Additive manufactured metals sometimes exhibit extraordinary microstructures and mechanical properties due to the particular processes. In this paper, we focus on a novel gradient TiAl alloys fabricated byhigh-power d...Additive manufactured metals sometimes exhibit extraordinary microstructures and mechanical properties due to the particular processes. In this paper, we focus on a novel gradient TiAl alloys fabricated byhigh-power direct laser deposition, whose chemical composition, microstructure, and mechanical property vary along the building direction. The results indicate that Al concentration dramatically decreasesfrom 39.5 at.% to 30.1 at.% as the height increases from the bottom to the top. Meanwhile, microstructural characterization indicates that the specimen appears basket-weave microstructure at the bottom,then the α_(2) and γ phase gradually decrease, and eventually it transforms into acicular martensite microstructure in the top region. The indentation analysis shows that the associated hardness increases asthe height increases, while the plasticity reaches a minimum value in the middle region. The increasingamount of β_(o)(ω) is considered to be responsible for the increasing hardness because of the strong precipitation strengthening effect. The high plasticity in the bottom and top regions results from the strongdeformation behaviors of the γ and β_(o) phases.展开更多
Tensile deformation and microvoid formation of quenched and tempered SA508 Gr.3 steel were studied using an in-situ digital image correlation technique and in-situ electron backscatter diffraction(EBSD)measurements.Th...Tensile deformation and microvoid formation of quenched and tempered SA508 Gr.3 steel were studied using an in-situ digital image correlation technique and in-situ electron backscatter diffraction(EBSD)measurements.The quenched steel with a mixture of up-per bainite and granular bainite exhibited a high ultimate tensile strength(UTS)of~795 MPa and an elongation of~25%.After temper-ing,long-rod carbides and accumulated carbide particles were formed at the interface of bainite–ferrite subunits and prior austenite grain boundaries(PAGBs),respectively.The UTS of the tempered steel decreased to~607 MPa,whereas the total elongation increased to 33.0%with a local strain of 191.0%at the necked area.In-situ EBSD results showed that strain localization in the bainite–ferrite pro-duced lattice rotation and dislocation pileup,thus leading to stress concentration at the discontinuities(e.g.,martensite–austenite islands and carbides).Consequently,the decohesion of PAGBs dotted with martensite–austenite islands was the dominant microvoid initiation mechanism in the quenched steel,whereas microvoids primarily initiated through the fracturing of long-rod carbides and the decohesion of PAGBs with carbides aggregation in the tempered steel.The fracture surfaces for both the quenched and tempered specimens featured dimples,indicating the ductile failure mechanism caused by microvoid coalescence.展开更多
While relationship between fracture mechanism and homogeneous microstructures has been fully understood,relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives le...While relationship between fracture mechanism and homogeneous microstructures has been fully understood,relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives less attention as it deserves.Fracture mechanism of the high-strength low-alloy(HSLA)steel considering the mesosegregation was investigated and its corre s ponding micro structure was characterized in this paper.Mesosegregation re fers to the inhomogeneous distribution of alloy elements during casting solidification,and leads to the formation of positive segregation zones(PSZ)and negative segregation zones(NSZ)in ingots.The fracture surface of impact sample exhibits the quasi-cleavage fracture at-21℃,and is divided into ductile and brittle fracture zone.Meanwhile,the PSZ and NSZ spread across ductile and brittle fracture zone randomly.In ductile fracture zone,micro-voids fracture mechanism covers the PSZ and NSZ,and higher deformation degree is shown in the PSZ.In brittle fracture zone,secondary cleavage cracks are observed in both PSZ and NSZ,but present bigger size and higher quantity in the NSZ.However,some regions of the PSZ still present micro-voids fracture mechanism in brittle fracture zone.It reveals that the microstructures in the PSZ exhibit a higher resistance ability to crack propagation than that in the NSZ.All observations above provide a better visualization of the microstructural factors that resist the crack propagation.It is important to map all information regarding the fracture mechanism and mesosegregation to allow for further acceptance and industrial use.展开更多
Porous titanium alloy is currently widely used in clinical treatment of orthopaedic diseases for its lower elastic modulus and ability to integrate with bone tissue.At the micro-level,cells can respond to different ge...Porous titanium alloy is currently widely used in clinical treatment of orthopaedic diseases for its lower elastic modulus and ability to integrate with bone tissue.At the micro-level,cells can respond to different geometries,and at the macro-level,the geometric design of implants will also affect the biological function of cells.In this study,three kinds of porous scaffolds with square,triangular and circle rod shapes were designed and 3D printed.This study observed the proliferation and differentiation of MC3T3-E1 cells during surface culture of the three types of scaffolds.It also evaluated the characteristics of the three scaffolds by means of compression tests and scanning electron microscopy to provide a reference for the design of porous titanium alloy implants for clinical applications.The trends of cell proliferation and gene expression between the three types of scaffolds were observed after treatment with two inhibitors.The results show that the square rod porous scaffolds have the best proliferative and osteogenic activities,and these findings may be due to differences in piezo-type mechanosensitive ion channel component 1(Piezo1)and Yes-associated protein(YAP)expression caused by the macro-geometric topography.展开更多
基金The authors acknowledge financial support from the National Natural Science Foundation of China(No.52101139 and No.51971145).
