The Experts below are selected from a list of 12411 Experts worldwide ranked by ideXlab platform
Moataz M Attallah - One of the best experts on this subject based on the ideXlab platform.
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Mesoscale modelling of selective Laser melting: Thermal fluid dynamics and microstructural evolution
Computational Materials Science, 2017Co-Authors: C. Panwisawas, Magnus J. Anderson, Richard P. Turner, Jeffery W. Brooks, Y. Sovani, Chunlei Qiu, Moataz M Attallah, H. C. BasoaltoAbstract:In this paper, an integrated computational materials science approach for selective Laser melting (SLM) at the mesoscale is presented. A particle dropping model was developed to simulate the representative powder-bed particle distribution of a measured titanium alloy powder. Thermal fluid flow and resulting microstructural evolution of a set of Laser scanned single tracks with different powder layer thicknesses and Scanning Speeds during SLM were also studied using both computational and experimental approaches. The simulated powder particle distribution was found to be consistent with experimental measurement. The thermal fluid flow model predicts that single Laser scanned tracks become increasingly irregular-shaped with increased powder layer thickness and increased Laser Scanning Speed. These findings were reinforced by Scanning electron microscopy analysis. The more dispersed dissipation of the localised heat for thicker powder layers is understood to cause increased melting and evaporation. This can lead to increased Marangoni force and recoil pressure which in turn destabilises the melt flow. The use of an argon atmosphere Speeds up the solidification process when compared with air but does not affect the morphology of single tracks significantly. The predicted microstructure was consistent with the electron backscattered diffraction data. The microstructure-based modelling methodology considering the representative powder size distribution provides a good predictive capability for the Laser-powder interaction behaviour, surface structure and porosity development.
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a new approach to develop palladium modified ti based alloys for biomedical applications
Materials & Design, 2016Co-Authors: Andrew Fones, Nicholas J E Adkins, Hugh Gavin Charles Hamilton, Moataz M AttallahAbstract:Abstract A new powder mixing/coating technique combined with selective Laser melting (SLM) or hot isostatic pressing has been used to modify Ti-6Al-4V (Ti64) with Pd with the aim of further improving its corrosion resistance. The modified alloy samples were characterised in terms of porosity, surface structure, microstructure and composition using optical microscopy (OM), Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and electron microprobe analysis (EPMA). Their corrosion properties were evaluated via electrochemical tests and the mechanical properties measured via tensile tests. Using a new physical powder mixing technique, Pd was homogeneously distributed among the base Ti alloy powder particles without damaging their sphericity. After HIPing Pd is mainly located at grain boundaries while during SLM Pd has dissolved into the matrix. The porosity in the as-SLMed samples and surface roughness both increase continuously with increased Laser Scanning Speed. Pd did not cause significant improvement in tensile properties but did enhance corrosion resistance in 2 M HCl by shifting the corrosion potential into the passive region of Ti64. The current work suggested that the new approach is a feasible route of synthesising modified alloys with both chemical and microstructural homogeneity as well as improved performance for biomedical application.
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influence of processing conditions on strut structure and compressive properties of cellular lattice structures fabricated by selective Laser melting
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Chunlei Qiu, Mark Ward, Sheng Yue, P D Lee, Nicholas J E Adkins, Hany Hassanin, P J Withers, Moataz M AttallahAbstract:Abstract AlSi10Mg cellular lattice structures have been fabricated by selective Laser melting (SLM) using a range of Laser Scanning Speeds and powers. The as-fabricated strut size, morphology and internal porosity were investigated using optical microscopy (OM), Scanning electron microscopy (SEM) and X-ray microtomography (micro-CT) and correlated to the compressive properties of the structure. Strut diameter was found to increase monotonically with Laser power while the porosity was largest at intermediate powers. Laser Scanning Speed was found to thicken the struts only at slow rates while the porosity was largest at intermediate Speeds. High Speed imaging showed the melt pool to be larger at high Laser powers. Further the melt pool shape was found to vary cyclically over time, steadily growing before becoming increasingly instable and irregularly shaped before abruptly falling in size due to splashing of molten materials and the process repeating. Upon compressive loading, lattice deformation was homogeneous prior to the peak stress before falling sharply due to the creation of a (one strut wide) shear band at around 45° to the compression axis. The specific yield strength expressed as the yield stress/(yield stress of the aluminium × relative density) is not independent of processing conditions, suggesting that further improvements in properties can be achieved by process optimisation. Lattice struts failed near nodes by a mixture of ductile and brittle fracture.
