Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104489
Ya-Chu Hsu, Dingchang Zhang, David C. Dunand
Equiatomic CoCuFeNi high-entropy alloy microlattices are created by 3D-extrusion printing of an ink containing a blend of binary oxides (Co3O4+CuO+Fe2O3+NiO) and graphite (C) powders. After printing, the green parts are subjected to a series of heat treatments under Ar leading to (i) carbon reduction of the oxides to form metallic particles, (ii) interdiffusion of these metallic particles to create an alloy, and (iii) sintering to remove porosity. The phase evolution in individual extruded filaments (similar to struts in the microlattices) is observed by in-situ X-ray diffraction, showing that intermediate suboxide phases (Cu2O, CoO, Fe3O4, CuFeO2, and FeO) form as the original oxides are reduced by carbon, before the final metallic alloy is formed. At 830 °C, the extruded filaments comprise a face-centered cubic CoCuNi(+Fe) alloy with unreduced FeO inclusions. After reduction and sintering at 1100 °C, homogeneous, densified, equiatomic CoCuFeNi microlattices are achieved, containing small amounts of a Cu-rich phase. At room temperature, the compressive strength of these CoCuFeNi microlattices increases as the strut diameter decreases from ∼260 to ∼130 µm, as expected from an observed drop in strut porosity resulting from more complete sintering. This is consistent with the easier escape of CO+CO2 gas created during carbothermic oxide reduction from the thinner struts undergoing reduction and sintering.
{"title":"Carbon reduction of 3D-ink-extruded oxide powders for synthesis of equiatomic CoCuFeNi microlattices","authors":"Ya-Chu Hsu, Dingchang Zhang, David C. Dunand","doi":"10.1016/j.addma.2024.104489","DOIUrl":"10.1016/j.addma.2024.104489","url":null,"abstract":"<div><div>Equiatomic CoCuFeNi high-entropy alloy microlattices are created by 3D-extrusion printing of an ink containing a blend of binary oxides (Co<sub>3</sub>O<sub>4</sub>+CuO+Fe<sub>2</sub>O<sub>3</sub>+NiO) and graphite (C) powders. After printing, the green parts are subjected to a series of heat treatments under Ar leading to (i) carbon reduction of the oxides to form metallic particles, (ii) interdiffusion of these metallic particles to create an alloy, and (iii) sintering to remove porosity. The phase evolution in individual extruded filaments (similar to struts in the microlattices) is observed by <em>in-situ</em> X-ray diffraction, showing that intermediate suboxide phases (Cu<sub>2</sub>O, CoO, Fe<sub>3</sub>O<sub>4</sub>, CuFeO<sub>2</sub>, and FeO) form as the original oxides are reduced by carbon, before the final metallic alloy is formed. At 830 °C, the extruded filaments comprise a face-centered cubic CoCuNi(+Fe) alloy with unreduced FeO inclusions. After reduction and sintering at 1100 °C, homogeneous, densified, equiatomic CoCuFeNi microlattices are achieved, containing small amounts of a Cu-rich phase. At room temperature, the compressive strength of these CoCuFeNi microlattices increases as the strut diameter decreases from ∼260 to ∼130 µm, as expected from an observed drop in strut porosity resulting from more complete sintering. This is consistent with the easier escape of CO+CO<sub>2</sub> gas created during carbothermic oxide reduction from the thinner struts undergoing reduction and sintering.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104489"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104486
Dac-Phuc Pham , Hong-Chuong Tran
Laser powder bed fusion (L-PBF) uses a controlled laser beam to melt specific regions of a metal powder bed in a layer-by-layer fashion to fabricate parts with an intricate geometry. However, due to the stochastic nature of the L-PBF process, many defects may occur during the build process, including distortion, porosity, and high surface roughness. A poor roughness of the upper surface is frequently associated with impaired mechanical properties and a lower corrosion resistance. Thus, laser polishing (LP) is commonly employed to smooth the surface of the component following the build process. The surface finish of the polished part is dependent not only on the initial morphology of the surface, but also the processing conditions employed in the polishing process (i.e., the laser power, scanning speed, and hatching space). The surface profile is also influenced by physical phenomena such as the surface tension force, recoil pressure, and Marangoni force. The present study thus proposes an integrated framework based on discrete element method (DEM) and computational fluid dynamics (CFD) simulations which takes account of all of these factors to predict the final surface morphology and roughness of L-PBF components following LP processing. The validity of the simulation model is confirmed by comparing the calculated mean surface roughness of the polished components (with the experimental values. It is found that the maximum error of the simulation results for different initial surface morphologies and LP processing conditions is less than 6.8 %.
