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20 pages, 13735 KiB

Open AccessArticle

Heterogeneous Material Additive Manufacturing for Hot-Stamping Die

by Myoung-Pyo Hong, Jin-Jae Kim, Woo-Sung Kim, Min-Kyu Lee, Ki-Man Bae, Young-Suk Kim and Ji-Hyun Sung

Metals 2020, 10(9), 1210; https://doi.org/10.3390/met10091210 - 9 Sep 2020

Cited by 8 | Viewed by 4503

Abstract

Additive manufacturing (AM) has recently been receiving global attention. As an innovative alternative to existing manufacturing technologies, AM can produce three-dimensional objects from various materials. In the manufacturing industry, AM improves production cost, time, and quality in comparison to existing methods. In addition, [...] Read more.

Additive manufacturing (AM) has recently been receiving global attention. As an innovative alternative to existing manufacturing technologies, AM can produce three-dimensional objects from various materials. In the manufacturing industry, AM improves production cost, time, and quality in comparison to existing methods. In addition, AM is applied in the fabrication and production of objects in diverse fields. In particular, metal AM has been continuously commercialized in high value-added industries such as aerospace and health care by many research and development projects. However, the applicability of metal AM to the mold and die industry and other low value-added industries is limited because AM is not as economical as current manufacturing technologies. Therefore, this paper proposes an effective solution to the problem. This study examines a method for using direct energy deposition and heterogeneous materials, a heterogeneous material additive-manufacturing process for metals used to optimize the cooling channels and a key process in manufacturing hot-stamping dies. The improvements in the cooling performances and uniform cooling were evaluated by heat-flow analysis in a continuous process. Finally, trial products were fabricated using the proposed method, and a trial for hot stamping was conducted to examine the possibility of it being used in commercial applications. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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18 pages, 4800 KiB

Open AccessArticle

Study on the Effect of Powder-Bed Fusion Process Parameters on the Quality of as-Built IN718 Parts Using Response Surface Methodology

by Bharath Bhushan Ravichander, Amirhesam Amerinatanzi and Narges Shayesteh Moghaddam

Metals 2020, 10(9), 1180; https://doi.org/10.3390/met10091180 - 2 Sep 2020

Cited by 32 | Viewed by 4458

Abstract

Inconel 718 (IN718) is a nickel-based superalloy which is widely used in aerospace, oil, and gas industries due to its outstanding mechanical properties at high temperatures, corrosion, fatigue resistance, and excellent weldability. Selective laser melting (SLM), one of the most used powder-bed based [...] Read more.

Inconel 718 (IN718) is a nickel-based superalloy which is widely used in aerospace, oil, and gas industries due to its outstanding mechanical properties at high temperatures, corrosion, fatigue resistance, and excellent weldability. Selective laser melting (SLM), one of the most used powder-bed based methods, is being extensively used to fabricate functional IN718 components with high accuracy. The accuracy and the properties of the SLM fabricated IN718 parts highly depend on the process parameters employed during fabrication. Thus, depending on the desired properties, the process parameters for a given material need to be optimized for improving the overall reliability of the SLM devices. In this study, design of experiment (DOE) was used to evaluate the dimensional accuracy, composition, and hardness corresponding to the interaction between the SLM process parameters such as laser power (P), scan speed (v), and hatch spacing (h). Contour plots were generated by co-relating the determined values for each characteristic and the process parameters to improve the as-built characteristics of the fabricated IN718 parts and reduce the post-processing time. The outcome of this study shows a range of energy density values for the IN718 superalloy needed to attain optimal values for each of the analyzed characteristics. Finally, an optimal processing region for SLM IN718 fabrication was identified which is in accordance with the values for each characteristic mentioned in literature. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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17 pages, 8525 KiB

Open AccessArticle

Three-Jet Powder Flow and Laser–Powder Interaction in Laser Melting Deposition: Modelling Versus Experimental Correlations

by Muhammad Arif Mahmood, Andrei C. Popescu, Mihai Oane, Carmen Ristoscu, Diana Chioibasu, Sabin Mihai and Ion N. Mihailescu

Metals 2020, 10(9), 1113; https://doi.org/10.3390/met10091113 - 19 Aug 2020

Cited by 26 | Viewed by 3953

Abstract

Powder flow and temperature distribution are recognized as essential factors in the laser melting deposition (LMD) process, which affect not only the layer formation but also its characteristics. In this study, two mathematical models were developed. Initially, the three-jet powder flow in the [...] Read more.

