In order to increase the sustainability of future lunar missions,techniques for in-situ resource utilization(ISRU)must be developed.In this context,the local melting of lunar dust(regolith)by laser radiation for the p...In order to increase the sustainability of future lunar missions,techniques for in-situ resource utilization(ISRU)must be developed.In this context,the local melting of lunar dust(regolith)by laser radiation for the production of parts and larger structures was investigated in detail.With different experimental setups in normal and microgravity,laser spots with diameters from 5 mm to 100 mm were realized to melt the regolith simulant EAC-1A and an 80%/20%mixture of TUBS-T and TUBS-M,which are used as a substitute for the actual lunar soil.In the experiments performed,the critical parameters are the size of the laser spot,the velocity of the laser spot on the surface of the powder bed,the gravity and the wettability of the powder bed by the melt.The stability of the melt pool as a function of these parameters was investigated and it was found that the formation of a stable melt pool is determined by gravity for large melt pool sizes in the range of 50 mm and by surface tension for small melt pool sizes in the range of a few mm.展开更多
The anisotropy of LPBF fabricated components is a serious concern and often increases the overall production cost by creating the necessity for secondary thermal homogenization processes.The microstructural features a...The anisotropy of LPBF fabricated components is a serious concern and often increases the overall production cost by creating the necessity for secondary thermal homogenization processes.The microstructural features are the main driving force behind these anisotropic behaviors.Whereas the unique and distinctive thermal history inside a melt pool and its transient transformation is the reason for the characteristic microstructural features of LPBF fabricated components.Therefore,this paper investigates the prominent thermal variables such as heating rate,cooling rate,solidification rate etc.,and their evolution inside the melt pool of 316 L stainless steel during LPBF process to provide a reference for further exploring the generation of various microstructural features.A numerical model for macroscale investigation of thermal behavior inside melt pool was established.A 3D Gaussian heat source model coupled with temperature and density dependent properties of powder and solid phase 316 L stainless steel was used.The variation and evolution of significant thermal variables inside the melt pool were then investigated with the established numerical model.The study found that the Gaussian profile of a laser beam influences the thermal variables inside a melt-pool,including cooling rates,solidification rates,and thermal gradients.The nodes lying under the laser edge receive less heat,resulting in higher cooling effects,which shapes the grain morphology.Finer grains can be formed near the bottom melt front as well as at the center of the melt-pool surface.However,reheating adjacent tracks can result in grain coarsening.Since the generation of microstructural features is dominantly dependent on the thermal behavior inside the melt pool,an assessment of these variables is important and provides basics for the understating of different features generated in the LPBF processed components.展开更多
Previous studies have revealed that laser power and energy density are significant factors affecting the quality of parts manufactured by selective laser melting(SLM).The normalized equivalent density E_(0)^(*) and di...Previous studies have revealed that laser power and energy density are significant factors affecting the quality of parts manufactured by selective laser melting(SLM).The normalized equivalent density E_(0)^(*) and dimensionless laser power q^(*),which can be regarded as a progress on the understanding of the corresponding dimensional quantities,are adopted in this study to examine the defects,melt pool shape,and primary dendrite spacing of the SLM-manufactured 316 L stainless steel,because it reflects the combined effect of process parameters and material features.It is found that the number of large defects decreases with increasing E_(0)^(*) due to enough heat input during the SLM process,but it will show an increasing trend when excessive heat input(i.e.,utilizing a high E_(0)^(*))is imported into the powder bed.The q^(*) plays an important role in controlling maximum temperature rising in the SLM process,and in turn,it affects the number of large defects.A large q^(*) value results in a low value of absolute frequency of large defects,whereas a maximum value of absolute frequency of large defects is achieved at a low q^(*) even if E_(0)^(*) is very high.The density of the built parts is greater at a higher q^(*) when E_(0)^(*)remains constant.Increasing the melt pool depth at relatively low value of E_(0)^(*) enhances the relative density of the parts.A narrow,deep melt pool can be easily generated at a high q^(*) when E_(0)^(*) is sumciently high,but it may increase melt pool instability and cause keyhole defects.It is revealed that a low E_(0)^(*) can lead to a high cooling rate,which results in a refined primary dendrite spacing.Relatively low E_(0)^(*) is emphasized in selecting the process parameters for the tensile test sample fabrication.It shows that excellent tensile properties,namely ultimate tensile strength,yield strength,and elongation to failure of 773 MPa,584 MPa,and 46%,respectively,can be achieved at a relatively low E_(0)^(*) without heat treatment.展开更多
