direct Energy Deposition 3D Print

by Myeongji Jo, Hyo-Seong Kim, Jeong Yeol Park, Seok Goo Lee, Byung Jun Kim, Hyoung Chan Kim, Yong-sik Ahn, Byoungkoo Kim, Namhyn Kang and Daegeun Nam

Metals 2022, 12(12), 2086; https://doi.org/10.3390/met12122086 - 5 Dec 2022

Viewed by 1916

Abstract

Functionally graded materials (FGMs) have a characteristic whereby the composition and structure are gradually changed according to the location, and the mechanical properties or chemical properties are gradually changed accordingly. In this study, using a multi-hopper direct energy deposition 3D printer, an FGM [...] Read more.

Functionally graded materials (FGMs) have a characteristic whereby the composition and structure are gradually changed according to the location, and the mechanical properties or chemical properties are gradually changed accordingly. In this study, using a multi-hopper direct energy deposition 3D printer, an FGM material whose composition changes gradually from P21 ferritic steel to stainless steel 316L austenitic steel was fabricated. From optical microscope, scanning electron microscope, and X-ray diffraction analysis, columnar, cell, and point type solidified micro-structure and precipitations were observed depending on the deposited compositions. Electron probe microanalysis and electron backscatter diffraction analysis confirmed the component segregation, ferrite austenite volume fraction and phase distribution behavior according to compositions. In the FGM specimen test, the ultimate tensile strength of STS316L, which was the most fragile, was measured, and the toughness was measured for the notch area, which did not represent the FGM characteristics. Hardness showed changes according to FGM position and was suitable for FGM analysis. The maximum hardness was measured in the FGM duplex area, which was caused by grain refinement, precipitate strengthening, and solid solution strengthening. In nuclear power plant welds high strength can cause adverse effects on stress corrosion cracking, and caution is needed in applying FGM. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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17 pages, 3992 KiB

Open AccessArticle

Investigation of Spatter Trajectories in an SLM Build Chamber under Argon Gas Flow

by Awad B. S. Alquaity and Bekir S. Yilbas

Metals 2022, 12(2), 343; https://doi.org/10.3390/met12020343 - 16 Feb 2022

Cited by 2 | Viewed by 2184

Abstract

Spatter particles ejected from the melt pool during selective laser melting processes can get redeposited on the build plate region and impact final part quality. Although an inert gas flow is used to purge the spattered particles away from the build plate region, [...] Read more.

Spatter particles ejected from the melt pool during selective laser melting processes can get redeposited on the build plate region and impact final part quality. Although an inert gas flow is used to purge the spattered particles away from the build plate region, some of the spatter particles get redeposited on the plate region leading to increased porosity and surface roughness. In this regard, the current study focuses on the numerical modeling of the interactions between the inert gas flow and spatter particles by using the discrete phase model. A Renishaw AM250 build chamber is used as the base geometry and the flow field within the build chamber is evaluated for various inert gas flow rates and nozzle diameters of 6 mm and 12 mm. For the first time, spatter trajectories are tracked at specific spatter diameters and ejection angles to pinpoint the influence of drag and gravitational forces on the evolution of spatter trajectories. The findings reveal that the spatter particles between 120 and 180 μm diameter travel beyond the build plate only at specific gas ejection angles and gas flow rates (≥750 L/min). Reducing the nozzle diameter to 6 mm increases the inert gas flow velocity in the build region and enhances the range of spatter particles. New correlations are proposed to relate the range of particles and inert gas flow rates, which can be used to identify the spatter diameters, ejection angles, and inert gas flow rates required to transport the particles beyond the sensitive build plate region. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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20 pages, 6630 KiB

Open AccessArticle

Grain Scale Investigation of the Mechanical Anisotropic Behavior of Electron Beam Powder Bed Additively Manufactured Ti6Al4V Parts

by Md Jamal Mian, Jafar Razmi and Leila Ladani

Metals 2022, 12(1), 163; https://doi.org/10.3390/met12010163 - 17 Jan 2022

Cited by 4 | Viewed by 1929

Abstract

Numerous factors, including variable grain structures and different inherent defects, impact the mechanical behavior of Ti6Al4V parts fabricated using metal Additive Manufacturing (AM) processes. This study focuses on an in-depth analysis of how different microstructural features, such as crystallographic texture, grain size, grain [...] Read more.