{"title":"Multi-physics simulation for predicting surface roughness of laser powder bed fused parts after laser polishing","authors":"Dac-Phuc Pham , Hong-Chuong Tran","doi":"10.1016/j.addma.2024.104486","DOIUrl":"10.1016/j.addma.2024.104486","url":null,"abstract":"<div><div>Laser powder bed fusion (L-PBF) uses a controlled laser beam to melt specific regions of a metal powder bed in a layer-by-layer fashion to fabricate parts with an intricate geometry. However, due to the stochastic nature of the L-PBF process, many defects may occur during the build process, including distortion, porosity, and high surface roughness. A poor roughness of the upper surface is frequently associated with impaired mechanical properties and a lower corrosion resistance. Thus, laser polishing (LP) is commonly employed to smooth the surface of the component following the build process. The surface finish of the polished part is dependent not only on the initial morphology of the surface, but also the processing conditions employed in the polishing process (i.e., the laser power, scanning speed, and hatching space). The surface profile is also influenced by physical phenomena such as the surface tension force, recoil pressure, and Marangoni force. The present study thus proposes an integrated framework based on discrete element method (DEM) and computational fluid dynamics (CFD) simulations which takes account of all of these factors to predict the final surface morphology and roughness of L-PBF components following LP processing. The validity of the simulation model is confirmed by comparing the calculated mean surface roughness of the polished components (<span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>)</mo><mspace></mspace></mrow></math></span>with the experimental values. It is found that the maximum error of the simulation results for different initial surface morphologies and LP processing conditions is less than 6.8 %.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104486"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534043","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104466
Clemens Maucher , Yeonse Kang , Stefan Bechler , Matthias Ruf , Holger Steeb , Hans-Christian Möhring , Fabian Hampp
Permeable, media transporting, components are an integral part in numerous technical applications. In gas turbines combustors, for example, gaseous oxidizer and fuel are transported separately into the burner, where they are injected and mixed, and subsequently combusted. The mixture homogeneity strongly affects the combustion performance and emissions formation and is, amongst other, determined by the spatial distribution of fuel injection ports. In this context, porous media provide the limiting case for a spatial distribution of media-injecting pores, yet is typically associated with a high pressure drop that yields a loss in efficiency. In this study, possibilities of achieving gas permeability in additively manufactured porous structures are investigated. The objective is to selectively functionalize the permeable layers for gaseous media supply with low pressure loss and, when needed, enable a targeted mixing of different gas streams. For this purpose, a laser-based powder bed fusion process (PBF-LB/M) was used in this study. It offers the opportunity to manufacture varying porosities inside complex monolithic metal parts. To produce the porous structures and to achieve gas permeability, the effect of scan rotation angle, hatch distance, build-up direction and length of the porous specimen is investigated. Due to the high temperatures present in combustion systems, the present work utilizes Inconel 718 material. The AM gas permeable specimen are experimentally characterized by means of surface topography, micro X-ray computed tomography (µXRCT) as well as flow and pressure loss test. The results show, that the AM process parameter provide effective control parameters to adjust the permeability. The strongest effect originates from the hatch distance for a given build-up direction. Depending on the scan rotation, the flow transitions from a turbulent pipe flow to a Darcy flow as present in conventional porous media. A structured alignment and connectivity of pores can be realized as evident in the µXRCT results, surface topography and the flow measurements. Residual powder, powder adhering to the pore walls and stochastic closure of pores or channels lead to deviations and need to be considered when designing respective parts. Nonetheless, the results further show that a directional dependence of the permeability and the build-up direction can be realized and controlled. Consequently, when considering the AM build-strategy in the design of components, this directed permeability can be functionalized in the generation of gas transporting and gas mixing layers separately by adjusting the AM processing parameter.
