The yield asymmetry between compression and tension of magnesium alloy Mg-3Al-1Zn（AZ31） with different grain sizes and textures has been studied by tensile and compressive testing of as-cast,as-extruded and equal ch...The yield asymmetry between compression and tension of magnesium alloy Mg-3Al-1Zn（AZ31） with different grain sizes and textures has been studied by tensile and compressive testing of as-cast,as-extruded and equal channel angular pressed（ECAPed） specimens.The significant yield asymmetry（the ratio of yield strength between compression and tension σyc/σyt is ～0.44） was found in as-extruded specimens and the corresponding microstructure evolution during deformation revealed that {10 ˉ 12} tensile twinning is the underlying reason for the large yield asymmetry.Strong texture and grain size are influential factors for large yield asymmetry.The separate contributions of grain size and texture on yield asymmetry were investigated.展开更多
Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is ...Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.展开更多
The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure ...The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure is influenced by several parameters including the number of ECAP passes, ECAP route, consequent heating temperature, and holding time. The effects of these parameters on the microstructural characteristics including grain size and shape factor of the 7075 aluminum alloy were studied using experimental tests and Taguchi method. The results indicate that five-pass ECAP in route BA and subsequent isothermal holding at 630 °C for 15 min are more appropriate for achieving a semi-solid microstructure. The processing route and holding time have the highest impact on the grain size while the number of ECAP passes and heating temperature have the least impact on the grain size. Meanwhile, the shape factor is significantly influenced by the processing route, holding time and heating temperature while it is less influenced by the number of ECAP passes.展开更多
To understand the relationships between channel size and ion selectivity,we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthrolineoxadiazole units with ...To understand the relationships between channel size and ion selectivity,we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthrolineoxadiazole units with a pore aperture 2.3A close to the diameter of the Na^(+)ion(2.04A).Successful preparation of high molecular weight helical polymers(HP1)gives rise to a 4.6 nm long artificial unimolecular transmembrane channel.The transport property of artificial channel HP1 was elaborately investigated by means of vesicle-based kinetic assay and symmetry/asymmetry bilayer membrane(BLM)experiments as well.These results unambiguously demonstrate that HP1 is a Na^(+)-selective channel with extremely high transport activity(EC_(50)=0.017 mol% relative to lipid).Moreover,the Na^(+)/K^(+)selectivity ratio of HP1 reaches 1.9,as determined by asymmetry BLM experiments.Owing to the narrowest 2.3A size constraint so far,HP1 transport naked Na^(+)ion across the membrane,which represents a different Na^(+)transport mode from that of natural Na^(+)channels,which transports partially hydrated Na^(+)ions during transmembrane conduction.This study provides crucial insights on the chemical basis of ion selectivity in the field of ion channels.展开更多
目的比较相似结石负荷下3种不同穿刺通道经皮肾镜手术在单侧单通道Ⅰ期经皮肾镜取石术中清石率的差异。方法回顾性分析2008年1月至2018年12月杭州市第一人民医院行单通道Ⅰ期PCNL手术677例患者的临床资料,根据结石体积按四分法均分为4组...目的比较相似结石负荷下3种不同穿刺通道经皮肾镜手术在单侧单通道Ⅰ期经皮肾镜取石术中清石率的差异。方法回顾性分析2008年1月至2018年12月杭州市第一人民医院行单通道Ⅰ期PCNL手术677例患者的临床资料,根据结石体积按四分法均分为4组,组内根据术式分为超微通道组(SMP)、微通道组(MPCNL)和标准通道组(SPCNL)。观察相似结石负荷下不同术式患者清石率差异。结果481例患者结石一次性清除,总体清石率为71.0%,小结石组清石率90.0%,中等结石组85.8%,较大结石组70.4%,大结石组37.9%;在结石体积不超过7640 mm 3时,相似结石负荷下,MPCNL及SPCNL清石率相当。结石体积超过5200 mm 3时,MPCNL及SPCNL组清石率均显著降低;多因素Logistic回归表明结石体积越大、分布越分散、术中出血越多,Ⅰ期清石率越低。结论①单发小体积结石,SMP应作为首选;②结石体积≤7640 mm 3时,通道大小对清石率影响较小,考虑患者出血等因素,建议选择MPCNL手术;③当结石体积>5200 mm 3时,无论通道大小,单通道Ⅰ期清石率较低,需考虑多通道、双镜联合或分期碎石等手术方案。展开更多
The effect of grain size on the flow stress in an ECAPed Ti with a constant texture was investigated,assuming that 2,4,5 and 6 passes microstructures have a similar texture.The average size of recrystallized grains de...The effect of grain size on the flow stress in an ECAPed Ti with a constant texture was investigated,assuming that 2,4,5 and 6 passes microstructures have a similar texture.The average size of recrystallized grains decreased to 0.5 μm,0.4 μm,and 0.3 μm with respect to the ECAP pass number of 2,4,and 6,respectively.The ultimate tensile strength (UTS) and yield strength (YS) increase with an increase in the number of pressing.The UTS and YS of the 6 passes ECAPed sample were found to be 740.2 MPa and 580.3 MPa,respectively.An equation for the flow stress of an ECAPed Ti with a constant texture as a function of the strain and grain size was derived for the ECAPed metal.The following equation was finally obtained:σ(ε)=103.9+1825ε-9.6ε1/2·d-1/2+8.3d-1/2.展开更多
Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route ...Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.50471082 and 50571102
文摘The yield asymmetry between compression and tension of magnesium alloy Mg-3Al-1Zn（AZ31） with different grain sizes and textures has been studied by tensile and compressive testing of as-cast,as-extruded and equal channel angular pressed（ECAPed） specimens.The significant yield asymmetry（the ratio of yield strength between compression and tension σyc/σyt is ～0.44） was found in as-extruded specimens and the corresponding microstructure evolution during deformation revealed that {10 ˉ 12} tensile twinning is the underlying reason for the large yield asymmetry.Strong texture and grain size are influential factors for large yield asymmetry.The separate contributions of grain size and texture on yield asymmetry were investigated.
