Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,...Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,microstructural evolution,and mechanical properties of SMCs was established.The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM processing.Particularly,the involved thermal cycling,which encompassed multiple layers,strongly affected the processing quality of SMCs.Sshaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs.However,due to large thermal stress,microcracks that were perpendicular to the building direction formed within the SMCs.By employing the checkerboard filling(CBF)hatching mode,the thermal stress arising during SLM can be significantly reduced,thus preventing the evolution of interlayer microcracks.The compressive properties of fabricated SMCs can be tailored at a high compressive strength(~3031.5 MPa)and fracture strain(~24.8%)by adopting the CBF hatching mode combined with the optimized scan sequence and stagger mode.This study demonstrates great feasibility in tuning the mechanical properties of SLM-fabricated SMCs without varying the set energy input,e.g.,laser power and scanning speed.展开更多
High-performance/multifunctional metallic components primarily determine the service performance of equip-ment applied in the aerospace,aviation,and automobile industries.Organisms have developed structures with speci...High-performance/multifunctional metallic components primarily determine the service performance of equip-ment applied in the aerospace,aviation,and automobile industries.Organisms have developed structures with specific properties over millions of years of natural evolution,thereby providing inspiration for the design of high-performance structures to satisfy the increasing demands of modern industries.From the perspective of manufacturing,the ability of conventional processing technologies is inadequate for fabricating these complex structural configurations.By contrast,laser additive manufacturing(AM)is an effective method for fabricating complex metallic bio-inspired structures owing to its layer-by-layer deposition advantage.Herein,recent devel-opments in the laser AM of bio-inspired cellular,plate,and truss structures,as well as the materials used in laser AM for bio-inspired printing are briefly reviewed.The organisms being imitated include butterfly,Norway spruce,mantis shrimp,beetle,and water spider,which expand the diversity of multifunctional structures for laser AM.The mechanical properties and functions of laser-AM-processed bio-inspired structures are discussed.Additionally,the challenges,possible outcomes,and directions of utilizing laser AM technology to fabricate high-performance/multifunctional metallic bio-inspired structures in the future are outlined.展开更多
Steel matrix composites(SMCs),reinforced by ceramic particles,have received a consistent attention in recent years.Using conventional methods to prepare SMCs is generally challenging,and the mechanical properties of c...Steel matrix composites(SMCs),reinforced by ceramic particles,have received a consistent attention in recent years.Using conventional methods to prepare SMCs is generally challenging,and the mechanical properties of conventionally fabricated SMCs are limited.In 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 particles.The effect of laser energy density on the phase formation,microstructural evolution,overall density and resulting mechanical properties of LPBF-fabricated composites was investigated.The 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 sub-grains.The 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 densities.The 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 input.The 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 obtained.The 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.展开更多
A three-dimensional laser absorption model based on ray tracing was established to describe the coupled interaction of a laser beam with particles in the powder layers of pure tungsten(W)material processed by selectiv...A three-dimensional laser absorption model based on ray tracing was established to describe the coupled interaction of a laser beam with particles in the powder layers of pure tungsten(W)material processed by selective laser melting(SLM).The influence of particle size on the powder-to-laser absorptivity and underlying absorption behavior was investigated.An intrinsic relationship between the absorption,distribution of absorbed irradiance within the powder layers,and surface morphology and geometric characteristics(e.g.,contact angle,width and height of tracks,and remelted depth)of the laser scanning tracks is presented here.Simulation conclusions indicate that the absorptivity of the powder layers considerably exceeds the single powder particle value or the dense solid material value.With an increase in particle size,the powder layer absorbs less laser energy.The maximum absorptivity of theWpowder layers reached 0.6030 at the particle size of 5 lm.The distribution of laser irradiance on the particle surface was sensitive to particle size,azimuthal angle,and the position of the powder particles on the substrate.The maximum irradiance in the powder layers decreased from 1.117×10^–3 to 0.85×10^–3W·μm^-2 and the contour of the irradiance distribution in the center of the irradiated area gradually contracted when the particle size increased from 5 to 45 lm.An experimental study on the surface morphologies and cross-sectional geometric characteristics of SLM-fabricated W material was performed,and the experimental results validated the mechanisms of the powder-to-laser-absorption behavior that were obtained in simulations.This work provides a scientific basis for the application of the ray-tracing model to predict the wetting and spreading ability of melted tracks during SLM additive manufacturing in order to yield a sound laser processability.展开更多
