35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface con...35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface conditions were evaluated by tensile modules of elasticity and Brinell hardness measurement. The results show that the overall Si Cp/Al interface condition in this experiment is good and three kinds of Si Cp/Al interfaces are present in the composites, which include vast majority of clean planer interfaces, few slight reaction interfaces and tiny amorphous interfaces. The combination mechanism of Si C and Al in the clean planer interface is the formation of a semi-coherent interface by closely matching of atoms and there are no fixed or preferential crystallographic orientation relationships between Si C and Al. MgAl2O4 spinel particles act as an intermediate to form semi-coherent interface with SiC and Al respectively at the slight reaction interfaces. When the composite is aged at 190 °C for 9 h after being solution-treated at 510 °C for 2 h, numerous discoid-shaped and needle-shaped nanosized precipitates dispersively exist in the composite and are semi-coherent of low mismatch with Al matrix. The Brinell hardness of composites arrives peak value at this time.展开更多
Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al...Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.展开更多
The effect of the pyrolytic carbon(PyC)interface thickness on the heat-stability of CansasⅡSiC_(f)/SiC composites under Ar up to 1500℃was studied in detail.After the heat treatment at 1500℃for 50 h,the interface bo...The effect of the pyrolytic carbon(PyC)interface thickness on the heat-stability of CansasⅡSiC_(f)/SiC composites under Ar up to 1500℃was studied in detail.After the heat treatment at 1500℃for 50 h,the interface bonding strength of the thin interface(about 200 nm)decreases from 74.4 to 20.1 MPa(73.0%),while that of the thick interface(about 2μm)declines from 7.3 to 3.2 MPa(52.7%).At the same time,the decline fraction of strength of the composites with the thin interface is 12.1%,less than that with the thick interface(42.0%).The fiber strength also decreases after heat treatment,which may be due to the significant growth ofβ-SiC grains and critical defects.The different heat-stability of the interface with the thin and thick thickness might be related to the inconsistency of the degree of the graphitization of PyC.Compared with the composites with the thick interface,the composites with the thin interface remained higher tensile strength after heat treatment due to the better interface bonding strength.The interface with strong bonding strength could protect the fiber by postponing the decomposition of amorphous phases SiC_(x)O_(y) and hindering the generation of fiber defects.展开更多
The interface structure and electronic properties of Fe(110)/Al(110) are investigated by the first-principles plane-wave pseudopotential method. The interface segregation position of Si and Mg is determined, and the e...The interface structure and electronic properties of Fe(110)/Al(110) are investigated by the first-principles plane-wave pseudopotential method. The interface segregation position of Si and Mg is determined, and the effect of Mg and Si on the interface binding of Fe(110)/Al(110) is analyzed by combining the work of separation and charge density. The results show that the Fe(110)/Al(110) interface energy of FeHollow coordination is smaller and the interface structure is more stable. The Fe(110)/Al(110) interface separation surface in the form of Fe-Hollow coordination appears at the sub interface layer on the side of Al(110)near the interface. The interface structure of Mg and Si segregation is similar to that of undoped alloy elements.The calculations also suggest that Mg and Si segregate on the Al(110) side of the interface and occupy the Al lattice on the Al(110) side. The segregation of Mg and Si elements will reduce the interface binding, primarily because the Fe-Si bond and Fe-Mg bond are weaker than Fe-Al bond.展开更多
The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceram...The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.展开更多
This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is...This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H-SiC BJT performance.展开更多
For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Rece...For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Recent-ly, a commercially produced foundry ingot,the Duralcan composite of A356 Al alloy +20展开更多
On the basis of first principles calculations, we report that the type and density of charge carriers of epitaxial graphene on SiC（O001） can be deliberately controlled by decorating the buffer layer with specific at...On the basis of first principles calculations, we report that the type and density of charge carriers of epitaxial graphene on SiC（O001） can be deliberately controlled by decorating the buffer layer with specific atoms （i.e., F, C1, O, or N）. More importantly, a fine tuning of the doping behavior from intrinsic n-type to charge neutrality to p-type and interface magnetism is achieved via increasing the doping concentration of F atoms on the buffer layer. Our results suggest an interesting avenue to the application of epitaxial graphene in nanoscale electronic and spintronic devices.展开更多