文摘Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.
文摘The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure is influenced by several parameters including the number of ECAP passes, ECAP route, consequent heating temperature, and holding time. The effects of these parameters on the microstructural characteristics including grain size and shape factor of the 7075 aluminum alloy were studied using experimental tests and Taguchi method. The results indicate that five-pass ECAP in route BA and subsequent isothermal holding at 630 °C for 15 min are more appropriate for achieving a semi-solid microstructure. The processing route and holding time have the highest impact on the grain size while the number of ECAP passes and heating temperature have the least impact on the grain size. Meanwhile, the shape factor is significantly influenced by the processing route, holding time and heating temperature while it is less influenced by the number of ECAP passes.
基金supported by the National Science Foundation of China(nos.22071078 and 21722403)the Program for JLU Science and Technology Innovative Research Team(JLUSTIRT)(no.2019TD-36).
文摘To understand the relationships between channel size and ion selectivity,we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthrolineoxadiazole units with a pore aperture 2.3A close to the diameter of the Na^(+)ion(2.04A).Successful preparation of high molecular weight helical polymers(HP1)gives rise to a 4.6 nm long artificial unimolecular transmembrane channel.The transport property of artificial channel HP1 was elaborately investigated by means of vesicle-based kinetic assay and symmetry/asymmetry bilayer membrane(BLM)experiments as well.These results unambiguously demonstrate that HP1 is a Na^(+)-selective channel with extremely high transport activity(EC_(50)=0.017 mol% relative to lipid).Moreover,the Na^(+)/K^(+)selectivity ratio of HP1 reaches 1.9,as determined by asymmetry BLM experiments.Owing to the narrowest 2.3A size constraint so far,HP1 transport naked Na^(+)ion across the membrane,which represents a different Na^(+)transport mode from that of natural Na^(+)channels,which transports partially hydrated Na^(+)ions during transmembrane conduction.This study provides crucial insights on the chemical basis of ion selectivity in the field of ion channels.
文摘目的比较相似结石负荷下3种不同穿刺通道经皮肾镜手术在单侧单通道Ⅰ期经皮肾镜取石术中清石率的差异。方法回顾性分析2008年1月至2018年12月杭州市第一人民医院行单通道Ⅰ期PCNL手术677例患者的临床资料,根据结石体积按四分法均分为4组,组内根据术式分为超微通道组(SMP)、微通道组(MPCNL)和标准通道组(SPCNL)。观察相似结石负荷下不同术式患者清石率差异。结果481例患者结石一次性清除,总体清石率为71.0%,小结石组清石率90.0%,中等结石组85.8%,较大结石组70.4%,大结石组37.9%;在结石体积不超过7640 mm 3时,相似结石负荷下,MPCNL及SPCNL清石率相当。结石体积超过5200 mm 3时,MPCNL及SPCNL组清石率均显著降低;多因素Logistic回归表明结石体积越大、分布越分散、术中出血越多,Ⅰ期清石率越低。结论①单发小体积结石,SMP应作为首选;②结石体积≤7640 mm 3时,通道大小对清石率影响较小,考虑患者出血等因素,建议选择MPCNL手术;③当结石体积>5200 mm 3时,无论通道大小,单通道Ⅰ期清石率较低,需考虑多通道、双镜联合或分期碎石等手术方案。
文摘The effect of grain size on the flow stress in an ECAPed Ti with a constant texture was investigated,assuming that 2,4,5 and 6 passes microstructures have a similar texture.The average size of recrystallized grains decreased to 0.5 μm,0.4 μm,and 0.3 μm with respect to the ECAP pass number of 2,4,and 6,respectively.The ultimate tensile strength (UTS) and yield strength (YS) increase with an increase in the number of pressing.The UTS and YS of the 6 passes ECAPed sample were found to be 740.2 MPa and 580.3 MPa,respectively.An equation for the flow stress of an ECAPed Ti with a constant texture as a function of the strain and grain size was derived for the ECAPed metal.The following equation was finally obtained:σ(ε)=103.9+1825ε-9.6ε1/2·d-1/2+8.3d-1/2.
基金financially supported by the National Natural Science Foundation of China (Nos.51175138, 50875072 and 51575153)the Program for New Century Excellent Talents in University (No.NCET-13-0765)。
文摘Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.
