The preparation and properties of ceramic short fiber reinforced Al-Si alloy matrix composite and it's application on the piston for internal combustion engines are presented. Alumina or aluminosilicatefiibers rei...The preparation and properties of ceramic short fiber reinforced Al-Si alloy matrix composite and it's application on the piston for internal combustion engines are presented. Alumina or aluminosilicatefiibers reinforced Al-Si alloy matrix composite has more excellent synthetical properties at elevated temperature than the matrix alloys. A partially reinforced Al-Si alloy matrix composite piston produced by squeeze casting technique has a firm interface between reinforced and unreinforced areas, low reject rate and good technical tolerance. As a new kind of piston material, it has been used for mass production of about 400,000 pieces of automobile engines piston. China has become one of a few countries in which aluminum alloy matrix composite materials have been used in automobile industry and attained industrialization.展开更多
By loading nanometer anatase onto exfoliated graphite with the sol-gel method, exfoliated graphite-TiO2 composite (EG-TiO2) can be prepared, which can adsorb oil and can also degrade oil. In a technologic condition ...By loading nanometer anatase onto exfoliated graphite with the sol-gel method, exfoliated graphite-TiO2 composite (EG-TiO2) can be prepared, which can adsorb oil and can also degrade oil. In a technologic condition for preparing EG-TiO2, the impregnated number of times is the most important factor to influence oil-adsorbing capability, that is, when the impregnated number of times increases, the amount of saturation-adsorbed oil decreases. The study of EG-TiO2 photocatalytic degradation of machine oil based on the weight-loss method and infrared spectrum method indicates that EG-TiO2 has obvious effect of photocatalytic degradation for machine oil. Its performance is superior to pure nanometer TiO2 powder because nanometer TiO2 in EG-TiO2 has three-dimension laminar structure and comparatively high adsorption capability.展开更多
M92Si reinforced Mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion (RE) after the composite was processed by homogenization heat t...M92Si reinforced Mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion (RE) after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of M92Si and the mechanical properties of the com- posite were investigated, to develop new ways to refine the M928i phase and improve its shape. The result showed that RE was very useful in refining the M92Si phase. The more the RE processing passes, the better the refining effect would be. Moreover, the uniform distribution of M928i phases would be more in the composite. After the composite was processed by RE for 12 passes, most M92Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 MPa, 211.4 MPa, and 3.3% at room temperature, whereas, 288.2 MPa, ,207.7 MPa, and 7.8%, respectively, at 150℃. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150℃. The M928i reinforced Mg-Al based composite possesses good heat resistance at 150℃. The excellent resistance to effect of heat is attributed to the high melting tempera- ture and good thermal stability of fine Mg2Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.展开更多
Hot deformation behaviors were studied by means of scanning electron microscopy (SEM) and uniaxial thermal tension. The effect of deformation temperature and strain rate on flow stress was evaluated, and deformation...Hot deformation behaviors were studied by means of scanning electron microscopy (SEM) and uniaxial thermal tension. The effect of deformation temperature and strain rate on flow stress was evaluated, and deformation mechanism was analyzed. The results show that the stress-strain curves of Ti-6Al-4V (TC4) alloy sheet and TC4 alloy bar at elevated temperatures have different forms and rules. Flow stress of TC4 is controlled by both strain rate and deformation temperature. The flow stress decreases with the increase of high temperature. Deformation mechanisms exhibit dynamic recovery and recrystallization feature within high temperature region and grain boundary slip behaviors at low temperature.展开更多
Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting (OCC) process and the microstructure was examined. It was found that the wire...Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting (OCC) process and the microstructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The microstructure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic a-Mg and β-Mg17 Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the "bridging effect" caused by incidental elements in the alloy.展开更多
In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60μm were obtained by a melt s...In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60μm were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-I.IY alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in α-Mg solute solution, and impede the formation of Mg3 Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the α-Mg solid solution and icosahedral Mg3 YZn6 quasicrystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: α- magnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.展开更多
