The influence of rare earth metals and heat treatment on the microstructure and performance of M42 steel has been investigated by means of an optical microscope OM scanning electron microscope SEM energy dispersive sp...The influence of rare earth metals and heat treatment on the microstructure and performance of M42 steel has been investigated by means of an optical microscope OM scanning electron microscope SEM energy dispersive spectroscopy EDS transmission electron microscope TEM electron back-scatter diffraction EBSD and X-ray diffraction XRD . The results show that M2 C is the prevailing type of eutectic carbides in M42 steel. After modification with rare earth metals M2 C eutectic carbides change from the ordered lamellar structure into a circular structure.Despite different morphologies the two carbides present the same characteristics of microstructure and growth orientation.Compared with lamellar carbides M2 C carbides with the circular structure are much easier to decompose and spheroidize after heating which remarkably refines the carbide dimensions.The refined carbides improve the supersaturation of alloying elements in martensite and increase the hardness of M42 steel by 1.5 HRC.展开更多
A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The ...A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The UHCS produced by this new process has a microstructure with recrystallized ferrite matrix and fine and uniform carbide particles. After this spheroidizing, the UHCS exhibits good mechanical properties at ambient temperature, for example σb= 1 100 MPa, σs =915 MPa, δ=8% and high ratio of σs/σb.展开更多
The low-strength and high-brittleness of AZ91 cast magnesium alloy mainly result from the coarse divorced eutectic phase. To solve these problems, the annealing treatment of AZ91 cast magnesium alloy was carried out a...The low-strength and high-brittleness of AZ91 cast magnesium alloy mainly result from the coarse divorced eutectic phase. To solve these problems, the annealing treatment of AZ91 cast magnesium alloy was carried out at 415 ℃ and held for 24 h in this study and the alloy was then slowly cooled to room temperature in furnace. The microstructures of the alloy were observed using a metallographic microscope, a transmission electron microscopy and an emission scanning electron microscopy, respectively. The phase analysis was performed using the X-ray diffraction, and the tensile test of the specimen at ambient temperature was performed on a material test machine. The results indicate that the coarse divorced eutectic phase dissolves into the Mg matrix during the isothermal process, and the lamellarβ-Mg17AI12 phase precipitates from the magnesium solid solution with a type of pearlite precipitation during furnace cooling. Consequently, the spheroidizing treatment was carried out at 320℃ for 20 h following the annealing process and the lamellar β-Mg17A12 phase was spheroidized. Compared with the as-cast alloy, the strength and ductility of the AZ91 magnesium alloy are increased obviously after annealing treatment; the yield strength and tensile strength are increased to 137.8 MPa and 240.4 MPa from 102.9 MPa and 199.3 MPa, respectively; and the elongation is improved to 6.12% from 4.35%. After being spheroidized, the strength and hardness decrease a little, but the ductility is elevated to 7.23%. The nucleation, growth and spheroidizing mechanism of the lamellarβ-Mg12TAI12 phase were also discussed.展开更多
The influences of Ce, K and Na on the structures and properties of Fe-W-C alloy were investigated, and the idea estimating spheroidizing effect of carbides using circular degree(C.D) was put forward. The result shows ...The influences of Ce, K and Na on the structures and properties of Fe-W-C alloy were investigated, and the idea estimating spheroidizing effect of carbides using circular degree(C.D) was put forward. The result shows that eutectic carbide turns into sphericity from network after modification, carbide is refined and uniformly distributed and C.D of eutectic carbide increases. The mechanism of carbide spheroidizing was analyzed. The impact toughness and abrasion resistance of Fe-W-C obviously improve with the rise of C.D of carbides. The service life of modified Fe-W-C roll is 30% higher than that of high chromium cast iron roll, while its production cost is reduced by 30%.展开更多