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influence of processing conditions on strut structure and compressive properties of cellular lattice structures fabricated by selective Laser melting
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Chunlei Qiu, Mark Ward, Sheng Yue, P D Lee, Nicholas J E Adkins, Hany Hassanin, P J Withers, Moataz M AttallahAbstract:Abstract AlSi10Mg cellular lattice structures have been fabricated by selective Laser melting (SLM) using a range of Laser Scanning Speeds and powers. The as-fabricated strut size, morphology and internal porosity were investigated using optical microscopy (OM), Scanning electron microscopy (SEM) and X-ray microtomography (micro-CT) and correlated to the compressive properties of the structure. Strut diameter was found to increase monotonically with Laser power while the porosity was largest at intermediate powers. Laser Scanning Speed was found to thicken the struts only at slow rates while the porosity was largest at intermediate Speeds. High Speed imaging showed the melt pool to be larger at high Laser powers. Further the melt pool shape was found to vary cyclically over time, steadily growing before becoming increasingly instable and irregularly shaped before abruptly falling in size due to splashing of molten materials and the process repeating. Upon compressive loading, lattice deformation was homogeneous prior to the peak stress before falling sharply due to the creation of a (one strut wide) shear band at around 45° to the compression axis. The specific yield strength expressed as the yield stress/(yield stress of the aluminium × relative density) is not independent of processing conditions, suggesting that further improvements in properties can be achieved by process optimisation. Lattice struts failed near nodes by a mixture of ductile and brittle fracture.
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On the role of melt flow into the surface structure and porosity development during selective Laser melting
Acta Materialia, 2015Co-Authors: Chunlei Qiu, Mark Ward, Jeffery W. Brooks, C. Panwisawas, H. C. Basoalto, Moataz M AttallahAbstract:In this study, the development of surface structure and porosity of Ti-6Al-4V samples fabricated by selective Laser melting under different Laser Scanning Speeds and powder layer thicknesses has been studied and correlated with the melt flow behaviour through both experimental and modelling approaches. The as-fabricated samples were investigated using optical microscopy (OM) and Scanning electron microscopy (SEM). The interaction between Laser beam and powder particles was studied by both high Speed imaging observation and computational fluid dynamics (CFD) calculation. It was found that at a high Laser power and a fixed powder layer thickness (20 μm), the samples contain particularly low porosity when the Laser Scanning Speeds are below 2700 mm/s. Further increase of Scanning Speed led to increase of porosity but not significantly. The porosity is even more sensitive to powder layer thickness with the use of thick powder layers (above 40 μm) leading to significant porosity. The increase of porosity with Laser Scanning Speed and powder layer thickness is not inconsistent with the observed increase in surface roughness complicated by increasingly irregular-shaped Laser scanned tracks and an increased number of discontinuity and cave-like pores on the top surfaces. The formation of pores and development of rough surfaces were found by both high Speed imaging and modelling, to be strongly associated with unstable melt flow and splashing of molten material.
Christian Coddet - One of the best experts on this subject based on the ideXlab platform.
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selective Laser melting of elemental powder blends for fabrication of homogeneous bulk material of near eutectic ni sn composition
Additive manufacturing, 2020Co-Authors: Han Lin Liao, Rijie Zhao, Nouredine Fenineche, Christian CoddetAbstract:Abstract Cubic specimens of near-eutectic Ni‒Sn composition were built by selective Laser melting of elemental powder blends and annealed. Microstructure of the specimens before and after annealing was investigated. Cracks and pores were present in all specimens due to thermal stresses and insufficient melting. Despite such defects, specimens built at low Laser power and low Laser Scanning Speed showed improved bulk chemical homogeneity compared to those built at high power and high Speeds. Microscopic studies showed that a dendritic structure was formed in specimens of hypoeutectic Ni83Sn17 composition, whereas a banded structure was formed in specimens of eutectic Ni81.3Sn18.7 and hypereutectic Ni80Sn20 composition. After annealing, these structures were converted into a similar anomalous eutectic-like structure. While the formation of the banded structure was attributed to a high liquid undercooling during selective Laser melting, the annealing effect was explained by assuming supersaturation of solute atoms in phase constituents. It is concluded that selective Laser melting of elemental powder blends followed by post annealing is a promising way of producing a two-phase bulk material of near-eutectic composition.