Nitrogen-containing carbons were prepared by modification of activated carbons.The modified carbons were used as electrode materials with improved electrochemical performance.Precursor anthracite was activated by KOH(...Nitrogen-containing carbons were prepared by modification of activated carbons.The modified carbons were used as electrode materials with improved electrochemical performance.Precursor anthracite was activated by KOH(KOH:anthracite= 1:1), modified by melamine or urea and then treated at 1173 K to obtain the modified carbons.The porous structure, the chemical composition and the electrochemical characteristics of the carbons were investigated by nitrogen sorption, XPS and electrochemical methods respectively.Electrochemical experiments were performed in an organic electrolytic solution of 1 M(C2H5)4NBF4/PC.The samples modified by the different methods showed differences in chemical composition that introduced varying degrees of electrochemical performance enhancement.The presence of nitrogen enhanced the electron donor properties and the surface wettability of the activated carbons:this ensured a sufficient utilization of the exposed surface for charge storage.展开更多
An icosahedral Mg3 YZn6 quasicrystalline phase can be produced in Mg-Zn- Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magne...An icosahedral Mg3 YZn6 quasicrystalline phase can be produced in Mg-Zn- Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1 Y alloy are analyzed. The microstructure of the as-cast Mg-6.4Zn-1.1 Y alloy consists of the α-Mg solid solution, icosahedral Mg3YZn6 quasicrystal, and Mg3 Y2Zn3 and MgZn2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, Mg3 Y2 Zn3 and MgZn2 phases dissolved into the matrix, whereas, Mg3 YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 MPa, 258.2 MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast Mg-6.4Zn-1.1 Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1 Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.展开更多
ZA27 alloy was prepared by casting with permanent mold and then annealed at 250℃ for 1-4h. The damping capaciG of the alloy was measured using a testing apparatus based on the cantilever beam technique. It was found ...ZA27 alloy was prepared by casting with permanent mold and then annealed at 250℃ for 1-4h. The damping capaciG of the alloy was measured using a testing apparatus based on the cantilever beam technique. It was found that the as-cast ZA27 alloy possesses high damping capacity with the value of 1.3 × 10^4 at 320Hz. After annealed at 250℃ for lh, the damping capacity decreases to 1.1 × 10^-3 and then remains constant even when the annealing time is increased to 4h. The microstructure of the as-cast ZA27 alloy consists of large dendrites of Al-rich PrimaG (x-phases, eutectoid (α + η) and nonequilibrium eutectic phases (α + η + ε). After annealing at 250℃ for lh, the e phase disappears due to dissolution into the matrix, and the spacing between the flakes of eutectoid increases. The further increase in the annealing time has little effect on the spacing. The damping mechanism of the alloy was discussed considering the thermoelastic damping and defect damping. The value of thermoelastic damping accounts only for 7%-8% in the overall damping in cantilever beam damping measurements and the damping capacity of the ZA27 alloy came mainly from defect damping.展开更多
CdZnTe(CZT)capacitive Frisch grid detectors can achieve a higher detecting resolution.The anode structure might have an important role in improving the weighting potential distribution of the detectors.In this paper, ...CdZnTe(CZT)capacitive Frisch grid detectors can achieve a higher detecting resolution.The anode structure might have an important role in improving the weighting potential distribution of the detectors.In this paper, four anode structures of capacitive Frisch grid structures have been analyzed with FE simulation,based on a 3-dimensional weighting potential analysis.The weighting potential distributions in modified anode devices(Model B, C and D)are optimized compared with a square device(Model A).In model C and D,the abrupt weighting potential can be well modified.However,with increased radius of the circular electrode in Model C the weighting potential platform away from the anode becomes higher and higher and in Model D,the weighting potential does not vary too much.展开更多
The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys (SMAs) through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased mor...The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys (SMAs) through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures (Ms) are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.展开更多
A coprecipitation/hydrothermal route was utilized to fabricate pure phase BiFeO3 powders using FeCl3·6H2O and Bi(NO3)3·5H2O as starting materials, ammonia as precipitant and NaOH as mineralizer. The synthe...A coprecipitation/hydrothermal route was utilized to fabricate pure phase BiFeO3 powders using FeCl3·6H2O and Bi(NO3)3·5H2O as starting materials, ammonia as precipitant and NaOH as mineralizer. The synthesized powders were characterized by XRD, SEM and DSC-TG analysis. In the process, single-phase BiFeO3 powders could be obtained at a hydrothermal reaction temperature of 180 ℃, with NaOH of 0.15 mol/L, in contrast to 200 ℃ and 4 mol/L for conventional hydrothermal route. Meanwhile, the micro-morphology of synthesized BiFeO3 powders changed with different reaction temperatures and concentrations of NaOH. The N6el temperature, Curie temperature and decomposition temperature of the synthesized BiFeO3 powders were detected to be 301 ℃, 828 ℃ and 964 ℃, respectively. The hydrothermal reactions mechanism to fabricate BiFeO3 powders were discussed based on the in-situ transformation process.展开更多