可渗透介质输送部件是众多技术应用中不可或缺的组成部分。例如，在燃气轮机的燃烧器中，气态氧化剂和燃料被分别输送到燃烧器中，在那里进行喷射和混合，然后进行燃烧。混合物的均匀性对燃烧性能和排放物的形成有很大影响，除其他外，还取决于燃料喷射口的空间分布。在这种情况下，多孔介质提供了介质喷射孔空间分布的极限情况，但通常与产生效率损失的高压力降有关。本研究探讨了在添加制造的多孔结构中实现气体渗透的可能性。其目的是有选择性地对透气层进行功能化处理，以便以较低的压力损失提供气体介质，并在需要时实现不同气流的定向混合。为此，本研究采用了激光粉末床熔融工艺（PBF-LB/M）。该工艺可在复杂的整体金属部件内制造不同的多孔结构。为了制造多孔结构并实现气体渗透性，研究了扫描旋转角度、舱口距离、堆积方向和多孔试样长度的影响。由于燃烧系统温度较高，本研究采用了铬镍铁合金 718 材料。通过表面形貌、微 X 射线计算机断层扫描 (µXRCT) 以及流量和压力损失测试，对 AM 气体渗透试样进行了实验表征。结果表明，AM 工艺参数提供了调整渗透性的有效控制参数。在给定的堆积方向上，最大的影响来自于舱口距离。根据扫描旋转的不同，流动会从湍流管流过渡到传统多孔介质中的达西流。从 µXRCT 结果、表面形貌和流动测量结果中可以明显看出，孔隙的结构排列和连通性得以实现。残留粉末、粘附在孔壁的粉末以及孔隙或通道的随机闭合会导致偏差，因此在设计相应部件时需要加以考虑。尽管如此，结果进一步表明，渗透率和堆积方向的定向依赖性是可以实现和控制的。因此，在设计部件时考虑 AM 构建策略时，可以通过调整 AM 加工参数，在生成气体输送层和气体混合层时将这种定向渗透性功能化。
{"title":"Towards bespoke gas permeability by functionally graded structures in laser-based powder bed fusion of metals","authors":"Clemens Maucher , Yeonse Kang , Stefan Bechler , Matthias Ruf , Holger Steeb , Hans-Christian Möhring , Fabian Hampp","doi":"10.1016/j.addma.2024.104466","DOIUrl":"10.1016/j.addma.2024.104466","url":null,"abstract":"<div><div>Permeable, media transporting, components are an integral part in numerous technical applications. In gas turbines combustors, for example, gaseous oxidizer and fuel are transported separately into the burner, where they are injected and mixed, and subsequently combusted. The mixture homogeneity strongly affects the combustion performance and emissions formation and is, amongst other, determined by the spatial distribution of fuel injection ports. In this context, porous media provide the limiting case for a spatial distribution of media-injecting pores, yet is typically associated with a high pressure drop that yields a loss in efficiency. In this study, possibilities of achieving gas permeability in additively manufactured porous structures are investigated. The objective is to selectively functionalize the permeable layers for gaseous media supply with low pressure loss and, when needed, enable a targeted mixing of different gas streams. For this purpose, a laser-based powder bed fusion process (PBF-LB/M) was used in this study. It offers the opportunity to manufacture varying porosities inside complex monolithic metal parts. To produce the porous structures and to achieve gas permeability, the effect of scan rotation angle, hatch distance, build-up direction and length of the porous specimen is investigated. Due to the high temperatures present in combustion systems, the present work utilizes Inconel 718 material. The AM gas permeable specimen are experimentally characterized by means of surface topography, micro X-ray computed tomography (µXRCT) as well as flow and pressure loss test. The results show, that the AM process parameter provide effective control parameters to adjust the permeability. The strongest effect originates from the hatch distance for a given build-up direction. Depending on the scan rotation, the flow transitions from a turbulent pipe flow to a Darcy flow as present in conventional porous media. A structured alignment and connectivity of pores can be realized as evident in the µXRCT results, surface topography and the flow measurements. Residual powder, powder adhering to the pore walls and stochastic closure of pores or channels lead to deviations and need to be considered when designing respective parts. Nonetheless, the results further show that a directional dependence of the permeability and the build-up direction can be realized and controlled. Consequently, when considering the AM build-strategy in the design of components, this directed permeability can be functionalized in the generation of gas transporting and gas mixing layers separately by adjusting the AM processing parameter.