High Al content inhibits the formation of B2 phase,which improves creep resistance in high Al/Nb-containing TiAl alloys.In this work,the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb(at.%...High Al content inhibits the formation of B2 phase,which improves creep resistance in high Al/Nb-containing TiAl alloys.In this work,the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb(at.%)with a high Al/Nb content,produced by the vacuum consumable electrode melting technology and the electromagnetic cold crucible melting technology,were studied.The microstructure of the Ti-46Al-8Nb alloy is composed ofα_(2)/ηphases arranged in layers with different orientations,which possesses smooth grain boundaries due to small-blocky segregation and irregular serrated grain boundaries caused by large-blocky segregation.Under conditions of 780-820℃and 125-175 MPa for 200 h,it exhibits typical power-law creep characteristics.The apparent activation energy of creep(Q)and apparent stress exponent(n)of the Ti-46Al-8Nb alloy are Q=274 kJ·mol^(-1)and n=1.97,respectively.The creep deformation mechanism is grain boundary sliding.Cracks easily form at the smooth boundary.The irregular serrated boundaries with small specific surface area hinder the dislocation movement,thereby improving the boundary creep resistance.When the stress concentration reaches a certain degree,the cracks will initiate between the lamellar structures within the grain.The crack usually propagates along the boundary perpendicular to or at an angle of 45 with the stress axis until creep failure occurs.展开更多
激光定向能量沉积(laser-directed energy deposition,LDED)成形Ti-Al合金的微观组织通常表现为贯穿多个熔池的粗大柱状晶,使得该合金较难获得均匀的力学性能。本文选用Nb作为Ti-Al二元合金的添加元素,通过LDED技术成形一系列Ti-6Al-x N...激光定向能量沉积(laser-directed energy deposition,LDED)成形Ti-Al合金的微观组织通常表现为贯穿多个熔池的粗大柱状晶,使得该合金较难获得均匀的力学性能。本文选用Nb作为Ti-Al二元合金的添加元素,通过LDED技术成形一系列Ti-6Al-x Nb(x=5、6.5、7.5,质量分数)三元合金,采用光学显微镜、X射线衍射仪、扫描电镜和电子背散射衍射仪对合金的微观形貌、室温拉伸性能以及变形机制进行研究,探究Nb含量对LDED成形Ti合金微观组织及拉伸性能的影响。结果表明:不同Nb含量合金的微观组织形貌较为接近,均主要由细长的针状或片层状α/α′相组成,且存在少量的残余β相。当Nb质量分数为6.5%时,合金具有最高的极限抗拉强度((902±35)MPa)和屈服强度((849±20)MPa),这主要归因于晶粒尺寸的减小。此外,随Nb含量增加,合金的伸长率逐渐降低。当Nb质量分数为7.5%时,合金的伸长率最低,为(10.2±1.4)%。展开更多
Passivated niobium/nitrogen(Nb-N) p-n co-doped zinc oxide nanoparticles were created by a simple precipitation process with in-situ self-formed NaCl "cage" to confine the nanoparticle growth followed by the ...Passivated niobium/nitrogen(Nb-N) p-n co-doped zinc oxide nanoparticles were created by a simple precipitation process with in-situ self-formed NaCl "cage" to confine the nanoparticle growth followed by the heat treatment in a flow of ammonia gas. Enhanced optical absorbance into the visible light region was observed in the Nb/N co-doped ZnO nanoparticle photocatalyst due to the Nb/N co-doping effect.It demonstrated a largely enhanced photocatalytic performance in the disinfection of Escherichia coli bacteria under visible light illumination, which could be attributed to the passivated co-doping of NbN to suppress the photogenerated charge carrier recombination on dopants. This robust approach for passivated p-n co-doping may also be applied to other material systems for a wide range of technical applications.展开更多
Nb and F co-doped anatase TiO2 layers were deposited by low pressure chemical vapor deposition (LPCVD) at pressure of 3 mtorr using titanium-tetra-iso-propoxide (TTIP), O2 and NbF5 as precursor, oxidant and dopant res...Nb and F co-doped anatase TiO2 layers were deposited by low pressure chemical vapor deposition (LPCVD) at pressure of 3 mtorr using titanium-tetra-iso-propoxide (TTIP), O2 and NbF5 as precursor, oxidant and dopant respectively. Resistivity beyond 100 Ωcm for undoped layer was decreased with increasing supply of the dopant and dependent on the supply ratio of O2 to TTIP and decreased to 0.2 Ωcm by the optimization. X-ray fluorescent spectroscopy showed Nb-content in the layer was decreased with the O2-supply ratio. X-ray photo-spectroscopy indicated that F substituted O-site in TiO2 by O2-supply but carbon-contamination and F missing substitution in the O-site were significantly increased by excess O2-supply. Further, it was suggested that the substituted F played an important role to reduce resistivity without significant contribution of O-vacancies. XRD spectra showed F missing substitution in the O-site degraded the crystallinity.展开更多