Ultrafine-grained pure aluminum L2 with a mean grain size of 1.01μm was produced by equal channel angular pressing (ECAP) and annealing at 150℃ for 2h. Damping behavior of the alloy was measured using a dynamic me...Ultrafine-grained pure aluminum L2 with a mean grain size of 1.01μm was produced by equal channel angular pressing (ECAP) and annealing at 150℃ for 2h. Damping behavior of the alloy was measured using a dynamic mechanical thermal analyzer. The alloy had an excellent damping capacity Q^-1 with the ambient value being 9.8×10^-3 at 1.0Hz when the strain amplitude was 2.0×10^-5. The damping behavior of the alloy showed a non-linear damping variation tendency, that is, with an increase in temperature and a decrease of frequency, the damping capacity of the alloy increased. The damping capacity increased with the strain amplitude when the strain amplitude was less than 4.6×10^-5. When the strain amplitude was higher than 4.6×10^-5, the damping capacity became a constant and independent of strain amplitude. The high damping capacity was attributed to dislocation unpinning and a drag of dislocation on pinning points.展开更多
Using first-principles pseudo-potential plane wave method, the energetics, geometrical and electronic structures of three Al13I cluster isomers were calculated. The calculation results of the binding energy indicate A...Using first-principles pseudo-potential plane wave method, the energetics, geometrical and electronic structures of three Al13I cluster isomers were calculated. The calculation results of the binding energy indicate Al13I cluster is more stable than Al13 cluster although its electrons are not a magic number as in Alia cluster, and among Al13I cluster isomers the "Bridge" structure is the most stable, the second is the "Ontop" structure, and the worst is the "Hollow" structure. By analyzing the geometrical structures of Al13I cluster isomers, it is found that after I atom and Al13 cluster combine the geometrical structures of Al13 moieties are changed besides Al13I Hollow cluster, in which the Alia moiety is still a regular icosahedron. For Al13I Ontop cluster, the Al13 moiety has a shrinking trend to I, whereas in Al13I Bridge cluster it is distorted. Mulliken population analysis shows for the interaction of electrons between Al-I atoms in Al13I cluster not only there exists an ionic bonding but there is a covalent bonding. Part of electrons in the Alia cluster transfer to I as Al13 cluster and I atom combine. The order of the strength of covalent bonding between Al13 moiety and I in Al13I cluster isomers is Al13IBridge〉Al13IHollow〉Al13I Ontop. Further analysis of electric structures of Al13 and Al13I clusters indicates a higher stability of Al13I cluster than Al13 cluster can be attributed to the s-p hybridization of 3s and 3p electrons of Al in Al13 moiety induced by 1 doped, which leads to fewer electrons N(EF) at EF in Al13I and a larger energy gap △EH-L between HOMO and LUMO levels in Al13I cluster. The distinguish of structural stability of Al13I cluster isomers mainly originates from their different magnitudes .in decrease of N(EF) and increase of △EH-L relative to Al13 cluster. The fewest N(EF) and the largest △EH-L are responsible for the high stability of Al13I Bridge cluster.展开更多
Tantalum nitride and tantalum carbide films were fabricated using magnetron sputtering of tantalum followed by nitrogen and carbon plasma-based ion implantation (N-PBII and C-PBII). The phase evolution and morpholog...Tantalum nitride and tantalum carbide films were fabricated using magnetron sputtering of tantalum followed by nitrogen and carbon plasma-based ion implantation (N-PBII and C-PBII). The phase evolution and morphology of the films were studied using glancing angle X-ray diffraction (GXRD) and transmission electron microscopy (TEM). It was found that the main phase in the tantalum nitride films was crystalline TaNo.1 whose grain size increases with increasing implantation voltage and phase content increases with increasing implantation dose. In the tantalum carbide film, the main phase was Ta2C. TaC phase also appeared as the implantation dose increased. XRD results from various glancing angles show that the phases with high nitrogen or carbon content, Ta4N5 and TaC, are present in the surface of the films. X-ray photoelectron spectra (XPS) from the tantalum carbide film reveal that the surface carbon content is higher than that of the inner film.展开更多
