For Ti-6Al-4V,a titanium alloy increasingly used in aerospace structure,selective laser melting(SLM)is an attractive additive manufacturing technology,which is attributed to its complex construction capability with hi...For Ti-6Al-4V,a titanium alloy increasingly used in aerospace structure,selective laser melting(SLM)is an attractive additive manufacturing technology,which is attributed to its complex construction capability with high accuracy and good surface quality.In order to obtain qualified mechanical properties,SLM parameters and post processing should be tailored for diverse service conditions.Fracture toughness and fatigue crack growth(FCG)behavior are critical characteristics for damage tolerance evaluation of such metallic structures,and they are affected by post processing technologies significantly.The objective of this study is to obtain the fracture toughness and fatigue crack growth behavior of Ti-6Al-4V manufactured by SLM,and to evaluate the influence of post-SLM thermomechanical treatment and surface machining.Fracture toughness and FCG tests were performed for SLM Ti-6Al-4V in three types of post processing status:as-built,heat treated and hot isostatically pressed(HIPed),respectively.Specimens with as-built and machined surface were tested.The microstructure and fractography were analyzed as well in order to investigate the relevance among manufacture process,microstructure and mechanical properties.The results demonstrate that as-built SLM Ti-6Al-4V presents poor ductility and FCG behavior due to martensitic microstructure and residual stresses.Both heat treatment and hot isostatic pressing improve the plane-stress fracture toughness and FCG performance considerably,while surface machining shows slight effect.展开更多
Selective laser melting （SLM） is a powerful additive manufacturing （AM） technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of t...Selective laser melting （SLM） is a powerful additive manufacturing （AM） technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6AI-4V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing （HIP） were investigated. The microstructures were analyzed by optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscopy （TEM）. The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the as- deposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900~C for 2-4 h and HIP at 920~C/100MPa for 2 h, the brittle martensite could be transformed into ductile lamellar （a＋~） microstructure and the static tensile properties of SLM-processed Ti-6AI-4V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed fi-6AI-4V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar （a＋13） microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.展开更多
The high-cycle fatigue and fracture behaviours of the selective laser melting(SLM)AlSi10Mg alloy were investigated.Flat specimens were designed directly in the shape required for the fatigue tests under pulsating load...The high-cycle fatigue and fracture behaviours of the selective laser melting(SLM)AlSi10Mg alloy were investigated.Flat specimens were designed directly in the shape required for the fatigue tests under pulsating loading in tension(R=0,R is the dynamic factor).The fatigue−life(S−N)curves were modelled with a conditional Weibull’s probability density function,where the real-valued genetic algorithm(GA)and the differential ant-stigmergy algorithm(DASA)were applied to estimating the needed Weibull’s parameters.The fractography of the fatigue specimens showed that the fatigue cracks initiated around the surface defects produced by SLM and then propagated in an unstable manner.However,the presence of large SLM defects mainly influenced the crack initiation period and did not have a strong influence on the crack propagation.The obtained experimental results present a basis for further investigation of the fatigue behaviour of advanced materials and structures(e.g.cellular metamaterials)fabricated by additive manufacturing(AM).Especially,in the case of two-dimensional cellular structures,the cross-section of cellular struts is usually rectangular which corresponds to the specimen shape considered in this work.展开更多
The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The s...The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.展开更多
The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of...The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.展开更多
Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles,which can crucially affect the quality of human life in terms of normal walking ...Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles,which can crucially affect the quality of human life in terms of normal walking or daily activities.For successful patient recovery,it is necessary to remove the cancer-affected minimal bone area and quickly replace it with a biocompatible metal implant within less than 2 weeks.An electron beam-melted Ti-6Al-4V implant was designed and applied in a patient to preserve the natural knee joint close to the bone tumor.The developed implant fits the bone defect well,and the independent ambulatory function of the natural knee joint was restored in the patient within six weeks after surgery.A delayed fracture occurred six months after the successful replacement of cancer-affected bone with Ti-6Al-4V implant at the proximal meshed junction of the implant because of a minor downward slip.Microstructural,mechanical,and computational analyses were conducted for the fractured area to find the main reason for the delayed fracture.Our findings pertaining to the mechanical and material investigation can help realize the safe implantation of the three-dimensionally printed titanium implant to preserve the natural joints of patients with massive bone defects of the extremities.展开更多
Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates...Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.展开更多
基金supported by the Innovation Fund of Aircraft Strength Research Institute of China(No.16-025-03)
文摘For Ti-6Al-4V,a titanium alloy increasingly used in aerospace structure,selective laser melting(SLM)is an attractive additive manufacturing technology,which is attributed to its complex construction capability with high accuracy and good surface quality.In order to obtain qualified mechanical properties,SLM parameters and post processing should be tailored for diverse service conditions.Fracture toughness and fatigue crack growth(FCG)behavior are critical characteristics for damage tolerance evaluation of such metallic structures,and they are affected by post processing technologies significantly.The objective of this study is to obtain the fracture toughness and fatigue crack growth behavior of Ti-6Al-4V manufactured by SLM,and to evaluate the influence of post-SLM thermomechanical treatment and surface machining.Fracture toughness and FCG tests were performed for SLM Ti-6Al-4V in three types of post processing status:as-built,heat treated and hot isostatically pressed(HIPed),respectively.Specimens with as-built and machined surface were tested.The microstructure and fractography were analyzed as well in order to investigate the relevance among manufacture process,microstructure and mechanical properties.The results demonstrate that as-built SLM Ti-6Al-4V presents poor ductility and FCG behavior due to martensitic microstructure and residual stresses.Both heat treatment and hot isostatic pressing improve the plane-stress fracture toughness and FCG performance considerably,while surface machining shows slight effect.