Delayed and nonhealing of diabetic wounds imposes substantial economic burdens and physical pain on patients.Mesenchymal stem cells(MSCs)promote diabetic wound healing.Particularly when MSCs aggregate into multicellul...Delayed and nonhealing of diabetic wounds imposes substantial economic burdens and physical pain on patients.Mesenchymal stem cells(MSCs)promote diabetic wound healing.Particularly when MSCs aggregate into multicellular spheroids,their therapeutic effect is enhanced.However,traditional culture platforms are inadequate for the efficient preparation and delivery of MSC spheroids,resulting in inefficiencies and inconveniences in MSC spheroid therapy.In this study,a three-dimensional porous nanofibrous dressing(NFD)is prepared using a combination of electrospinning and homogeneous freeze-drying.Using thermal crosslinking,the NFD not only achieves satisfactory elasticity but also maintains notable cytocompatibility.Through the design of its structure and chemical composition,the NFD allows MSCs to spontaneously form MSC spheroids with controllable sizes,serving as MSC spheroid delivery systems for diabetic wound sites.Most importantly,MSC spheroids cultured on the NFD exhibit improved secretion of vascular endothelial growth factor,basic fibroblast growth factor,and hepatocyte growth factor,thereby accelerating diabetic wound healing.The NFD provides a competitive strategy for MSC spheroid formation and delivery to promote diabetic wound healing.展开更多
Tissue engineering has been striving toward designing and producing natural and functional human tissues.Cells are the fundamental building blocks of tissues.Compared with traditional two-dimensional cultured cells,ce...Tissue engineering has been striving toward designing and producing natural and functional human tissues.Cells are the fundamental building blocks of tissues.Compared with traditional two-dimensional cultured cells,cell spheres are threedimensional(3D)structures that can naturally form complex cell–cell and cell–matrix interactions.This structure is close to the natural environment of cells in living organisms.In addition to being used in disease modeling and drug screening,spheroids have significant potential in tissue regeneration.The 3D bioprinting is an advanced biofabrication technique.It accurately deposits bioinks into predesigned 3D shapes to create complex tissue structures.Although 3D bioprinting is efficient,the time required for cells to develop into complex tissue structures can be lengthy.The 3D bioprinting of spheroids significantly reduces the time required for their development into large tissues/organs during later cultivation stages by printing them with high cell density.Combining spheroid fabrication and bioprinting technology should provide a new solution to many problems in regenerative medicine.This paper systematically elaborates and analyzes the spheroid fabrication methods and 3D bioprinting strategies by introducing spheroids as building blocks.Finally,we present the primary challenges faced by spheroid fabrication and 3D bioprinting with future requirements and some recommendations.展开更多
The present work aims to investigate the effect of heating temperature(400,600 and 800°C)and inoculating elements(Ca,Ca-Ba,Ca-RE)on oxidation behavior of ductile irons containing 5.25%Si and 4.8%Si-2.3%Mo in dry ...The present work aims to investigate the effect of heating temperature(400,600 and 800°C)and inoculating elements(Ca,Ca-Ba,Ca-RE)on oxidation behavior of ductile irons containing 5.25%Si and 4.8%Si-2.3%Mo in dry air and combustion gas containing water vapour(natural gas burning).The oxidation is influenced by the gas atmosphere type,the iron alloying system,and the inoculating elements depending on the heating temperature.The weight gain increases from 0.001%-0.1%(400°C)to 0.05%-0.70%(600°C)and up to 0.10%-2.15%(800°C).No particular effects of the considered influencing factors are found when heating at 400°C,while at 600°C,mainly the oxidation gas atmosphere type shows a visible influence.At the highest heating temperature of 800°C,a limited increase of the weight gain is found for dry air atmosphere(up to 0.25%),but it drastically increases for combustion atmospheres(0.65%-2.15%).The water vapour presence in the combustion