Laser powder bed fusion(LPBF)has made significant progress in producing solid and porous metal parts with complex shapes and geometries.However,LPBF produced parts often have defects(e.g.,porosity,residual stress,and i...Laser powder bed fusion(LPBF)has made significant progress in producing solid and porous metal parts with complex shapes and geometries.However,LPBF produced parts often have defects(e.g.,porosity,residual stress,and incomplete melting)that hinder its large-scale industrial commercialization.The LPBF process involves complex heat transfer andfluidflow,and the melt pool is a critical component of the process.The melt pool stability is a critical factor in determining the microstructure,mechanical properties,and corrosion resistance of LPBF produced metal parts.Furthermore,optimizing process parameters for new materials and designed structures is challenging due to the complexity of the LPBF process.This requires numerous trial-and-error cycles to minimize defects and enhance properties.This review examines the behavior of the melt pool during the LPBF process,including its effects and formation mechanisms.This article summarizes the experimental results and simulations of melt pool and identifies various factors that influence its behavior,which facilitates a better understanding of the melt pool's behavior during LPBF.This review aims to highlight key aspects of the investigation of melt pool tracks and microstructural characterization,with the goal of enhancing a better understanding of the relationship between alloy powder-process-microstructure-properties in LPBF from both single-and multi-melt pool track perspectives.By identifying the challenges and opportunities in investigating single-and multi-melt pool tracks,this review could contribute to the advancement of LPBF processes,optimal process window,and quality optimization,which ultimately improves accuracy in process parameters and efficiency in qualifying alloy powders.展开更多
Although laser powder bed fusion(LPBF)technology is considered one of the most promising additive man-ufacturing techniques,the fabricated parts still suffer from porosity defects,which can severely impact their mecha...Although laser powder bed fusion(LPBF)technology is considered one of the most promising additive man-ufacturing techniques,the fabricated parts still suffer from porosity defects,which can severely impact their mechanical performance.Monitoring the printing process using a variety of sensors to collect process signals can realize a comprehensive capture of the processing status;thus,the monitoring accuracy can be improved.However,existing multi-sensing signals are mainly optical and acoustic,and camera-based signals are mostly layer-wise images captured after printing,preventing real-time monitoring.This paper proposes a real-time melt-pool-based in-situ quality monitoring method for LPBF using multiple sensors.High-speed cameras,photodiodes,and microphones were used to collect signals during the experimental process.All three types of signals were transformed from one-dimensional time-domain signals into corresponding two-dimensional grayscale images,which enabled the capture of more localized features.Based on an improved LeNet-5 model and the weighted Dempster-Shafer evidence theory,single-sensor,dual-sensor and triple-sensor fusion monitoring models were in-vestigated with the three types of signals,and their performances were compared.The results showed that the triple-sensor fusion monitoring model achieved the highest recognition accuracy,with accuracy rates of 97.98%,92.63%,and 100%for high-,medium-,and low-quality samples,respectively.Hence,a multi-sensor fusion based melt pool monitoring system can improve the accuracy of quality monitoring in the LPBF process,which has the potential to reduce porosity defects.Finally,the experimental analysis demonstrates that the convolutional neural network proposed in this study has better classification accuracy compared to other machine learning models.展开更多
In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process i...In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.展开更多
A thermal conduction model is applied to speed up the numerical analysis of the temperature distribution and the weld pool geometry of full penetration in gas tungsten arc （GTA） welding. With considering both top an...A thermal conduction model is applied to speed up the numerical analysis of the temperature distribution and the weld pool geometry of full penetration in gas tungsten arc （GTA） welding. With considering both top and bottom flee surface deformation of full-penetrated weld pool, three-dimensional weld pool with melting front and solidification front is predicted. Welding experiments are conducted to measure the melting front curves at the top surface and the longitudinal section of the weld. It shows that the predicted and measured results are in good agreement.展开更多