Effective improvement in electrical properties of NO passivated SiC/SiO2 interface after being irradiated by electrons is demonstrated.The density of interface traps after being irradiated by 100-kGy electrons decreas...Effective improvement in electrical properties of NO passivated SiC/SiO2 interface after being irradiated by electrons is demonstrated.The density of interface traps after being irradiated by 100-kGy electrons decreases by about one order of magnitude,specifically,from 3×1012 cm-2·eV-1 to 4×1011 cm-2·eV-1 at 0.2 eV below the conduction band of 4H-SiC without any degradation of electric breakdown field.Particularly,the results of x-ray photoelectron spectroscopy measurement show that the C-N bonds are generated near the interface after electron irradiation,indicating that the carbon-related defects are further reduced.展开更多
Near-interface oxide traps （NIOTs） in 4H-SiC metal-oxide-semiconductor （MOS） structures fabricated with and without annealing in NO are systematically investigated in this paper. The properties of NIOTs in SiC MOS...Near-interface oxide traps （NIOTs） in 4H-SiC metal-oxide-semiconductor （MOS） structures fabricated with and without annealing in NO are systematically investigated in this paper. The properties of NIOTs in SiC MOS structures prepared with and without annealing in NO are studied and compared in detail. Two main categories of the NIOTs, the “slow” and “fast” NIOTs, are revealed and extracted. The densities of the “fast” NIOTs are determined to be 0.761011 cm-2 and 0.471011 cm-2 for the N2 post oxidation annealing （POA） sample and NO POA sample, respectively. The densities of “slow” NIOTs are 0.791011 cm-2 and 9.441011 cm-2 for the NO POA sample and N2 POA sample, respectively. It is found that the NO POA process only can significantly reduce “slow” NIOTs. However, it has a little effect on “fast” NIOTs. The negative and positive constant voltage stresses （CVS） reveal that electrons captured by those “slow” NIOTs and bulk oxide traps （BOTs） are hardly emitted by the constant voltage stress.展开更多
A Fe/Al clad tube was prepared by explosive welding.Then the bonding characteristic of the interface was investigated by compression,flattening and compression-shear test.The test results exhibit that the clad tubes p...A Fe/Al clad tube was prepared by explosive welding.Then the bonding characteristic of the interface was investigated by compression,flattening and compression-shear test.The test results exhibit that the clad tubes possessing good bonding interface have higher shear strength than that of pure aluminum and can bear both axial and radial deformation.The original interface between aluminum layer and ferrite layer was observed by scanning electron microscopy（SEM）.The results show that the clad tubes with good bonding properties possess the interface in wave and straight shape.The Fe/Al clad tube was used to manufacture the T-shape by hydro-bulging.It is found that the good-bonding interface of the Fe/Al clad tube plays a dominant role in the formation of the T-shape.展开更多
A nickel-based coating was deposited on the pure Al substrate by immersion plating,and the Al/Cu bimetals were prepared by diffusion bonding in the temperature range of 450-550 ℃.The interce microstructure and fractu...A nickel-based coating was deposited on the pure Al substrate by immersion plating,and the Al/Cu bimetals were prepared by diffusion bonding in the temperature range of 450-550 ℃.The interce microstructure and fracture surface of Al/Cu joints were studied by scanning electron microscopy（SEM） and X-ray diffraction（XRD）.The mechanical properties of the Al/Cu bimetals were measured by tensile shear and microhardness tests.The results show that the Ni interiayer can effectively eliminate the formation of Al-Cu intermetallic compounds.The Al/Ni interface consists of the Al3Ni and Al3Ni2 phases,while it is Ni-Cu solid solution at the Ni/Cu interce.The tensile shear strength of the joints is improved by the addition of Ni interiayer.The joint with Ni interiayer annealed at 500 ℃ exhibits a maximum value of tensile shear strength of 34.7 MPa.展开更多
基金Project(51371077)supported by the National Natural Science Foundation of China
文摘35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface conditions were evaluated by tensile modules of elasticity and Brinell hardness measurement. The results show that the overall Si Cp/Al interface condition in this experiment is good and three kinds of Si Cp/Al interfaces are present in the composites, which include vast majority of clean planer interfaces, few slight reaction interfaces and tiny amorphous interfaces. The combination mechanism of Si C and Al in the clean planer interface is the formation of a semi-coherent interface by closely matching of atoms and there are no fixed or preferential crystallographic orientation relationships between Si C and Al. MgAl2O4 spinel particles act as an intermediate to form semi-coherent interface with SiC and Al respectively at the slight reaction interfaces. When the composite is aged at 190 °C for 9 h after being solution-treated at 510 °C for 2 h, numerous discoid-shaped and needle-shaped nanosized precipitates dispersively exist in the composite and are semi-coherent of low mismatch with Al matrix. The Brinell hardness of composites arrives peak value at this time.
