The effect of Ag in solid solution on the microstructure,texture and the deformation behaviour of indirectly extruded Mg was investigated.Ag as a solid solution strengthener affects the behaviour during extrusion,resu...The effect of Ag in solid solution on the microstructure,texture and the deformation behaviour of indirectly extruded Mg was investigated.Ag as a solid solution strengthener affects the behaviour during extrusion,resulting in enhanced deformation related heating and corresponding coarser grained microstructures.No substantial effect on the texture development is revealed.The mechanical properties simultaneously increase in stress and strain levels with increasing Ag content,especially in tension as a result of the changing impact of the slip modes which can be associated with a decrease of the lattice parameters as well as the c/a ratio of the hcp lattice structure.In compression tests with twin dominated flow,the impact is much smaller on the compressive yield stress but higher with respect to the twinning related strain hardening rate.Solid solution strength functions for Fleischer and Labusch were determined,also confirming the anisotropic behaviour of the extruded Mg alloys.展开更多
The precipitation of MgZn2 phase in aging process of Al-Zn-Mg-Cu alloy forging was characterized qualitatively after transmission electron microscope(TEM)observation,X-ray diffraction phase analysis and the exact meas...The precipitation of MgZn2 phase in aging process of Al-Zn-Mg-Cu alloy forging was characterized qualitatively after transmission electron microscope(TEM)observation,X-ray diffraction phase analysis and the exact measure of lattice parameter.And,the precipitation of the second-phase in aging process was simulated after test the resistivity of the alloy in a continuous heating process and delayed time processing.The results show that when heating in the same rate,the alloy resistivity increases with temperature first,a mutation point appears at 110℃,and the resistivity reaches its peak at 120℃.Then,the resistivity decreases and achieves a minimum at about 170℃.Afterwards,it increases again.The change of resistivity results from a combined effect of the temperature and phase transformation.The volume precipitation of η' phase dominates at about 120℃,and the resistivity of forgings decreases accordingly.When the specimen cools in a furnace at 240℃,the phase transformation finishes basically and the alloy content of Al-matix keeps stable,thus,the alloy resistivity depends on the temperature only.It decreases with temperature and time since the end of precipitation.The higher the temperature is,the bigger it will be.With a big descending rate of the resistivity curve,the time to reach the stable value becomes shorter.展开更多
The ZnAl<sub>x</sub>Fe<sub>2-x</sub>O<sub>4</sub> (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diff...The ZnAl<sub>x</sub>Fe<sub>2-x</sub>O<sub>4</sub> (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diffraction of all the three samples showed sharp Bragg peaks indicating the formation of a single phase spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using the Nelson-Riley extrapolation method. The lattice parameters, cation distribution and oxygen position parameters have also been determined by refining the data by the Rietveld method. Rietveld refinement of the XRD data reveals all the samples to possess cubic symmetry corresponding to the space group Fd3m. Lattice parameters were found to decrease with increasing Al concentration, i.e. 8.4322, 8.4002, and 8.3984 Åfor x = 0.0, 0.2 and 0.4, respectively.展开更多
Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated ...Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated to the grain boundaries. Lattice parameter and density measurements with different V concentrations have been correlated with lattice distortion. Mechanical properties studies were carried out, showing a decreasing behavior in microhardness while fracture toughness value increases at intermediate concentrations. Results indicated that vanadium alloying produces a significant effect on grain growth behavior and second phase precipitation.展开更多
In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of t...In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.展开更多
A series of polycrystalline samples of Co_(1-x)Zn_(x)Fe_(2)O_(4)where(x=0.1,0.2,0.3,0.4,0.5 and 0.6)were prepared by the usual ceramic technique.X-ray diffraction patterns confirmed the spinel cubic structure.The diff...A series of polycrystalline samples of Co_(1-x)Zn_(x)Fe_(2)O_(4)where(x=0.1,0.2,0.3,0.4,0.5 and 0.6)were prepared by the usual ceramic technique.X-ray diffraction patterns confirmed the spinel cubic structure.The diffusion coefficients of oxygen vacancies were estimated from dc conductivity measurements.It was noticed that the diffusion coefficient decreases with increasing Zn^(2+)concentrations.An increase of temperature increases the diffusion of lattice vacancies.The Curie temperature,lattice parameter and jump length of electrons were studied as a function of Zn^(2+)concentration.From the correlation between the ionic radius and the radii of octahedral and tetrahedral sites,the theoretical lattice parameters were calculated and suggested cation distribution for the given ferrites was determined.展开更多
Intrinsic partial occupation of Cu induces strong phonon scattering for an extremely low lattice thermal conductivity in TmCuTe_(2),which leads this material to be a promising candidate for thermoelectric applications...Intrinsic partial occupation of Cu induces strong phonon scattering for an extremely low lattice thermal conductivity in TmCuTe_(2),which leads this material to be a promising candidate for thermoelectric applications.This work focus on the electronic and phononic transport properties of TmCuTe_(2) with Agalloying on the Cu site.Such a Ag/Cu substitution is found to enable a decrease in Hall carrier concentration from 141019 to 81019 cm^(3) for an evaluation of the charge transport based on a single parabolic band(SPB)model with acoustic scattering.In addition,Ag-substitution simultaneously introduces Cu/Ag point defects for extra phonon scattering,leading the lattice thermal conductivity to be as low as~0.25 W/m-K in a broad temperature.The optimization in carrier concentration and the reduction in lattice thermal conductivity contribute to a~40%improvement in average thermoelectric figure of merit(zT).The determination of band parameters enables a guidance for further advancements in this promising thermoelectric material.展开更多
基金This research was partly funded by Helmholtz Association in the frame of Helmholtz-Russian Science Foundation Joint Research Group grant num-ber HRSF-0025.