Powder flow and temperature distribution are recognized as essential factors in the laser melting deposition (LMD) process, which affect not only the layer formation but also its characteristics. In this study, two mathematical models were developed. Initially, the three-jet powder flow in the Gaussian shape was simulated for the LMD process. Next, the Gaussian powder flow was coaxially added along with the moving laser beam to investigate the effect of powder flow on temperature distribution at the substrate. The powder particles’ inflight and within melt-pool heating times were controlled to avoid vapors or plasma formation due to excessive heat. Computations were carried out via MATLAB software. A high-speed imaging camera was used to monitor the powder stream distribution, experimentally, while temperature distribution results were compared with finite element simulations and experimental analyses. A close correlation was observed among analytical computation, numerical simulations, and experimental results. An investigation was conducted to investigate the effect of the focal point position on powder stream distribution. It was found that the focal point position plays a key role in determining the shape of the powder stream, such that an increment in the distance from the focus point will gradually transform the powder stream from the Gaussian to Transition, and from the Transition to Annular streams. By raising the powder flow rate, the attenuation ratio prevails in the LMD process, hence, decreasing the laser energy density arriving at the substrate. The computations indicate that, if the particle’s heating temperature surpasses the boiling point, a strong possibility exists for vapors and plasma formation. Consequently, an excessive amount of laser energy is absorbed by the produced vapors and plasma, thus impeding the deposition process. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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12 pages, 4496 KiB

Open AccessArticle

Effect of Laser Cladding Stellite 6-Cr₃C₂-WS₂ Self-Lubricating Composite Coating on Wear Resistance and Microstructure of H13

by Wei Chen, Bo Liu, Long Chen, Jiangping Xu and Yingxia Zhu

Metals 2020, 10(6), 785; https://doi.org/10.3390/met10060785 - 13 Jun 2020

Cited by 15 | Viewed by 3288

Abstract

In order to prevent the wear failure of the hot-working die, the composite coatings of Stellite 6-Cr₃C₂-WS₂ was fabricated on H13 hot-working die steel by laser cladding. The composite coating was prepared through the in-situ generation technology, that [...] Read more.

In order to prevent the wear failure of the hot-working die, the composite coatings of Stellite 6-Cr₃C₂-WS₂ was fabricated on H13 hot-working die steel by laser cladding. The composite coating was prepared through the in-situ generation technology, that can give H13 the ability of self-lubricating at the working temperature (about 200 °C). The effect of the various WS₂ percentages on the properties of the coating was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness test, friction and wear test. In addition, the phase constitutions, microstructures and wear properties were also investigated systematically. The obtained hardness of the cladding coating is approximately 2.5 times higher than the substrate because of the constituents of γ-(Fe, Co)/Cr₇C₃ eutectic colony, (Cr, W)C carbide and dendritic crystals in the coating. Furthermore, the friction coefficient decreases to 70% of the substrate due to the CrS self-lubricating phase. The analyses results suggest that an 85% Stellite 6-10% Cr₃C₂-5% WS₂ composite coating has excellent material properties. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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11 pages, 1395 KiB

Open AccessArticle

Pulsed Laser Influence on Temperature Distribution during Dual Beam Laser Metal Deposition

by Marius Gipperich, Jan Riepe, Kristian Arntz and Thomas Bergs

Metals 2020, 10(6), 766; https://doi.org/10.3390/met10060766 - 9 Jun 2020

Cited by 7 | Viewed by 3889

Abstract

Wire-based Laser Metal Deposition (LMD-w) is a suitable manufacturing technology for a wide range of applications such as repairing, coating, or additive manufacturing. Employing a pulsed wave (pw) laser additionally to the continuous wave (cw) process laser has several positive effects on the [...] Read more.

Wire-based Laser Metal Deposition (LMD-w) is a suitable manufacturing technology for a wide range of applications such as repairing, coating, or additive manufacturing. Employing a pulsed wave (pw) laser additionally to the continuous wave (cw) process laser has several positive effects on the LMD process stability. The pw-plasma has an influence on the cw-absorption and thus the temperature distribution in the workpiece. In this article, several experiments are described aiming to characterize the heat input during dual beam LMD. In the first setup, small aluminum and steel disks are heated up either by only cw or by combined cw and pw radiation. The absorbed energy is then determined by dropping the samples into water at ambient temperature and measuring the water’s temperature rise. In a second experiment, the temperature distribution in the deposition zone under real process conditions is examined by two-color pyrometer measurements. According to the results, the pw plasma leads to an increase of the effective absorption coefficient by more than 20%. The aim of this work is to achieve a deeper understanding of the physical phenomena acting during dual beam LMD and to deploy them selectively for a better and more flexible process control. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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14 pages, 3846 KiB