The laser remelting with a two-layer material system (upper material was Al-30 % Ti-20 % Ni alloy,substrate was commercial aluminum alloy) and the laser cladding of a commercial 45 steel with copper Powder (including ...The laser remelting with a two-layer material system (upper material was Al-30 % Ti-20 % Ni alloy,substrate was commercial aluminum alloy) and the laser cladding of a commercial 45 steel with copper Powder (including 25%SiC) were carried out using a 2kW continuous CO2 laser. For the case of laser remelting, a upper Pool in the alloying layer and a lower Pool in the substrate separated by the unmelted Al-Ti-Ni alloy were observed. For laser cladding, a stratified Pool was observed, whose top layer was Cu alloy liquid and bottom was Fe alloy liquid. The mechanism of laser Pool separation and stratification is illustrated by numerical calculation of heat transter process of the two-layer system, combining with material physical properties (especially mixed enthalpy). A classification criterion for laser Pool with the two-layer material system has been presented and four types of the laser Pool are divided into unique Pool, separated Pool, mixed Pool and stratified pool,which provides a theoretical basis for obtaining a excellent surface coating.展开更多
Selective laser melting（SLM） was employed to fabricate Nb-37 Ti-13 Cr-2 Al-1 Si（at%）alloy, using pre-alloyed powders prepared by plasma rotating electrode processing（PREP）. A series of single tracks and single l...Selective laser melting（SLM） was employed to fabricate Nb-37 Ti-13 Cr-2 Al-1 Si（at%）alloy, using pre-alloyed powders prepared by plasma rotating electrode processing（PREP）. A series of single tracks and single layers under different processing parameters was manufactured to evaluate the processing feasibility by SLM, including laser power, scanning speed, and hatch distance.Results showed that continuous single tracks could be fabricated using proper laser powers and scanning velocities. Both the width of a single track and its penetration depth into a substrate increased with an increase of the linear laser beam energy density（LED）, i.e., an increase of the laser power and a decrease of the scanning speed. Nb, Ti, Si, Cr, and Al elements distributed heterogeneously over the melt pool in the form of swirl-like patterns. An excess of the hatch distance was not able to interconnect neighboring tracks. Under improper processing parameters, a balling phenomenon occurred, but could be eliminated with an increased LED. This work testified the SLMprocessing feasibility of Nb-based alloy and promoted the application of SLM to the manufacture of niobium-based alloys.展开更多
AlSi10Mg alloy was prepared by selected laser melting(SLM)in a high laser power range 300–400 W.The effects of energy density on the relative density,microstructure and mechanical properties of the SLMed AlSi10Mg all...AlSi10Mg alloy was prepared by selected laser melting(SLM)in a high laser power range 300–400 W.The effects of energy density on the relative density,microstructure and mechanical properties of the SLMed AlSi10Mg alloy were studied.The results showed that the SLMed AlSi10Mg alloy fabricated at a laser power of 400 W and a scanning speed of 1800 mm/s had a relative density of 99.4%,a hardness of 147.8 HV,a tensile strength of 471.3 MPa,a yield strength of 307.1 MPa,and an elongation of 9.6%,exhibiting excellent comprehensive mechanical properties.The unique combination of the melt pool structure and microstructure caused by the large laser power and fast scanning was responsible for the excellent performance.The wide and shallow melt pool structure with few defects and proper overlapping between the continuous melt pools were obtained.The growth of columnar crystals was inhibited by a large proportion of equiaxed grains formed at the border of melt pools,and numerous sub-structures were observed within theα-Al grains.This study provided a more efficient process parameters for the preparation of the SLMed AlSi10Mg alloy.The enhanced mechanical property will help to broaden the application of the AlSi10Mg alloy in industry.展开更多
This article presents the microstructure and hardness variation of an Al 8.5Fe-1.3V 1.7Si （wt%, FVS0812） alloy after selective laser melting （SLM） modification. Three zones were distinguished across the melting po...This article presents the microstructure and hardness variation of an Al 8.5Fe-1.3V 1.7Si （wt%, FVS0812） alloy after selective laser melting （SLM） modification. Three zones were distinguished across the melting pool of the SLM-processed FVS0812 alloy： the laser melted zone （LMZ）, the melting pool border, and the heat affected zone （HAZ） in the previously deposited area around the melting pool. Inside the LMZ, either an extremely fine cellular-dendritic structure or a mixture zone of the α-Al matrix and nanoscale Al12（Fe,V）3Si particles appeared. With a decreased laser beam scanning speed, the cellular-dendritic structure zone within the LMZ shrank significantly while the mixture zone expanded. The α-Al and Al12（Fe,V）3Si mixture zone was also observed in the HAZ, but another phase, submicron θ-Al13Fe4 particles with rectangular or hexagonal shapes, formed along the melting pool border. Microhardness tests indicated that the hardness of the SLM-processed FVS0812 samples far exceeded that of the as-cast FVS0812 alloy.展开更多
1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and...1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and can directly form complex metal parts.During SLM,the interaction of laser with metal powder forms a tiny melt pool.Following the rapid movement of the laser,the cooling rate of the melt pool can be as high as 105-106 K s−1[1].Such a fast cool-ing rate inhibits grain growth and element segregation in the alloy,leading to a notable enhancement in strength and toughness[2].Therefore,SLM enables unlimited possibilities in the fabrication of complex parts with high performance.To date,the most extensively researched Al alloys for SLM are Al-Si alloys,such as AlSi10Mg,Al-12Si,and AlSi7Mg[2-5].展开更多
