通过对激光粉末床熔化(laser powder bed fusion,L-PBF)成形FGH4096M镍基粉末高温合金进行不同温度的退火处理,采用SEM、EBSD等分析了合金的微观组织结构,并对其进行了拉伸测试,进而研究退火工艺对激光粉末床熔化成形FGH4096M镍基粉末...通过对激光粉末床熔化(laser powder bed fusion,L-PBF)成形FGH4096M镍基粉末高温合金进行不同温度的退火处理,采用SEM、EBSD等分析了合金的微观组织结构,并对其进行了拉伸测试,进而研究退火工艺对激光粉末床熔化成形FGH4096M镍基粉末高温合金中显微组织的演变及力学性能的影响。结果表明:随着退火温度的升高,成形态合金中胞状晶组织和柱状晶组织出现了消失的趋势,当退火温度为900℃时,开始发现有大量γ′相析出;其硬度值先升高后降低,抗拉强度和屈服强度均呈现先上升后降低趋势,但其断后延伸率在逐渐降低。通过对晶粒取向差分布分析,可知退火能够消除部分残余应力。这一研究成果为激光粉末床熔化成形镍基粉末高温合金性能的提升提供了有效的数据支撑。展开更多
Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build c...Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build chamber with a single gas inlet exhibits a pronounced tendency for gas to flow upward near the outlet.This phenomenon results in the formation of a large vortex within the build chamber.The vortex leads to the chaotic motion trajectory of the spatter in the build chamber.The design defects of the existing build chamber based on dual gas inlets are shown in this paper.We established a coupled computational fluid dynamics-discrete phase model(CFD-DPM)model to optimize the build chamber by adjusting the position and structure of the second gas inlet.The homogeneity of the flow is increased with a distance of 379 mm between the two inlets and a wider-reaching second inlet.The Coanda effect is also crucial in the spatter-removal process.The Coanda effect is reduced by modifying the right sidewall of the build chamber and increasing the pressure difference between the inlet and outlet.Finally,we found that the spatter-removal rate rose from 8.9%to 76.1%between the conventional build chamber with a single gas inlet and the optimized build chamber with two gas inlets.展开更多
目的采用超声辅助化学蚀刻的方法,去除激光粉末床熔化(Laser Beam Powder Bed Fusion,L-PBF)技术成形的多孔结构表面残粉,提升多孔结构的表面精度和质量。方法利用超声辅助化学蚀刻试验平台,探究溶液配比、蚀刻时间、蚀刻温度对粉末去...目的采用超声辅助化学蚀刻的方法,去除激光粉末床熔化(Laser Beam Powder Bed Fusion,L-PBF)技术成形的多孔结构表面残粉,提升多孔结构的表面精度和质量。方法利用超声辅助化学蚀刻试验平台,探究溶液配比、蚀刻时间、蚀刻温度对粉末去除效果的影响。对比分析不同工艺参数处理后的试件表面形貌、支杆直径、质量变化。结果超声辅助可以显著提升化学蚀刻后的表面质量;蚀刻温度在30~60℃范围内,试件蚀刻后的尺寸精度最高;采用溶液体积比为HF∶HNO_(3)∶H_(2)O=4∶14∶82,加热温度为50℃,蚀刻9 min,试件的尺寸精度误差可低至0.24%。结论通过蚀刻时间与溶液浓度的合理配比,可以有效去除试件表面的残粉,提升试件的表面质量,残粉去除率达到了91.9%;通过增加酸性溶液浓度、控制溶液温度,可以将蚀刻效率提升2倍以上,同时达到有效去除残粉和提升蚀刻效率的效果。展开更多
Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion(LPBF...Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion(LPBF) in artificial saliva at 37.C. The passivity of L-PBF NiTi shows to be influenced by the process parameters and resulting morphological and physicochemical surface properties. The results show that the defects at the surface of L-PBF Ni Ti can promote the passivation rate in the early stages of exposure but a slowly formed passive film shows the best corrosion protection. The thickness of the passive film is positively correlated with its corrosion protective performance. The L-PBF NiTi alloy prepared at a linear energy density of 0.2 J·m^(-1) and volumetric energy density of 56 J·mm^(-3) shows the least defects and best corrosion protection. An outer Ti-rich and inner Ni-rich dense passive film could be also obtained showing higher corrosion resistance.展开更多
This study investigated the impact of thermal cycling effects on the microstructure and mechanical properties of IN738LC alloy manufactured by laser powder bed fusion,considering different volumetric energy densities(...This study investigated the impact of thermal cycling effects on the microstructure and mechanical properties of IN738LC alloy manufactured by laser powder bed fusion,considering different volumetric energy densities(VEDs)and interlayer times(ILTs)as part of the experimental parameters.The results show that low VED and long ILT samples displayed superior quality,with an average grain size of 10.97μm and relatively low strain accumulation level.In contrast,samples with high VED and long ILT exhibit increased cracking and porosity,the average grain size is 14.63μm and present higher strain accumulation degree.The nano-primary MC phase within the alloy transformed into a spherical secondary MC phase inside the grain and a polygonal secondary MC phase on the grain boundary.In the low VED and long ILT,the mean equivalent diameter(MED)of MC carbide within the grain and on the grain boundary was 63 and 140 nm,respectively,the tensile strength was 1072±21 MPa.By contrast,for the high VED and long ILT,the MED of MC carbide in the grain and on the grain boundary were 47 and105 nm,respectively,and the tensile strength was794±31 MPa.The tensile strength of high VED and long ILT decreased by 26%compared with low VED and long ILT.展开更多
Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF)...Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in question.In the present research,first,a thermo-fluid computational fluid dynamics(CFD)model is developed and validated against experimental data.Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool dynamics.It is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass loss.Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of defects.Finally,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in L-PBF.In summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBF.展开更多
High-entropy alloys(HEAs)are considered alternatives to traditional structural materials because of their superior mechanical,physical,and chemical properties.However,alloy composition combinations are too numerous to...High-entropy alloys(HEAs)are considered alternatives to traditional structural materials because of their superior mechanical,physical,and chemical properties.However,alloy composition combinations are too numerous to explore.Finding a rapid synthesis method to accelerate the development of HEA bulks is imperative.Existing in situ synthesis methods based on additive manufacturing are insufficient for efficiently controlling the uniformity and accuracy of components.In this work,laser powder bed fusion(L-PBF)is adopted for the in situ synthesis of equiatomic CoCrFeMnNi HEA from elemental powder mixtures.High composition accuracy is achieved in parallel with ensuring internal density.The L-PBF-based process parameters are optimized;and two different methods,namely,a multi-melting process and homogenization heat treatment,are adopted to address the problem of incompletely melted Cr particles in the single-melted samples.X-ray diffraction indicates that HEA microstructure can be obtained from elemental powders via L-PBF.In the triple-melted samples,a strong crystallographic texture can be observed through electron backscatter diffraction,with a maximum polar density of 9.92 and a high ultimate tensile strength(UTS)of(735.3±14.1)MPa.The homogenization heat-treated samples appear more like coarse equiaxed grains,with a UTS of(650.8±16.1)MPa and an elongation of(40.2%±1.3%).Cellular substructures are also observed in the triple-melted samples,but not in the homogenization heat-treated samples.The differences in mechanical properties primarily originate from the changes in strengthening mechanism.The even and flat fractographic morphologies of the homogenization heat-treated samples represent a more uniform internal microstructure that is different from the complex morphologies of the triple-melted samples.Relative to the multi-melted samples,the homogenization heat-treated samples exhibit better processability,with a smaller composition deviation,i.e.,≤0.32 at.%.The two methods presented in this study are expected to have considerable potential for developing HEAs with high composition accuracy and composition flexibility.展开更多