Open AccessArticle

Effect of Post-Heat Treatment on the AISI M4 Layer Deposited by Directed Energy Deposition

by Gyeong Yun Baek, Gwang Yong Shin, Ki Yong Lee and Do Sik Shim

Metals 2020, 10(6), 703; https://doi.org/10.3390/met10060703 - 26 May 2020

Cited by 13 | Viewed by 3304

Abstract

Currently, high-speed steel (HSS) powders are deposited locally on a metal surface through direct energy deposition (DED) onto hardface tool steel. Although the HSS powder enhances the hardness and the abrasion resistance of a metal surface, it makes the tool steel brittle because [...] Read more.

Currently, high-speed steel (HSS) powders are deposited locally on a metal surface through direct energy deposition (DED) onto hardface tool steel. Although the HSS powder enhances the hardness and the abrasion resistance of a metal surface, it makes the tool steel brittle because of its high carbon content. In addition, the steel is likely to break when subjected to a high load over time. This study focused on improving the steel toughness by applying a post-heat treatment. To fabricate a uniformly deposited layer through DED, M4 powder was deposited onto a pre-heated substrate (AISI D2). In addition, four post-heat-treated specimens were prepared, and their mechanical properties were compared. The Charpy impact and hardness tests were conducted to evaluate the durability required for the D2 die. The deposited M4 powder possessed a high hardness but a relatively low impact toughness. During laser melting, a stable bond formed between M4 and D2 without any cracks or delamination. The hardness of the initial M4 deposited layer was 63 HRC, which changed to 54–63 HRC depending on the effect of the post-heat treatment. Moreover, the post-heat-treatment process improves the impact toughness of the M4 deposited layer by changing its microstructure. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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19 pages, 5180 KiB

Open AccessArticle

High Temperature Oxidation Behavior of Selective Laser Melting Manufactured IN 625

by Mihaela Raluca Condruz, Gheorghe Matache, Alexandru Paraschiv, Teodor Badea and Viorel Badilita

Metals 2020, 10(5), 668; https://doi.org/10.3390/met10050668 - 20 May 2020

Cited by 22 | Viewed by 3628

Abstract

The high-temperature oxidation behavior of selective laser melting (SLM) manufactured IN 625 was studied over 96 h of exposure at 900 °C and 1050 °C in air. An extensive analysis was performed to characterize the oxide scale formed and its evolution during the [...] Read more.

The high-temperature oxidation behavior of selective laser melting (SLM) manufactured IN 625 was studied over 96 h of exposure at 900 °C and 1050 °C in air. An extensive analysis was performed to characterize the oxide scale formed and its evolution during the 96 h, including mass gain analysis, EDS, XRD, and morphological analysis of the oxide scale. The mass gain rate of the bare material increases rapidly during the first 8 h of temperature holding and diminishes at higher holding periods for both oxidation temperatures. High-temperature exposure for short periods (24 h) follows a parabolic law and promotes the precipitation of δ phase, Ni-rich intermetallics, and carbides. Within the first 24 h of exposure at 900 °C, a Cr₂O₃ and a (Ni, Fe)Cr₂O₄ spinel scale were formed, while at a higher temperature, a more complex oxide was registered, consisting of (Ni, Fe)Cr₂O₄, Cr₂O₃, and rutile-type oxides. Prolonged exposure of IN 625 at 900 °C induces the preservation of the Cr₂O₃ scale and the dissolution of carbides. Other phases and intermetallics, such as γ, δ phases, and MoNi₄ are still present. The exposure for 96 h at 1050 °C led to the dissolution of all intermetallics, while the same complex oxide scale was formed. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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20 pages, 7647 KiB

Open AccessArticle

Experimental and Numerical Analysis of Gas/Powder Flow for Different LMD Nozzles

by Elise Ferreira, Morgan Dal, Christophe Colin, Guillaume Marion, Cyril Gorny, Damien Courapied, Jason Guy and Patrice Peyre

Metals 2020, 10(5), 667; https://doi.org/10.3390/met10050667 - 20 May 2020

Cited by 33 | Viewed by 5199

Abstract

The Laser Metal Deposition (LMD) process is an additive manufacturing method, which generates 3D structures through the interaction of a laser beam and a gas/powder stream. The stream diameter, surface density and focal plan position affect the size, efficiency and regularity of the [...] Read more.

