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Effect of Trace Addition of Ceramic on Microstructure Development and Mechanical Properties of Selective Laser Melted AlSi10Mg Alloy

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Chinese Journal of Mechanical Engineering 2020年第2期33卷 56-68页

作者： Yuxin Li dongdong gu Han Zhang Lixia Xi College of Materials Science and Technology Nanjing University of Aeronautics and AstronauticsNanjing 211106China

Selective laser melting(SLM)is an emerging additive manufacturing technology for fabricating aluminum alloys and aluminum matrix ***,it remains unclear how to improve the properties of laser manufactured aluminum alloy by adding ceramic reinforcing *** the effect of trace addition of TiB2 ceramic(1%weight fraction)on microstructural and mechanical properties of SLM-produced AlSi10Mg composite parts was *** densification level increased with increasing laser power and decreasing scan speed.A near fully dense composite part(99.37%)with smooth surface morphology and elevated inter-layer bonding was successfully obtained.A decrease of lattice plane distance was identified by X-ray diffraction with the laser scan speed decreased,which implied that the crystal lattices were distorted due to the dissolution of Si and TiB2 particles.A homogeneous composite microstructure with the distribution of surface-smoothened TiB2 particles was present,and a small amount of Si particles precipitated at the interface between reinforcing particles and *** contrast to the AlSi10Mg alloy,the composites showed a stabilized microhardness distribution.A higher ultimate tensile strength of 380.0 MPa,yield strength of 250.4 MPa and elongation of 3.43%were obtained even with a trace amount of ceramic *** improvement of tensile properties can be attributed to multiple mechanisms including solid solution strengthening,load-bearing strengthening and dispersion *** research provides a theoretical basis for ceramic reinforced aluminum matrix composites by additive manufacturing.

关键词： Selective laser melting TiB2 Aluminum matrix composites Mechanical properties Strengthening mechanism

Influence of additive multilayer feature on thermodynamics, stress and microstructure development during laser 3D printing of aluminum-based material

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Science Bulletin 2017年第11期62卷 779-787页

作者： Donghua Dai dongdong gu Reinhart Poprawe Mujian Xia College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China Institute of Additive Manufacturing (3D Printing) Nanjing University of Aeronautics and Astronautics Nanjing 210016 China Fraunhofer Institute for Laser Technology ILT/Chair for Laser Technology LLT RWTH Aachen Steinbachstraβe 15 D-52074 Aachen Germany

A transient three dimensional model for describing the temperature behavior, thermo-capillary convection, microstructure evolution and the resultant mechanical properties during selective laser melting of AIN/AlSilOMg composite is proposed. The powder-solid transformation, temperature dependent physical properties and the preservation of the heat are taken into account. The effect of the additive manufacturing multilayer feature on the molten pool dynamics, cooling rate, crystal size, microstructure morphology, micro-hardness and types of the residual stress has been investigated. It shows that the operating temperature and the thermo-capillary convection obtained within the molten pool generally increases as the processing multilayers are successively added, while the thermal effect depth is negatively reduced. The preferential direction of the heat diffusion generally changes from a downward pattern, then to the slightly strengthened horizontal direction and finally to a typically horizontal one for various deposited layers being processed. Therefore, the microstructure of the solidified part along the building direction （Region 1 to Region V） undergoes an interesting transformation： directional columnar cellular microstructure, crosswise-extended cellular microstructure, refined cellular microstructure, fragmentation microstructure and the coarse cellular microstructure. The tensile stress and the compressive stress are comprehensively obtained within the finally solidified layers, significantly influencing the microhardness.

关键词： Additive manufacturing Selective laser melting Thermodynamics behavior Microstructure evolution Residual stress

Anisotropic corrosion resistance of TiC reinforced Ni-based composites fabricated by selective laser melting

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Journal of Materials Science & Technology 2019年第6期35卷 1128-1136页

作者： Hongmei Zhang dongdong gu Lixia Xi Han Zhang Mujian Xia Chenglong Ma College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China Jiangsu Provincial Engineering Laboratory for Laser Additive Manufacturing of High-Performance Metallic Components Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

Electrochemical measurements on three planes of TiC/Inconel 718 composites fabricated by selective laser melting(SLM) were performed to study the corrosion property. The results showed that the YZplane with dense and fine columnar structures possessed high microhardness and superior corrosion resistance in 3.5 wt% NaCl solution. For the XZ-plane, a decreased anti-corrosion property was observed owing to its inhomogeneous microstructures. While the XY-plane with large irregular pores and clustered ring-like structures was more susceptible to corrosion compared with the other two planes. Comparative analysis suggested that the anisotropic corrosion behaviors were significantly dependent on the surface defects, microstructure characteristics and added reinforcements.