atmosphere is an important oxidising factor at 600-800°C.The alloying system appears to influence the oxidation behavior mainly at a heating temperature of 800°C in the combustion atmosphere,as evidenced by the lower weight gain in 5.25%silicon cast iron.Positive effects of inoculating elements increase with the heating temperature,with Ca and Ba-FeSi inoculation generally showing better performance.Irons inoculated with CaRE-FeSi exhibit a higher degree of oxidation.These results are in good relationship with the previous reported data:Ca-Ba-inoculation system appears to be better than simple Ca for improving the graphite parameters,while RE-bearing inoculant negatively affects the compactness degree of graphite particles in high-Si ductile irons.As the lower compactness degree is typical for graphite nodules in high-Si ductile irons,which negatively affects the oxidation resistance,it is necessary to employ specific metallurgical treatments to improve nodule quality.Inoculation,in particular,is a potential method to achieve this improvement.展开更多
In order to reduce the intrinsic interference of the filter bank multicarrier-quadrature amplitude modulation(FBMC-QAM)system,a novel filter optimization scheme based on discrete prolate spheroidal sequences(DPSS)is p...In order to reduce the intrinsic interference of the filter bank multicarrier-quadrature amplitude modulation(FBMC-QAM)system,a novel filter optimization scheme based on discrete prolate spheroidal sequences(DPSS)is proposed.Firstly,a prototype filter function based on DPSS is designed,since the eigenvalue can be used as an indicator of the energy concentration of DPSS,so a threshold is set,and the sequence with the most concentrated energy is selected under the threshold,that is,the sequence with the eigenvalue higher than the threshold,and the prototype filter function is rewritten as a weighted sum function of multiple eigenvectors.Under the energy constraints of the filter,the relationship between the eigenvectors and the intrinsic interference function is established,and the function problem is transformed into an optimization problem for the weighted coefficients.Through the interior point method,the most suitable weight is found to obtain the minimum intrinsic interference result.Theoretical analysis and simulation results show that compared with the prototype filters such as Type1 and CaseC,the DPSS filter applying the proposed optimization algorithm can effectively suppress the intrinsic interference of the system and obtain a better bit error rate(BER)performance.展开更多
基金The National Natural Science Foundation of China(No.51301038,51201031,51371050)the Industry-AcademiaResearch Cooperative Innovation Fund of Jiangsu Province(No.BY2014127-03)+1 种基金the Natural Science Foundation of Jiangsu Province(No.BK20141306)the Scientific and Technological Innovation Fund of Danyang(No.SY201305)
文摘The influence of rare earth metals and heat treatment on the microstructure and performance of M42 steel has been investigated by means of an optical microscope OM scanning electron microscope SEM energy dispersive spectroscopy EDS transmission electron microscope TEM electron back-scatter diffraction EBSD and X-ray diffraction XRD . The results show that M2 C is the prevailing type of eutectic carbides in M42 steel. After modification with rare earth metals M2 C eutectic carbides change from the ordered lamellar structure into a circular structure.Despite different morphologies the two carbides present the same characteristics of microstructure and growth orientation.Compared with lamellar carbides M2 C carbides with the circular structure are much easier to decompose and spheroidize after heating which remarkably refines the carbide dimensions.The refined carbides improve the supersaturation of alloying elements in martensite and increase the hardness of M42 steel by 1.5 HRC.
基金Item Sponsored by Provincial Natural Science Foundation of Hebei Province of China (500023)
文摘A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The UHCS produced by this new process has a microstructure with recrystallized ferrite matrix and fine and uniform carbide particles. After this spheroidizing, the UHCS exhibits good mechanical properties at ambient temperature, for example σb= 1 100 MPa, σs =915 MPa, δ=8% and high ratio of σs/σb.