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104466"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vat photopolymerization (VP) based digital light processing (DLP) 3D printing technology gains prominence in biomedical fields, particularly for creating complex tissue structures and aiding in regeneration. Hydrogels, known for their high-water content and biocompatibility, serve as an ideal material used in VP based DLP 3D printing for mimicking biological tissues. The review examines the crucial components of VP based DLP 3D printing of hydrogels in three categories: materials, including monomers and crosslinkers that make up of hydrogels; equipment, featuring various types of VP based DLP 3D printers; and printing parameters, such as light source and exposure time. The application of VP based DLP 3D printed hydrogels at different levels of biomedical field is discussed, providing an overview of the current trends and future possibilities of VP based DLP 3D printing hydrogels in biomedical science.
{"title":"Vat photopolymerization based digital light processing 3D printing hydrogels in biomedical fields: Key parameters and perspective","authors":"Zhe Lu , Weizi Gao , Fukang Liu, Jingjing Cui, Shiwei Feng, Chen Liang, Yunlong Guo, Zhenxiang Wang, Zhijie Mao, Biao Zhang","doi":"10.1016/j.addma.2024.104443","DOIUrl":"10.1016/j.addma.2024.104443","url":null,"abstract":"<div><div>Vat photopolymerization (VP) based digital light processing (DLP) 3D printing technology gains prominence in biomedical fields, particularly for creating complex tissue structures and aiding in regeneration. Hydrogels, known for their high-water content and biocompatibility, serve as an ideal material used in VP based DLP 3D printing for mimicking biological tissues. The review examines the crucial components of VP based DLP 3D printing of hydrogels in three categories: materials, including monomers and crosslinkers that make up of hydrogels; equipment, featuring various types of VP based DLP 3D printers; and printing parameters, such as light source and exposure time. The application of VP based DLP 3D printed hydrogels at different levels of biomedical field is discussed, providing an overview of the current trends and future possibilities of VP based DLP 3D printing hydrogels in biomedical science.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104443"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142328285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104453
Jingxun Wei , Changshu He , Mofan Qie , Yunan Liu , Hao Zhou , Chenxi Kang , Gaowu Qin
The coarse grain size and poor mechanical properties of wire-arc directed energy deposition (DED) magnesium (Mg) alloys have hindered their wider application. In this study, the AZ91 Mg alloy component was fabricated by wire-arc DED assisted by interlayer friction stir processing (IFSP), and the highest strength and elongation were obtained in wire-arc DED AZ91 Mg alloy, which was mainly attributed to grain refinement, fragmentation/dispersion/dissolution of β-Mg17Al12 phase and heterogeneous microstructure in the IFSP stir zone (SZ). The formation of heterogeneous structure is caused by the fact that the refined grains in the SZ of the previous layer are affected by the thermal cycling of the subsequent additive manufacturing process, which led to different degrees of grain growth in different micro-zones within a SZ, and ultimately formed the microstructure characteristics with alternating distribution of coarse and fine grains. Compared with the wire-arc DED samples, the ultimate tensile strength of the wire-arc DED + IFSP samples in the perpendicular and parallel to the building directions increased from 284 and 264 MPa to 315 and 324 MPa, respectively. These values are comparable to those of their wrought counterparts, and the elongation increased by over 50 %. This study thus provides new insights into microstructure modification and performance enhancement of wire-arc DED fabricated Mg-alloys via a novel IFSP technique.