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In-situ synthesis of aluminum/nano-quasicrystalline Al-Fe-Cr composite by using selective Laser melting
Composites Part B: Engineering, 2018Co-Authors: N. Kang, M. El Mansori, X. Lin, F. Guittonneau, H.l. Liao, W.d. Huang, Christian CoddetAbstract:In this research, Al-Fe-Cr quasicrystal (QC) reinforced Al-based metal matrix composites were in-situ manufactured by using selective Laser melting (SLM) from the powder mixture. The parametrical optimization based on our previous work was performed with focus on Laser Scanning Speed. From the optimized parameters, an almost dense (99.7%) free-crack sample was fabricated with an ultra-fine microstructure. A phase transition from decagonal QC Al65Cu25Fe10Cr5 to icosahedral QC Al91Fe4Cr5 could be observed as Laser Scanning Speed decreases. Differential Scanning calorimetry curves show that the QC phase is quiet stable until 500 °C. And then, the effects of annealing temperature on the microstructural and mechanical properties were determined. The results indicate that the recrystallization and growth behavior of α-Al grains could be prevented by QC particle during annealing. Furthermore, the growth of QC particle, which tends to form a porous structure, leads an improvement of Young modulus and decline of ductility.
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microstructure and strength analysis of eutectic al si alloy in situ manufactured using selective Laser melting from elemental powder mixture
Journal of Alloys and Compounds, 2017Co-Authors: Nan Kang, Han Lin Liao, Lucas Dembinski, Pierre Coddet, Christian CoddetAbstract:Abstract In this study, dense eutectic Al-Si alloys (about 99%) were in-situ fabricated using selective Laser melting (SLM) from the powder mixture of Al and Si under argon environment. Compared with the sample obtained from pre-alloyed powder feedstock, a dense eutectic Al-Si alloy manufactured using SLM from powder mixtures needs higher input energy density. The effects of process parameters on microstructure and mechanical properties are investigated with particular emphasis on understanding the in-situ reaction during the SLM process. The microstructural analysis shows that the SLM processed samples present an ultrafine microstructure consisting of supersaturated Al-rich α-Al cellular and nano-sized Si particles. The distribution and morphology of nano-sized Si particles are significantly influenced by Laser Scanning Speed and Laser power respectively. The in-situ fabricated eutectic Al-Si alloy present a lower ultimate tensile strength and higher ductility than the sample fabricated from pre-alloyed powder. Moreover, both tensile strength and ductility of SLM processed eutectic Al-Si alloys decrease as the Laser Scanning Speed increases.
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fabrication of nicr alloy parts by selective Laser melting columnar microstructure and anisotropic mechanical behavior
Materials & Design, 2014Co-Authors: Bo Song, Han Lin Liao, Pierre Coddet, Shujuan Dong, Christian CoddetAbstract:Abstract NiCr alloy, because of its wide applications in electrical elements and dental field was widely studied in the past. In this work, NiCr cubes and tensile specimens were fabricated by using a new processing technique-selective Laser melting (SLM). Microstructural and mechanical behavior characterization of SLM-processed NiCr components was performed. An unusual columnar microstructural architecture composed of 〈1 0 0〉 texture (corresponding to (2 0 0) plane) oriented the building direction was observed. Moreover, it was found that the columnar grain growth across the melt pools occurred during the SLM process and the growth trend became stronger with the decrease of the Laser Scanning Speed. Associated with the microstructural characteristic, an anisotropic mechanical behavior at different reference planes (i.e., at the horizontal and vertical surfaces) was demonstrated for the samples fabricated using different processing parameters. The results showed that with increasing the Laser Scanning Speed, the microhardness at the horizontal surface decreased, while at the vertical surface it increased; an increase of the yield strength (YS) and the ultimate tensile strength (UTS) was observed.