A new type of lead-free solder alloy Sn2.0Ag0.7CuRE was fabricated under vacuum condition. The microstructure and properties of the material, such as tensile strength, elongation, melting range, conductance and spread...A new type of lead-free solder alloy Sn2.0Ag0.7CuRE was fabricated under vacuum condition. The microstructure and properties of the material, such as tensile strength, elongation, melting range, conductance and spreading area were all investigated. Result shows that when the content of RE ≤ 0.1% (mass fraction), RE distribute uniformly in the solder alloy, and the tensile strength and conductance of Sn2.0Ag0.7CuRE solder alloy are better than those of traditional Sn37Pb solder. Its elongation and spreading area are almost equal to those of Sn37Pb solder. When the content of RE reaches 0.5%, RE compounds can be easily found around the boundaries of grains and phases, and the tensile strength and elongation and spreading area of Sn2.0Ag0.7CuRE solder alloy all decrease sharply. Therefore, RE amount added to the Sn2.0Ag0.7CuRE solder alloy under 0.1% is proper.展开更多
Based on the dual peak resonance of long-period fiber grating(LPFG), a novel film sensor is presented, in which films sensitive to the surrounding gases are coated on the cladding of the fiber grating region, and the ...Based on the dual peak resonance of long-period fiber grating(LPFG), a novel film sensor is presented, in which films sensitive to the surrounding gases are coated on the cladding of the fiber grating region, and the intervals of the dual peak resonant wavelengths change with the film refractive index. According to the coupled-mode theory, a triple-clad numerical model is developed to analyze the relation between the sensitivity Sn and the thin film optical parameters (the film thickness h3 and the refractive index n3) and the fiber grating parameters (the grating period Λ and the core index modulation σ). By using optimization method, the optimal film optical parameters and the grating structure parameters are obtained. Numerical simulation shows that the sensitivity of this scheme to refractive index of the films is predicted to be more than 10-7. The theoretic analysis provides straightforward foundation for the actual highly sensitive film sensors.展开更多
A 3D coupling mathematical simulation program of the fluid flow, thermal transfer and solidification was developed based on the slab continuous casting process. Some characteristics such as fluid flow, solidification ...A 3D coupling mathematical simulation program of the fluid flow, thermal transfer and solidification was developed based on the slab continuous casting process. Some characteristics such as fluid flow, solidification and temperature distribution near the submerged entry nozzle (SEN) and the corner of the mold were simulated and analyzed. The result of the calculation indicates that the flow of molten metal forms two big cycling zones in the mold after it flows out of the SEN, and the temperature at the center of the two zones is relatively low. Moreover, there is a small narrow cycling zone near the narrow side of the mold due to casting. The velocity of the surface flow, the turbulent kinetic energy and the F value might reveal the relationship between the fluctuation of meniscus and the quality of the slab to some degree.展开更多
In this study, the temperature field model of twin-roll thin strip continuous casting was developed, and the interface heat transfer coefficient between the air and the strip surface was computed by using the inverse ...In this study, the temperature field model of twin-roll thin strip continuous casting was developed, and the interface heat transfer coefficient between the air and the strip surface was computed by using the inverse method. The effects of the process parameters including the casting speed, liquid level height, pouring temperature and thickness of the thin strip on the outlet temperature of the rotating rolls and the surface temperature of the thin strip were analyzed.展开更多
This study presents a simple simulator for measuring the transient interfacial heat transfer between the molten steel and the copper casting roll for strip casting. The calculation principle of the heat flux is introd...This study presents a simple simulator for measuring the transient interfacial heat transfer between the molten steel and the copper casting roll for strip casting. The calculation principle of the heat flux is introduced in detail. Results show that the heat flux reaches the peak value of 9 MW/m^2 ,and decreases rapidly to 4 MW/m^2, and then fluctuates within the range of 2 MW/m^2 to 5 MW/m2. It agrees with the previous study. It also indicates the simulator can be effectively used to analyze the heat transfer during strip casting.展开更多
文摘The preparation and properties of ceramic short fiber reinforced Al-Si alloy matrix composite and it's application on the piston for internal combustion engines are presented. Alumina or aluminosilicatefiibers reinforced Al-Si alloy matrix composite has more excellent synthetical properties at elevated temperature than the matrix alloys. A partially reinforced Al-Si alloy matrix composite piston produced by squeeze casting technique has a firm interface between reinforced and unreinforced areas, low reject rate and good technical tolerance. As a new kind of piston material, it has been used for mass production of about 400,000 pieces of automobile engines piston. China has become one of a few countries in which aluminum alloy matrix composite materials have been used in automobile industry and attained industrialization.
