The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepare...The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepared by the RSC process and then subjected to heat treatment.The microstructure evolution and mechanical properties of AZX912 alloy during heat treatment were investigated.It was found that during solid solution treatment at 410°C,β-Mg_(17)Al_(12) phase with low melting point dissolves intoα-Mg matrix,while the connected network-like Al_2Ca phase with high melting point tends to separate gradually,and the tips of Al_2Ca phase is partially spheroidized.With the increase of solid solution time,the yield strength(YS)of AZX912 alloy decreases gradually while the ultimate tensile strength(UTS)and elongation to failure(E_f)increase continuously.Isothermal ageing at 225°C promotes the precipitation ofβ-Mg_(17)Al_(12) phase in the matrix of AZX912 alloy.The hardness reaches the peak after ageing for 96 h and the increase in hardness is about 24.8%.The precipitation ofβ-Mg_(17)Al_(12) phase during ageing treatment is beneficial to YS but harmful to E_f.The mechanism of microstructure evolution during heat treatment and its effect on mechanical properties are discussed.展开更多
The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental r...The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 （θ phase） precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformatinn temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.展开更多
The microstructure and mechanical properties of magnesium （Mg） alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient an...The microstructure and mechanical properties of magnesium （Mg） alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2wt.% Ca （AZX912） Mg alloy samples prepared by gravity casting （GC）, squeeze casting （SC） and rheo-squeeze casting （RSC）, respectively, was carried out. The results show that mMg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 ~C to 200 ~C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.展开更多
The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron mi...The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron microscopy(SEM)and tensile test.It is found that,as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist ofα-Mg+β-Li duplex matrix,MgLiAl2 and Li2Mg Sn phases.Increasing Sn content leads to grain refinement ofα-Mg dendrites and increase in content of Li2MgSn phase.During hot extrusion,complete dynamic recrystallization(DRX)takes place inβ-Li phase while incomplete DRX takes place inα-Mg phase.As Sn content is increased,the volume fraction of DRXedα-Mg grains is increased and the average grain size of DRXedα-Mg grains is decreased.Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys.Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.展开更多
The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca （TZX621）（mass fraction, %） alloy was investigated. It is found that incomplete dynamic recrystallization （DR...The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca （TZX621）（mass fraction, %） alloy was investigated. It is found that incomplete dynamic recrystallization （DRX） took place in as-extrudedTZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXedgrains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particlesand fine Mg2Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation ofas-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%,17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.展开更多
Metal/semiconductor memristive heterostructures have potential applications in nonvolatile memory and computing devices.To enhance the performance of the memristive devices,it requires a comprehensive engineering to t...Metal/semiconductor memristive heterostructures have potential applications in nonvolatile memory and computing devices.To enhance the performance of the memristive devices,it requires a comprehensive engineering to the metal/semiconductor interfaces.Here in this paper,we discuss the effects of oxygen vacancies and temperature on the memristive behaviors of perovskite-oxide Schottky junctions,each consisting of SrRuO3 thin films epitaxially grown on Nb:SrTiO3 substrates.The oxygen partial pressure and laser fluence are controlled during the film growth to tune the oxygen defects in SrRuO3 films,and the Schottky barrier height can be controlled by both the temperature and oxygen vacancies.The resistive switching measurements demonstrate that the largest resistance switching ratio can be obtained by controlling oxygen vacancy concentration at lower temperature.It suggests that reducing Schottky barrier height can enhance the resistive switching performance of the SrRuO3/Nb:SrTiO3 heterostructures.This work can conduce to the development of high-performance metal-oxide/semiconductor memristive devices.展开更多
{001}facets dominated single crystalline anatase TiO_(2)nanosheet array(TNSA)was synthe-sized through an optimized organic solvothermal route on uorine-doped tin oxide substrate.The field emission scanning electron mi...{001}facets dominated single crystalline anatase TiO_(2)nanosheet array(TNSA)was synthe-sized through an optimized organic solvothermal route on uorine-doped tin oxide substrate.The field emission scanning electron microscopy images and X-ray diffraction patterns re-vealed that the{001}synthesized facets dominated TNSA exhibited much higher orientation than that synthesized by hydrothermal route.The TNSAs were loaded with Pt nanoparti-cles in uniformly size by using a photodecomposition method,which were further con rmed by high resolution transmission electron microscopy(HRTEM).The HRTEM images also revealed that Pt nanoparticles preferred to deposit on{001}facets.With loading of Pt nanoparticles,the optical absorbance was significantly enhanced,while the photolumines-cence(PL)was inhibited.The photocatalytic activity of TNSA was signi cantly improved by Pt loading and reached the maximum with optimal amount of Pt loading.The optimal amount of Pt on{001}facets is far less than that on TiO_(2)nanoparticles,which may be attributed to the specific atom structure of reactive{001}facets.展开更多
基金financially supported by National Natural Science Foundation of China(No.51601076 and No.51401093)Natural Science Fund for Colleges and Universities in Jiangsu Province(No.16KJB430013)
文摘The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepared by the RSC process and then subjected to heat treatment.The microstructure evolution and mechanical properties of AZX912 alloy during heat treatment were investigated.It was found that during solid solution treatment at 410°C,β-Mg_(17)Al_(12) phase with low melting point dissolves intoα-Mg matrix,while the connected network-like Al_2Ca phase with high melting point tends to separate gradually,and the tips of Al_2Ca phase is partially spheroidized.With the increase of solid solution time,the yield strength(YS)of AZX912 alloy decreases gradually while the ultimate tensile strength(UTS)and elongation to failure(E_f)increase continuously.Isothermal ageing at 225°C promotes the precipitation ofβ-Mg_(17)Al_(12) phase in the matrix of AZX912 alloy.The hardness reaches the peak after ageing for 96 h and the increase in hardness is about 24.8%.The precipitation ofβ-Mg_(17)Al_(12) phase during ageing treatment is beneficial to YS but harmful to E_f.The mechanism of microstructure evolution during heat treatment and its effect on mechanical properties are discussed.
