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
The tri-metal Ti-Al-Nb composites were processed through three procedures:hot pressing,rolling,and hot pressing,followed by subsequent rolling.The fabricated composites were then subjected to annealing at 600,625,and ...The tri-metal Ti-Al-Nb composites were processed through three procedures:hot pressing,rolling,and hot pressing,followed by subsequent rolling.The fabricated composites were then subjected to annealing at 600,625,and 650℃ temperatures at different times.Microstructure observation at the interfaces reveals that the increase in plastic deformation strain significantly affects TiAl_(3) intermetallic layers’evolution and accelerates the layers’growth.On the contrary,the amount of applied strain does not significantly affect the evolution of the NbAl_(3) intermetallic layer thickness.It was also found that Al and Ti atoms’diffusion has occurred throughout the TiAl_(3) layer,but only Al atoms diffuse through the NbAl_(3) layer.The slow growth rate of the NbAl_(3) intermetallic layer is due to the lack of diffusion of Nb atoms and the high activation energy of Al atoms’reaction with Nb atoms.展开更多
In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3A...In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ＂Flat/steep＂ band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.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
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The tri-metal Ti-Al-Nb composites were processed through three procedures:hot pressing,rolling,and hot pressing,followed by subsequent rolling.The fabricated composites were then subjected to annealing at 600,625,and 650℃ temperatures at different times.Microstructure observation at the interfaces reveals that the increase in plastic deformation strain significantly affects TiAl_(3) intermetallic layers’evolution and accelerates the layers’growth.On the contrary,the amount of applied strain does not significantly affect the evolution of the NbAl_(3) intermetallic layer thickness.It was also found that Al and Ti atoms’diffusion has occurred throughout the TiAl_(3) layer,but only Al atoms diffuse through the NbAl_(3) layer.The slow growth rate of the NbAl_(3) intermetallic layer is due to the lack of diffusion of Nb atoms and the high activation energy of Al atoms’reaction with Nb atoms.
基金financially supported by the Science Foundation for International Cooperation of Sichuan Province (2014HH0016)the Fundamental Research Funds for the Central Universities (SWJTU2014: A0920502051113-10000)National Magnetic Confinement Fusion Science Program (2011GB112001)
文摘In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ＂Flat/steep＂ band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.
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)%。