Three types of scanning strategies,including the chessboard scanning strategy,the zigzag scanning strategy and the remelting scanning strategy,were conducted to study the effects of scanning strategies on surface morp...Three types of scanning strategies,including the chessboard scanning strategy,the zigzag scanning strategy and the remelting scanning strategy,were conducted to study the effects of scanning strategies on surface morphology,microstructure,mechanical properties and the grain orientation of selective laser melted pure tungsten.The results showed that the pores and cracks were main defects in SLM-processed tungsten parts.The pores could be eliminated using the remelting scanning strategy.However,the cracks seemed to be inevitable regardless of the applied scanning strategies.The microstructures of SLM-processed tungsten were columnar grains and showed strong epitaxial growth along the building direction.A compressive strength of 923 MPa with an elongation of 7.7%was obtained when the zigzag scanning strategy was applied,which was the highest among the three scanning strategies.By changing the scanning strategies,the texture of SLM-processed tungsten in the direction of processing could be changed.展开更多
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 interact...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 melting.Influence 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 studied.It 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 density.Meanwhile,the laser energy effect depth was maintained the positive relationship with the laser energy density.The 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 volume.Therefore,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.展开更多
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 mechanica...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.展开更多
To develop self-recovery intelligent components based on resistance heating and obtain satisfactory performance in practical applications,this study optimized the forming quality,dimensional accuracy,and phase transfo...To develop self-recovery intelligent components based on resistance heating and obtain satisfactory performance in practical applications,this study optimized the forming quality,dimensional accuracy,and phase transformation temperatures of Nickel-titanium(NiTi)alloys by controlling the process parameters.The tensile properties and shape-memory effects of the NiTi alloys prepared using the optimized process were clarified.The relationship between the change in temperature and the shape recovery process of the deformed structure under electrical excitation was investigated.The results show that the suitable processing window for ensuring the forming quality without noticeable distortion and macro cracks depends on the laser parameters.In both the X and Y directions,the measured dimensions increased with an increase in laser power and first decreased and then stabilized with an increase in scanning speed.The XRD results showed that all the as-built samples consisted of B2 austenite and B19’martensite phases and Ni3Ti.Mechanical tests suggested that excellent tensile properties with a tensile strength of 753.28 MPa and elongation of 6.81%could be obtained under the optimal parameters of 250 W and 1200 mm/s.An excellent shape-recovery rate of 88.23%was achieved under the optimal parameters.Subsequently,chiral lattice structures were successfully fabricated by laser powder bed fusion(LPBF)under the optimal parameters,and a shape-recovery rate of 96.7%was achieved under electrical actuation for a structure with a pre-compressed strain of 20%.This study also found that the temperatures at the grasp regions were always higher than those at other positions because of the generation of contact resistance at the grasp regions.This facilitates the rapid recovery of the structure at the grasp regions,which has important implications for the design iteration of NiTi smart components.展开更多
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 ...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.展开更多
The inherent capabilities of additive manufacturing(AM)to fabricate porous lattice structures with controllable structural and functional properties have raised interest in the design methods for the production of ext...The inherent capabilities of additive manufacturing(AM)to fabricate porous lattice structures with controllable structural and functional properties have raised interest in the design methods for the production of extremely in-tricate internal geometries.Current popular methods of porous lattice structure design still follow the traditional flow,which mainly consists of computer-aided design(CAD)model construction,STereoLithography(STL)model conversion,slicing model acquisition,and toolpath configuration,which causes a loss of accuracy and manufac-turability uncertainty in AM preparation stages.Moreover,toolpath configuration relies on a knowledge-based approach summarized by expert systems.In this process,geometrical construction information is always ignored when a CAD model is created or constructed.To fully use this geometrical information,avoid accuracy loss and ensure qualified manufacturability of porous lattice structures,this paper proposes a novel toolpath-based con-structive design method to directly generate toolpath printing file of parametric and controllable porous lattice structures to facilitate model data exchange during the AM preparation stages.To optimize the laser jumping route between lattice cells,we use a hybrid travelling salesman problem(TSP)solver to determine the laser jumping points on contour scans.Four kinds of laser jumping orders are calculated and compared to select a minimal laser jumping route for sequence planning inside lattice cells.Hence,the proposed method can achieve high-precision lattice printing and avoid computational consumption in model conversion stages from a geomet-rical view.The optical metallographic images show that the shape accuracy of lattice patterns can be guaranteed.The existence of“grain boundaries”brought about by the multi-contour scanning strategy may lead to different mechanical properties.展开更多
基金the National Key Research and Development Program“Additive Manufacturing and Laser Manufacturing”(No.2016YFB1100101)the National Natural Science Foundation of China(No.51735005)+3 种基金the Basic Strengthening Program of Science and Technology(No.2019-JCJQ-JJ-331)the 5th Jiangsu Province 333 High Level Talents Training Project,China(No.BRA2019048)the 15th Batch of“Six Talents Peaks”Innovative Talents Team Program“Laser Precise Additive Manufacturing of Structure-Performance Integrated Lightweight Alloy Components”(No.TD-GDZB-001)and the 2017 Excellent Scientific and Technological Innovation Teams of Universities in Jiangsu“Laser Additive Manufacturing Technologies for Metallic Components”funded by Jiangsu Provincial Department of Education of China(No.51921003).Konrad Kosiba acknowledges the support from DFG under Grant No.KO 5771/1-1.