基金supported by the National Science&Technology Pillar Program of China(Grant No.2006BAE04B05-1)the Natural Science Foundation of Shanxi Province(Grant No.2012JQ6020)the Doctor Foundation of Xian University of Science & Technology of China(2011QDJ017)
文摘The low-strength and high-brittleness of AZ91 cast magnesium alloy mainly result from the coarse divorced eutectic phase. To solve these problems, the annealing treatment of AZ91 cast magnesium alloy was carried out at 415 ℃ and held for 24 h in this study and the alloy was then slowly cooled to room temperature in furnace. The microstructures of the alloy were observed using a metallographic microscope, a transmission electron microscopy and an emission scanning electron microscopy, respectively. The phase analysis was performed using the X-ray diffraction, and the tensile test of the specimen at ambient temperature was performed on a material test machine. The results indicate that the coarse divorced eutectic phase dissolves into the Mg matrix during the isothermal process, and the lamellarβ-Mg17AI12 phase precipitates from the magnesium solid solution with a type of pearlite precipitation during furnace cooling. Consequently, the spheroidizing treatment was carried out at 320℃ for 20 h following the annealing process and the lamellar β-Mg17A12 phase was spheroidized. Compared with the as-cast alloy, the strength and ductility of the AZ91 magnesium alloy are increased obviously after annealing treatment; the yield strength and tensile strength are increased to 137.8 MPa and 240.4 MPa from 102.9 MPa and 199.3 MPa, respectively; and the elongation is improved to 6.12% from 4.35%. After being spheroidized, the strength and hardness decrease a little, but the ductility is elevated to 7.23%. The nucleation, growth and spheroidizing mechanism of the lamellarβ-Mg12TAI12 phase were also discussed.
文摘The influences of Ce, K and Na on the structures and properties of Fe-W-C alloy were investigated, and the idea estimating spheroidizing effect of carbides using circular degree(C.D) was put forward. The result shows that eutectic carbide turns into sphericity from network after modification, carbide is refined and uniformly distributed and C.D of eutectic carbide increases. The mechanism of carbide spheroidizing was analyzed. The impact toughness and abrasion resistance of Fe-W-C obviously improve with the rise of C.D of carbides. The service life of modified Fe-W-C roll is 30% higher than that of high chromium cast iron roll, while its production cost is reduced by 30%.
基金supported by Fundamental Research Program of Shanxi Province(202203021222199)the Taiyuan University of Science and Technology Scientific Research Initial Funding(20222090)the National Natural Science Foundation of China(21975019).
文摘Delayed and nonhealing of diabetic wounds imposes substantial economic burdens and physical pain on patients.Mesenchymal stem cells(MSCs)promote diabetic wound healing.Particularly when MSCs aggregate into multicellular spheroids,their therapeutic effect is enhanced.However,traditional culture platforms are inadequate for the efficient preparation and delivery of MSC spheroids,resulting in inefficiencies and inconveniences in MSC spheroid therapy.In this study,a three-dimensional porous nanofibrous dressing(NFD)is prepared using a combination of electrospinning and homogeneous freeze-drying.Using thermal crosslinking,the NFD not only achieves satisfactory elasticity but also maintains notable cytocompatibility.Through the design of its structure and chemical composition,the NFD allows MSCs to spontaneously form MSC spheroids with controllable sizes,serving as MSC spheroid delivery systems for diabetic wound sites.Most importantly,MSC spheroids cultured on the NFD exhibit improved secretion of vascular endothelial growth factor,basic fibroblast growth factor,and hepatocyte growth factor,thereby accelerating diabetic wound healing.The NFD provides a competitive strategy for MSC spheroid formation and delivery to promote diabetic wound healing.
基金supported by the National Natural Science Foundation of China(Nos.61973206,61703265,61803250,and 61933008)the Shanghai Science and Technology Committee Rising-Star Program(No.19QA1403700)the National Center for Translational Medicine(Shanghai)SHU Branch.