文摘Additive manufactured metals sometimes exhibit extraordinary microstructures and mechanical properties due to the particular processes. In this paper, we focus on a novel gradient TiAl alloys fabricated byhigh-power direct laser deposition, whose chemical composition, microstructure, and mechanical property vary along the building direction. The results indicate that Al concentration dramatically decreasesfrom 39.5 at.% to 30.1 at.% as the height increases from the bottom to the top. Meanwhile, microstructural characterization indicates that the specimen appears basket-weave microstructure at the bottom,then the α_(2) and γ phase gradually decrease, and eventually it transforms into acicular martensite microstructure in the top region. The indentation analysis shows that the associated hardness increases asthe height increases, while the plasticity reaches a minimum value in the middle region. The increasingamount of β_(o)(ω) is considered to be responsible for the increasing hardness because of the strong precipitation strengthening effect. The high plasticity in the bottom and top regions results from the strongdeformation behaviors of the γ and β_(o) phases.
基金financially supported by the National Natural Science Foundation of China(No.52171042),the National Key Research and Development Program of China(No.2023YFB3406804)the“Jianbing”R&D Program of Zhejiang Province,China(No.2023C01081)the Na-tional Engineering Research Center for Advanced Manufac-turing Technology and Equipment of Heavy Castings and Forgings(Erzhong(Deyang)Heavy Equipment Co.,Ltd.).
文摘Tensile deformation and microvoid formation of quenched and tempered SA508 Gr.3 steel were studied using an in-situ digital image correlation technique and in-situ electron backscatter diffraction(EBSD)measurements.The quenched steel with a mixture of up-per bainite and granular bainite exhibited a high ultimate tensile strength(UTS)of~795 MPa and an elongation of~25%.After temper-ing,long-rod carbides and accumulated carbide particles were formed at the interface of bainite–ferrite subunits and prior austenite grain boundaries(PAGBs),respectively.The UTS of the tempered steel decreased to~607 MPa,whereas the total elongation increased to 33.0%with a local strain of 191.0%at the necked area.In-situ EBSD results showed that strain localization in the bainite–ferrite pro-duced lattice rotation and dislocation pileup,thus leading to stress concentration at the discontinuities(e.g.,martensite–austenite islands and carbides).Consequently,the decohesion of PAGBs dotted with martensite–austenite islands was the dominant microvoid initiation mechanism in the quenched steel,whereas microvoids primarily initiated through the fracturing of long-rod carbides and the decohesion of PAGBs with carbides aggregation in the tempered steel.The fracture surfaces for both the quenched and tempered specimens featured dimples,indicating the ductile failure mechanism caused by microvoid coalescence.
基金This work was financially supported by the National Natural Science Foundation of China(No.51801126).
文摘While relationship between fracture mechanism and homogeneous microstructures has been fully understood,relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives less attention as it deserves.Fracture mechanism of the high-strength low-alloy(HSLA)steel considering the mesosegregation was investigated and its corre s ponding micro structure was characterized in this paper.Mesosegregation re fers to the inhomogeneous distribution of alloy elements during casting solidification,and leads to the formation of positive segregation zones(PSZ)and negative segregation zones(NSZ)in ingots.The fracture surface of impact sample exhibits the quasi-cleavage fracture at-21℃,and is divided into ductile and brittle fracture zone.Meanwhile,the PSZ and NSZ spread across ductile and brittle fracture zone randomly.In ductile fracture zone,micro-voids fracture mechanism covers the PSZ and NSZ,and higher deformation degree is shown in the PSZ.In brittle fracture zone,secondary cleavage cracks are observed in both PSZ and NSZ,but present bigger size and higher quantity in the NSZ.However,some regions of the PSZ still present micro-voids fracture mechanism in brittle fracture zone.It reveals that the microstructures in the PSZ exhibit a higher resistance ability to crack propagation than that in the NSZ.All observations above provide a better visualization of the microstructural factors that resist the crack propagation.It is important to map all information regarding the fracture mechanism and mesosegregation to allow for further acceptance and industrial use.
基金This study was carried out at the 3D Printing Innovation Research Centre of the Ninth People's Hospital Affiliated to the School of Medicine of Shanghai Jiao Tong University,and the authors thank the founding support from the Shanghai Municipal Key Clinical Specialty-Biomedical Materials(shslczdzk06701)the 3-year Action Plan of Shen kang Development Centre(SHDC2020CR2019B)+2 种基金the Huangpu District Industrial Support Fund(XK2020009)the Shanghai Engineering Research Centre of Innovative Orthopedic Instruments and Personalized Medicine(19DZ2250200)the Industry Standard Study on 3D Printing Personalized Titanium Alloy Pelvic Reconstruction Prosthesis(21DZ2201500).
文摘Porous titanium alloy is currently widely used in clinical treatment of orthopaedic diseases for its lower elastic modulus and ability to integrate with bone tissue.At the micro-level,cells can respond to different geometries,and at the macro-level,the geometric design of implants will also affect the biological function of cells.In this study,three kinds of porous scaffolds with square,triangular and circle rod shapes were designed and 3D printed.This study observed the proliferation and differentiation of MC3T3-E1 cells during surface culture of the three types of scaffolds.It also evaluated the characteristics of the three scaffolds by means of compression tests and scanning electron microscopy to provide a reference for the design of porous titanium alloy implants for clinical applications.The trends of cell proliferation and gene expression between the three types of scaffolds were observed after treatment with two inhibitors.The results show that the square rod porous scaffolds have the best proliferative and osteogenic activities,and these findings may be due to differences in piezo-type mechanosensitive ion channel component 1(Piezo1)and Yes-associated protein(YAP)expression caused by the macro-geometric topography.