Numerous factors, including variable grain structures and different inherent defects, impact the mechanical behavior of Ti6Al4V parts fabricated using metal Additive Manufacturing (AM) processes. This study focuses on an in-depth analysis of how different microstructural features, such as crystallographic texture, grain size, grain boundary misorientation angles, and inherent defects, as byproducts of the electron beam powder bed fusion (EB-PBF) AM process, impact its anisotropic mechanical behavior. Standard tensile testing, conducted on samples produced at different orientations relative to the build table, showed significant anisotropy in elastic-plastic constitutive characteristics. Furthermore, X-ray computed tomography (CT) and electron back-scattered diffraction (EBSD) analyses were conducted on as-built samples to assess the effects of inherent defects and microstructural anomalies on such behavior. The samples arranged vertically and parallel to build direction had an average porosity of 0.05%, while the horizontally built samples, which were perpendicular to the build direction, had an average porosity of 0.17%. Moreover, the vertical samples showed larger grain sizes, with an average of 6.6 µm, wider α lath sizes, a lower average misorientation angle, and subsequently lower strength values than the other two horizontal samples. Among the three strong preferred grain orientations of the α phases, <1 1

\bar{2}

1> and <1 1

\bar{2}

0> were dominant in the horizontally built samples, whereas the <0 0 0 1> orientation was dominant in vertically built samples. Finally, larger grain sizes and higher beta-phase volume ratios were observed in the areas located at distances further away from the build plate. This was possibly due to the change in thermal gradients, cooling rates, and some thermal annealing phenomena resultant from the elevated build chamber temperature. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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13 pages, 1795 KiB

Open AccessArticle

Process Parameter Optimization in Metal Laser-Based Powder Bed Fusion Using Image Processing and Statistical Analyses

by Faiyaz Ahsan, Jafar Razmi and Leila Ladani

Metals 2022, 12(1), 87; https://doi.org/10.3390/met12010087 - 4 Jan 2022

Cited by 5 | Viewed by 3564

Abstract

The powder bed fusion additive manufacturing process has received widespread interest because of its capability to manufacture components with a complicated design and better surface finish compared to other additive techniques. Process optimization to obtain high quality parts is still a concern, which [...] Read more.

The powder bed fusion additive manufacturing process has received widespread interest because of its capability to manufacture components with a complicated design and better surface finish compared to other additive techniques. Process optimization to obtain high quality parts is still a concern, which is impeding the full-scale production of materials. Therefore, it is of paramount importance to identify the best combination of process parameters that produces parts with the least defects and best features. This work focuses on gaining useful information about several features of the bead area, such as contact angle, porosity, voids, melt pool size and keyhole that were achieved using several combinations of laser power and scan speed to produce single scan lines. These features are identified and quantified using process learning, which is then used to conduct a comprehensive statistical analysis that allows to estimate the effect of the process parameters, such as laser power and scan speed on the output features. Both single and multi-response analyses are applied to analyze the response parameters, such as contact angle, porosity and melt pool size individually as well as in a collective manner. Laser power has been observed to have a more influential effect on all the features. A multi-response analysis showed that 150 W of laser power and 200 mm/s produced a bead with the best possible features. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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17 pages, 6553 KiB

Open AccessArticle

In Situ Alloying of a Modified Inconel 625 via Laser Powder Bed Fusion: Microstructure and Mechanical Properties

by Giulio Marchese, Margherita Beretta, Alberta Aversa and Sara Biamino

Metals 2021, 11(6), 988; https://doi.org/10.3390/met11060988 - 21 Jun 2021

Cited by 6 | Viewed by 2458

Abstract

This study investigates the in situ alloying of a Ni-based superalloy processed by means of laser powder bed fusion (LPBF). For this purpose, Inconel 625 powder is mixed with 1 wt.% of Ti6Al4V powder. The modified alloy is characterized by densification levels similar [...] Read more.

This study investigates the in situ alloying of a Ni-based superalloy processed by means of laser powder bed fusion (LPBF). For this purpose, Inconel 625 powder is mixed with 1 wt.% of Ti6Al4V powder. The modified alloy is characterized by densification levels similar to the base alloy, with relative density superior to 99.8%. The material exhibits Ti-rich segregations along the melt pool contours. Moreover, Ti tends to be entrapped in the interdendritic areas during solidification in the as-built state. After heat treatments, the modified Inconel 625 version presents greater hardness and tensile strengths than the base alloy in the same heat-treated conditions. For the solution annealed state, this is mainly attributed to the elimination of the segregations into the interdendritic structures, thus triggering solute strengthening. Finally, for the aged state, the further increment of mechanical properties can be attributed to a more intense formation of phases than the base alloy, due to elevated precipitation strengthening ability under heat treatments. It is interesting to note how slight chemical composition modification can directly develop new alloys by the LPBF process. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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20 pages, 6906 KiB

Open AccessFeature PaperArticle

Process Optimization and Microstructure Analysis to Understand Laser Powder Bed Fusion of 316L Stainless Steel

by Nathalia Diaz Vallejo, Cameron Lucas, Nicolas Ayers, Kevin Graydon, Holden Hyer and Yongho Sohn

Metals 2021, 11(5), 832; https://doi.org/10.3390/met11050832 - 19 May 2021

Cited by 32 | Viewed by 4109

Abstract

The microstructural development of 316L stainless steel (SS) was investigated over a wide range of systematically varied laser powder bed fusion (LPBF) parameters, such as laser power, scan speed, hatch spacing and volumetric energy density. Relative density, melt pool width and depth, and [...] Read more.