关键词： Selective laser melting Corrosion resistance Nickel based composite Microstructure

Selective laser melting 3D printing of Ni-based superalloy： understanding thermodynamic mechanisms

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Science Bulletin 2016年第13期61卷 1013-1022页

作者： Mujian Xia dongdong gu guanqun Yu Donghua Dai Hongyu Chen Qimin Shi College of Materials Science and Technology Nanjing University of Aeronautics and AstronauticsNanjing 210016 China Institute of Additive Manufacturing (3D Printing) Nanjing University of Aeronautics and AstronauticsNanjing 210016 China

A mesoscopic model has been established to investigate the thermodynamic mechanisms and densification behavior of nickel-based superalloy during additive manufacturing/three-dimensional （3D） printing （AM/3DP） by numerical simulation, using a finite volume method （FVM）. The influence of the applied linear energy density （LED） on dimensions of the molten pool, thermodynamic mechanisms within the pool, bubbles migration and resultant densification behavior of AM/3DP-processed superalloy has been discussed. It reveals that the center of the molten pool slightly shifts with a lagging of 4 ktm towards the center of the moving laser beam. The Mar- angoni convection, which has various flow patterns, plays a crucial role in intensifying the convective heat and mass transfer, which is responsible for the bubbles migration and densification behavior of AM/3DP-processed parts. At an optimized LED of 221.5 J/m, the outward convection favors the numerous bubbles to escape from the molten pool easily and the resultant considerably high relative density of 98.9 % is achieved. However, as the applied LED further increases over 249.5 J/m, the convection pattern is apparently intensified with the formation of vortexes and the bubbles tend to be entrapped by the rotating flow within the molten pool, resulting in a large amount of residual porosity and a sharp reduction in densification of the superalloy. The change rules of the relative density and the corresponding distribution of porosity obtained by experiments are in accordance with the simulation results.

关键词： Selective laser melting 3D printing Mesoscopic simulation - Thermodynamics Densification Porosity

A Multiscale Understanding of the Thermodynamic and Kinetic Mechanisms of Laser Additive Manufacturing

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Engineering 2017年第5期3卷 675-684页

作者： dongdong gu Chenglong Ma Mujian Xia Donghua Dai Qimin Shi College of Material Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China Institute of Additive Manufacturing (3D Printing) Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

Selective laser melting （SLM） additive manufacturing （AM） technology has become an important option for the precise manufacturing of complex-shaped metallic parts with high performance. The SLM AM process involves complicated physicochemical phenomena, thermodynamic behavior, and phase transformation as a high-energy laser beam melts loose powder particles. This paper provides multiscale modeling and coordinated control for the SLM of metallic materials including an aluminum （Al）-based alloy （AlSi10Mg）, a nickel （Ni）-based super-alloy （Inconel 718）, and ceramic particle-reinforced Al-based and Ni-based composites. The migration and distribution mechanisms of aluminium nitride （AIN） particles in SLM-processed Al- based nanocomposites and the in situ formation of a gradient interface between the reinforcement and the matrix in SLM-processed tungsten carbide （WC）/Inconel 718 composites were studied in the microscale. The laser absorption and melting/densification behaviors of AISilOMg and Inconel 718 alloy powder were dis- closed in the mesoscale. Finally, the stress development during line-by-line localized laser scanning and the parameter-dependent control methods for the deformation of SLM-processed composites were proposed in the macroscale. Multiscale numerical simulation and experimental verification methods are beneficial in monitoring the complicated powder-laser interaction, heat and mass transfer behavior, and microstructural and mechanical properties development during the SLM AM process.