基金financially supported by the National Program on Key Basic Research Project of China(973 Program)under Grant(No.613281)the National Natural Science Foundation of China(No.51505451)+3 种基金the Natural Science Foundation of Beijing(No.3172042)supported by EMUSIC which is part of an EU-China collaborationthe European Union’s Horizon 2020 research and innovation programme under Grant Agreement No.690725MIIT under the programme number MJ-2015-H-G-104
文摘Selective laser melting （SLM） is a powerful additive manufacturing （AM） technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6AI-4V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing （HIP） were investigated. The microstructures were analyzed by optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscopy （TEM）. The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the as- deposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900~C for 2-4 h and HIP at 920~C/100MPa for 2 h, the brittle martensite could be transformed into ductile lamellar （a＋~） microstructure and the static tensile properties of SLM-processed Ti-6AI-4V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed fi-6AI-4V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar （a＋13） microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.
基金the research core funding(No.P2-0063)the basic research project(No.J2-8186)from the Slovenian Research Agency.
文摘The high-cycle fatigue and fracture behaviours of the selective laser melting(SLM)AlSi10Mg alloy were investigated.Flat specimens were designed directly in the shape required for the fatigue tests under pulsating loading in tension(R=0,R is the dynamic factor).The fatigue−life(S−N)curves were modelled with a conditional Weibull’s probability density function,where the real-valued genetic algorithm(GA)and the differential ant-stigmergy algorithm(DASA)were applied to estimating the needed Weibull’s parameters.The fractography of the fatigue specimens showed that the fatigue cracks initiated around the surface defects produced by SLM and then propagated in an unstable manner.However,the presence of large SLM defects mainly influenced the crack initiation period and did not have a strong influence on the crack propagation.The obtained experimental results present a basis for further investigation of the fatigue behaviour of advanced materials and structures(e.g.cellular metamaterials)fabricated by additive manufacturing(AM).Especially,in the case of two-dimensional cellular structures,the cross-section of cellular struts is usually rectangular which corresponds to the specimen shape considered in this work.
基金financially supported by the National Natural Science Foundation of China(NSFC)under Gtrant No.50401019the“Hun-dred of Talent Project"by Chinese Academy of Sciences+1 种基金National Outstanding Young Scientist Foundation for Z.F.Zhang under Grant No.50625103the financial support of the Alexander-von-Humboldt(AvH)Foundation.
文摘The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.
基金support from the National Natural Science Foundation of China(NSFC,Project Nos.91860136 and 51801231)the Key R&D Plan of Guangdong Province(Grant No.2018B090905001)the Key Science and Technology project of Shaanxi Province(Grant No.2018zdzx01-04-01).
文摘The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.
基金supported by the National Cancer Center Grant(No.NCC-2110270)the Ulsan National Institute of Science and Technology(No.1.200110.01)+1 种基金the National Research Foundation of Korea(NRF)Grant funded by the Korea government(MSIP)(No.2018R1A5A6075959)the Korea government(MSIT)(No.2021M2D2A1A01050059).
文摘Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles,which can crucially affect the quality of human life in terms of normal walking or daily activities.For successful patient recovery,it is necessary to remove the cancer-affected minimal bone area and quickly replace it with a biocompatible metal implant within less than 2 weeks.An electron beam-melted Ti-6Al-4V implant was designed and applied in a patient to preserve the natural knee joint close to the bone tumor.The developed implant fits the bone defect well,and the independent ambulatory function of the natural knee joint was restored in the patient within six weeks after surgery.A delayed fracture occurred six months after the successful replacement of cancer-affected bone with Ti-6Al-4V implant at the proximal meshed junction of the implant because of a minor downward slip.Microstructural,mechanical,and computational analyses were conducted for the fractured area to find the main reason for the delayed fracture.Our findings pertaining to the mechanical and material investigation can help realize the safe implantation of the three-dimensionally printed titanium implant to preserve the natural joints of patients with massive bone defects of the extremities.
文摘Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.