Many processes may be used for manufacturing functionally graded materials.Among them,additive manufacturing seems to be predestined due to near-net shape manufacturing of complex geometries combined with the possibil...Many processes may be used for manufacturing functionally graded materials.Among them,additive manufacturing seems to be predestined due to near-net shape manufacturing of complex geometries combined with the possibility of applying different materials in one component.By adjusting the powder composition of the starting material layer by layer,a macroscopic and step-like gradient can be achieved.To further improve the step-like gradient,an enhancement of the in-situ mixing degree,which is limited according to the state of the art,is necessary.In this paper,a novel technique for an enhancement of the in-situ material mixing degree in the melt pool by applying laser remelting(LR)is described.The effect of layer-wise LR on the formation of the interface was investigated using pure copper and low-alloy steel in a laser powder bed fusion process.Subsequent cross-sectional selective electron microscopic analyses were carried out.By applying LR,the mixing degree was enhanced,and the reaction zone thickness between the materials was increased.Moreover,an additional copper and iron-based phase was formed in the interface,resulting in a smoother gradient of the chemical composition than the case without LR.The Marangoni convection flow and thermal diffusion are the driving forces for the observed effect.展开更多
文摘通过对激光粉末床熔化(laser powder bed fusion,L-PBF)成形FGH4096M镍基粉末高温合金进行不同温度的退火处理,采用SEM、EBSD等分析了合金的微观组织结构,并对其进行了拉伸测试,进而研究退火工艺对激光粉末床熔化成形FGH4096M镍基粉末高温合金中显微组织的演变及力学性能的影响。结果表明:随着退火温度的升高,成形态合金中胞状晶组织和柱状晶组织出现了消失的趋势,当退火温度为900℃时,开始发现有大量γ′相析出;其硬度值先升高后降低,抗拉强度和屈服强度均呈现先上升后降低趋势,但其断后延伸率在逐渐降低。通过对晶粒取向差分布分析,可知退火能够消除部分残余应力。这一研究成果为激光粉末床熔化成形镍基粉末高温合金性能的提升提供了有效的数据支撑。
基金supported by the Natural Science Foundation of Jiangxi Province(Nos.20224BAB214061 and 20224ACB214008)the National Natural Science Foundation of China(Nos.52165043 and 52166002)+2 种基金the Jiangxi Provincial Cultivation Program for Academic and Technical Leaders of Major Subjects(No.20225BCJ23008)the Anhui Provincial Natural Science Foundation(No.2308085ME171)the University Synergy Innovation Program of Anhui Province(Nos.GXXT-2023-025 and GXXT-2023-026),China。
文摘Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build chamber with a single gas inlet exhibits a pronounced tendency for gas to flow upward near the outlet.This phenomenon results in the formation of a large vortex within the build chamber.The vortex leads to the chaotic motion trajectory of the spatter in the build chamber.The design defects of the existing build chamber based on dual gas inlets are shown in this paper.We established a coupled computational fluid dynamics-discrete phase model(CFD-DPM)model to optimize the build chamber by adjusting the position and structure of the second gas inlet.The homogeneity of the flow is increased with a distance of 379 mm between the two inlets and a wider-reaching second inlet.The Coanda effect is also crucial in the spatter-removal process.The Coanda effect is reduced by modifying the right sidewall of the build chamber and increasing the pressure difference between the inlet and outlet.Finally,we found that the spatter-removal rate rose from 8.9%to 76.1%between the conventional build chamber with a single gas inlet and the optimized build chamber with two gas inlets.
基金financially supported by the financial support from the International Postdoctoral Exchange Fellowship Program 2019 by the Office of China Postdoctoral Council (No. 20190086)the support from the Russian Science Foundation Grant (No. 19-79-30002)。
文摘Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion(LPBF) in artificial saliva at 37.C. The passivity of L-PBF NiTi shows to be influenced by the process parameters and resulting morphological and physicochemical surface properties. The results show that the defects at the surface of L-PBF Ni Ti can promote the passivation rate in the early stages of exposure but a slowly formed passive film shows the best corrosion protection. The thickness of the passive film is positively correlated with its corrosion protective performance. The L-PBF NiTi alloy prepared at a linear energy density of 0.2 J·m^(-1) and volumetric energy density of 56 J·mm^(-3) shows the least defects and best corrosion protection. An outer Ti-rich and inner Ni-rich dense passive film could be also obtained showing higher corrosion resistance.