The corrosion behavior and mechanical properties of 316 L stainless steel(SS) fabricated via selective laser melting(SLM) were clarified by potentiodynamic polarization measurements, immersion tests, and tensile exper...The corrosion behavior and mechanical properties of 316 L stainless steel(SS) fabricated via selective laser melting(SLM) were clarified by potentiodynamic polarization measurements, immersion tests, and tensile experiments. The microstructural anisotropy of SLMed 316 L SS was also investigated by electron back-scattered diffraction and transmission electron microscopy. The grain sizes of the SLMed 316 L SS in the XOZ plane were smaller than those of the SLMed 316 L SS in the XOY plane, and a greater number of low-angle boundaries were present in the XOY plane, resulting in lower elongation for the XOY plane than for the XOZ plane. The SLMed 316 L was expected to exhibit higher strength but lower ductility than the wrought 316 L, which was attributed to the high density of dislocations. The pitting potentials of the SLMed 316 L samples were universally higher than those of the wrought sample in chloride solutions because of the annihilation of MnS or(Ca,Al)-oxides during the rapid solidification. However, the molten pool boundaries preferentially dissolved in aggressive solutions and the damage of the SLMed 316 L in FeCl3 solution was more serious after long-term service, indicating poor durability.展开更多
Laser additive manufacturing(LAM)has been widely used in high-end manufacturing fields such as aerospace,nuclear power,and shipbuilding.However,it is a grand challenge for direct and continuous observation of complex ...Laser additive manufacturing(LAM)has been widely used in high-end manufacturing fields such as aerospace,nuclear power,and shipbuilding.However,it is a grand challenge for direct and continuous observation of complex laser-matter interaction,melt flow,and defect formation during LAM due to extremely large temperature gradient,fast cooling rate,and small time(millisecond)and space(micron)scales.The emergence of synchrotron radiation provides a feasible approach for in situ observation of the LAM process.This paper outlines the current development in real-time characterization of LAM by synchrotron radiation,including laser-matter interaction,molten pool evolution,solidification structure evolution,and defects formation and elimination.Furthermore,the future development direction and application-oriented research are also discussed.展开更多
A novel Cu−4.8Cr−2.2Nb−0.15Y(at.%)alloy was fabricated by employing the laser powder bed fusion with different processing parameters.The influence of laser power(P),scanning speed(v),and laser linear energy density(El...A novel Cu−4.8Cr−2.2Nb−0.15Y(at.%)alloy was fabricated by employing the laser powder bed fusion with different processing parameters.The influence of laser power(P),scanning speed(v),and laser linear energy density(El)on the defects,melt pool morphology,microstructure,and properties of the alloy was systematically investigated.The results show that the optimized process parameters for preparing Cu−Cr−Nb−Y alloy with relative density over 99.5%are P=300−350 W and v=650−800 mm/s,corresponding to El=0.375−0.538 J/mm.When E_(l)<0.3 J/mm,increasing P or decreasing v can enhance the continuity and size of the melt pool,reduce the lack-of-fusion defects,and increase the relative density.However,excessively high E_(l)leads to a deeper melt pool,more keyholes,and reduced relative density.The grain size of the as-built Cu−Cr−Nb−Y alloy shows a bimodal distribution,with fine grains at the center and coarse grains at the edge of the melt pool.Increasing P or decreasing v increases the average grain size and(110)texture intensity.The alloy fabricated with P=350 W and v=800 mm/s displays the highest relative density of 99.82%.The yield strength,tensile strength,and elongation are(443±5)MPa,(699±4)MPa,and(17.1±0.7)%,respectively.展开更多
基金supported by 40th DLR Parabolic Flight Campaign and within the project"Powder based Additive Manufacturing at reduced Gravitation"(Grant No.FKZ:50WM2068)European Space Agency,OSIP Off-Earth Manufacturing and Construction Campaign(Grant No.4000134280/21/NL/GLC/mk)。
文摘In order to increase the sustainability of future lunar missions,techniques for in-situ resource utilization(ISRU)must be developed.In this context,the local melting of lunar dust(regolith)by laser radiation for the production of parts and larger structures was investigated in detail.With different experimental setups in normal and microgravity,laser spots with diameters from 5 mm to 100 mm were realized to melt the regolith simulant EAC-1A and an 80%/20%mixture of TUBS-T and TUBS-M,which are used as a substitute for the actual lunar soil.In the experiments performed,the critical parameters are the size of the laser spot,the velocity of the laser spot on the surface of the powder bed,the gravity and the wettability of the powder bed by the melt.The stability of the melt pool as a function of these parameters was investigated and it was found that the formation of a stable melt pool is determined by gravity for large melt pool sizes in the range of 50 mm and by surface tension for small melt pool sizes in the range of a few mm.
