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
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
The effect of different regimes of heat treatment on the tensile strength of SiC coated composite of C fibers reinforced Al wires has been investigated.Their tensile strength may increase under treatment either at 500...The effect of different regimes of heat treatment on the tensile strength of SiC coated composite of C fibers reinforced Al wires has been investigated.Their tensile strength may increase under treatment either at 500℃ for 2h or 550℃ for 1h,but decrease over 600℃.After the strength tests of extracted fibers from composite wires,the SiC coating is an excellent protection to C fibers.EPMA and EDAX showed that the C/Al interface of the composite wires is stable under treatment below 600℃,but unstable at 650℃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
SCS-6 SiC continuous fiber-reinforced Ti-Al intermetallics-matrix composites were fabricated by HIP method and then heat-treated in vacuum under different conditions. The interfacial reaction kinetics and mechanism we...SCS-6 SiC continuous fiber-reinforced Ti-Al intermetallics-matrix composites were fabricated by HIP method and then heat-treated in vacuum under different conditions. The interfacial reaction kinetics and mechanism were studied by using SEM, EDS and XRD. The results show that the content fluctuation of reactive elements such as C, Ti and Si appears in interfacial reaction layers, and multi-layer interfacial reaction compounds form. Alloying element Nb in matrix remarkably diffuses into interfacial reaction zone and changes the activation energy for the interfacial reaction layer growth following a role of parabolic rate. The activation energy (Qk) and (k0) of SCS-6 SiC/super α2 and SCS-6 SiC/Ti2AlNb are 317.664 kJ/mol, 175.709 kJ/mol and 5.4438×10-2 m/s1/2, 1.44×10-5 m/s1/2; respectively, and the diffusion coefficient (DC) is about 10-18—10-20 m2/s. It is confirmed that the SCS-6 SiC/Ti-Al intermetallic composites have higher interface compatibility and stability. Furthermore, compared with SCS-6 SiC/super α2, the interface compatibility and stability of SCS-6 SiC/Ti2AlNb are even higher.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
The motion of intervariant intedeces under the action of applied stress in the internally faulted 18R martensite in a Cu-Zn-Al shape memory alloy has been studied. Transmission electron microscopy in situ observations...The motion of intervariant intedeces under the action of applied stress in the internally faulted 18R martensite in a Cu-Zn-Al shape memory alloy has been studied. Transmission electron microscopy in situ observations show that the interfaces between 24 martensite variants have different reaction to applied stress. The A/C type and A/B type interfaces have good mobil-ity, the A/D type interface has bad mobiIity, and the different-group-intervariant interfaces are basically immobile.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
The structure change of α2/γ interface in a Ti-45Al-10Nb alloy induced by hot deformation was investigated by conventional and high-resolution transmission eIectron microscopy. Two types of hot deformation induced s...The structure change of α2/γ interface in a Ti-45Al-10Nb alloy induced by hot deformation was investigated by conventional and high-resolution transmission eIectron microscopy. Two types of hot deformation induced special α2/γ intedeces, coherent intedeces with high density of ledges and semi-coherent α2/γ intedeces were found to be due to the absorption of mobile dislocations into the α2/γ inteface. For the misoriented semi-coherent α2/γ interfaces, the densities of dislocation ledges increase with the misoriented angle between (111)γ and (0001)α2 planes, and 1/3[111] Frank partial dislocations were involved in the dislocation ledges. Formation mechanism of these deformation-induced α2/γ interfaces was discussed to be related to the role of α2/γ interface5 adjusting the deformation as a dislocation sink absorbing the slipping dislocations in the γ phase展开更多
Detailed crystallographic analysis has been undertaken on the various combinations Of 24 martensite variants in the 18R martensite of a Cu-Zn-Al shape memory alloy. Based upon the calculated crystallographic data, the...Detailed crystallographic analysis has been undertaken on the various combinations Of 24 martensite variants in the 18R martensite of a Cu-Zn-Al shape memory alloy. Based upon the calculated crystallographic data, the interface energy of different twin interfaces was calculated using a lowangle-grain-interface model. For the variant/variant pairs in a self-accommodating group. the A/C type and A/B type interfaces have low interface energy, and A/D type interface is an intermediate one. In contrast, the intervariant interfaces that belong to different plate groups have high intrface energy. The calculated results are consiStent with the previous observations of the mobility of intervariant interfaces.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
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The effect of different regimes of heat treatment on the tensile strength of SiC coated composite of C fibers reinforced Al wires has been investigated.Their tensile strength may increase under treatment either at 500℃ for 2h or 550℃ for 1h,but decrease over 600℃.After the strength tests of extracted fibers from composite wires,the SiC coating is an excellent protection to C fibers.EPMA and EDAX showed that the C/Al interface of the composite wires is stable under treatment below 600℃,but unstable at 650℃
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.