{"title":"Achieving high strength-ductility of AZ91 magnesium alloy via wire-arc directed energy deposition assisted by interlayer friction stir processing","authors":"Jingxun Wei , Changshu He , Mofan Qie , Yunan Liu , Hao Zhou , Chenxi Kang , Gaowu Qin","doi":"10.1016/j.addma.2024.104453","DOIUrl":"10.1016/j.addma.2024.104453","url":null,"abstract":"<div><div>The coarse grain size and poor mechanical properties of wire-arc directed energy deposition (DED) magnesium (Mg) alloys have hindered their wider application. In this study, the AZ91 Mg alloy component was fabricated by wire-arc DED assisted by interlayer friction stir processing (IFSP), and the highest strength and elongation were obtained in wire-arc DED AZ91 Mg alloy, which was mainly attributed to grain refinement, fragmentation/dispersion/dissolution of β-Mg<sub>17</sub>Al<sub>12</sub> phase and heterogeneous microstructure in the IFSP stir zone (SZ). The formation of heterogeneous structure is caused by the fact that the refined grains in the SZ of the previous layer are affected by the thermal cycling of the subsequent additive manufacturing process, which led to different degrees of grain growth in different micro-zones within a SZ, and ultimately formed the microstructure characteristics with alternating distribution of coarse and fine grains. Compared with the wire-arc DED samples, the ultimate tensile strength of the wire-arc DED + IFSP samples in the perpendicular and parallel to the building directions increased from 284 and 264 MPa to 315 and 324 MPa, respectively. These values are comparable to those of their wrought counterparts, and the elongation increased by over 50 %. This study thus provides new insights into microstructure modification and performance enhancement of wire-arc DED fabricated Mg-alloys via a novel IFSP technique.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104453"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142318868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104471
Zhouyang He , Xingbao Qiu , Xilei Bian , Shiwei Wu , Xiaolong Yu , Chenwei Liu , Zhen Hu , Yuefei Jia , Weisen Zheng , Jinqiang Shi , Zhibin Wu , Xiaogang Lu , Yandong Jia , Gang Wang
Eutectic high entropy alloys (EHEAs) have garnered significant attention due to their unique heterogeneous lamella structure, which imparts a desirable strength-ductility combination. Additive manufacturing (AM) techniques further exploit the advantageous properties of EHEAs through efficient fabrication and rapid heating/cooling processes. In this study, we fabricate near-fully dense and crack-free AlCoCrFeNi2.1 EHEA samples with an alternating nano-scale eutectic lamellar structure composed of disordered face-centered cubic (FCC) and ordered B2 phases using the laser directed energy deposition (LDED) method. By using a novel and simple interlayer pause strategy, we have found that the eutectic lamellar structure can be significantly refined, achieving approximately 40% greater refinement compared to the case without interlayer pause. The optimized EHEA exhibits an exceptionally high strength of 1214 MPa and a sufficient uniform elongation of 16.3%, outperforming the non-interlayer-pause counterpart by 14% in strength and 47% in uniform elongation. The superior mechanical properties of the AlCoCrFeNi2.1 EHEA are attributed to the synergistic effects of heterogeneous deformation-induced (HDI) strengthening and strain hardening mechanisms. Furthermore, the refined eutectic lamellar structure can effectively mitigate stress concentration mediated the formation of microcracks, thereby delaying fracture and maintaining plasticity. The interlayer pause strategy presented in this work offers a simple yet effective approach and valuable insights for the preparation of metallic materials with exceptional mechanical properties via LDED process.