The Laser Metal Deposition (LMD) process is an additive manufacturing method, which generates 3D structures through the interaction of a laser beam and a gas/powder stream. The stream diameter, surface density and focal plan position affect the size, efficiency and regularity of the deposit tracks. Therefore, a precise knowledge of the gas/powder streams characteristics is essential to control the process and improve its reliability and reproducibly for industrial applications. This paper proposes multiple experimental techniques, such as gas pressure measurement, optical and weighting methods, to analyze the gas and particle velocity, the powder stream diameter, its focal plan position and density. This was carried out for three nozzle designs and multiple gas and powder flow rates conditions. The results reveal that (1) the particle stream follows a Gaussian distribution while the gas velocity field is closer to a top hat one; (2) axial, carrier and shaping gas flow significantly impact the powder stream’s focal plan position; (3) only shaping gas, powder flow rates and nozzle design impact the powder stream diameter. 2D axisymmetric models of the gas and powder streams with RANS turbulent model are then performed on each of the three nozzles and highlight good agreements with experimental results but an over-estimation of the gas velocity by pressure measurements. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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20 pages, 20005 KiB

Open AccessArticle

Microstructure Evolution of Selective Laser Melted Inconel 718: Influence of High Heating Rates

by Seyedmohammad Tabaie, Farhad Rézaï-Aria and Mohammad Jahazi

Metals 2020, 10(5), 587; https://doi.org/10.3390/met10050587 - 29 Apr 2020

Cited by 15 | Viewed by 4810

Abstract

Inconel 718 (IN718) superalloy samples fabricated by selective laser melting (SLM) were submitted to different heating cycles and their microstructural characteristics were investigated. The selected heating rates, ranging from 10 °C/min to 400 °C/s, represent different regions in the heat-affected zone (HAZ) of [...] Read more.

Inconel 718 (IN718) superalloy samples fabricated by selective laser melting (SLM) were submitted to different heating cycles and their microstructural characteristics were investigated. The selected heating rates, ranging from 10 °C/min to 400 °C/s, represent different regions in the heat-affected zone (HAZ) of welded additively manufactured specimens. A combination of differential thermal analysis (DTA), high-resolution dilatometry, as well as laser confocal and electron microscopy were used to study the precipitation and dissolution of the secondary phases and microstructural features. For this purpose, the microstructure of the additively manufactured specimen was investigated from the bottom, in contact with the support, to the top surface. The results showed that the dissolution of γ″ and δ phases were delayed under high heating rates and shifted to higher temperatures. Microstructural analysis revealed that the Laves phase at the interdendritic regions was decomposed in specific zones near the surface of the samples. It was determined that the thickness and area fraction of these zones were inversely related to the applied heating rate. A possible mechanism based on the influence of heating rate on Nb diffusion in the interdendritic regions and core of the dendrites is proposed to interpret the observed changes in the microstructure. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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20 pages, 7882 KiB

Open AccessArticle

Effects of Gravity and Non-Perpendicularity during Powder-Fed Directed Energy Deposition of Ni-Based Alloy 718 through Two Types of Coaxial Nozzle

by Pedro Ramiro-Castro, Mikel Ortiz, Amaia Alberdi and Aitzol Lamikiz

Metals 2020, 10(5), 560; https://doi.org/10.3390/met10050560 - 26 Apr 2020

Cited by 7 | Viewed by 4024

Abstract

The consequences of gravity and the nozzle inclination angle in the powder-fed Directed Energy Deposition (DED) process were examined in this study. We also sought to define guidelines and manufacturing strategies, depending on the DED system configuration and the nozzle type. To do [...] Read more.

The consequences of gravity and the nozzle inclination angle in the powder-fed Directed Energy Deposition (DED) process were examined in this study. We also sought to define guidelines and manufacturing strategies, depending on the DED system configuration and the nozzle type. To do so, two nozzle types were used: a continuous coaxial nozzle with a slit of 0.5 mm and a four-stream discrete coaxial nozzle. Although the main effects of the configurations and the nozzles are well-known, their effects on the clad characteristics and the deposition strategy are as yet unclear. In this paper, measurements of a single clad and the effects of different deposition strategies on cladding applications and inclined walls are presented, and the consequences for manufacturing processes are discussed. Based on a complete study of a single clad, working vertically, five different tilted deposition strategies were applied: three to a single clad and two to an inclined wall. The results for both the single clad and the inclined wall reflect a pattern of changes to height, width, area, and efficiency, at both small and large nozzle angles and deposition strategies. The inclined wall presents a maximum horizontal displacement that can be reached per layer, without geometrical distortions. The amount of material per layer has to be adapted to this limitation. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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14 pages, 2357 KiB