文摘Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,microstructural evolution,and mechanical properties of SMCs was established.The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM processing.Particularly,the involved thermal cycling,which encompassed multiple layers,strongly affected the processing quality of SMCs.Sshaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs.However,due to large thermal stress,microcracks that were perpendicular to the building direction formed within the SMCs.By employing the checkerboard filling(CBF)hatching mode,the thermal stress arising during SLM can be significantly reduced,thus preventing the evolution of interlayer microcracks.The compressive properties of fabricated SMCs can be tailored at a high compressive strength(~3031.5 MPa)and fracture strain(~24.8%)by adopting the CBF hatching mode combined with the optimized scan sequence and stagger mode.This study demonstrates great feasibility in tuning the mechanical properties of SLM-fabricated SMCs without varying the set energy input,e.g.,laser power and scanning speed.
基金supported by National Natural Science Foundation of China(Grant No.51735005)National Natural Science Foundation of China for Creative Research Groups(Grant No.51921003)+1 种基金“Six Talents Peak”Innovation Talent Team of Jiangsu Province(the 15th batch)(Grant No.TD-GDZB-001)Postgraduate Research&Practice Inno-vation Program of Jiangsu Province(Grant No.KYCX20_0194).
文摘High-performance/multifunctional metallic components primarily determine the service performance of equip-ment applied in the aerospace,aviation,and automobile industries.Organisms have developed structures with specific properties over millions of years of natural evolution,thereby providing inspiration for the design of high-performance structures to satisfy the increasing demands of modern industries.From the perspective of manufacturing,the ability of conventional processing technologies is inadequate for fabricating these complex structural configurations.By contrast,laser additive manufacturing(AM)is an effective method for fabricating complex metallic bio-inspired structures owing to its layer-by-layer deposition advantage.Herein,recent devel-opments in the laser AM of bio-inspired cellular,plate,and truss structures,as well as the materials used in laser AM for bio-inspired printing are briefly reviewed.The organisms being imitated include butterfly,Norway spruce,mantis shrimp,beetle,and water spider,which expand the diversity of multifunctional structures for laser AM.The mechanical properties and functions of laser-AM-processed bio-inspired structures are discussed.Additionally,the challenges,possible outcomes,and directions of utilizing laser AM technology to fabricate high-performance/multifunctional metallic bio-inspired structures in the future are outlined.
基金the financial support from the National Natural Science Foundation of China(No.51735005)Basic Strengthening Program of Science and Technology(No.2019-JCJQJJ-331)+3 种基金the 5th Jiangsu Province 333 High Level Talents Training Project(BRA2019048)The 15th Batch of“Six Talents Peaks”Innovative Talents Team Program“Laser Precise Additive Manufacturing of Structure-Performance Integrated Lightweight Alloy Components”(No.TD-GDZB-001)2017 Excellent Scientific and Technological Innovation Teams of Universities in Jiangsu“Laser Additive Manufacturing Technologies for Metallic Components”funded by Jiangsu Provincial Department of Education of China(No.51921003)the support from DFG under grant no.KO 5771/1-1。
文摘Steel matrix composites(SMCs),reinforced by ceramic particles,have received a consistent attention in recent years.Using conventional methods to prepare SMCs is generally challenging,and the mechanical properties of conventionally fabricated SMCs are limited.In 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 particles.The effect of laser energy density on the phase formation,microstructural evolution,overall density and resulting mechanical properties of LPBF-fabricated composites was investigated.The 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 sub-grains.The 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 densities.The 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 input.The 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 obtained.The 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.