基金supported by the Foundational Research Plan of Jiangsu Province,China (NoBK2005025)
文摘The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 （θ phase） precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformatinn temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.
基金financially supported by the National Natural Science Foundation of China(No.51601076)the Natural Science Fund for Colleges and Universities in Jiangsu Province(No.16KJB430013,17KJA430005)
文摘The microstructure and mechanical properties of magnesium （Mg） alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2wt.% Ca （AZX912） Mg alloy samples prepared by gravity casting （GC）, squeeze casting （SC） and rheo-squeeze casting （RSC）, respectively, was carried out. The results show that mMg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 ~C to 200 ~C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.
基金Project(51601076)supported by the National Natural Science Foundation of ChinaProject(17KJA430005)supported by the Natural Science Fund for Colleges and Universities in Jiangsu Province,ChinaProject(2019M650096)supported by China Postdoctoral Science Foundation。
文摘The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron microscopy(SEM)and tensile test.It is found that,as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist ofα-Mg+β-Li duplex matrix,MgLiAl2 and Li2Mg Sn phases.Increasing Sn content leads to grain refinement ofα-Mg dendrites and increase in content of Li2MgSn phase.During hot extrusion,complete dynamic recrystallization(DRX)takes place inβ-Li phase while incomplete DRX takes place inα-Mg phase.As Sn content is increased,the volume fraction of DRXedα-Mg grains is increased and the average grain size of DRXedα-Mg grains is decreased.Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys.Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.
基金Project(51601076)supported by the National Natural Science Foundation of ChinaProjects(16KJB430013,17KJA430005)supported by the Natural Science Fund for Colleges and Universities in Jiangsu Province,China
文摘The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca （TZX621）（mass fraction, %） alloy was investigated. It is found that incomplete dynamic recrystallization （DRX） took place in as-extrudedTZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXedgrains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particlesand fine Mg2Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation ofas-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%,17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51627901 and 11574287)the National Key Research and Development Program of China(Grant No.2016YFA0401004)the Anhui Initiative in Quantum Information Technologies,China(Grant No.AHY100000)
文摘Metal/semiconductor memristive heterostructures have potential applications in nonvolatile memory and computing devices.To enhance the performance of the memristive devices,it requires a comprehensive engineering to the metal/semiconductor interfaces.Here in this paper,we discuss the effects of oxygen vacancies and temperature on the memristive behaviors of perovskite-oxide Schottky junctions,each consisting of SrRuO3 thin films epitaxially grown on Nb:SrTiO3 substrates.The oxygen partial pressure and laser fluence are controlled during the film growth to tune the oxygen defects in SrRuO3 films,and the Schottky barrier height can be controlled by both the temperature and oxygen vacancies.The resistive switching measurements demonstrate that the largest resistance switching ratio can be obtained by controlling oxygen vacancy concentration at lower temperature.It suggests that reducing Schottky barrier height can enhance the resistive switching performance of the SrRuO3/Nb:SrTiO3 heterostructures.This work can conduce to the development of high-performance metal-oxide/semiconductor memristive devices.
基金This work is supported by the National Basic Research Program of China(No.2012CB9222000).
文摘{001}facets dominated single crystalline anatase TiO_(2)nanosheet array(TNSA)was synthe-sized through an optimized organic solvothermal route on uorine-doped tin oxide substrate.The field emission scanning electron microscopy images and X-ray diffraction patterns re-vealed that the{001}synthesized facets dominated TNSA exhibited much higher orientation than that synthesized by hydrothermal route.The TNSAs were loaded with Pt nanoparti-cles in uniformly size by using a photodecomposition method,which were further con rmed by high resolution transmission electron microscopy(HRTEM).The HRTEM images also revealed that Pt nanoparticles preferred to deposit on{001}facets.With loading of Pt nanoparticles,the optical absorbance was significantly enhanced,while the photolumines-cence(PL)was inhibited.The photocatalytic activity of TNSA was signi cantly improved by Pt loading and reached the maximum with optimal amount of Pt loading.The optimal amount of Pt on{001}facets is far less than that on TiO_(2)nanoparticles,which may be attributed to the specific atom structure of reactive{001}facets.