Open AccessArticle

Element Vaporization of Ti-6Al-4V Alloy during Selective Laser Melting

by Guohao Zhang, Jing Chen, Min Zheng, Zhenyu Yan, Xufei Lu, Xin Lin and Weidong Huang

Metals 2020, 10(4), 435; https://doi.org/10.3390/met10040435 - 27 Mar 2020

Cited by 27 | Viewed by 5789

Abstract

The present study aims to reveal the mechanism of element vaporization of Ti-6Al-4V alloy during selective laser melting (SLM). The equations of Redlich–Kister and the thermodynamics principles were employed to calculate the vaporization thermodynamics, which contributes to the obtaining the vaporization kinetic based [...] Read more.

The present study aims to reveal the mechanism of element vaporization of Ti-6Al-4V alloy during selective laser melting (SLM). The equations of Redlich–Kister and the thermodynamics principles were employed to calculate the vaporization thermodynamics, which contributes to the obtaining the vaporization kinetic based on the Chapman-Enskog theory and the diffusion model. According to the achieved vaporization model, the elements with the most prominent tendency and flux to vaporize were distinguished. Moreover, the effect of the process parameters on the vaporization of Al and Ti is experimentally investigated using inductively coupled plasma optical emission spectrometer (ICP) technology. The analyzed results of the chemical composition of the powders and builds show a great agreement with the kinetic results calculated by the vaporization model. Notably, the element vaporization can be curbed by regulating the laser energy input. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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17 pages, 10489 KiB

Open AccessArticle

Thermal Fatigue Properties of H13 Hot-Work Tool Steels Processed by Selective Laser Melting

by Mei Wang, Yan Wu, Qingsong Wei and Yusheng Shi

Metals 2020, 10(1), 116; https://doi.org/10.3390/met10010116 - 12 Jan 2020

Cited by 29 | Viewed by 6069

Abstract

Currently, selective laser melting (SLM) is gaining widespread popularity as an alternative manufacturing technique for complex and customized parts, especially for hot-work and injection molding applications. In the present study, as the major factors for the failure of H13 hot-work die steels during [...] Read more.

Currently, selective laser melting (SLM) is gaining widespread popularity as an alternative manufacturing technique for complex and customized parts, especially for hot-work and injection molding applications. In the present study, as the major factors for the failure of H13 hot-work die steels during hot-working, thermal fatigue (TF) properties of H13 processed by SLM and a conventional technique were investigated. TF tests (650 °C/30 °C) were conducted on the as-selective laser melted (As-SLMed), thermally treated selective laser melted (T-SLMed), and forged (Forged) H13. Results show that the As-SLMed H13 exhibited the best TF resistance properties among the specimens herein (the shortest total crack length and highest hardness of 687 ± 12 HV₅), whereas the Forged H13 exhibited the poorest TF resistance properties (the longest total crack length and lowest hardness of 590 ± 11 HV₅) after TF tests. TF resistance properties were closely related to the initial and final hardness. Further microstructural investigations revealed that the typical cell-like substructures, increased amount of retained austenite, and most importantly, refined grain size were the main reasons for the improved TF resistance properties in the As-SLMed H13 compared to the Forged counterparts. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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12 pages, 4402 KiB

Open AccessArticle

Acoustic Properties of 316L Stainless Steel Lattice Structures Fabricated via Selective Laser Melting

by Xiaojing Sun, Fengchun Jiang and Jiandong Wang

Metals 2020, 10(1), 111; https://doi.org/10.3390/met10010111 - 11 Jan 2020

Cited by 20 | Viewed by 5365

Abstract

A bulk specimen and two different lattice sandwich structures composed of 316L stainless steel were fabricated via selective laser melting. This study analysed the acoustic properties, including sound insulation and sound absorption, of the three kinds of structures, which were produced via selective [...] Read more.