文摘By loading nanometer anatase onto exfoliated graphite with the sol-gel method, exfoliated graphite-TiO2 composite (EG-TiO2) can be prepared, which can adsorb oil and can also degrade oil. In a technologic condition for preparing EG-TiO2, the impregnated number of times is the most important factor to influence oil-adsorbing capability, that is, when the impregnated number of times increases, the amount of saturation-adsorbed oil decreases. The study of EG-TiO2 photocatalytic degradation of machine oil based on the weight-loss method and infrared spectrum method indicates that EG-TiO2 has obvious effect of photocatalytic degradation for machine oil. Its performance is superior to pure nanometer TiO2 powder because nanometer TiO2 in EG-TiO2 has three-dimension laminar structure and comparatively high adsorption capability.
基金This study was financially supported by the Scientific Research Project of Education Department of Shaanxi Province (No. 07JK358);the National Natural Science Foundation of China (No.50271054); the Shaanxi Provincial Natural Scientific Research Project (No.2003E111); SRF for ROCS, SEM (101-220325).
文摘M92Si reinforced Mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion (RE) after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of M92Si and the mechanical properties of the com- posite were investigated, to develop new ways to refine the M928i phase and improve its shape. The result showed that RE was very useful in refining the M92Si phase. The more the RE processing passes, the better the refining effect would be. Moreover, the uniform distribution of M928i phases would be more in the composite. After the composite was processed by RE for 12 passes, most M92Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 MPa, 211.4 MPa, and 3.3% at room temperature, whereas, 288.2 MPa, ,207.7 MPa, and 7.8%, respectively, at 150℃. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150℃. The M928i reinforced Mg-Al based composite possesses good heat resistance at 150℃. The excellent resistance to effect of heat is attributed to the high melting tempera- ture and good thermal stability of fine Mg2Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.
文摘Hot deformation behaviors were studied by means of scanning electron microscopy (SEM) and uniaxial thermal tension. The effect of deformation temperature and strain rate on flow stress was evaluated, and deformation mechanism was analyzed. The results show that the stress-strain curves of Ti-6Al-4V (TC4) alloy sheet and TC4 alloy bar at elevated temperatures have different forms and rules. Flow stress of TC4 is controlled by both strain rate and deformation temperature. The flow stress decreases with the increase of high temperature. Deformation mechanisms exhibit dynamic recovery and recrystallization feature within high temperature region and grain boundary slip behaviors at low temperature.
基金the Shaanxi Provincial Natural Science Research Project(No.2003E111)Scientific research project of Education Department of Shaanxi Province(No.07JK358)the Industrialization Cultivation Project of Education Department of Shaanxi Province(No.04JC24).
文摘Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting (OCC) process and the microstructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The microstructure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic a-Mg and β-Mg17 Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the "bridging effect" caused by incidental elements in the alloy.
