The laser technology has made remarkable progress over the past couple of decades.It is being widely employed in diverse domains,such as holography,space sciences,spectroscopy,medical sciences,micro and power electron...The laser technology has made remarkable progress over the past couple of decades.It is being widely employed in diverse domains,such as holography,space sciences,spectroscopy,medical sciences,micro and power electronics,industrial engineering,and most distinctively,as directed energy military weapons.Owing to their active transmissions,laser systems are similar to microwave radars to some extent;however,unlike conventional radars,the laser operates at very high frequencies thus making it a potent enabler of narrow-beam and high energy aerial deployments,both in offensive and defensive roles.In modern avionics systems,laser target indicators and beam riders are the most common devices that are used to direct the Laser Guided Weapons(LGW)accurately to the ground targets.Additionally,compact size and outstanding angular resolution of laser-based systems motivate their use for drones and unmanned aerial applications.Moreover,the narrow-beam divergence of laser emissions offers a low probability of intercept,making it a suitable contender for secure transmissions and safety-critical operations.Furthermore,the developments in space sciences and laser technology have given synergistic potential outcomes to use laser systems in space operations.This paper comprehensively reviews laser applications and projects for strategic defense actions on the ground or in space.Additionally,a detailed analysis has been done on recent advancements of the laser technology for target indicators and range-finders.It also reviews the advancements in the field of laser communications for surveillance,its earlier state of the art,and ongoing scientific research and advancements in the domain of high energy directed laser weapons that have revolutionized the evolving military battlefield.Besides offering a comprehensive taxonomy,the paper also critically analyzes some of the recent contributions in the associated domains.展开更多
Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because o...Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because of their special properties.High-energy beam additive manufacturing(HEB-AM)of nickel-based superalloys has shown great application potential in aerospace and other fields.However,HEB-AM of nickel-based superalloys faces serious cracking problems because of the unique characteristics of superalloys,and this has become the most significant bottleneck restricting their application.In this review,the current research status related to the types,formation mechanisms,and suppression methods of cracks in nickel-based superalloys produced by HEB-AM is described.The initiation and propagation mechanisms of cracks and their multiple influencing factors are also analyzed and discussed.Then,several possible research directions to solve the cracking problems in nickel-based superalloys produced by HEB-AM are outlined.This review provides an in-depth and comprehensive understanding of the cracking problem in AM nickel-based superalloys.It also provides valuable references for AM crack-free nickel-based superalloy components.展开更多
NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emph...NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.展开更多
Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstrea...Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.展开更多
In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed ener...In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10μm from 16μm,the orientation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.展开更多
This paper presents a novel approach to economic dispatch in smart grids equipped with diverse energy devices.This method integrates features including photovoltaic(PV)systems,energy storage coupling,varied energy rol...This paper presents a novel approach to economic dispatch in smart grids equipped with diverse energy devices.This method integrates features including photovoltaic(PV)systems,energy storage coupling,varied energy roles,and energy supply and demand dynamics.The systemmodel is developed by considering energy devices as versatile units capable of fulfilling various functionalities and playing multiple roles simultaneously.To strike a balance between optimality and feasibility,renewable energy resources are modeled with considerations for forecasting errors,Gaussian distribution,and penalty factors.Furthermore,this study introduces a distributed event-triggered surplus algorithm designed to address the economic dispatch problem by minimizing production costs.Rooted in surplus theory and finite time projection,the algorithm effectively rectifies network imbalances caused by directed graphs and addresses local inequality constraints.The algorithm greatly reduces the communication burden through event triggering mechanism.Finally,both theoretical proofs and numerical simulations verify the convergence and event-triggered nature of the algorithm.展开更多
Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality...Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.展开更多
The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experi...The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experimental characterizations were performed to examine the impact of IHT on the micros true ture and mechanical properties of LDED-fabricated CrCoNi medium-entropy alloy(MEA).The results show that the intensity of the IHT is proportional to the utilized laser energy density(LED).As the LED increased,significant dynamic recrystallization and grain refinement occurred within the alloy due to the enhanced intensity of IHT.However,the high LED leads to severe hot cracking within the as-built MEA,resulting in inferior ductility.By decreasing LED,the hot cracking was effectively eliminated.Meanwhile,low LED weakened the intensity of IHT and consequently inhibited kinetic conditions of dynamic recrystallization,resulting in a heterogeneous grain structure characterized by multi-scale-sized grains.This structure provides significant hetero-deformation-induced hardening during plastic deformation,enabling the alloy to have a sustainable work-hardening capacity.We expect that this work will have implications in taking full advantage of the unique IHT of the LDED process to fabricate ME As with excellent metallurgical quality and mechanical performance.展开更多
Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheat...Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.展开更多
The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples...The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.展开更多
The effect of spatial temperature gradient on the microstructural evolution of a 308L stainless steel during the directed energy deposition(DED)process was experimentally investigated.A novel cooling system was design...The effect of spatial temperature gradient on the microstructural evolution of a 308L stainless steel during the directed energy deposition(DED)process was experimentally investigated.A novel cooling system was designed and incorporated to a DED system in order to control the temperature gradient along the deposition direction during solidification.During deposition,the workpiece was placed on a lifting platform,and as the deposition process proceeded,the platform and workpiece were gradually lowered into cooling water so that the temperature gradient along the deposition direction could be controlled and maintained stable during the deposition process.The microstructure characterization results indicated that a deposition strategy with higher G and G/R values(where G is temperature gradient and R is solidification rate)produced finer cellular grains that were better aligned with the deposition direction,while a deposition strategy with lower G and G/R values produced columnar grains with larger primary arm spacing and less aligned with the deposition direction.展开更多
Coarse columnar β grains result in anisotropic mechanical properties in Ti alloys deposited by additive manufacturing. This study reports that Ti-6Al-4V alloy fabricated by coaxial electron beam wire feeding additive...Coarse columnar β grains result in anisotropic mechanical properties in Ti alloys deposited by additive manufacturing. This study reports that Ti-6Al-4V alloy fabricated by coaxial electron beam wire feeding additive manufacturing presents a weak anisotropy, high strength and ductility. The superior tensile property arises from a microstructure with fine equiaxed β grains(EGβ), discontinuous grain boundary α phase and short intragranular α lamellae. A large region of fine EGβ arises from a special combination of the temperature gradient and solidification rate, and attractive α morphology is caused by solid phase transformations during interpass thermal cycling and post heat treatments.展开更多
文摘The laser technology has made remarkable progress over the past couple of decades.It is being widely employed in diverse domains,such as holography,space sciences,spectroscopy,medical sciences,micro and power electronics,industrial engineering,and most distinctively,as directed energy military weapons.Owing to their active transmissions,laser systems are similar to microwave radars to some extent;however,unlike conventional radars,the laser operates at very high frequencies thus making it a potent enabler of narrow-beam and high energy aerial deployments,both in offensive and defensive roles.In modern avionics systems,laser target indicators and beam riders are the most common devices that are used to direct the Laser Guided Weapons(LGW)accurately to the ground targets.Additionally,compact size and outstanding angular resolution of laser-based systems motivate their use for drones and unmanned aerial applications.Moreover,the narrow-beam divergence of laser emissions offers a low probability of intercept,making it a suitable contender for secure transmissions and safety-critical operations.Furthermore,the developments in space sciences and laser technology have given synergistic potential outcomes to use laser systems in space operations.This paper comprehensively reviews laser applications and projects for strategic defense actions on the ground or in space.Additionally,a detailed analysis has been done on recent advancements of the laser technology for target indicators and range-finders.It also reviews the advancements in the field of laser communications for surveillance,its earlier state of the art,and ongoing scientific research and advancements in the domain of high energy directed laser weapons that have revolutionized the evolving military battlefield.Besides offering a comprehensive taxonomy,the paper also critically analyzes some of the recent contributions in the associated domains.
基金National Natural Science Foundation of China(Grant Nos.52201040,52275333)China Postdoctoral Science Foundation(Grant No.2021M701291)+2 种基金AVIC Manufacturing Technology Institute of China(Grant No.KZ571801)Hubei Provincial Department of Science and Technology 2020 Provincial Key R&D Plan of China(Grant No.2020BAB049)Wuhan Science and Technology Project of China(Grant No.2020010602012037).
文摘Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because of their special properties.High-energy beam additive manufacturing(HEB-AM)of nickel-based superalloys has shown great application potential in aerospace and other fields.However,HEB-AM of nickel-based superalloys faces serious cracking problems because of the unique characteristics of superalloys,and this has become the most significant bottleneck restricting their application.In this review,the current research status related to the types,formation mechanisms,and suppression methods of cracks in nickel-based superalloys produced by HEB-AM is described.The initiation and propagation mechanisms of cracks and their multiple influencing factors are also analyzed and discussed.Then,several possible research directions to solve the cracking problems in nickel-based superalloys produced by HEB-AM are outlined.This review provides an in-depth and comprehensive understanding of the cracking problem in AM nickel-based superalloys.It also provides valuable references for AM crack-free nickel-based superalloy components.
基金Project(2020JJ2046)supported by the Science Fund for Hunan Distinguished Young Scholars,ChinaProject(S2020GXKJGG0416)supported by the Special Project for Hunan Innovative Province Construction,China+1 种基金Project(2018RS3007)supported by the Huxiang Young Talents,ChinaProject(GuikeAB19050002)supported by the Science Project of Guangxi,China。
文摘NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.
基金supported by the 2022 MTC Young Individual Research Grants(Grant No.M22K3c0097)the Singapore Research,Innovation and Enterprise(RIE)2025 PlanSingapore Aerospace Programme Cycle 16(Grant No.M2215a0073)。
文摘Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.