{"title":"Laser directed energy deposited eutectic high entropy alloy with tailored lamella structure via interlayer pause strategy","authors":"Zhouyang He , Xingbao Qiu , Xilei Bian , Shiwei Wu , Xiaolong Yu , Chenwei Liu , Zhen Hu , Yuefei Jia , Weisen Zheng , Jinqiang Shi , Zhibin Wu , Xiaogang Lu , Yandong Jia , Gang Wang","doi":"10.1016/j.addma.2024.104471","DOIUrl":"10.1016/j.addma.2024.104471","url":null,"abstract":"<div><div>Eutectic high entropy alloys (EHEAs) have garnered significant attention due to their unique heterogeneous lamella structure, which imparts a desirable strength-ductility combination. Additive manufacturing (AM) techniques further exploit the advantageous properties of EHEAs through efficient fabrication and rapid heating/cooling processes. In this study, we fabricate near-fully dense and crack-free AlCoCrFeNi<sub>2.1</sub> EHEA samples with an alternating nano-scale eutectic lamellar structure composed of disordered face-centered cubic (FCC) and ordered B2 phases using the laser directed energy deposition (LDED) method. By using a novel and simple interlayer pause strategy, we have found that the eutectic lamellar structure can be significantly refined, achieving approximately 40% greater refinement compared to the case without interlayer pause. The optimized EHEA exhibits an exceptionally high strength of 1214 MPa and a sufficient uniform elongation of 16.3%, outperforming the non-interlayer-pause counterpart by 14% in strength and 47% in uniform elongation. The superior mechanical properties of the AlCoCrFeNi<sub>2.1</sub> EHEA are attributed to the synergistic effects of heterogeneous deformation-induced (HDI) strengthening and strain hardening mechanisms. Furthermore, the refined eutectic lamellar structure can effectively mitigate stress concentration mediated the formation of microcracks, thereby delaying fracture and maintaining plasticity. The interlayer pause strategy presented in this work offers a simple yet effective approach and valuable insights for the preparation of metallic materials with exceptional mechanical properties via LDED process.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104471"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104496
Ju Yao, Qiyang Tan, Jeffrey Venezuela, Andrej Atrens, Ming-Xing Zhang
Additive manufacturing (AM) has revolutionised steel part fabrication, yet not all steels are amenable to its unique solidification features, characterised by cyclic and rapid heating/cooling, and directional solidification. These conditions often result in challenges such as columnar grain formation, microstructural heterogeneity, and consequently, inferior mechanical performance, brittleness and severe anisotropy in particular. Recent studies have adopted inoculation or post-fabrication treatments to address this issue, but often entailing extra cost and processing time. This study aims to verify that some steels such as AISI 4340 steel are inherently compatible to AM, producing components that are innately robust and ready for use in the as-built state. The medium carbon content and low alloying element concentration enable AM processing to produce a uniform and refined bainite microstructure with minimal elemental segregation, avoiding the formation of unstable retained austenite. The high AM-processability of this steel is demonstrated by achieving high densification (>99.9 %) across a broad processing window, which allows precise microstructural control via proper tunning the processing parameter modifications, inducing a transition from upper bainite to lower bainite dominance, to tailor mechanical properties for specific applications. The as AM-fabricated AISI 4340 steel exhibits a good combination of strength, ductility, and toughness, manifested by a yield strength range from 1240 to 1370 MPa, an ultimate tensile strength from 1360 to 1740 MPa, an elongation from 7 % to 14 %, and an impact toughness range of 11–44 J. The mechanical properties of the AM-fabricated 4340 steel are comparable to those of the wrought counterpart and superior to the majority of other AM-fabricated steels. This research reveals the high potential of AM to process high-strength low-alloy steels.