Shengfeng Zhou - One of the best experts on this subject based on the ideXlab platform.
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enhanced corrosion and wear resistance properties of carbon fiber reinforced ni based composite coating by Laser cladding
Surface & Coatings Technology, 2018Co-Authors: Jianbo Lei, Shengfeng Zhou, Chuan Shi, Laichang ZhangAbstract:Abstract To enhance the wear resistance and corrosion resistance of Ni-based coatings, carbon fibers reinforced nickel-based composite coatings (CFs/Ni) were fabricated on the surface of 1Cr13 stainless steel by Laser cladding (LC). The microstructure characteristics, microhardness, wear and corrosion performances of the composite coatings were investigated. The results show that CFs can effectively improve the corrosion and wear resistances of Ni-based coatings. With increasing Laser Scanning Speed, the morphology of CFs in composite coatings is more integral and the corrosion and wear resistances of the composite coatings are improved. Especially, when Laser Scanning Speed is increased to 8 mm/s, the average microhardness of the composite coating reaches up to 405 HV0.2, which is about 1.3 times higher than that of Ni-based coating. Moreover, the corrosion current density and the wear rate of the composite coating are only 7% and 55% of those of the Ni-based coating, respectively, which is attributed to the good properties and homogeneous distribution of CFs and finer microstructure of composite coating.
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microstructure and wear resistance of fe based wc coating by multi track overlapping Laser induction hybrid rapid cladding
Optics and Laser Technology, 2012Co-Authors: Shengfeng Zhou, Xiaoqin Dai, Haizhong ZhengAbstract:Abstract The carck-free Fe-based +20 wt% WC coating with large area was produced by mutli-track overlapping Laser induction hybrid rapid cladding. The results showed that the maximum Laser Scanning Speed and the maximum feeding rate of powder can be increased to 3500 mm/min and 120 g/min, respectively. The cast WC particles were dissolved almost completely and had a worse wettability with Fe-based metal matrix. The precipitated carbides such as M 12 C and M 23 C 6 (M=Fe, W, Cr) formed an intergranular network around the primary Fe-based phase enriched with tungsten. The microhardness of coating decreased first, and then increased slightly with an increase in the track. The first track had the highest microhardness (i.e. 870HV 0.2 ). Moreover, the wear weight of coating approximately had a linear relationship with the sliding distance, and increased with an increase in the sliding Speed. The wear rate approximately remained constant with an increase in the sliding distance and was two times lower than that of the hardened steel AISI 1045 with a hardness of 60HRC. The wear mechanism during the dry sliding wear was a combination of oxidation wear and abrasion wear.
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analysis of crack behavior for ni based wc composite coatings by Laser cladding and crack free realization
Applied Surface Science, 2008Co-Authors: Shengfeng Zhou, Xiaoyan Zeng, Yongjun HuangAbstract:Abstract The crack behavior of Ni-based WC composite coatings by Laser cladding was investigated. The results showed that cracks originated from the interface of the composite coating and the substrate, and then passed through the precipitated carbides due to the dissolution of WC particles. To increase the efficiency of Laser cladding and eliminate the well-known crack problems in the composite coatings, Laser induction hybrid rapid cladding (LIHRC) was carried out experiments to produce Ni-based WC composite coatings on A3 mild steel. The Laser Scanning Speed and the powder flow rate increased with the increasing of the preheated average temperature of the substrate during LIHRC. The dissolution of WC particles decreased due to high Laser Scanning Speed, contributing to reduce the porosities in the composite coatings. Moreover, the temperature gradient decreased with the increasing of the preheated average temperature of the substrate during LIHRC, which was the main reason why Ni-based WC composite coatings were free of cracks.
