Two TiAl alloys,Ti-47.5Al-3.7(Cr,V,Zr)and Ti-47.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying s...Two TiAl alloys,Ti-47.5Al-3.7(Cr,V,Zr)and Ti-47.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying strengthening.The creep behavior and mechanism for the improvement in creep properties by carbon addition were investigated by mechanical tests and electron microscopy characterizations.The results show that obvious improvements on the creep properties at 760°C and 276 MPa are achieved by 0.1 at.%C addition into TiAl alloy with directional lamellar microstructure,which promotes the creep strain and minimum creep rate decreasing with a large content.The minimum creep rate is reduced from 4.37×10^(-8) to 3.97×10^(-9) s^(-1),and the duration entering into creep acceleration is prolonged for more than 10 times.The mechanism for creep property improvement by 0.1%C addition is attributed to two aspects.The first one is that Ti_(2) AlC is found to be strong obstacles of 1/2[110]dislocations when moving across the lamellar interface in the carbon containing alloy.The other one is that the in terfacial dislocatio ns are effectively impeded and the release process is hindered by dynamic precipitation of Ti_(3) AlC,which is proposed to be the special mechanism for creep resistance improvement of this hard-oriented directional lamellar microstructure.展开更多
Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys...Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys followed by hot isostatic pressing and heat treatment.Ti2AlC carbides were identified in the alloy with C addition.Stress rupture tests were carried out at 800 and 850°C,with tensile stress from 220 to 400 MPa,respectively.It was shown that the alloy with C experienced much longer lives than the other,especially under the condition of 800°C/260 MPa,800°C/300 MPa,850°C/220 MPa,850°C/240 MPa and 850°C/260 MPa.Observation of ruptured specimens revealed that the microstructure stability was improved significantly in the alloy with C addition which is attributed to the strengthening effect of Ti-Al-C carbides.The Ti2AlC carbides mainly increased the resistance of dislocation passing through the interfaces and kept the integrity of the interfaces.And Ti3AlC carbide was formed during stress rupture process,which could not only effectively act as the barrier of dislocation movement inside the lamellae,but also strengthen the lamellae itself.展开更多
Pericentric inversion of chromosome 9(inv[9])is a common chromosomal structural variant,but its impact on clinical outcomesremains debated.The screening criteria of sperm banks are rarely mentioned to individuals with...Pericentric inversion of chromosome 9(inv[9])is a common chromosomal structural variant,but its impact on clinical outcomesremains debated.The screening criteria of sperm banks are rarely mentioned to individuals with inv(9).In this study,we evaluatedthe fertility of sperm donors with inv(9)who met eligibility criteria for sperm banks(inv[9]-eligible donors).From March 2004 toMay 2022,chromosomal analysis of 16124 sperm donors at CITIC-Xiangya Human Sperm Bank in Hunan Province(Changsha,China)found that 251(1.6%)had chromosome variations,with inv(9)being the most prevalent at 1.1%.All 169 inv(9)-eligibledonors were contacted to collect fertility outcome data,along with 206 eligible donors without inv(9)as controls.In addition,semen samples from inv(9)-eligible donors and eligible donors underwent assessments of sperm fluorescence in situ hybridization(FISH),mitochondrial membrane potential,DNA fragmentation index,acrosome integrity,reactive oxygen species(ROS),andsperm morphology.Results showed that inv(9)did not significantly increase reproductive risks overall.Despite detecting ROSlevel differences,the clinical impact may be insignificant.This study provides new data on the inv(9)population that can serveas a valuable reference for decision-making by sperm banks as well as for genetic counseling and clinical guidance for individualscarrying inv(9)variant.展开更多
基金National Natural Science Foundation of China(51788104,51390471,51527803 and 51761135131)National 973 Project of China(2015CB654902)National Key Research and Development Pro gram(2016YFB0700402)。
文摘Two TiAl alloys,Ti-47.5Al-3.7(Cr,V,Zr)and Ti-47.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying strengthening.The creep behavior and mechanism for the improvement in creep properties by carbon addition were investigated by mechanical tests and electron microscopy characterizations.The results show that obvious improvements on the creep properties at 760°C and 276 MPa are achieved by 0.1 at.%C addition into TiAl alloy with directional lamellar microstructure,which promotes the creep strain and minimum creep rate decreasing with a large content.The minimum creep rate is reduced from 4.37×10^(-8) to 3.97×10^(-9) s^(-1),and the duration entering into creep acceleration is prolonged for more than 10 times.The mechanism for creep property improvement by 0.1%C addition is attributed to two aspects.The first one is that Ti_(2) AlC is found to be strong obstacles of 1/2[110]dislocations when moving across the lamellar interface in the carbon containing alloy.The other one is that the in terfacial dislocatio ns are effectively impeded and the release process is hindered by dynamic precipitation of Ti_(3) AlC,which is proposed to be the special mechanism for creep resistance improvement of this hard-oriented directional lamellar microstructure.
基金National 973 Project of China(2015CB654902)Chinese National Natural Science Foundation(11374174,51390471 and 51527803).
文摘Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys followed by hot isostatic pressing and heat treatment.Ti2AlC carbides were identified in the alloy with C addition.Stress rupture tests were carried out at 800 and 850°C,with tensile stress from 220 to 400 MPa,respectively.It was shown that the alloy with C experienced much longer lives than the other,especially under the condition of 800°C/260 MPa,800°C/300 MPa,850°C/220 MPa,850°C/240 MPa and 850°C/260 MPa.Observation of ruptured specimens revealed that the microstructure stability was improved significantly in the alloy with C addition which is attributed to the strengthening effect of Ti-Al-C carbides.The Ti2AlC carbides mainly increased the resistance of dislocation passing through the interfaces and kept the integrity of the interfaces.And Ti3AlC carbide was formed during stress rupture process,which could not only effectively act as the barrier of dislocation movement inside the lamellae,but also strengthen the lamellae itself.
基金financial supported by National Natural Science Foundationof China(No.82001634)the China Postdoctoral Science Foundation(No.2019M661521).
文摘Pericentric inversion of chromosome 9(inv[9])is a common chromosomal structural variant,but its impact on clinical outcomesremains debated.The screening criteria of sperm banks are rarely mentioned to individuals with inv(9).In this study,we evaluatedthe fertility of sperm donors with inv(9)who met eligibility criteria for sperm banks(inv[9]-eligible donors).From March 2004 toMay 2022,chromosomal analysis of 16124 sperm donors at CITIC-Xiangya Human Sperm Bank in Hunan Province(Changsha,China)found that 251(1.6%)had chromosome variations,with inv(9)being the most prevalent at 1.1%.All 169 inv(9)-eligibledonors were contacted to collect fertility outcome data,along with 206 eligible donors without inv(9)as controls.In addition,semen samples from inv(9)-eligible donors and eligible donors underwent assessments of sperm fluorescence in situ hybridization(FISH),mitochondrial membrane potential,DNA fragmentation index,acrosome integrity,reactive oxygen species(ROS),andsperm morphology.Results showed that inv(9)did not significantly increase reproductive risks overall.Despite detecting ROSlevel differences,the clinical impact may be insignificant.This study provides new data on the inv(9)population that can serveas a valuable reference for decision-making by sperm banks as well as for genetic counseling and clinical guidance for individualscarrying inv(9)variant.