基金supported by the National Natural Science Foundation of China(No.52425401)the Foundation of National Key Laboratory for Precision Hot Processing of Metals(No.JCKYS2021603C001)+1 种基金the Fundamental Research Funds for the Central Universities(No.2023FRFK06014)the Major Science and Technology Achievement Transformation Project of Heilongjiang Province(No.ZC2023SH0075)。
文摘High Al content inhibits the formation of B2 phase,which improves creep resistance in high Al/Nb-containing TiAl alloys.In this work,the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb(at.%)with a high Al/Nb content,produced by the vacuum consumable electrode melting technology and the electromagnetic cold crucible melting technology,were studied.The microstructure of the Ti-46Al-8Nb alloy is composed ofα_(2)/ηphases arranged in layers with different orientations,which possesses smooth grain boundaries due to small-blocky segregation and irregular serrated grain boundaries caused by large-blocky segregation.Under conditions of 780-820℃and 125-175 MPa for 200 h,it exhibits typical power-law creep characteristics.The apparent activation energy of creep(Q)and apparent stress exponent(n)of the Ti-46Al-8Nb alloy are Q=274 kJ·mol^(-1)and n=1.97,respectively.The creep deformation mechanism is grain boundary sliding.Cracks easily form at the smooth boundary.The irregular serrated boundaries with small specific surface area hinder the dislocation movement,thereby improving the boundary creep resistance.When the stress concentration reaches a certain degree,the cracks will initiate between the lamellar structures within the grain.The crack usually propagates along the boundary perpendicular to or at an angle of 45 with the stress axis until creep failure occurs.
文摘激光定向能量沉积(laser-directed energy deposition,LDED)成形Ti-Al合金的微观组织通常表现为贯穿多个熔池的粗大柱状晶,使得该合金较难获得均匀的力学性能。本文选用Nb作为Ti-Al二元合金的添加元素,通过LDED技术成形一系列Ti-6Al-x Nb(x=5、6.5、7.5,质量分数)三元合金,采用光学显微镜、X射线衍射仪、扫描电镜和电子背散射衍射仪对合金的微观形貌、室温拉伸性能以及变形机制进行研究,探究Nb含量对LDED成形Ti合金微观组织及拉伸性能的影响。结果表明:不同Nb含量合金的微观组织形貌较为接近,均主要由细长的针状或片层状α/α′相组成,且存在少量的残余β相。当Nb质量分数为6.5%时,合金具有最高的极限抗拉强度((902±35)MPa)和屈服强度((849±20)MPa),这主要归因于晶粒尺寸的减小。此外,随Nb含量增加,合金的伸长率逐渐降低。当Nb质量分数为7.5%时,合金的伸长率最低,为(10.2±1.4)%。
基金supported financially by the Basic Science Innovation Program of Shenyang National Laboratory for Materials Science (Nos.Y4N56R1161 and Y5N56F2161)the National Key Research and Development Program of China (No.2017YFB0406300)+2 种基金the Science and Technology Plan of Guangdong Province (Nos.2014B090907002 and 2017B090907004)the China Postdoctoral Science Foundation (No.2018M631461)the Science and Technology Plan of Shenzhen City (No.JCYJ20170412171554022)
文摘Passivated niobium/nitrogen(Nb-N) p-n co-doped zinc oxide nanoparticles were created by a simple precipitation process with in-situ self-formed NaCl "cage" to confine the nanoparticle growth followed by the heat treatment in a flow of ammonia gas. Enhanced optical absorbance into the visible light region was observed in the Nb/N co-doped ZnO nanoparticle photocatalyst due to the Nb/N co-doping effect.It demonstrated a largely enhanced photocatalytic performance in the disinfection of Escherichia coli bacteria under visible light illumination, which could be attributed to the passivated co-doping of NbN to suppress the photogenerated charge carrier recombination on dopants. This robust approach for passivated p-n co-doping may also be applied to other material systems for a wide range of technical applications.
文摘Nb and F co-doped anatase TiO2 layers were deposited by low pressure chemical vapor deposition (LPCVD) at pressure of 3 mtorr using titanium-tetra-iso-propoxide (TTIP), O2 and NbF5 as precursor, oxidant and dopant respectively. Resistivity beyond 100 Ωcm for undoped layer was decreased with increasing supply of the dopant and dependent on the supply ratio of O2 to TTIP and decreased to 0.2 Ωcm by the optimization. X-ray fluorescent spectroscopy showed Nb-content in the layer was decreased with the O2-supply ratio. X-ray photo-spectroscopy indicated that F substituted O-site in TiO2 by O2-supply but carbon-contamination and F missing substitution in the O-site were significantly increased by excess O2-supply. Further, it was suggested that the substituted F played an important role to reduce resistivity without significant contribution of O-vacancies. XRD spectra showed F missing substitution in the O-site degraded the crystallinity.