增材制造（AM）为钢部件制造带来了革命性的变化，但并非所有钢材都能适应其独特的凝固特性，其特点是循环快速加热/冷却和定向凝固。这些条件通常会导致柱状晶粒形成、微观结构异质性等挑战，从而导致机械性能下降、脆性增加，尤其是严重的各向异性。最近的研究采用接种或制造后处理来解决这一问题，但往往需要额外的成本和加工时间。本研究旨在验证某些钢材（如 AISI 4340 钢）与 AM 的内在兼容性，生产出的部件天生坚固耐用，可在竣工状态下使用。中碳含量和低合金元素浓度使 AM 加工能够产生均匀、细化的贝氏体微观结构，元素偏析最小，避免形成不稳定的残余奥氏体。这种钢在宽广的加工窗口内实现了高致密化（99.9%），从而证明了 AM 加工的高可用性，通过适当调整加工参数，可以精确控制微观结构，实现从上贝氏体为主到下贝氏体为主的转变，为特定应用定制机械性能。AM 制造的 AISI 4340 钢具有良好的强度、延展性和韧性组合，屈服强度范围为 1240 至 1370 兆帕，极限抗拉强度范围为 1360 至 1740 兆帕，伸长率范围为 7 % 至 14 %，冲击韧性范围为 11-44 J。AM 制造的 4340 钢的机械性能与锻造钢相当，优于大多数其他 AM 制造钢。这项研究揭示了 AM 在加工高强度低合金钢方面的巨大潜力。
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Pub Date : 2024-08-25DOI: 10.1016/j.addma.2024.104505
Chenxi Tian , Jenniffer Bustillos , Akane Wakai , Ashlee Gabourel , Samuel J. Clark , Kamel Fezzaa , Atieh Moridi
Porous metals find extensive applications in soundproofing, filtration, catalysis, and energy-absorbing structures, thanks to their unique internal pore structure and high specific strength. In recent years, there has been an increasing interest in fabricating porous metals using additive manufacturing (AM), leveraging its unique advantages, including improved design freedom, spatial material control, and cost-effective small-batch production. In this study, we conducted pioneering operando visualization of AM porous metal using a laser powder bed fusion (L-PBF) setup combined with a high-speed synchrotron x-ray imaging system. Single track printing experiments using Ti6Al4V (Ti64) combined with titanium hydride (TiH2) and sodium carbonate (Na2CO3) as foaming agents, with varying mixing ratios were performed under different processing conditions. The results elucidate the dynamic development of porosity formation. The average pore size is significantly influenced by the particle size of foaming agents when pore coalescence is absent. For all foaming agent content tested in the current study, the number of pores is found to be more sensitive to changes in laser power than in laser scanning speed. Increasing linear energy density (increasing laser power or reducing laser scanning speed) promotes the foaming agent activation thereby porosity formation. However, high linear energy density skews pore distribution towards the surface despite forming deeper melt pools. In addition, the impact of additional factors including foaming agent’s laser absorptivity and decomposition kinetics with respect to AM time scales should be carefully considered to avoid ineffective activation of foaming agents during the AM of porous metals.
多孔金属凭借其独特的内部孔隙结构和高比强度，在隔音、过滤、催化和吸能结构等领域得到广泛应用。近年来，人们对利用增材制造（AM）制造多孔金属的兴趣与日俱增，因为它具有设计自由度高、空间材料可控、小批量生产成本低等独特优势。在本研究中，我们利用激光粉末床熔融（L-PBF）装置结合高速同步辐射 X 射线成像系统，对 AM 多孔金属进行了开创性的可视化操作。在不同的加工条件下，使用 Ti6Al4V (Ti64)，结合氢化钛 (TiH2) 和碳酸钠 (Na2CO3) 作为发泡剂，以不同的混合比例进行了单轨打印实验。结果阐明了孔隙形成的动态发展过程。在没有孔隙凝聚的情况下，平均孔隙大小受发泡剂颗粒大小的影响很大。对于当前研究中测试的所有发泡剂含量，孔隙数量对激光功率变化的敏感性高于激光扫描速度的变化。增加线性能量密度（增加激光功率或降低激光扫描速度）可促进发泡剂的活化，从而促进孔隙的形成。然而，高线性能量密度会使孔隙分布偏向表面，尽管会形成更深的熔池。此外，还应仔细考虑发泡剂的激光吸收率和分解动力学等其他因素对 AM 时间尺度的影响，以避免在多孔金属的 AM 过程中发泡剂无法有效激活。
{"title":"Operando visualization of porous metal additive manufacturing with foaming agents through high-speed x-ray imaging","authors":"Chenxi Tian , Jenniffer Bustillos , Akane Wakai , Ashlee Gabourel , Samuel J. Clark , Kamel Fezzaa , Atieh Moridi","doi":"10.1016/j.addma.2024.104505","DOIUrl":"10.1016/j.addma.2024.104505","url":null,"abstract":"<div><div>Porous metals find extensive applications in soundproofing, filtration, catalysis, and energy-absorbing structures, thanks to their unique internal pore structure and high specific strength. In recent years, there has been an increasing interest in fabricating porous metals using additive manufacturing (AM), leveraging its unique advantages, including improved design freedom, spatial material control, and cost-effective small-batch production. In this study, we conducted pioneering operando visualization of AM porous metal using a laser powder bed fusion (L-PBF) setup combined with a high-speed synchrotron x-ray imaging system. Single track printing experiments using Ti6Al4V (Ti64) combined with titanium hydride (TiH<sub>2</sub>) and sodium carbonate (Na<sub>2</sub>CO<sub>3</sub>) as foaming agents, with varying mixing ratios were performed under different processing conditions. The results elucidate the dynamic development