A bulk specimen and two different lattice sandwich structures composed of 316L stainless steel were fabricated via selective laser melting. This study analysed the acoustic properties, including sound insulation and sound absorption, of the three kinds of structures, which were produced via selective laser melting under the same process parameters. The results showed that the difference in the unit structures, rather than microstructural difference, was the main reason for the difference in acoustic properties between the samples. Under the same process parameters, the microstructure of the different structures had the same cell structure. However, the sound absorption properties of the lattice sandwich structures were better than those of the bulk sample in the measured frequency range of 1–6.3 kHz. The lattice sandwich structure with 2.5 × 2.5 × 2.5 mm³ unit structures exhibited excellent sound insulation properties in the frequency range of 1–5 kHz. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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22 pages, 10450 KiB

Open AccessArticle

Influence of the Chemical Composition of the Used Powder on the Fatigue Behavior of Additively Manufactured Materials

by Bastian Blinn, Florian Krebs, Maximilian Ley, Christopher Gläßner, Marek Smaga, Jan C. Aurich, Roman Teutsch and Tilmann Beck

Metals 2019, 9(12), 1285; https://doi.org/10.3390/met9121285 - 29 Nov 2019

Cited by 10 | Viewed by 2762

Abstract

To exploit the whole potential of Additive Manufacturing (AM), a sound knowledge about the mechanical and especially cyclic properties of AM materials as well as their dependency on the process parameters is indispensable. In the presented work, the influence of chemical composition of [...] Read more.

To exploit the whole potential of Additive Manufacturing (AM), a sound knowledge about the mechanical and especially cyclic properties of AM materials as well as their dependency on the process parameters is indispensable. In the presented work, the influence of chemical composition of the used powder on the fatigue behavior of Selectively Laser Melted (SLM) and Laser Deposition Welded (LDW) specimens made of austenitic stainless steel AISI 316L was investigated. Therefore, in each manufacturing process two variations of chemical composition of the used powder were utilized. For qualitative characterization of the materials cyclic deformation behavior, load increase tests (LITs) were performed and further used for the physically based lifetime calculation method (PhyBaL_LIT), enabling an efficient determination of stress (S)–number of cycles to failure (N_f) curves (S–N_f), which show excellent correlation to additionally performed constant amplitude tests (CATs). Moreover, instrumented cyclic indentation tests (PhyBaL_CHT) were utilized to characterize the materials’ defect tolerance in a comparably short time. All material variants exhibit a high influence of microstructural defects on the fatigue properties. Consequently, for the SLM process a higher fatigue lifetime at lower stress amplitudes could be observed for the batch with a higher defect tolerance, resulting from a more pronounced deformation induced austenite–α’-martensite transformation. In correspondence to that, the batch of LDW material with an increased defect tolerance exhibit a higher fatigue strength. However, the differences in defect tolerance between the LDW batches is only slightly influenced by phase transformation and seems to be mainly governed by differences in hardening potential of the austenitic microstructure. Furthermore, a significantly higher fatigue strength could be observed for SLM material in relation to LDW specimens, because of a refined microstructure and smaller microstructural defects of SLM specimens. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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13 pages, 7251 KiB

Open AccessArticle

Investigation on Ti-6Al-4V Microstructure Evolution in Selective Laser Melting

by Ling Ding, Zhonggang Sun, Zulei Liang, Feng Li, Guanglong Xu and Hui Chang

Metals 2019, 9(12), 1270; https://doi.org/10.3390/met9121270 - 27 Nov 2019

Cited by 12 | Viewed by 4113

Abstract

Selective laser melting (SLM) is an advanced additive manufacturing technique that can produce complex and accurate metal samples. Since the process performs local high heat input during a very short interaction time, the physical parameters in the solidification are difficult to measure experimentally. [...] Read more.

Selective laser melting (SLM) is an advanced additive manufacturing technique that can produce complex and accurate metal samples. Since the process performs local high heat input during a very short interaction time, the physical parameters in the solidification are difficult to measure experimentally. In this work, the microstructure evolution of Ti-6Al-4V alloy in additive manufacturing was studied. With the increase of scanning speed, the cooling rate and the temperature gradient of molten pool position increased, which was attributed to the gradual decrease of energy density. The phase-field simulation resulted in the overall microstructure morphology of columnar crystals owing to the very large temperature gradient and cooling rate obtained from the temperature field. Microsegregation was observed during dendritic formation, and the solute was enriched in the liquid phase near the dendritic tip and between the dendritic arms due to the lower equilibrium distribution coefficient. The scanning speed had an effect on the dendrite spacing. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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14 pages, 3914 KiB

Open AccessArticle

Influence of HIP Treatment on Mechanical Properties of Ti6Al4V Scaffolds Prepared by L-PBF Process

by Lili Liu, Huade Zheng and Chunlin Deng

Metals 2019, 9(12), 1267; https://doi.org/10.3390/met9121267 - 27 Nov 2019

Cited by 6 | Viewed by 2367

Abstract

To improve biocompatibility and mechanical compatibility, post-treatment is necessary for porous scaffolds of bone tissue engineering. Hot isostatic pressing (HIP) is introduced into post-treatment of metal implants to enhance their mechanical properties by eliminating residual stress and pores. Additionally, oxide film formed on [...] Read more.