基金funded by the National Natural Science Foundation of China(Grant No.50271054)the Shaanxi Provincial Nature Scientific Research Project(Grant No.2003E1 11)SRF for ROCS,SEM(101-220325).
文摘In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60μm were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-I.IY alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in α-Mg solute solution, and impede the formation of Mg3 Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the α-Mg solid solution and icosahedral Mg3 YZn6 quasicrystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: α- magnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.
基金Projects 50672025 and 50730003 supported by the National Natural Science Foundation of China
文摘Nitrogen-containing carbons were prepared by modification of activated carbons.The modified carbons were used as electrode materials with improved electrochemical performance.Precursor anthracite was activated by KOH(KOH:anthracite= 1:1), modified by melamine or urea and then treated at 1173 K to obtain the modified carbons.The porous structure, the chemical composition and the electrochemical characteristics of the carbons were investigated by nitrogen sorption, XPS and electrochemical methods respectively.Electrochemical experiments were performed in an organic electrolytic solution of 1 M(C2H5)4NBF4/PC.The samples modified by the different methods showed differences in chemical composition that introduced varying degrees of electrochemical performance enhancement.The presence of nitrogen enhanced the electron donor properties and the surface wettability of the activated carbons:this ensured a sufficient utilization of the exposed surface for charge storage.
基金supported by the National Natural Science Foundation of China(Grant No.50271054)Shaanxi Provincial Nature Scientific Research Project(Grant No.2003E1 11)SRF for ROCS,SEM(101-220325).
文摘An icosahedral Mg3 YZn6 quasicrystalline phase can be produced in Mg-Zn- Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1 Y alloy are analyzed. The microstructure of the as-cast Mg-6.4Zn-1.1 Y alloy consists of the α-Mg solid solution, icosahedral Mg3YZn6 quasicrystal, and Mg3 Y2Zn3 and MgZn2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, Mg3 Y2 Zn3 and MgZn2 phases dissolved into the matrix, whereas, Mg3 YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 MPa, 258.2 MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast Mg-6.4Zn-1.1 Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1 Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.
基金This work was supported by the National Natural Science Foundation of China(No.50075068)Scientific Research Project of Department of Education of Shaanxi Province(No.03JK132)Natural Science Foundation of Shaanxi Province(No.2003E1 11).
文摘ZA27 alloy was prepared by casting with permanent mold and then annealed at 250℃ for 1-4h. The damping capaciG of the alloy was measured using a testing apparatus based on the cantilever beam technique. It was found that the as-cast ZA27 alloy possesses high damping capacity with the value of 1.3 × 10^4 at 320Hz. After annealed at 250℃ for lh, the damping capacity decreases to 1.1 × 10^-3 and then remains constant even when the annealing time is increased to 4h. The microstructure of the as-cast ZA27 alloy consists of large dendrites of Al-rich PrimaG (x-phases, eutectoid (α + η) and nonequilibrium eutectic phases (α + η + ε). After annealing at 250℃ for lh, the e phase disappears due to dissolution into the matrix, and the spacing between the flakes of eutectoid increases. The further increase in the annealing time has little effect on the spacing. The damping mechanism of the alloy was discussed considering the thermoelastic damping and defect damping. The value of thermoelastic damping accounts only for 7%-8% in the overall damping in cantilever beam damping measurements and the damping capacity of the ZA27 alloy came mainly from defect damping.
基金Supported by National Natural Science Foundation of China(Grant No.60676002 and No.10675080).
文摘CdZnTe(CZT)capacitive Frisch grid detectors can achieve a higher detecting resolution.The anode structure might have an important role in improving the weighting potential distribution of the detectors.In this paper, four anode structures of capacitive Frisch grid structures have been analyzed with FE simulation,based on a 3-dimensional weighting potential analysis.The weighting potential distributions in modified anode devices(Model B, C and D)are optimized compared with a square device(Model A).In model C and D,the abrupt weighting potential can be well modified.However,with increased radius of the circular electrode in Model C the weighting potential platform away from the anode becomes higher and higher and in Model D,the weighting potential does not vary too much.
文摘The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys (SMAs) through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures (Ms) are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.