文摘A three-dimensional laser absorption model based on ray tracing was established to describe the coupled interaction of a laser beam with particles in the powder layers of pure tungsten(W)material processed by selective laser melting(SLM).The influence of particle size on the powder-to-laser absorptivity and underlying absorption behavior was investigated.An intrinsic relationship between the absorption,distribution of absorbed irradiance within the powder layers,and surface morphology and geometric characteristics(e.g.,contact angle,width and height of tracks,and remelted depth)of the laser scanning tracks is presented here.Simulation conclusions indicate that the absorptivity of the powder layers considerably exceeds the single powder particle value or the dense solid material value.With an increase in particle size,the powder layer absorbs less laser energy.The maximum absorptivity of theWpowder layers reached 0.6030 at the particle size of 5 lm.The distribution of laser irradiance on the particle surface was sensitive to particle size,azimuthal angle,and the position of the powder particles on the substrate.The maximum irradiance in the powder layers decreased from 1.117×10^–3 to 0.85×10^–3W·μm^-2 and the contour of the irradiance distribution in the center of the irradiated area gradually contracted when the particle size increased from 5 to 45 lm.An experimental study on the surface morphologies and cross-sectional geometric characteristics of SLM-fabricated W material was performed,and the experimental results validated the mechanisms of the powder-to-laser-absorption behavior that were obtained in simulations.This work provides a scientific basis for the application of the ray-tracing model to predict the wetting and spreading ability of melted tracks during SLM additive manufacturing in order to yield a sound laser processability.
基金the financial support by Science Challenge Project(Nos.TZ2018006-0301-02 and TZ2018006-0303-03)National Natural Science Foundation of China(No.51735005)National Natural Science Foundation of China for Creative Research Groups(Grant No.51921003)。
文摘Three types of scanning strategies,including the chessboard scanning strategy,the zigzag scanning strategy and the remelting scanning strategy,were conducted to study the effects of scanning strategies on surface morphology,microstructure,mechanical properties and the grain orientation of selective laser melted pure tungsten.The results showed that the pores and cracks were main defects in SLM-processed tungsten parts.The pores could be eliminated using the remelting scanning strategy.However,the cracks seemed to be inevitable regardless of the applied scanning strategies.The microstructures of SLM-processed tungsten were columnar grains and showed strong epitaxial growth along the building direction.A compressive strength of 923 MPa with an elongation of 7.7%was obtained when the zigzag scanning strategy was applied,which was the highest among the three scanning strategies.By changing the scanning strategies,the texture of SLM-processed tungsten in the direction of processing could be changed.
基金We are grateful for the financial support from the National Key Research and Development Program“Additive Manufacturing and Laser Manufacturing”(Nos.2016YFB1100101,2018YFB1106302)the National Natural Science Foundation of China(Nos.51790175,51735005)+3 种基金the Fundamental Research Funds for the Central Universities(No.NC2020004),the financial support from the Innovation Fund of National Engineering and Research Center for Commercial Aircraft Manufacturing(No.COMAC-SFGS-2016-33238)National Natural Science Foundation of China for Creative Research Groups(Grant No.51921003)The 15th Batch of“Six Talents Peaks”Innovative Talents Team Program“Laser Precise Additive Manufacturing of Structure-Performance Integrated Lightweight Alloy Components”(No.TD-GDZB-001)(Jiangsu Provincial Department of Human Resources and Social Security of China)2017 Excellent Scientific and Technological Innovation Teams of Universities in Jiangsu“Laser Additive Manufacturing Technologies for Metallic Components”(Jiangsu Provincial Department of Education of China).
文摘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 melting.Influence 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 studied.It 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 density.Meanwhile,the laser energy effect depth was maintained the positive relationship with the laser energy density.The 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 volume.Therefore,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.