文摘The anisotropy of LPBF fabricated components is a serious concern and often increases the overall production cost by creating the necessity for secondary thermal homogenization processes.The microstructural features are the main driving force behind these anisotropic behaviors.Whereas the unique and distinctive thermal history inside a melt pool and its transient transformation is the reason for the characteristic microstructural features of LPBF fabricated components.Therefore,this paper investigates the prominent thermal variables such as heating rate,cooling rate,solidification rate etc.,and their evolution inside the melt pool of 316 L stainless steel during LPBF process to provide a reference for further exploring the generation of various microstructural features.A numerical model for macroscale investigation of thermal behavior inside melt pool was established.A 3D Gaussian heat source model coupled with temperature and density dependent properties of powder and solid phase 316 L stainless steel was used.The variation and evolution of significant thermal variables inside the melt pool were then investigated with the established numerical model.The study found that the Gaussian profile of a laser beam influences the thermal variables inside a melt-pool,including cooling rates,solidification rates,and thermal gradients.The nodes lying under the laser edge receive less heat,resulting in higher cooling effects,which shapes the grain morphology.Finer grains can be formed near the bottom melt front as well as at the center of the melt-pool surface.However,reheating adjacent tracks can result in grain coarsening.Since the generation of microstructural features is dominantly dependent on the thermal behavior inside the melt pool,an assessment of these variables is important and provides basics for the understating of different features generated in the LPBF processed components.
基金supported by the National Natural Science Foundation of China(Grant No.11772344)the National Key R&D Program of China(Project No.2016YFB1100700)。
文摘Previous studies have revealed that laser power and energy density are significant factors affecting the quality of parts manufactured by selective laser melting(SLM).The normalized equivalent density E_(0)^(*) and dimensionless laser power q^(*),which can be regarded as a progress on the understanding of the corresponding dimensional quantities,are adopted in this study to examine the defects,melt pool shape,and primary dendrite spacing of the SLM-manufactured 316 L stainless steel,because it reflects the combined effect of process parameters and material features.It is found that the number of large defects decreases with increasing E_(0)^(*) due to enough heat input during the SLM process,but it will show an increasing trend when excessive heat input(i.e.,utilizing a high E_(0)^(*))is imported into the powder bed.The q^(*) plays an important role in controlling maximum temperature rising in the SLM process,and in turn,it affects the number of large defects.A large q^(*) value results in a low value of absolute frequency of large defects,whereas a maximum value of absolute frequency of large defects is achieved at a low q^(*) even if E_(0)^(*) is very high.The density of the built parts is greater at a higher q^(*) when E_(0)^(*)remains constant.Increasing the melt pool depth at relatively low value of E_(0)^(*) enhances the relative density of the parts.A narrow,deep melt pool can be easily generated at a high q^(*) when E_(0)^(*) is sumciently high,but it may increase melt pool instability and cause keyhole defects.It is revealed that a low E_(0)^(*) can lead to a high cooling rate,which results in a refined primary dendrite spacing.Relatively low E_(0)^(*) is emphasized in selecting the process parameters for the tensile test sample fabrication.It shows that excellent tensile properties,namely ultimate tensile strength,yield strength,and elongation to failure of 773 MPa,584 MPa,and 46%,respectively,can be achieved at a relatively low E_(0)^(*) without heat treatment.
