Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.T...Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.The aim of this study is to enhance the understanding of this action by analyzing the mechanism of droplet oscillation.The pendant droplet oscillation phenomenon hinders the stable transfer of droplets to the molten pool and limits the feasibility of manufacturing complex lattice structures by EB–DED.Hence,another aim of this study is to create an oscillation suppression method.An escalating asymmetric amplitude is the main characteristic of droplet oscillation.The primary oscillationinducing force is the recoil force generated from the EB-acted local surface of the droplet.The physical mechanism of this force is the rapid increase and uneven distribution of the local surface temperature caused by the partial action of the EB.The prerequisites for droplet oscillation include vacuum conditions,high power densities,and bypass wire feeding processes.The proposed EB–dynamic surrounding melting(DSM)method can be applied to conveniently and effectively suppress oscillations,enable the accurate transfer of droplets to the molten pool,and achieve stable processes for preparing the strut elements of lattice structures.Lowering the temperature and improving the uniformity of its distribution are the mechanisms of oscillation suppression in EB–DSM.In this study,the physical basis for interpreting the mechanism by which EBs act on droplets and the technical basis for using EB–DED to prepare complex lattice structure parts are provided.展开更多
Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different pr...Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different processing histories.Here,the microstructures and wear behavior of different zones(substrate,HAZ,and deposit)are investigated for the IC10 directionally solidified superalloy repaired by the directed energy deposition process.It is found that the microstructure of the deposited layers is strongly textured with a<001>-fiber texture in the building direction,and the texture intensity is continuously increased along the building direction.Two kinds ofγ’phase(primary and secondaryγ’phase)can be found in the heat-affected zone(HAZ),and the average size of primaryγ’phase is smaller than that in the substrate due to liquation.In the deposit layers,the size ofγ’phase is much smaller than those in the substrate and the primaryγ’phase of HAZ;both size and the fraction of theγ’phase decreases with the increase of building height.The wear rate of the substrate is the smallest,indicating the best wear resistance;while the wear rate of HAZ is the largest,indicating the worst wear resistance in the repaired sample.The wear rates in the deposit layers increase from the bottom to the top zones,showing a decreasing wear resistance.Abrasive wear is found to be the dominant wear mechanism of the repaired alloy,and the resistance to which is closely related to the fraction ofγ’phase in the microstructure.The understanding of the influence of microstructure on wear resistance allows for a more informed application of inhomogeneous superalloy components repaired by directed energy deposition in industry.展开更多
For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-f...For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.展开更多
Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its applic...Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its application is restricted currently due to the limitations of traditional processing methods.Recently,our group first successfully prepared this alloy with an unconventional approach named wire-based in-situ additive manufacturing(AM)technology,and great mechanical performance has been obtained.The unbalanced thermal process of AM easily causes inconsistent or undesired microstructures,as well as mechanical properties.Therefore,in this study,we further carried out post-heat treatment research on the as-printed sample so as to optimize its mechanical performance.Results show that theα2-phase will precipitate from the as-deposited samples(B2/β+O)after solution treatment(ST),while all precipitates were dissolved to the B2/β-matrix when the solution temperature was 1100℃.The aging treatment(AT)promoted a great number of O-phases precipitated and led to an increase in its proportion.With the increase in aging temperature,the tensile strength decreased(995 to 821 MPa)gradually coupling the increase of fracture strain(1.65%to 2.12%),while the aging duration time did not show an obvious ef-fect on its performance.In addition,after proper heat treatment,the high temperature(650℃)tensile strength of the samples was as high as 818 and 792 MPa.This research not only promotes the develop-ment of Ti_(2) AlNb-based alloy fabricated through in-situ AM,but also facilitates its further application in the aerospace field.展开更多
基金supported by the National Natural Science Foundation of China(52375349)the Beijing Municipal Natural Science Foundation(3222008).