基金the National Natural Science Foundation of China(No.50372039)
文摘A coprecipitation/hydrothermal route was utilized to fabricate pure phase BiFeO3 powders using FeCl3·6H2O and Bi(NO3)3·5H2O as starting materials, ammonia as precipitant and NaOH as mineralizer. The synthesized powders were characterized by XRD, SEM and DSC-TG analysis. In the process, single-phase BiFeO3 powders could be obtained at a hydrothermal reaction temperature of 180 ℃, with NaOH of 0.15 mol/L, in contrast to 200 ℃ and 4 mol/L for conventional hydrothermal route. Meanwhile, the micro-morphology of synthesized BiFeO3 powders changed with different reaction temperatures and concentrations of NaOH. The N6el temperature, Curie temperature and decomposition temperature of the synthesized BiFeO3 powders were detected to be 301 ℃, 828 ℃ and 964 ℃, respectively. The hydrothermal reactions mechanism to fabricate BiFeO3 powders were discussed based on the in-situ transformation process.
基金the National Natural Science Foundation of China (No. 59671026) Shaanxi Provincial Natural Science Foundation of China (No. 2003E1 11).
文摘Ultrafine-grained pure aluminum L2 with a mean grain size of 1.01μm was produced by equal channel angular pressing (ECAP) and annealing at 150℃ for 2h. Damping behavior of the alloy was measured using a dynamic mechanical thermal analyzer. The alloy had an excellent damping capacity Q^-1 with the ambient value being 9.8×10^-3 at 1.0Hz when the strain amplitude was 2.0×10^-5. The damping behavior of the alloy showed a non-linear damping variation tendency, that is, with an increase in temperature and a decrease of frequency, the damping capacity of the alloy increased. The damping capacity increased with the strain amplitude when the strain amplitude was less than 4.6×10^-5. When the strain amplitude was higher than 4.6×10^-5, the damping capacity became a constant and independent of strain amplitude. The high damping capacity was attributed to dislocation unpinning and a drag of dislocation on pinning points.
基金This work was supported by the Science & Technology Major Programs of Ministry of Education of China (No. 101139)
文摘Using first-principles pseudo-potential plane wave method, the energetics, geometrical and electronic structures of three Al13I cluster isomers were calculated. The calculation results of the binding energy indicate Al13I cluster is more stable than Al13 cluster although its electrons are not a magic number as in Alia cluster, and among Al13I cluster isomers the "Bridge" structure is the most stable, the second is the "Ontop" structure, and the worst is the "Hollow" structure. By analyzing the geometrical structures of Al13I cluster isomers, it is found that after I atom and Al13 cluster combine the geometrical structures of Al13 moieties are changed besides Al13I Hollow cluster, in which the Alia moiety is still a regular icosahedron. For Al13I Ontop cluster, the Al13 moiety has a shrinking trend to I, whereas in Al13I Bridge cluster it is distorted. Mulliken population analysis shows for the interaction of electrons between Al-I atoms in Al13I cluster not only there exists an ionic bonding but there is a covalent bonding. Part of electrons in the Alia cluster transfer to I as Al13 cluster and I atom combine. The order of the strength of covalent bonding between Al13 moiety and I in Al13I cluster isomers is Al13IBridge〉Al13IHollow〉Al13I Ontop. Further analysis of electric structures of Al13 and Al13I clusters indicates a higher stability of Al13I cluster than Al13 cluster can be attributed to the s-p hybridization of 3s and 3p electrons of Al in Al13 moiety induced by 1 doped, which leads to fewer electrons N(EF) at EF in Al13I and a larger energy gap △EH-L between HOMO and LUMO levels in Al13I cluster. The distinguish of structural stability of Al13I cluster isomers mainly originates from their different magnitudes .in decrease of N(EF) and increase of △EH-L relative to Al13 cluster. The fewest N(EF) and the largest △EH-L are responsible for the high stability of Al13I Bridge cluster.