文摘Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.
基金Funded by the National Science and Technology Major Project(No.2017-IV-0005-0042)the China Postdoctoral Science Foundation(No.2021M691566)。
文摘The effect of the pyrolytic carbon(PyC)interface thickness on the heat-stability of CansasⅡSiC_(f)/SiC composites under Ar up to 1500℃was studied in detail.After the heat treatment at 1500℃for 50 h,the interface bonding strength of the thin interface(about 200 nm)decreases from 74.4 to 20.1 MPa(73.0%),while that of the thick interface(about 2μm)declines from 7.3 to 3.2 MPa(52.7%).At the same time,the decline fraction of strength of the composites with the thin interface is 12.1%,less than that with the thick interface(42.0%).The fiber strength also decreases after heat treatment,which may be due to the significant growth ofβ-SiC grains and critical defects.The different heat-stability of the interface with the thin and thick thickness might be related to the inconsistency of the degree of the graphitization of PyC.Compared with the composites with the thick interface,the composites with the thin interface remained higher tensile strength after heat treatment due to the better interface bonding strength.The interface with strong bonding strength could protect the fiber by postponing the decomposition of amorphous phases SiC_(x)O_(y) and hindering the generation of fiber defects.
基金the National Natural Science Foundation of China(No.51871030)the Higher Education Science Foundation of Jiangsu Province of China (No.17KJA430006)。
文摘The interface structure and electronic properties of Fe(110)/Al(110) are investigated by the first-principles plane-wave pseudopotential method. The interface segregation position of Si and Mg is determined, and the effect of Mg and Si on the interface binding of Fe(110)/Al(110) is analyzed by combining the work of separation and charge density. The results show that the Fe(110)/Al(110) interface energy of FeHollow coordination is smaller and the interface structure is more stable. The Fe(110)/Al(110) interface separation surface in the form of Fe-Hollow coordination appears at the sub interface layer on the side of Al(110)near the interface. The interface structure of Mg and Si segregation is similar to that of undoped alloy elements.The calculations also suggest that Mg and Si segregate on the Al(110) side of the interface and occupy the Al lattice on the Al(110) side. The segregation of Mg and Si elements will reduce the interface binding, primarily because the Fe-Si bond and Fe-Mg bond are weaker than Fe-Al bond.
基金Supported by the National Basic Research Program of China("973" Program)(613135)
文摘The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.
文摘This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H-SiC BJT performance.
文摘For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Recent-ly, a commercially produced foundry ingot,the Duralcan composite of A356 Al alloy +20
基金supported by the National Natural Science Foundation of China(Grant Nos.61335006,61378073,and 61527817)the Beijing Municipal Science and Technology Committee,China(Grant No.Z151100003315006)Fundamental Research Funds for the Central Universities of Beijing Jiaotong University,China(Grant No.2012YJS123)
文摘On the basis of first principles calculations, we report that the type and density of charge carriers of epitaxial graphene on SiC（O001） can be deliberately controlled by decorating the buffer layer with specific atoms （i.e., F, C1, O, or N）. More importantly, a fine tuning of the doping behavior from intrinsic n-type to charge neutrality to p-type and interface magnetism is achieved via increasing the doping concentration of F atoms on the buffer layer. Our results suggest an interesting avenue to the application of epitaxial graphene in nanoscale electronic and spintronic devices.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0100601)the National Natural Science Foundation of China(Grant Nos.61674169 and 61974159).