文摘The effect of Ag in solid solution on the microstructure,texture and the deformation behaviour of indirectly extruded Mg was investigated.Ag as a solid solution strengthener affects the behaviour during extrusion,resulting in enhanced deformation related heating and corresponding coarser grained microstructures.No substantial effect on the texture development is revealed.The mechanical properties simultaneously increase in stress and strain levels with increasing Ag content,especially in tension as a result of the changing impact of the slip modes which can be associated with a decrease of the lattice parameters as well as the c/a ratio of the hcp lattice structure.In compression tests with twin dominated flow,the impact is much smaller on the compressive yield stress but higher with respect to the twinning related strain hardening rate.Solid solution strength functions for Fleischer and Labusch were determined,also confirming the anisotropic behaviour of the extruded Mg alloys.
基金Sponsored by the Matching Project of Commission of Scientific and Technical Industry on National Defence(JPPT-×××-1)
文摘The precipitation of MgZn2 phase in aging process of Al-Zn-Mg-Cu alloy forging was characterized qualitatively after transmission electron microscope(TEM)observation,X-ray diffraction phase analysis and the exact measure of lattice parameter.And,the precipitation of the second-phase in aging process was simulated after test the resistivity of the alloy in a continuous heating process and delayed time processing.The results show that when heating in the same rate,the alloy resistivity increases with temperature first,a mutation point appears at 110℃,and the resistivity reaches its peak at 120℃.Then,the resistivity decreases and achieves a minimum at about 170℃.Afterwards,it increases again.The change of resistivity results from a combined effect of the temperature and phase transformation.The volume precipitation of η' phase dominates at about 120℃,and the resistivity of forgings decreases accordingly.When the specimen cools in a furnace at 240℃,the phase transformation finishes basically and the alloy content of Al-matix keeps stable,thus,the alloy resistivity depends on the temperature only.It decreases with temperature and time since the end of precipitation.The higher the temperature is,the bigger it will be.With a big descending rate of the resistivity curve,the time to reach the stable value becomes shorter.
文摘The ZnAl<sub>x</sub>Fe<sub>2-x</sub>O<sub>4</sub> (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diffraction of all the three samples showed sharp Bragg peaks indicating the formation of a single phase spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using the Nelson-Riley extrapolation method. The lattice parameters, cation distribution and oxygen position parameters have also been determined by refining the data by the Rietveld method. Rietveld refinement of the XRD data reveals all the samples to possess cubic symmetry corresponding to the space group Fd3m. Lattice parameters were found to decrease with increasing Al concentration, i.e. 8.4322, 8.4002, and 8.3984 Åfor x = 0.0, 0.2 and 0.4, respectively.
文摘Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated to the grain boundaries. Lattice parameter and density measurements with different V concentrations have been correlated with lattice distortion. Mechanical properties studies were carried out, showing a decreasing behavior in microhardness while fracture toughness value increases at intermediate concentrations. Results indicated that vanadium alloying produces a significant effect on grain growth behavior and second phase precipitation.
基金This report is part of the fundamental research report with contract No.486 127/UN14.2/PNL.01.03.00/2016.
文摘In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.
文摘A series of polycrystalline samples of Co_(1-x)Zn_(x)Fe_(2)O_(4)where(x=0.1,0.2,0.3,0.4,0.5 and 0.6)were prepared by the usual ceramic technique.X-ray diffraction patterns confirmed the spinel cubic structure.The diffusion coefficients of oxygen vacancies were estimated from dc conductivity measurements.It was noticed that the diffusion coefficient decreases with increasing Zn^(2+)concentrations.An increase of temperature increases the diffusion of lattice vacancies.The Curie temperature,lattice parameter and jump length of electrons were studied as a function of Zn^(2+)concentration.From the correlation between the ionic radius and the radii of octahedral and tetrahedral sites,the theoretical lattice parameters were calculated and suggested cation distribution for the given ferrites was determined.
基金supported by the National Natural Science Foundation of China(Grant No.52022068,51861145305 and 51772215)the National Key Research and Development Program of China(2018YFB0703600)the Innovation Program of Shanghai Municipal Education Commission and Shanghai Natural Science Foundation(19ZR1459900).
文摘Intrinsic partial occupation of Cu induces strong phonon scattering for an extremely low lattice thermal conductivity in TmCuTe_(2),which leads this material to be a promising candidate for thermoelectric applications.This work focus on the electronic and phononic transport properties of TmCuTe_(2) with Agalloying on the Cu site.Such a Ag/Cu substitution is found to enable a decrease in Hall carrier concentration from 141019 to 81019 cm^(3) for an evaluation of the charge transport based on a single parabolic band(SPB)model with acoustic scattering.In addition,Ag-substitution simultaneously introduces Cu/Ag point defects for extra phonon scattering,leading the lattice thermal conductivity to be as low as~0.25 W/m-K in a broad temperature.The optimization in carrier concentration and the reduction in lattice thermal conductivity contribute to a~40%improvement in average thermoelectric figure of merit(zT).The determination of band parameters enables a guidance for further advancements in this promising thermoelectric material.