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microstructure characteristics of ni based wc composite coatings by Laser induction hybrid rapid cladding
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Shengfeng Zhou, Yongjun Huang, Xiaoyan ZengAbstract:Abstract To avoid low cladding rate and cracks of cladding layer, Laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite coatings at the different Laser Scanning Speed were investigated. For low Laser Scanning Speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W2C + Fe3W3C carbides, and bar-like (W, Cr, Ni)23C6 carbides were formed. With increasing Laser Scanning Speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W2C + FeW3C + W6C2.54 carbides. With further increasing Laser Scanning Speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W2C + W6C2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of Laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.
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a study of ni based wc composite coatings by Laser induction hybrid rapid cladding with elliptical spot
Applied Surface Science, 2008Co-Authors: Shengfeng Zhou, Yongjun Huang, Xiaoyan ZengAbstract:Abstract Ni-based WC composite coatings by Laser induction hybrid rapid cladding (LIHRC) with elliptical spot were investigated. Results indicate that the efficiency using the elliptical spot of 6 mm × 4 mm (the major and minor axis of Laser beam are 6 mm and 4 mm, respectively, the major axis is parallel to the direction of Laser Scanning) is higher than that using the elliptical spot of 4 mm × 6 mm (the major axis is perpendicular to the direction of Laser Scanning). The precipitated carbides with the blocky and bar-like shape indicate that WC particles suffer from the heat damage of “the disintegration pattern + the growth pattern”, whichever elliptical spot is used at low Laser Scanning Speed. However, at high Laser Scanning Speed, the blocky carbides are only formed if the elliptical spot of 6 mm × 4 mm is adopted, showing that WC particles present the heat damage of “the disintegration pattern”, whereas the fine carbides are precipitated when the elliptical spot of 4 mm × 6 mm is used, showing that WC particles take on the heat damage of “the radiation pattern”. Especially, the efficiency of LIHRC is increased much four times higher than that of the general Laser cladding and crack-free ceramic-metal coatings can be obtained.
Xiaoyan Zeng - One of the best experts on this subject based on the ideXlab platform.
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analysis of crack behavior for ni based wc composite coatings by Laser cladding and crack free realization
Applied Surface Science, 2008Co-Authors: Shengfeng Zhou, Xiaoyan Zeng, Yongjun HuangAbstract:Abstract The crack behavior of Ni-based WC composite coatings by Laser cladding was investigated. The results showed that cracks originated from the interface of the composite coating and the substrate, and then passed through the precipitated carbides due to the dissolution of WC particles. To increase the efficiency of Laser cladding and eliminate the well-known crack problems in the composite coatings, Laser induction hybrid rapid cladding (LIHRC) was carried out experiments to produce Ni-based WC composite coatings on A3 mild steel. The Laser Scanning Speed and the powder flow rate increased with the increasing of the preheated average temperature of the substrate during LIHRC. The dissolution of WC particles decreased due to high Laser Scanning Speed, contributing to reduce the porosities in the composite coatings. Moreover, the temperature gradient decreased with the increasing of the preheated average temperature of the substrate during LIHRC, which was the main reason why Ni-based WC composite coatings were free of cracks.
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microstructure characteristics of ni based wc composite coatings by Laser induction hybrid rapid cladding
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Shengfeng Zhou, Yongjun Huang, Xiaoyan ZengAbstract:Abstract To avoid low cladding rate and cracks of cladding layer, Laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite coatings at the different Laser Scanning Speed were investigated. For low Laser Scanning Speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W2C + Fe3W3C carbides, and bar-like (W, Cr, Ni)23C6 carbides were formed. With increasing Laser Scanning Speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W2C + FeW3C + W6C2.54 carbides. With further increasing Laser Scanning Speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W2C + W6C2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of Laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.