关键词： Additive manufacturing Selective laser melting Multiscale modeling Thermodynamics Kinetics

Laser Powder Bed Fusion of Multifunctional Bio-inspired Vertical Honeycomb Sandwich Structures:For the Application of Lightweight Bipolar Plates of Proton Exchange Membrane Fuel Cells

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Chinese Journal of Mechanical Engineering 2024年第5期37卷 60-75页

作者： Kaijie Lin Yong Xu dongdong gu Junhao Shan Keyu Shi Wanli Zhang College of Materials Science and Technology Nanjing University of Aeronautics and AstronauticsNanjing 210016China Jiangsu Provincial Research Center for Laser Additive Manufacturing of High-Performance Components Nanjing 210016China

The bipolar plate(BPP)is a crucial component of proton exchange membrane fuel cells(PEMFC).However,the weight of BPPs can account for around 80%of a PEMFC stack,posing a hindrance to the commercialization of ***,the lightweight design of BPPs should be considered as a *** sandwich structures meet some requirements for bipolar plates,such as high mechanical strength and *** and plants in nature provide many excellent structures with characteristics such as low density and high energy absorption *** this work,inspired by the microstructures of the Cybister elytra,a novel bio-inspired vertical honeycomb sandwich(BVHS)structure was designed and manufactured by laser powder bed fusion(LPBF)for the application of lightweight *** with the conventional vertical honeycomb sandwich(CVHS)structure formed by LPBF under the same process parameters setting,the introduction of fractal thin walls enabled self-supporting and thus improved LPBF *** addition,the BVHS structure exhibited superior energy absorption(EA)capability and bending *** is worth noting that,compared with the CVHS structure,the specific energy absorption(SEA)and specific bending strength of the BVHS structure increased by 56.99%and 46.91%,*** element analysis(FEA)was employed to study stress distributions in structures during bending and analyze the influence mechanism of the fractal feature on the mechanical properties of BVHS *** electrical conductivity of structures were also studied in this work,the BVHS structures were slightly lower than the CVHS *** was also conducted to analyze the current flow direction and current density distribution of BVHS structures under a constant voltage,illustrating the influence mechanism of fractal angles on electrical conductivity ***,in order to solve the problem of trapped powder inside the enclosed unit cells,a droplet-shaped powder outlet

关键词： Lightweight bipolar plates Bio-inspired honeycomb sandwich structures Laser powder bed fusion Forming quality Bending properties Electrical conductivity

Laser additive manufactured high-performance Fe-based composites with unique strengthening structure

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Journal of Materials Science & Technology 2021年第30期89卷 242-252页

作者： Hongyu Chen dongdong gu Liang Deng Tiwen Lu Uta Kühn Konrad Kosiba College of Materials Science and Technology Nanjing University of Aeronautics and AstronauticsNanjing 210016China Jiangsu Provincial Engineering Laboratory for Laser Additive Manufacturing of High-Performance Metallic Components Nanjing University of Aeronautics and AstronauticsNanjing 210016China Leibniz IFW Dresden Institute for Complex MaterialsP.O.Box 270116D-01069 DresdenGermany

Steel matrix composites(SMCs),reinforced by ceramic particles,have received a consistent attention in recent *** conventional methods to prepare SMCs is generally challenging,and the mechanical properties of conventionally fabricated SMCs are *** this study,we successfully fabricated highperformance SMCs by laser powder bed fusion(LPBF)of a composite powder consisting of Fe-based alloy powder and submicron-sized WC *** effect of laser energy density on the phase formation,microstructural evolution,overall density and resulting mechanical properties of LPBF-fabricated composites was *** present results show that a novel Fe_(2)W_(4)C carbidic network precipitates in the solidified microstructure entailing segregations along the boundaries of cellular *** presence of this carbidic network hampers the growth of sub-grains even at elevated temperatures,and hence,stabilizes the grain size though prepared at a broad range of different energy *** exact distribution of the Fe_(2)W_(4)C carbides depends on the employed laser energy densities,as for instance they are more uniformly distributed at higher energy *** density of LPBF samples reaches the maximum value of 99.4%at 150 J/mm^(3).In this parameter set,high microhardness of~753 HV,compression strength of~3350 MPa and fracture strain of~24.4%are *** enhanced mechanical properties are ascribed to less metallurgical defects,higher volume fraction of the martensitic phase and increasing pile-up dislocations resulting from the pinning effect by Fe_(2)W_(4)C carbide.