基金financially supported by Gansu Key Research and Development Program(No.22YF7GA156)the Major Science and Technology Project of Gansu Province(No.22ZD6GA008)Hong Liu First-Class Discipline Construction Plan of Lanzhou University of Technology(No.CGZH001)。
文摘This study investigated the impact of thermal cycling effects on the microstructure and mechanical properties of IN738LC alloy manufactured by laser powder bed fusion,considering different volumetric energy densities(VEDs)and interlayer times(ILTs)as part of the experimental parameters.The results show that low VED and long ILT samples displayed superior quality,with an average grain size of 10.97μm and relatively low strain accumulation level.In contrast,samples with high VED and long ILT exhibit increased cracking and porosity,the average grain size is 14.63μm and present higher strain accumulation degree.The nano-primary MC phase within the alloy transformed into a spherical secondary MC phase inside the grain and a polygonal secondary MC phase on the grain boundary.In the low VED and long ILT,the mean equivalent diameter(MED)of MC carbide within the grain and on the grain boundary was 63 and 140 nm,respectively,the tensile strength was 1072±21 MPa.By contrast,for the high VED and long ILT,the MED of MC carbide in the grain and on the grain boundary were 47 and105 nm,respectively,and the tensile strength was794±31 MPa.The tensile strength of high VED and long ILT decreased by 26%compared with low VED and long ILT.
基金the financial supports received from Wenner-Gren foundation(UPD2021-0229),JernkontoretSTT(Stiftelsen för Tillämpad Termodynamik).
文摘Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in question.In the present research,first,a thermo-fluid computational fluid dynamics(CFD)model is developed and validated against experimental data.Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool dynamics.It is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass loss.Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of defects.Finally,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in L-PBF.In summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBF.
文摘High-entropy alloys(HEAs)are considered alternatives to traditional structural materials because of their superior mechanical,physical,and chemical properties.However,alloy composition combinations are too numerous to explore.Finding a rapid synthesis method to accelerate the development of HEA bulks is imperative.Existing in situ synthesis methods based on additive manufacturing are insufficient for efficiently controlling the uniformity and accuracy of components.In this work,laser powder bed fusion(L-PBF)is adopted for the in situ synthesis of equiatomic CoCrFeMnNi HEA from elemental powder mixtures.High composition accuracy is achieved in parallel with ensuring internal density.The L-PBF-based process parameters are optimized;and two different methods,namely,a multi-melting process and homogenization heat treatment,are adopted to address the problem of incompletely melted Cr particles in the single-melted samples.X-ray diffraction indicates that HEA microstructure can be obtained from elemental powders via L-PBF.In the triple-melted samples,a strong crystallographic texture can be observed through electron backscatter diffraction,with a maximum polar density of 9.92 and a high ultimate tensile strength(UTS)of(735.3±14.1)MPa.The homogenization heat-treated samples appear more like coarse equiaxed grains,with a UTS of(650.8±16.1)MPa and an elongation of(40.2%±1.3%).Cellular substructures are also observed in the triple-melted samples,but not in the homogenization heat-treated samples.The differences in mechanical properties primarily originate from the changes in strengthening mechanism.The even and flat fractographic morphologies of the homogenization heat-treated samples represent a more uniform internal microstructure that is different from the complex morphologies of the triple-melted samples.Relative to the multi-melted samples,the homogenization heat-treated samples exhibit better processability,with a smaller composition deviation,i.e.,≤0.32 at.%.The two methods presented in this study are expected to have considerable potential for developing HEAs with high composition accuracy and composition flexibility.
文摘Many processes may be used for manufacturing functionally graded materials.Among them,additive manufacturing seems to be predestined due to near-net shape manufacturing of complex geometries combined with the possibility of applying different materials in one component.By adjusting the powder composition of the starting material layer by layer,a macroscopic and step-like gradient can be achieved.To further improve the step-like gradient,an enhancement of the in-situ mixing degree,which is limited according to the state of the art,is necessary.In this paper,a novel technique for an enhancement of the in-situ material mixing degree in the melt pool by applying laser remelting(LR)is described.The effect of layer-wise LR on the formation of the interface was investigated using pure copper and low-alloy steel in a laser powder bed fusion process.Subsequent cross-sectional selective electron microscopic analyses were carried out.By applying LR,the mixing degree was enhanced,and the reaction zone thickness between the materials was increased.Moreover,an additional copper and iron-based phase was formed in the interface,resulting in a smoother gradient of the chemical composition than the case without LR.The Marangoni convection flow and thermal diffusion are the driving forces for the observed effect.