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a study of ni based wc composite coatings by Laser induction hybrid rapid cladding with elliptical spot
Applied Surface Science, 2008Co-Authors: Shengfeng Zhou, Yongjun Huang, Xiaoyan ZengAbstract:Abstract Ni-based WC composite coatings by Laser induction hybrid rapid cladding (LIHRC) with elliptical spot were investigated. Results indicate that the efficiency using the elliptical spot of 6 mm × 4 mm (the major and minor axis of Laser beam are 6 mm and 4 mm, respectively, the major axis is parallel to the direction of Laser Scanning) is higher than that using the elliptical spot of 4 mm × 6 mm (the major axis is perpendicular to the direction of Laser Scanning). The precipitated carbides with the blocky and bar-like shape indicate that WC particles suffer from the heat damage of “the disintegration pattern + the growth pattern”, whichever elliptical spot is used at low Laser Scanning Speed. However, at high Laser Scanning Speed, the blocky carbides are only formed if the elliptical spot of 6 mm × 4 mm is adopted, showing that WC particles present the heat damage of “the disintegration pattern”, whereas the fine carbides are precipitated when the elliptical spot of 4 mm × 6 mm is used, showing that WC particles take on the heat damage of “the radiation pattern”. Especially, the efficiency of LIHRC is increased much four times higher than that of the general Laser cladding and crack-free ceramic-metal coatings can be obtained.
Chunlei Qiu - One of the best experts on this subject based on the ideXlab platform.
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Mesoscale modelling of selective Laser melting: Thermal fluid dynamics and microstructural evolution
Computational Materials Science, 2017Co-Authors: C. Panwisawas, Magnus J. Anderson, Richard P. Turner, Jeffery W. Brooks, Y. Sovani, Chunlei Qiu, Moataz M Attallah, H. C. BasoaltoAbstract:In this paper, an integrated computational materials science approach for selective Laser melting (SLM) at the mesoscale is presented. A particle dropping model was developed to simulate the representative powder-bed particle distribution of a measured titanium alloy powder. Thermal fluid flow and resulting microstructural evolution of a set of Laser scanned single tracks with different powder layer thicknesses and Scanning Speeds during SLM were also studied using both computational and experimental approaches. The simulated powder particle distribution was found to be consistent with experimental measurement. The thermal fluid flow model predicts that single Laser scanned tracks become increasingly irregular-shaped with increased powder layer thickness and increased Laser Scanning Speed. These findings were reinforced by Scanning electron microscopy analysis. The more dispersed dissipation of the localised heat for thicker powder layers is understood to cause increased melting and evaporation. This can lead to increased Marangoni force and recoil pressure which in turn destabilises the melt flow. The use of an argon atmosphere Speeds up the solidification process when compared with air but does not affect the morphology of single tracks significantly. The predicted microstructure was consistent with the electron backscattered diffraction data. The microstructure-based modelling methodology considering the representative powder size distribution provides a good predictive capability for the Laser-powder interaction behaviour, surface structure and porosity development.
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influence of processing conditions on strut structure and compressive properties of cellular lattice structures fabricated by selective Laser melting
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Chunlei Qiu, Mark Ward, Sheng Yue, P D Lee, Nicholas J E Adkins, Hany Hassanin, P J Withers, Moataz M AttallahAbstract:Abstract AlSi10Mg cellular lattice structures have been fabricated by selective Laser melting (SLM) using a range of Laser Scanning Speeds and powers. The as-fabricated strut size, morphology and internal porosity were investigated using optical microscopy (OM), Scanning electron microscopy (SEM) and X-ray microtomography (micro-CT) and correlated to the compressive properties of the structure. Strut diameter was found to increase monotonically with Laser power while the porosity was largest at intermediate powers. Laser Scanning Speed was found to thicken the struts only at slow rates while the porosity was largest at intermediate Speeds. High Speed imaging showed the melt pool to be larger at high Laser powers. Further the melt pool shape was found to vary cyclically over time, steadily growing before becoming increasingly instable and irregularly shaped before abruptly falling in size due to splashing of molten materials and the process repeating. Upon compressive loading, lattice deformation was homogeneous prior to the peak stress before falling sharply due to the creation of a (one strut wide) shear band at around 45° to the compression axis. The specific yield strength expressed as the yield stress/(yield stress of the aluminium × relative density) is not independent of processing conditions, suggesting that further improvements in properties can be achieved by process optimisation. Lattice struts failed near nodes by a mixture of ductile and brittle fracture.