关键词： Laser additive manufacturing Laser powder bed fusion Steel matrix composite Microstructures Mechanical properties

Compressive mechanical properties and shape memory effect of NiTi gradient lattice structures fabricated by laser powder bed fusion

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International Journal of Extreme Manufacturing 2022年第4期4卷 189-205页

作者： Wei Chen dongdong gu Jiankai Yang Qin Yang Jie Chen Xianfeng Shen Jiangsu Provincial Engineering Laboratory for Laser Additive Manufacturing of High-Performance Metallic Components College of Materials Science and TechnologyNanjing University of Aeronautics and AstronauticsYudao Street 29Nanjing 210016People's Republic of China Institute of Machinery Manufacturing Technology China Academy of Engineering PhysicsMianyangSichuan 621000People's Republic of China

Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanical equipment application fields. In this study, we designed four gradient lattice structures (GLSs) using the topology optimization method, including the unidirectional GLS, the bi-directional increasing GLS, the bi-directional decreasing GLS and the none-GLS. All GLSs were manufactureed by laser powder bed fusion (LPBF). The uniaxial compression tests and finite element analysis were conducted to investigate the influence of gradient distribution features on deformation modes and energy absorption performance of GLSs. The results showed that, compared with the 45° shear fracture characteristic of the none-GLS, the unidirectional GLS, the bi-directional increasing GLS and the bi-directional decreasing GLS had the characteristics of the layer-by-layer fracture, showing considerably improved energy absorption capacity. The bi-directional increasing GLS showed a unique combination of shear fracture and layer-by-layer fracture, having the optimal energy absorption performance with energy absorption and specific energy absorption of 235.6 J and 9.5 J g-1 at 0.5 strain, respectively. Combined with the shape memory effect of NiTi alloy, multiple compression-heat recovery experiments were carried out to verify the shape memory function of LPBF-processed NiTi GLSs. These findings have potential value for the future design of GLSs and the realization of shape memory function of NiTi components through laser AM.

关键词： additive manufacturing laser powder bed fusion gradient lattice structures deformation behavior shape memory effect

Thermodynamics of Molten Pool Predicted by Computational Fluid Dynamics in Selective Laser Melting of Ti6Al4V:Surface Morphology Evolution and Densification Behavior

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Computer Modeling in Engineering & Sciences 2020年第9期124卷 1085-1098页

作者： Donghua Dai dongdong gu Qing Ge Chenglong Ma Xinyu Shi Han Zhang College of Materials Science and Technology Nanjing University of Aeronautics and AstronauticsNanjing210016China Jiangsu Provincial Engineering Laboratory for Laser Additive Manufacturing of High-Performance Metallic Components Nanjing University of Aeronautics and AstronauticsNanjing210016China

The three-dimensional physical model of the randomly packed powder material irradiated by the laser beam was established,taking into account the transformation of the material phase,the melt spreading and the interaction of the free surface of the molten pool and the recoiling pressure caused by the material evaporation during the selective laser *** of the processing parameters on the thermal behavior,the material evaporation,the surface morphology and the densification behavior in the connection region of the molten pool and the substrate was *** was shown that the powder material underwent the transformation from the partial melting state to the complete melting state and finally to the overheating state with the applied laser energy density increasing from 167 J/mm^(3) to 417 J/mm^(3).Therefore,the solidified track ranged from the discontinuous tracks with the rough surface to the continuous tracks with residual porosities,then to the continuous and dense tracks and terminally to the fluctuated tracks with the increase in the laser energy ***,the laser energy effect depth was maintained the positive relationship with the laser energy *** vortex velocity obtained in the free surface of the molten pool towards to the rear region in the opposite laser scan direction promoted the melt convection to the edge region of the molten pool as the laser energy density was higher than 277 J/mm^(3),demonstrating the efficient energy dissipation from the center of the irradiation region to the whole part of the molten pool and the attendant production of the sufficient melt ***,the efficient spreading of the molten pool and the metallurgical bonding ability of the melt with the substrate was obtained at the optimized laser energy density of 277 J/mm^(3).However,the severe material evaporation would take place as the melt was overheated,resulting in the formation of the residual pores and poor surface quality.

关键词： Additive manufacturing melt convection surface morphology densification behavior numerical simulation