of porosity formation. The average pore size is significantly influenced by the particle size of foaming agents when pore coalescence is absent. For all foaming agent content tested in the current study, the number of pores is found to be more sensitive to changes in laser power than in laser scanning speed. Increasing linear energy density (increasing laser power or reducing laser scanning speed) promotes the foaming agent activation thereby porosity formation. However, high linear energy density skews pore distribution towards the surface despite forming deeper melt pools. In addition, the impact of additional factors including foaming agent’s laser absorptivity and decomposition kinetics with respect to AM time scales should be carefully considered to avoid ineffective activation of foaming agents during the AM of porous metals.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104505"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533991","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Support-free slicing technology plays a critical role in additive manufacturing by reducing costs and simplifying post-processing. However, due to the complexity of geometric features, existing support-free slicing strategies often lack the necessary universality in industry. This paper proposes a method library comprising six basic support-free slicing methods to enhance the applicability and computational efficiency. The general methods in the library include facet-based methods and voxel-based methods, the former facilitates rapid slicing, while the latter enables the re-decomposition of complex structural parts. For parts that cannot be covered by general methods, customized methods are developed. These include constructing a support bridge for multi-direction slicing of overhanging regions in an arch model and extracting the optimal central axis for internal channels to achieve precise channel decomposition. Additionally, the methods in the library can be flexibly combined. By recognizing surface features and incorporating manual intervention, models can be decomposed into multiple sub-models, with the most computationally efficient method is matched to each sub-model. The layers and tool-paths of each sub-model are generated by the optimal method. Four typical models are deposited without any support in a five-axis printer to verify the feasibility of the proposed methods.
{"title":"A comprehensive support-free slicing method library for variable posture additive manufacturing","authors":"Zhengren Tong , Xiaoling Yu , Chen Yang , Hongyao Shen","doi":"10.1016/j.addma.2024.104508","DOIUrl":"10.1016/j.addma.2024.104508","url":null,"abstract":"<div><div>Support-free slicing technology plays a critical role in additive manufacturing by reducing costs and simplifying post-processing. However, due to the complexity of geometric features, existing support-free slicing strategies often lack the necessary universality in industry. This paper proposes a method library comprising six basic support-free slicing methods to enhance the applicability and computational efficiency. The general methods in the library include facet-based methods and voxel-based methods, the former facilitates rapid slicing, while the latter enables the re-decomposition of complex structural parts. For parts that cannot be covered by general methods, customized methods are developed. These include constructing a support bridge for multi-direction slicing of overhanging regions in an arch model and extracting the optimal central axis for internal channels to achieve precise channel decomposition. Additionally, the methods in the library can be flexibly combined. By recognizing surface features and incorporating manual intervention, models can be decomposed into multiple sub-models, with the most computationally efficient method is matched to each sub-model. The layers and tool-paths of each sub-model are generated by the optimal method. Four typical models are deposited without any support in a five-axis printer to verify the feasibility of the proposed methods.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"94 ","pages":"Article 104508"},"PeriodicalIF":10.3,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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