基金the Australian Government Research Training Program Scholarship,and the Australian Research Council through Discovery Projects(DP110101653,DP130103592)。
文摘Laser powder bed fusion(LPBF)has made significant progress in producing solid and porous metal parts with complex shapes and geometries.However,LPBF produced parts often have defects(e.g.,porosity,residual stress,and incomplete melting)that hinder its large-scale industrial commercialization.The LPBF process involves complex heat transfer andfluidflow,and the melt pool is a critical component of the process.The melt pool stability is a critical factor in determining the microstructure,mechanical properties,and corrosion resistance of LPBF produced metal parts.Furthermore,optimizing process parameters for new materials and designed structures is challenging due to the complexity of the LPBF process.This requires numerous trial-and-error cycles to minimize defects and enhance properties.This review examines the behavior of the melt pool during the LPBF process,including its effects and formation mechanisms.This article summarizes the experimental results and simulations of melt pool and identifies various factors that influence its behavior,which facilitates a better understanding of the melt pool's behavior during LPBF.This review aims to highlight key aspects of the investigation of melt pool tracks and microstructural characterization,with the goal of enhancing a better understanding of the relationship between alloy powder-process-microstructure-properties in LPBF from both single-and multi-melt pool track perspectives.By identifying the challenges and opportunities in investigating single-and multi-melt pool tracks,this review could contribute to the advancement of LPBF processes,optimal process window,and quality optimization,which ultimately improves accuracy in process parameters and efficiency in qualifying alloy powders.
基金supported by Key Research and Development Pro-gram of Jiangsu Province(Grant Nos.BE2022069-1 and BE2022069-2)Natural Science Research Project of Jiangsu Higher Education Institu-tions(Grant Nos.22KJB460030 and 22KJB460004)+2 种基金Suzhou Science and Technology Development Plan(Grant No.SYC2022020)startup fund-ing at the Nanjing Normal University(Grant No.184080H202B318)2022 Nanjing Carbon Peak and Neutrality Technology Innovation Special Fund(Grant No.202211017).
文摘Although laser powder bed fusion(LPBF)technology is considered one of the most promising additive man-ufacturing techniques,the fabricated parts still suffer from porosity defects,which can severely impact their mechanical performance.Monitoring the printing process using a variety of sensors to collect process signals can realize a comprehensive capture of the processing status;thus,the monitoring accuracy can be improved.However,existing multi-sensing signals are mainly optical and acoustic,and camera-based signals are mostly layer-wise images captured after printing,preventing real-time monitoring.This paper proposes a real-time melt-pool-based in-situ quality monitoring method for LPBF using multiple sensors.High-speed cameras,photodiodes,and microphones were used to collect signals during the experimental process.All three types of signals were transformed from one-dimensional time-domain signals into corresponding two-dimensional grayscale images,which enabled the capture of more localized features.Based on an improved LeNet-5 model and the weighted Dempster-Shafer evidence theory,single-sensor,dual-sensor and triple-sensor fusion monitoring models were in-vestigated with the three types of signals,and their performances were compared.The results showed that the triple-sensor fusion monitoring model achieved the highest recognition accuracy,with accuracy rates of 97.98%,92.63%,and 100%for high-,medium-,and low-quality samples,respectively.Hence,a multi-sensor fusion based melt pool monitoring system can improve the accuracy of quality monitoring in the LPBF process,which has the potential to reduce porosity defects.Finally,the experimental analysis demonstrates that the convolutional neural network proposed in this study has better classification accuracy compared to other machine learning models.
基金This work was financially supported by the National Key R&D Program of China(Grant No.2017YFB1103900)National Natural Science Foundation of China(Grant No.11972084)+1 种基金National Science and Technology Major Project(2017-VI-0003-0073)Beijing National Science Foundation(1192014).
文摘In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.
基金The authors are grateful to the financial support for this project from the National Natural Science Foundation of China under grant No. 50475131.
文摘A thermal conduction model is applied to speed up the numerical analysis of the temperature distribution and the weld pool geometry of full penetration in gas tungsten arc （GTA） welding. With considering both top and bottom flee surface deformation of full-penetrated weld pool, three-dimensional weld pool with melting front and solidification front is predicted. Welding experiments are conducted to measure the melting front curves at the top surface and the longitudinal section of the weld. It shows that the predicted and measured results are in good agreement.