基金supported by National Key Research and Development Program(No.2017YFB1103701)National Natural Science Foundation of China(No.51671101)+1 种基金Natural Science Foundation of Jiangxi Province(No.20171BCD40003)the Innovative Funding for Graduate Students in Nanchang University(No.CX2019068)。
文摘In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10μm from 16μm,the orientation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.
基金The Science and Technology Project of the State Grid Corporation of China(Research and Demonstration of Loss Reduction Technology Based on Reactive Power Potential Exploration and Excitation of Distributed Photovoltaic-Energy Storage Converters:5400-202333241A-1-1-ZN).
文摘This paper presents a novel approach to economic dispatch in smart grids equipped with diverse energy devices.This method integrates features including photovoltaic(PV)systems,energy storage coupling,varied energy roles,and energy supply and demand dynamics.The systemmodel is developed by considering energy devices as versatile units capable of fulfilling various functionalities and playing multiple roles simultaneously.To strike a balance between optimality and feasibility,renewable energy resources are modeled with considerations for forecasting errors,Gaussian distribution,and penalty factors.Furthermore,this study introduces a distributed event-triggered surplus algorithm designed to address the economic dispatch problem by minimizing production costs.Rooted in surplus theory and finite time projection,the algorithm effectively rectifies network imbalances caused by directed graphs and addresses local inequality constraints.The algorithm greatly reduces the communication burden through event triggering mechanism.Finally,both theoretical proofs and numerical simulations verify the convergence and event-triggered nature of the algorithm.
基金supported by the National Natural Science Foundation of China(51975112,52375412)Fundamental Research Funds for Central Universities(N2203011)。
文摘Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.
基金financially supported by the funding from Guangdong Province Basic and Applied Research Key Projects (No.2020B0301030001)National Key R&D Programme,Ministry of Science and Technology of China (Nos. 2018YFB1105200 and 2019YFA0209904)the National Natural Science Foundation of China (Nos.52371106 and 52371025)。
文摘The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experimental characterizations were performed to examine the impact of IHT on the micros true ture and mechanical properties of LDED-fabricated CrCoNi medium-entropy alloy(MEA).The results show that the intensity of the IHT is proportional to the utilized laser energy density(LED).As the LED increased,significant dynamic recrystallization and grain refinement occurred within the alloy due to the enhanced intensity of IHT.However,the high LED leads to severe hot cracking within the as-built MEA,resulting in inferior ductility.By decreasing LED,the hot cracking was effectively eliminated.Meanwhile,low LED weakened the intensity of IHT and consequently inhibited kinetic conditions of dynamic recrystallization,resulting in a heterogeneous grain structure characterized by multi-scale-sized grains.This structure provides significant hetero-deformation-induced hardening during plastic deformation,enabling the alloy to have a sustainable work-hardening capacity.We expect that this work will have implications in taking full advantage of the unique IHT of the LDED process to fabricate ME As with excellent metallurgical quality and mechanical performance.
基金the financial support of the Hunan Innovation Platform and Talent Plan(2022RC3033)Natural Science Foundation of Shandong Province(ZR2020ZD04)Ganzhou Science and Technology Planning Project(Grant No.Ganshikefa[2019]60)。
文摘Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.
基金financial support of the National Natural Science Foundation of China(Nos.52130110 and U22A20189)the Research Fund of the State Key Laboratory of Solidification Processing(No.2023-TS-10)。
文摘The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.
基金This work was supported by National Key R&D Program of China(Grant No.2022YFB4601000).
文摘The effect of spatial temperature gradient on the microstructural evolution of a 308L stainless steel during the directed energy deposition(DED)process was experimentally investigated.A novel cooling system was designed and incorporated to a DED system in order to control the temperature gradient along the deposition direction during solidification.During deposition,the workpiece was placed on a lifting platform,and as the deposition process proceeded,the platform and workpiece were gradually lowered into cooling water so that the temperature gradient along the deposition direction could be controlled and maintained stable during the deposition process.The microstructure characterization results indicated that a deposition strategy with higher G and G/R values(where G is temperature gradient and R is solidification rate)produced finer cellular grains that were better aligned with the deposition direction,while a deposition strategy with lower G and G/R values produced columnar grains with larger primary arm spacing and less aligned with the deposition direction.
基金supported by the internal funding source from University of Shanghai for Science and Technology.
文摘Coarse columnar β grains result in anisotropic mechanical properties in Ti alloys deposited by additive manufacturing. This study reports that Ti-6Al-4V alloy fabricated by coaxial electron beam wire feeding additive manufacturing presents a weak anisotropy, high strength and ductility. The superior tensile property arises from a microstructure with fine equiaxed β grains(EGβ), discontinuous grain boundary α phase and short intragranular α lamellae. A large region of fine EGβ arises from a special combination of the temperature gradient and solidification rate, and attractive α morphology is caused by solid phase transformations during interpass thermal cycling and post heat treatments.