基金supported by the National Basic Research Program of China (No. 2007CB607602)the Science Found for Distinguished Yong Scholars of Heilongjiang Province,China (No. JC200901)+1 种基金the National Natural Science Foundation of China (No. 50875058)the Program of Excellent Teams of Harbin Institute of Technology
文摘Tantalum nitride and tantalum carbide films were fabricated using magnetron sputtering of tantalum followed by nitrogen and carbon plasma-based ion implantation (N-PBII and C-PBII). The phase evolution and morphology of the films were studied using glancing angle X-ray diffraction (GXRD) and transmission electron microscopy (TEM). It was found that the main phase in the tantalum nitride films was crystalline TaNo.1 whose grain size increases with increasing implantation voltage and phase content increases with increasing implantation dose. In the tantalum carbide film, the main phase was Ta2C. TaC phase also appeared as the implantation dose increased. XRD results from various glancing angles show that the phases with high nitrogen or carbon content, Ta4N5 and TaC, are present in the surface of the films. X-ray photoelectron spectra (XPS) from the tantalum carbide film reveal that the surface carbon content is higher than that of the inner film.
文摘A new type of lead-free solder alloy Sn2.0Ag0.7CuRE was fabricated under vacuum condition. The microstructure and properties of the material, such as tensile strength, elongation, melting range, conductance and spreading area were all investigated. Result shows that when the content of RE ≤ 0.1% (mass fraction), RE distribute uniformly in the solder alloy, and the tensile strength and conductance of Sn2.0Ag0.7CuRE solder alloy are better than those of traditional Sn37Pb solder. Its elongation and spreading area are almost equal to those of Sn37Pb solder. When the content of RE reaches 0.5%, RE compounds can be easily found around the boundaries of grains and phases, and the tensile strength and elongation and spreading area of Sn2.0Ag0.7CuRE solder alloy all decrease sharply. Therefore, RE amount added to the Sn2.0Ag0.7CuRE solder alloy under 0.1% is proper.
基金the National Natural Science Foundation of China (No 60777035)Research Project of the Education Committee of Shanghai(No 07ZZ87)Shanghai Leading Aca-demic Discipline Project (No T0501)
文摘Based on the dual peak resonance of long-period fiber grating(LPFG), a novel film sensor is presented, in which films sensitive to the surrounding gases are coated on the cladding of the fiber grating region, and the intervals of the dual peak resonant wavelengths change with the film refractive index. According to the coupled-mode theory, a triple-clad numerical model is developed to analyze the relation between the sensitivity Sn and the thin film optical parameters (the film thickness h3 and the refractive index n3) and the fiber grating parameters (the grating period Λ and the core index modulation σ). By using optimization method, the optimal film optical parameters and the grating structure parameters are obtained. Numerical simulation shows that the sensitivity of this scheme to refractive index of the films is predicted to be more than 10-7. The theoretic analysis provides straightforward foundation for the actual highly sensitive film sensors.
文摘A 3D coupling mathematical simulation program of the fluid flow, thermal transfer and solidification was developed based on the slab continuous casting process. Some characteristics such as fluid flow, solidification and temperature distribution near the submerged entry nozzle (SEN) and the corner of the mold were simulated and analyzed. The result of the calculation indicates that the flow of molten metal forms two big cycling zones in the mold after it flows out of the SEN, and the temperature at the center of the two zones is relatively low. Moreover, there is a small narrow cycling zone near the narrow side of the mold due to casting. The velocity of the surface flow, the turbulent kinetic energy and the F value might reveal the relationship between the fluctuation of meniscus and the quality of the slab to some degree.
文摘In this study, the temperature field model of twin-roll thin strip continuous casting was developed, and the interface heat transfer coefficient between the air and the strip surface was computed by using the inverse method. The effects of the process parameters including the casting speed, liquid level height, pouring temperature and thickness of the thin strip on the outlet temperature of the rotating rolls and the surface temperature of the thin strip were analyzed.
文摘This study presents a simple simulator for measuring the transient interfacial heat transfer between the molten steel and the copper casting roll for strip casting. The calculation principle of the heat flux is introduced in detail. Results show that the heat flux reaches the peak value of 9 MW/m^2 ,and decreases rapidly to 4 MW/m^2, and then fluctuates within the range of 2 MW/m^2 to 5 MW/m2. It agrees with the previous study. It also indicates the simulator can be effectively used to analyze the heat transfer during strip casting.