To improve biocompatibility and mechanical compatibility, post-treatment is necessary for porous scaffolds of bone tissue engineering. Hot isostatic pressing (HIP) is introduced into post-treatment of metal implants to enhance their mechanical properties by eliminating residual stress and pores. Additionally, oxide film formed on the material surface can be contributed to improve its biocompatibility. Ti6Al4V porous scaffolds fabricated by laser-powder bed fusion (L-PBF) process is studied in this paper, their mechanical properties are measured by pressure test, and the macroscopic surface morphology and microstructure are observed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). After HIP treatment, an oxide layer of 0.8 μm thickness forms on the surface of Ti6Al4V porous scaffolds and the microstructure of Ti6Al4V transforms from α’ phase to α + β dual-phase, as expected. However, the pressure test results of Ti6Al4V porous scaffolds show a definitely different variation trend of mechanical properties from solid parts, unexpectedly. Concerning Ti6Al4V porous scaffolds, the compression stiffness and critical stress improves clearly using HIP treatment, and the fracture morphology shows obvious brittle fracture. Both the strengthening and brittleness transition of Ti6Al4V porous scaffolds result from the formation of an oxide layer and an oxygen atom diffusion layer. The critical stress of Ti6Al4V porous scaffolds can be calculated by fully considering these two strengthening layers. To obtain a porous scaffold with specific mechanical properties, the effect of post-treatment should be considered during structural design. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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10 pages, 1316 KiB

Open AccessArticle

Construction of Cellular Substructure in Laser Powder Bed Fusion

by Yafei Wang, Chenglu Zhang, Chenfan Yu, Leilei Xing, Kailun Li, Jinhan Chen, Jing Ma, Wei Liu and Zhijian Shen

Metals 2019, 9(11), 1231; https://doi.org/10.3390/met9111231 - 18 Nov 2019

Cited by 9 | Viewed by 3394

Abstract

Cellular substructure has been widely observed in the sample fabricated by laser powder bed fusion, while its growth direction and the crystallographic orientation have seldom been studied. This research tries to build a general model to construct the substructure from its two-dimensional morphology. [...] Read more.

Cellular substructure has been widely observed in the sample fabricated by laser powder bed fusion, while its growth direction and the crystallographic orientation have seldom been studied. This research tries to build a general model to construct the substructure from its two-dimensional morphology. All the three Bunge Euler angles to specify a unique growth direction are determined, and the crystallographic orientation corresponding to the growth direction is also obtained. Based on the crystallographic orientation, the substructure in the single track of austenitic stainless steel 316L is distinguished between the cell-like dendrite and the cell. It is found that, with the increase of scanning velocity, the substructure transits from cell-like dendrite to cell. When the power is 200 W, the critical growth rate of the transition in the single track can be around 0.31 ms⁻¹. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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Review

Jump to: Research

20 pages, 5310 KiB

Open AccessReview

Integration of Simulation Driven DfAM and LCC Analysis for Decision Making in L-PBF

by Patricia Nyamekye, Anna Unt, Antti Salminen and Heidi Piili

Metals 2020, 10(9), 1179; https://doi.org/10.3390/met10091179 - 2 Sep 2020

Cited by 5 | Viewed by 4446

Abstract

Laser based powder bed fusion (L-PBF) is used to manufacture parts layer by layer with the energy of laser beam. The use of L-PBF for building functional parts originates from the design freedom, flexibility, customizability, and energy efficiency of products applied in dynamic [...] Read more.