文摘The laser remelting with a two-layer material system (upper material was Al-30 % Ti-20 % Ni alloy,substrate was commercial aluminum alloy) and the laser cladding of a commercial 45 steel with copper Powder (including 25%SiC) were carried out using a 2kW continuous CO2 laser. For the case of laser remelting, a upper Pool in the alloying layer and a lower Pool in the substrate separated by the unmelted Al-Ti-Ni alloy were observed. For laser cladding, a stratified Pool was observed, whose top layer was Cu alloy liquid and bottom was Fe alloy liquid. The mechanism of laser Pool separation and stratification is illustrated by numerical calculation of heat transter process of the two-layer system, combining with material physical properties (especially mixed enthalpy). A classification criterion for laser Pool with the two-layer material system has been presented and four types of the laser Pool are divided into unique Pool, separated Pool, mixed Pool and stratified pool,which provides a theoretical basis for obtaining a excellent surface coating.
基金supported by the National Natural Science Foundation of China (Nos. 51471013 and 51571004)
文摘Selective laser melting（SLM） was employed to fabricate Nb-37 Ti-13 Cr-2 Al-1 Si（at%）alloy, using pre-alloyed powders prepared by plasma rotating electrode processing（PREP）. A series of single tracks and single layers under different processing parameters was manufactured to evaluate the processing feasibility by SLM, including laser power, scanning speed, and hatch distance.Results showed that continuous single tracks could be fabricated using proper laser powers and scanning velocities. Both the width of a single track and its penetration depth into a substrate increased with an increase of the linear laser beam energy density（LED）, i.e., an increase of the laser power and a decrease of the scanning speed. Nb, Ti, Si, Cr, and Al elements distributed heterogeneously over the melt pool in the form of swirl-like patterns. An excess of the hatch distance was not able to interconnect neighboring tracks. Under improper processing parameters, a balling phenomenon occurred, but could be eliminated with an increased LED. This work testified the SLMprocessing feasibility of Nb-based alloy and promoted the application of SLM to the manufacture of niobium-based alloys.
基金financially supported by the National Natural Science Foundation of China(Nos.51974032,52174355,51604034 and 51701021).
文摘AlSi10Mg alloy was prepared by selected laser melting(SLM)in a high laser power range 300–400 W.The effects of energy density on the relative density,microstructure and mechanical properties of the SLMed AlSi10Mg alloy were studied.The results showed that the SLMed AlSi10Mg alloy fabricated at a laser power of 400 W and a scanning speed of 1800 mm/s had a relative density of 99.4%,a hardness of 147.8 HV,a tensile strength of 471.3 MPa,a yield strength of 307.1 MPa,and an elongation of 9.6%,exhibiting excellent comprehensive mechanical properties.The unique combination of the melt pool structure and microstructure caused by the large laser power and fast scanning was responsible for the excellent performance.The wide and shallow melt pool structure with few defects and proper overlapping between the continuous melt pools were obtained.The growth of columnar crystals was inhibited by a large proportion of equiaxed grains formed at the border of melt pools,and numerous sub-structures were observed within theα-Al grains.This study provided a more efficient process parameters for the preparation of the SLMed AlSi10Mg alloy.The enhanced mechanical property will help to broaden the application of the AlSi10Mg alloy in industry.
基金financially supported by the National Natural Science Foundation of China (No. 51101003)
文摘This article presents the microstructure and hardness variation of an Al 8.5Fe-1.3V 1.7Si （wt%, FVS0812） alloy after selective laser melting （SLM） modification. Three zones were distinguished across the melting pool of the SLM-processed FVS0812 alloy： the laser melted zone （LMZ）, the melting pool border, and the heat affected zone （HAZ） in the previously deposited area around the melting pool. Inside the LMZ, either an extremely fine cellular-dendritic structure or a mixture zone of the α-Al matrix and nanoscale Al12（Fe,V）3Si particles appeared. With a decreased laser beam scanning speed, the cellular-dendritic structure zone within the LMZ shrank significantly while the mixture zone expanded. The α-Al and Al12（Fe,V）3Si mixture zone was also observed in the HAZ, but another phase, submicron θ-Al13Fe4 particles with rectangular or hexagonal shapes, formed along the melting pool border. Microhardness tests indicated that the hardness of the SLM-processed FVS0812 samples far exceeded that of the as-cast FVS0812 alloy.
基金supported by the National Natu-ral Science Foundation of China(Nos.52071262,52301197,and 52234009)the National Key Research and Development Program(No.2022YFB3404203)+3 种基金the Natural Science Basic Research Pro-gram of Shaanxi Province,China(No.2023-JC-QN-0421)the Re-search Fund of the State Key Laboratory of Solidification Processing(NPU),China(Nos.2024-ZD-06 and 2024-TS-06)the Fundamental Research Funds for the Central Universities(No.D5000240144)the Young Talent Fund of Xi’an Association for Science and Tech-nology(No.959202413014).