文摘Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.The aim of this study is to enhance the understanding of this action by analyzing the mechanism of droplet oscillation.The pendant droplet oscillation phenomenon hinders the stable transfer of droplets to the molten pool and limits the feasibility of manufacturing complex lattice structures by EB–DED.Hence,another aim of this study is to create an oscillation suppression method.An escalating asymmetric amplitude is the main characteristic of droplet oscillation.The primary oscillationinducing force is the recoil force generated from the EB-acted local surface of the droplet.The physical mechanism of this force is the rapid increase and uneven distribution of the local surface temperature caused by the partial action of the EB.The prerequisites for droplet oscillation include vacuum conditions,high power densities,and bypass wire feeding processes.The proposed EB–dynamic surrounding melting(DSM)method can be applied to conveniently and effectively suppress oscillations,enable the accurate transfer of droplets to the molten pool,and achieve stable processes for preparing the strut elements of lattice structures.Lowering the temperature and improving the uniformity of its distribution are the mechanisms of oscillation suppression in EB–DSM.In this study,the physical basis for interpreting the mechanism by which EBs act on droplets and the technical basis for using EB–DED to prepare complex lattice structure parts are provided.
基金financial support to this work from the Tribology Science Fund of the State Key Laboratory of Tribology(SKLT2020C09)National Natural Science Foundation of China(No.51675303)National Key Research and Development Program of China(2017YFB1103300)。
文摘Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different processing histories.Here,the microstructures and wear behavior of different zones(substrate,HAZ,and deposit)are investigated for the IC10 directionally solidified superalloy repaired by the directed energy deposition process.It is found that the microstructure of the deposited layers is strongly textured with a<001>-fiber texture in the building direction,and the texture intensity is continuously increased along the building direction.Two kinds ofγ’phase(primary and secondaryγ’phase)can be found in the heat-affected zone(HAZ),and the average size of primaryγ’phase is smaller than that in the substrate due to liquation.In the deposit layers,the size ofγ’phase is much smaller than those in the substrate and the primaryγ’phase of HAZ;both size and the fraction of theγ’phase decreases with the increase of building height.The wear rate of the substrate is the smallest,indicating the best wear resistance;while the wear rate of HAZ is the largest,indicating the worst wear resistance in the repaired sample.The wear rates in the deposit layers increase from the bottom to the top zones,showing a decreasing wear resistance.Abrasive wear is found to be the dominant wear mechanism of the repaired alloy,and the resistance to which is closely related to the fraction ofγ’phase in the microstructure.The understanding of the influence of microstructure on wear resistance allows for a more informed application of inhomogeneous superalloy components repaired by directed energy deposition in industry.
基金This work was financially supported by the Tribology Science Fund of the State Key Laboratory of Tribology(No.SKLT2022C20)the National Natural Science Foundation of China(Nos.51875309 and 51905310)the Natural Science Foundation of Shandong Province(No.ZR2020YQ39).
文摘For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.
基金financially supported by the National Natural Sci-ence Foundation of China(No.51875309)the Beijing Municipal Natural Science Foundation(CN)(No.3222008).
文摘Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its application is restricted currently due to the limitations of traditional processing methods.Recently,our group first successfully prepared this alloy with an unconventional approach named wire-based in-situ additive manufacturing(AM)technology,and great mechanical performance has been obtained.The unbalanced thermal process of AM easily causes inconsistent or undesired microstructures,as well as mechanical properties.Therefore,in this study,we further carried out post-heat treatment research on the as-printed sample so as to optimize its mechanical performance.Results show that theα2-phase will precipitate from the as-deposited samples(B2/β+O)after solution treatment(ST),while all precipitates were dissolved to the B2/β-matrix when the solution temperature was 1100℃.The aging treatment(AT)promoted a great number of O-phases precipitated and led to an increase in its proportion.With the increase in aging temperature,the tensile strength decreased(995 to 821 MPa)gradually coupling the increase of fracture strain(1.65%to 2.12%),while the aging duration time did not show an obvious ef-fect on its performance.In addition,after proper heat treatment,the high temperature(650℃)tensile strength of the samples was as high as 818 and 792 MPa.This research not only promotes the develop-ment of Ti_(2) AlNb-based alloy fabricated through in-situ AM,but also facilitates its further application in the aerospace field.