基金supported by the financial support from the National Natural Science Foundation of China(Nos.51735005 and U1930207)the Basic Strengthening Program(No.2019-JCJQ-JJ-331)+1 种基金National Natural Science Founda-tion of China for Creative Research Groups(No.51921003)the 15th Batch of‘Six Talents Peaks’Innovative Talents Team Program(No.TD-GDZB-001).
文摘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.
基金National Natural Science Foundation of China(Grant Nos.52225503,U1930207,and 51735005)Basic Strengthening Program of China(Grant No.2019-JCJQ-JJ-331)+1 种基金National Natural Science Foundation of China for Creative Research Groups of China(Grant No.51921003)Postgraduate Research&Practice Innovation Program of Jiangsu Provincial of China(Grant No.KYCX21-0207).
文摘To develop self-recovery intelligent components based on resistance heating and obtain satisfactory performance in practical applications,this study optimized the forming quality,dimensional accuracy,and phase transformation temperatures of Nickel-titanium(NiTi)alloys by controlling the process parameters.The tensile properties and shape-memory effects of the NiTi alloys prepared using the optimized process were clarified.The relationship between the change in temperature and the shape recovery process of the deformed structure under electrical excitation was investigated.The results show that the suitable processing window for ensuring the forming quality without noticeable distortion and macro cracks depends on the laser parameters.In both the X and Y directions,the measured dimensions increased with an increase in laser power and first decreased and then stabilized with an increase in scanning speed.The XRD results showed that all the as-built samples consisted of B2 austenite and B19’martensite phases and Ni3Ti.Mechanical tests suggested that excellent tensile properties with a tensile strength of 753.28 MPa and elongation of 6.81%could be obtained under the optimal parameters of 250 W and 1200 mm/s.An excellent shape-recovery rate of 88.23%was achieved under the optimal parameters.Subsequently,chiral lattice structures were successfully fabricated by laser powder bed fusion(LPBF)under the optimal parameters,and a shape-recovery rate of 96.7%was achieved under electrical actuation for a structure with a pre-compressed strain of 20%.This study also found that the temperatures at the grasp regions were always higher than those at other positions because of the generation of contact resistance at the grasp regions.This facilitates the rapid recovery of the structure at the grasp regions,which has important implications for the design iteration of NiTi smart components.
基金financially supported by the National Natural Science Foundation of China(Nos.51735005 and 51575267)the National Key Research and Development Program “Additive Manufacturing and Laser Manufacturing”(No.2016YFB1100101)
文摘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.
文摘The inherent capabilities of additive manufacturing(AM)to fabricate porous lattice structures with controllable structural and functional properties have raised interest in the design methods for the production of extremely in-tricate internal geometries.Current popular methods of porous lattice structure design still follow the traditional flow,which mainly consists of computer-aided design(CAD)model construction,STereoLithography(STL)model conversion,slicing model acquisition,and toolpath configuration,which causes a loss of accuracy and manufac-turability uncertainty in AM preparation stages.Moreover,toolpath configuration relies on a knowledge-based approach summarized by expert systems.In this process,geometrical construction information is always ignored when a CAD model is created or constructed.To fully use this geometrical information,avoid accuracy loss and ensure qualified manufacturability of porous lattice structures,this paper proposes a novel toolpath-based con-structive design method to directly generate toolpath printing file of parametric and controllable porous lattice structures to facilitate model data exchange during the AM preparation stages.To optimize the laser jumping route between lattice cells,we use a hybrid travelling salesman problem(TSP)solver to determine the laser jumping points on contour scans.Four kinds of laser jumping orders are calculated and compared to select a minimal laser jumping route for sequence planning inside lattice cells.Hence,the proposed method can achieve high-precision lattice printing and avoid computational consumption in model conversion stages from a geomet-rical view.The optical metallographic images show that the shape accuracy of lattice patterns can be guaranteed.The existence of“grain boundaries”brought about by the multi-contour scanning strategy may lead to different mechanical properties.
基金Project supported by the National Natural Science Foundation of China(No.51735005)the National Key Technology Research and Development Program of China(No.2016YFB1100101)+1 种基金the Key Research and Development Program of Jiangsu Provincial Department of Science and Technology of China(No.BE2016181)the Priority Academic Program Development of Jiangsu Higher Education Institutions,China