文摘Tissue engineering has been striving toward designing and producing natural and functional human tissues.Cells are the fundamental building blocks of tissues.Compared with traditional two-dimensional cultured cells,cell spheres are threedimensional(3D)structures that can naturally form complex cell–cell and cell–matrix interactions.This structure is close to the natural environment of cells in living organisms.In addition to being used in disease modeling and drug screening,spheroids have significant potential in tissue regeneration.The 3D bioprinting is an advanced biofabrication technique.It accurately deposits bioinks into predesigned 3D shapes to create complex tissue structures.Although 3D bioprinting is efficient,the time required for cells to develop into complex tissue structures can be lengthy.The 3D bioprinting of spheroids significantly reduces the time required for their development into large tissues/organs during later cultivation stages by printing them with high cell density.Combining spheroid fabrication and bioprinting technology should provide a new solution to many problems in regenerative medicine.This paper systematically elaborates and analyzes the spheroid fabrication methods and 3D bioprinting strategies by introducing spheroids as building blocks.Finally,we present the primary challenges faced by spheroid fabrication and 3D bioprinting with future requirements and some recommendations.
基金supported by a grant from National Program for Research of the National Association of Technical Universities-GNAC ARUT 2023.
文摘The present work aims to investigate the effect of heating temperature(400,600 and 800°C)and inoculating elements(Ca,Ca-Ba,Ca-RE)on oxidation behavior of ductile irons containing 5.25%Si and 4.8%Si-2.3%Mo in dry air and combustion gas containing water vapour(natural gas burning).The oxidation is influenced by the gas atmosphere type,the iron alloying system,and the inoculating elements depending on the heating temperature.The weight gain increases from 0.001%-0.1%(400°C)to 0.05%-0.70%(600°C)and up to 0.10%-2.15%(800°C).No particular effects of the considered influencing factors are found when heating at 400°C,while at 600°C,mainly the oxidation gas atmosphere type shows a visible influence.At the highest heating temperature of 800°C,a limited increase of the weight gain is found for dry air atmosphere(up to 0.25%),but it drastically increases for combustion atmospheres(0.65%-2.15%).The water vapour presence in the combustion atmosphere is an important oxidising factor at 600-800°C.The alloying system appears to influence the oxidation behavior mainly at a heating temperature of 800°C in the combustion atmosphere,as evidenced by the lower weight gain in 5.25%silicon cast iron.Positive effects of inoculating elements increase with the heating temperature,with Ca and Ba-FeSi inoculation generally showing better performance.Irons inoculated with CaRE-FeSi exhibit a higher degree of oxidation.These results are in good relationship with the previous reported data:Ca-Ba-inoculation system appears to be better than simple Ca for improving the graphite parameters,while RE-bearing inoculant negatively affects the compactness degree of graphite particles in high-Si ductile irons.As the lower compactness degree is typical for graphite nodules in high-Si ductile irons,which negatively affects the oxidation resistance,it is necessary to employ specific metallurgical treatments to improve nodule quality.Inoculation,in particular,is a potential method to achieve this improvement.
基金the National Natural Science Foundation of China(No.61601296,61201244)the Science and Technology Innovation Action Plan Project of Shanghai Science and Technology Commission(No.20511103500)the Talent Program of Shanghai University of Engineering Science(No.2018RC43)。
文摘In order to reduce the intrinsic interference of the filter bank multicarrier-quadrature amplitude modulation(FBMC-QAM)system,a novel filter optimization scheme based on discrete prolate spheroidal sequences(DPSS)is proposed.Firstly,a prototype filter function based on DPSS is designed,since the eigenvalue can be used as an indicator of the energy concentration of DPSS,so a threshold is set,and the sequence with the most concentrated energy is selected under the threshold,that is,the sequence with the eigenvalue higher than the threshold,and the prototype filter function is rewritten as a weighted sum function of multiple eigenvectors.Under the energy constraints of the filter,the relationship between the eigenvectors and the intrinsic interference function is established,and the function problem is transformed into an optimization problem for the weighted coefficients.Through the interior point method,the most suitable weight is found to obtain the minimum intrinsic interference result.Theoretical analysis and simulation results show that compared with the prototype filters such as Type1 and CaseC,the DPSS filter applying the proposed optimization algorithm can effectively suppress the intrinsic interference of the system and obtain a better bit error rate(BER)performance.