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influence of processing conditions on strut structure and compressive properties of cellular lattice structures fabricated by selective Laser melting
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Chunlei Qiu, Mark Ward, Sheng Yue, P D Lee, Nicholas J E Adkins, Hany Hassanin, P J Withers, Moataz M AttallahAbstract:Abstract AlSi10Mg cellular lattice structures have been fabricated by selective Laser melting (SLM) using a range of Laser Scanning Speeds and powers. The as-fabricated strut size, morphology and internal porosity were investigated using optical microscopy (OM), Scanning electron microscopy (SEM) and X-ray microtomography (micro-CT) and correlated to the compressive properties of the structure. Strut diameter was found to increase monotonically with Laser power while the porosity was largest at intermediate powers. Laser Scanning Speed was found to thicken the struts only at slow rates while the porosity was largest at intermediate Speeds. High Speed imaging showed the melt pool to be larger at high Laser powers. Further the melt pool shape was found to vary cyclically over time, steadily growing before becoming increasingly instable and irregularly shaped before abruptly falling in size due to splashing of molten materials and the process repeating. Upon compressive loading, lattice deformation was homogeneous prior to the peak stress before falling sharply due to the creation of a (one strut wide) shear band at around 45° to the compression axis. The specific yield strength expressed as the yield stress/(yield stress of the aluminium × relative density) is not independent of processing conditions, suggesting that further improvements in properties can be achieved by process optimisation. Lattice struts failed near nodes by a mixture of ductile and brittle fracture.
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On the role of melt flow into the surface structure and porosity development during selective Laser melting
Acta Materialia, 2015Co-Authors: Chunlei Qiu, Mark Ward, Jeffery W. Brooks, C. Panwisawas, H. C. Basoalto, Moataz M AttallahAbstract:In this study, the development of surface structure and porosity of Ti-6Al-4V samples fabricated by selective Laser melting under different Laser Scanning Speeds and powder layer thicknesses has been studied and correlated with the melt flow behaviour through both experimental and modelling approaches. The as-fabricated samples were investigated using optical microscopy (OM) and Scanning electron microscopy (SEM). The interaction between Laser beam and powder particles was studied by both high Speed imaging observation and computational fluid dynamics (CFD) calculation. It was found that at a high Laser power and a fixed powder layer thickness (20 μm), the samples contain particularly low porosity when the Laser Scanning Speeds are below 2700 mm/s. Further increase of Scanning Speed led to increase of porosity but not significantly. The porosity is even more sensitive to powder layer thickness with the use of thick powder layers (above 40 μm) leading to significant porosity. The increase of porosity with Laser Scanning Speed and powder layer thickness is not inconsistent with the observed increase in surface roughness complicated by increasingly irregular-shaped Laser scanned tracks and an increased number of discontinuity and cave-like pores on the top surfaces. The formation of pores and development of rough surfaces were found by both high Speed imaging and modelling, to be strongly associated with unstable melt flow and splashing of molten material.
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microstructure and tensile properties of selectively Laser melted and of hiped Laser melted ti 6al 4v
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Chunlei Qiu, Nicholas J E Adkins, Moataz M AttallahAbstract:Abstract Ti–6Al–4V samples have been prepared by selective Laser melting (SLM) with varied processing conditions. Some of the samples were stress-relieved or hot isostatically pressed (HIPed). The microstructures of all samples were characterised using optical microscopy (OM), Scanning electron microscopy (SEM) and X-ray diffraction (XRD) and the tensile properties measured before and after HIPing. It was found that the porosity level generally decreased with increase of Laser power and Laser Scanning Speed. Horizontally built samples were found to have a higher level of porosity than vertically built samples. The as-fabricated microstructure was dominated by columnar grains and martensites. HIPing closed the majority of the pores and also fully transformed the martensite into α and β phases. The as-fabricated microstructure exhibits very high tensile strengths but poor ductility with elongation generally smaller than 10%. The horizontally built samples show even lower elongation than vertically built samples. HIPing considerably improved ductility but led to a reduction in strength. With HIPing, the SLMed samples were found to show tensile properties comparable with those thermomechanically processed and annealed samples.