基金Project(50371069) suppported by the National Natural Science Foundation of China Project(20030699013) suported by the State Educational Ministry Doctoral Foundation+1 种基金 Project(04G53044) supported by the Foundation of Aviation Science Project(ZX200301014) supported by the Materials Engineering Center Foundation of Jiangxi Province, China
文摘SCS-6 SiC continuous fiber-reinforced Ti-Al intermetallics-matrix composites were fabricated by HIP method and then heat-treated in vacuum under different conditions. The interfacial reaction kinetics and mechanism were studied by using SEM, EDS and XRD. The results show that the content fluctuation of reactive elements such as C, Ti and Si appears in interfacial reaction layers, and multi-layer interfacial reaction compounds form. Alloying element Nb in matrix remarkably diffuses into interfacial reaction zone and changes the activation energy for the interfacial reaction layer growth following a role of parabolic rate. The activation energy (Qk) and (k0) of SCS-6 SiC/super α2 and SCS-6 SiC/Ti2AlNb are 317.664 kJ/mol, 175.709 kJ/mol and 5.4438×10-2 m/s1/2, 1.44×10-5 m/s1/2; respectively, and the diffusion coefficient (DC) is about 10-18—10-20 m2/s. It is confirmed that the SCS-6 SiC/Ti-Al intermetallic composites have higher interface compatibility and stability. Furthermore, compared with SCS-6 SiC/super α2, the interface compatibility and stability of SCS-6 SiC/Ti2AlNb are even higher.
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The motion of intervariant intedeces under the action of applied stress in the internally faulted 18R martensite in a Cu-Zn-Al shape memory alloy has been studied. Transmission electron microscopy in situ observations show that the interfaces between 24 martensite variants have different reaction to applied stress. The A/C type and A/B type interfaces have good mobil-ity, the A/D type interface has bad mobiIity, and the different-group-intervariant interfaces are basically immobile.
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.
文摘The structure change of α2/γ interface in a Ti-45Al-10Nb alloy induced by hot deformation was investigated by conventional and high-resolution transmission eIectron microscopy. Two types of hot deformation induced special α2/γ intedeces, coherent intedeces with high density of ledges and semi-coherent α2/γ intedeces were found to be due to the absorption of mobile dislocations into the α2/γ inteface. For the misoriented semi-coherent α2/γ interfaces, the densities of dislocation ledges increase with the misoriented angle between (111)γ and (0001)α2 planes, and 1/3[111] Frank partial dislocations were involved in the dislocation ledges. Formation mechanism of these deformation-induced α2/γ interfaces was discussed to be related to the role of α2/γ interface5 adjusting the deformation as a dislocation sink absorbing the slipping dislocations in the γ phase
文摘Detailed crystallographic analysis has been undertaken on the various combinations Of 24 martensite variants in the 18R martensite of a Cu-Zn-Al shape memory alloy. Based upon the calculated crystallographic data, the interface energy of different twin interfaces was calculated using a lowangle-grain-interface model. For the variant/variant pairs in a self-accommodating group. the A/C type and A/B type interfaces have low interface energy, and A/D type interface is an intermediate one. In contrast, the intervariant interfaces that belong to different plate groups have high intrface energy. The calculated results are consiStent with the previous observations of the mobility of intervariant interfaces.
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.