文摘1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and can directly form complex metal parts.During SLM,the interaction of laser with metal powder forms a tiny melt pool.Following the rapid movement of the laser,the cooling rate of the melt pool can be as high as 105-106 K s−1[1].Such a fast cool-ing rate inhibits grain growth and element segregation in the alloy,leading to a notable enhancement in strength and toughness[2].Therefore,SLM enables unlimited possibilities in the fabrication of complex parts with high performance.To date,the most extensively researched Al alloys for SLM are Al-Si alloys,such as AlSi10Mg,Al-12Si,and AlSi7Mg[2-5].
基金financially supported by the Shanghai Materials Genome Institute No. 5 (No. 16DZ2260605)the Shanghai Sailing Program (No. 17YF1405400)the Project to Strengthen Industrial Development at the Grass-roots Level (No. TC160A310/19)
文摘The corrosion behavior and mechanical properties of 316 L stainless steel(SS) fabricated via selective laser melting(SLM) were clarified by potentiodynamic polarization measurements, immersion tests, and tensile experiments. The microstructural anisotropy of SLMed 316 L SS was also investigated by electron back-scattered diffraction and transmission electron microscopy. The grain sizes of the SLMed 316 L SS in the XOZ plane were smaller than those of the SLMed 316 L SS in the XOY plane, and a greater number of low-angle boundaries were present in the XOY plane, resulting in lower elongation for the XOY plane than for the XOZ plane. The SLMed 316 L was expected to exhibit higher strength but lower ductility than the wrought 316 L, which was attributed to the high density of dislocations. The pitting potentials of the SLMed 316 L samples were universally higher than those of the wrought sample in chloride solutions because of the annihilation of MnS or(Ca,Al)-oxides during the rapid solidification. However, the molten pool boundaries preferentially dissolved in aggressive solutions and the damage of the SLMed 316 L in FeCl3 solution was more serious after long-term service, indicating poor durability.
基金supported by the National Natural Science Foundation of China-Distinguished Young Scholars(No.52325407)the National Natural Science Foundation of China-Key Program(No.52234010)the Open Research Fund of the State Key Laboratory of Rolling and Automation,Northeastern University(No.2022RALKFKT004).
文摘Laser additive manufacturing(LAM)has been widely used in high-end manufacturing fields such as aerospace,nuclear power,and shipbuilding.However,it is a grand challenge for direct and continuous observation of complex laser-matter interaction,melt flow,and defect formation during LAM due to extremely large temperature gradient,fast cooling rate,and small time(millisecond)and space(micron)scales.The emergence of synchrotron radiation provides a feasible approach for in situ observation of the LAM process.This paper outlines the current development in real-time characterization of LAM by synchrotron radiation,including laser-matter interaction,molten pool evolution,solidification structure evolution,and defects formation and elimination.Furthermore,the future development direction and application-oriented research are also discussed.
基金financially supported by the Project of Chinese Academy of Engineering(Nos.2019-XZ-11 and 2023-XY-18)the Open Fund of National Joint Engineering Research Center for Abrasion Control and Molding of Metal Materials of China(No.HKDNM201907)。
文摘A novel Cu−4.8Cr−2.2Nb−0.15Y(at.%)alloy was fabricated by employing the laser powder bed fusion with different processing parameters.The influence of laser power(P),scanning speed(v),and laser linear energy density(El)on the defects,melt pool morphology,microstructure,and properties of the alloy was systematically investigated.The results show that the optimized process parameters for preparing Cu−Cr−Nb−Y alloy with relative density over 99.5%are P=300−350 W and v=650−800 mm/s,corresponding to El=0.375−0.538 J/mm.When E_(l)<0.3 J/mm,increasing P or decreasing v can enhance the continuity and size of the melt pool,reduce the lack-of-fusion defects,and increase the relative density.However,excessively high E_(l)leads to a deeper melt pool,more keyholes,and reduced relative density.The grain size of the as-built Cu−Cr−Nb−Y alloy shows a bimodal distribution,with fine grains at the center and coarse grains at the edge of the melt pool.Increasing P or decreasing v increases the average grain size and(110)texture intensity.The alloy fabricated with P=350 W and v=800 mm/s displays the highest relative density of 99.82%.The yield strength,tensile strength,and elongation are(443±5)MPa,(699±4)MPa,and(17.1±0.7)%,respectively.