The microstructural development of 316L stainless steel (SS) was investigated over a wide range of systematically varied laser powder bed fusion (LPBF) parameters, such as laser power, scan speed, hatch spacing and volumetric energy density. Relative density, melt pool width and depth, and the size of sub-grain cellular structure were quantified and related to the temperature field estimated by Rosenthal solution. Use of volumetric energy density between 46 and 127 J/mm³ produced nearly fully dense (≥99.8%) samples, and this included the best parameter set: power = 200 W; scan speed = 800 mm/s; hatch spacing = 0.12 mm; slice thickness = 0.03; energy density = 69 J/mm³). Cooling rate of 10⁵ to 10⁷ K/s was estimated base on the size of cellular structure within melt pools. Using the optimized LPBF parameters, the as-built 316L SS had, on average, yield strength of 563 MPa, Young’s modulus of 179 GPa, tensile strength of 710 MPa, and 48% strain at failure. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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Graphical abstract

19 pages, 6313 KiB

Open AccessArticle

Robust Additive Manufacturing Performance through a Control Oriented Digital Twin

by Panagiotis Stavropoulos, Alexios Papacharalampopoulos, Christos K. Michail and George Chryssolouris

Metals 2021, 11(5), 708; https://doi.org/10.3390/met11050708 - 26 Apr 2021

Cited by 46 | Viewed by 5434

Abstract

The additive manufacturing process control utilizing digital twins is an emerging issue. However, robustness in process performance is still an open aspect, due to uncertainties, e.g., in material properties. To this end, in this work, a digital twin offering uncertainty management and robust [...] Read more.

The additive manufacturing process control utilizing digital twins is an emerging issue. However, robustness in process performance is still an open aspect, due to uncertainties, e.g., in material properties. To this end, in this work, a digital twin offering uncertainty management and robust process control is designed and implemented. As a process control design method, the Linear Matrix Inequalities are adopted. Within specific uncertainty limits, the performance of the process is proven to be acceptably constant, thus achieving robust additive manufacturing. Variations of the control law are also investigated, in order for the applicability of the control to be demonstrated in different machine architectures. The comparison of proposed controllers is done against a fine-tuned conventional proportional–integral–derivative (PID) and the initial open-loop model for metals manufacturing. As expected, the robust control design achieved a 68% faster response in the settling time metric, while a well-calibrated PID only achieved 38% compared to the initial model. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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Review

Jump to: Research

58 pages, 45027 KiB

Open AccessReview

Review of Powder Bed Fusion Additive Manufacturing for Metals

by Leila Ladani and Maryam Sadeghilaridjani

Metals 2021, 11(9), 1391; https://doi.org/10.3390/met11091391 - 1 Sep 2021

Cited by 72 | Viewed by 12766

Abstract

Additive manufacturing (AM) as a disruptive technology has received much attention in recent years. In practice, however, much effort is focused on the AM of polymers. It is comparatively more expensive and more challenging to additively manufacture metallic parts due to their high [...] Read more.

Additive manufacturing (AM) as a disruptive technology has received much attention in recent years. In practice, however, much effort is focused on the AM of polymers. It is comparatively more expensive and more challenging to additively manufacture metallic parts due to their high temperature, the cost of producing powders, and capital outlays for metal additive manufacturing equipment. The main technology currently used by numerous companies in the aerospace and biomedical sectors to fabricate metallic parts is powder bed technology, in which either electron or laser beams are used to melt and fuse the powder particles line by line to make a three-dimensional part. Since this technology is new and also sought by manufacturers, many scientific questions have arisen that need to be answered. This manuscript gives an introduction to the technology and common materials and applications. Furthermore, the microstructure and quality of parts made using powder bed technology for several materials that are commonly fabricated using this technology are reviewed and the effects of several process parameters investigated in the literature are examined. New advances in fabricating highly conductive metals such as copper and aluminum are discussed and potential for future improvements is explored. Full article

(This article belongs to the Special Issue Optimization of Metal Additive Manufacturing Processes)

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