文摘Effective improvement in electrical properties of NO passivated SiC/SiO2 interface after being irradiated by electrons is demonstrated.The density of interface traps after being irradiated by 100-kGy electrons decreases by about one order of magnitude,specifically,from 3×1012 cm-2·eV-1 to 4×1011 cm-2·eV-1 at 0.2 eV below the conduction band of 4H-SiC without any degradation of electric breakdown field.Particularly,the results of x-ray photoelectron spectroscopy measurement show that the C-N bonds are generated near the interface after electron irradiation,indicating that the carbon-related defects are further reduced.
基金Project supported by the National Key Basic Research Program of China(Grant No.2015CB759600)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.2017JM6003)the National Natural Science Foundation of China(Grant Nos.61774117 61404098 and 61274079)
文摘Near-interface oxide traps （NIOTs） in 4H-SiC metal-oxide-semiconductor （MOS） structures fabricated with and without annealing in NO are systematically investigated in this paper. The properties of NIOTs in SiC MOS structures prepared with and without annealing in NO are studied and compared in detail. Two main categories of the NIOTs, the “slow” and “fast” NIOTs, are revealed and extracted. The densities of the “fast” NIOTs are determined to be 0.761011 cm-2 and 0.471011 cm-2 for the N2 post oxidation annealing （POA） sample and NO POA sample, respectively. The densities of “slow” NIOTs are 0.791011 cm-2 and 9.441011 cm-2 for the NO POA sample and N2 POA sample, respectively. It is found that the NO POA process only can significantly reduce “slow” NIOTs. However, it has a little effect on “fast” NIOTs. The negative and positive constant voltage stresses （CVS） reveal that electrons captured by those “slow” NIOTs and bulk oxide traps （BOTs） are hardly emitted by the constant voltage stress.
基金Project(BA2006067)supported by Achievement Transitional Foundation of Jiangsu Province,China
文摘A Fe/Al clad tube was prepared by explosive welding.Then the bonding characteristic of the interface was investigated by compression,flattening and compression-shear test.The test results exhibit that the clad tubes possessing good bonding interface have higher shear strength than that of pure aluminum and can bear both axial and radial deformation.The original interface between aluminum layer and ferrite layer was observed by scanning electron microscopy（SEM）.The results show that the clad tubes with good bonding properties possess the interface in wave and straight shape.The Fe/Al clad tube was used to manufacture the T-shape by hydro-bulging.It is found that the good-bonding interface of the Fe/Al clad tube plays a dominant role in the formation of the T-shape.
基金Projects (51274054,51375070,51271042) supported by the National Natural Science Foundation of ChinaProjects (2013M530913) supported by the China Postdoctoral Science Foundation
文摘A nickel-based coating was deposited on the pure Al substrate by immersion plating,and the Al/Cu bimetals were prepared by diffusion bonding in the temperature range of 450-550 ℃.The interce microstructure and fracture surface of Al/Cu joints were studied by scanning electron microscopy（SEM） and X-ray diffraction（XRD）.The mechanical properties of the Al/Cu bimetals were measured by tensile shear and microhardness tests.The results show that the Ni interiayer can effectively eliminate the formation of Al-Cu intermetallic compounds.The Al/Ni interface consists of the Al3Ni and Al3Ni2 phases,while it is Ni-Cu solid solution at the Ni/Cu interce.The tensile shear strength of the joints is improved by the addition of Ni interiayer.The joint with Ni interiayer annealed at 500 ℃ exhibits a maximum value of tensile shear strength of 34.7 MPa.
基金financially supported by the Major Special Projects in Anhui Province,China(No.202003c08020005)the Key Projects in Hunan Province,China(No.2020GK2045)+1 种基金the Science and Technology Innovation Program of Hunan Province,China(No.2021RC4036)Postgraduate Scientific Research Innovation Project of Hunan Province,China(No.CX20211079)。