Laser based powder bed fusion (L-PBF) is used to manufacture parts layer by layer with the energy of laser beam. The use of L-PBF for building functional parts originates from the design freedom, flexibility, customizability, and energy efficiency of products applied in dynamic application fields such as aerospace and automotive. There are challenges and drawbacks that need to be defined and overcome before its adaptation next to rivaling traditional manufacturing methods. Factors such as high cost of L-PBF machines, metal powder, post-preprocessing, and low productivity may deter its acceptance as a mainstream manufacturing technique. Understanding the key cost drivers of L-PBF that influence productivity throughout the whole lifespan of products will facilitate the decision-making process. Functional and operational decisions can yield profitability and increase competitiveness among advanced manufacturing sectors. Identifying the relationships between the phases of the life cycle of products influences cost-effectiveness. The aim of the study is to investigate the life cycle cost (LCC) and the impact of design to it in additive manufacturing (AM) with L-PBF. The article provides a review of simulation driven design for additive manufacturing (simulation driven DfAM) and LCC for metallic L-PBF processes and examines the state of the art to outline the merits, demerits, design rules, and life cycle models of L-PBF. Practical case studies of L-PBF are discussed and analysis of the interrelating factors of the different life phases are presented. This study shows that simulation driven DfAM in the design phase increases the productivity throughout the whole production and life span of L-PBF parts. The LCC model covers the whole holistic lifecycle engineering of products and offers guidelines for decision making. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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26 pages, 7268 KiB

Open AccessReview

Review of Laser Powder Bed Fusion of Gamma-Prime-Strengthened Nickel-Based Superalloys

by Olutayo Adegoke, Joel Andersson, Håkan Brodin and Robert Pederson

Metals 2020, 10(8), 996; https://doi.org/10.3390/met10080996 - 23 Jul 2020

Cited by 42 | Viewed by 6646

Abstract

This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are [...] Read more.

This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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23 pages, 4300 KiB

Open AccessReview

Corrosion Behaviors of Selective Laser Melted Aluminum Alloys: A Review

by Hongwei Chen, Chaoqun Zhang, Dan Jia, Daniel Wellmann and Wen Liu

Metals 2020, 10(1), 102; https://doi.org/10.3390/met10010102 - 9 Jan 2020

Cited by 60 | Viewed by 7653

Abstract

Selective laser melting (SLM) is an ideal method to directly fabricate products with high geometrical complexity. With low density and good corrosion resistance, aluminum alloys are widely used as important structural materials. Microstructures and mechanical properties of SLMed aluminum alloys have been recently [...] Read more.

Selective laser melting (SLM) is an ideal method to directly fabricate products with high geometrical complexity. With low density and good corrosion resistance, aluminum alloys are widely used as important structural materials. Microstructures and mechanical properties of SLMed aluminum alloys have been recently widely studied. Corrosion behavior as a vital concern during the service of SLMed aluminum alloy parts has also drawn many attentions. Previous studies have found that SLM-processed aluminum alloys exhibit better corrosion resistance compared to the casted and wrought counterparts for both Al-Si alloys and high strength 2xxx Al alloys, which is mainly due to the unique microstructure features of SLMed Al alloys. For Al-Si alloys, with different shapes of Si networks, the different building planes show discrepant corrosion behaviors. Owing to the rougher surface with relatively larger numbers of defects, the as-printed surface is vulnerable to corrosion than the polished. Heat treatment has a negative effect on corrosion resistance due to the breakup of Si networks. The microstructure features correlated with the corrosion behaviors were also reviewed in this paper. Some suggestions on the future study of corrosion behaviors of SLMed Al alloys were put forward. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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35 pages, 3638 KiB

Open AccessReview

Review: The Impact of Metal Additive Manufacturing on the Aerospace Industry

by Shahir Mohd Yusuf, Samuel Cutler and Nong Gao

Metals 2019, 9(12), 1286; https://doi.org/10.3390/met9121286 - 29 Nov 2019

Cited by 205 | Viewed by 29652

Abstract

Metal additive manufacturing (AM) has matured from its infancy in the research stage to the fabrication of a wide range of commercial functional applications. In particular, at present, metal AM is now popular in the aerospace industry to build and repair various components [...] Read more.

Metal additive manufacturing (AM) has matured from its infancy in the research stage to the fabrication of a wide range of commercial functional applications. In particular, at present, metal AM is now popular in the aerospace industry to build and repair various components for commercial and military aircraft, as well as outer space vehicles. Firstly, this review describes the categories of AM technologies that are commonly used to fabricate metallic parts. Then, the evolution of metal AM used in the aerospace industry from just prototyping to the manufacturing of propulsion systems and structural components is also highlighted. In addition, current outstanding issues that prevent metal AM from entering mass production in the aerospace industry are discussed, including the development of standards and qualifications, sustainability, and supply chain development. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)

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