A first-principles density functional approach is used to study the electronic and the elastic properties of Nb15X （X = Ti, Zr, Hf, V, Ta, Cr, Mo, and W） alloys. The elastic constants cn and c12, the shear modulus C...A first-principles density functional approach is used to study the electronic and the elastic properties of Nb15X （X = Ti, Zr, Hf, V, Ta, Cr, Mo, and W） alloys. The elastic constants cn and c12, the shear modulus CI, and the elastic modulus E（lOO） are found to exhibit similar tendencies, each as a function of valence electron number per atom （EPA）, while c44 seems unclear. Both cu and c12 of Nb15X alloys increase monotonically with the increase of EPA. The C/ and E000） also show similar tendencies. The elastic constants （except c44） increase slightly when alloying with neighbours of a higher d-transition series. Our results are supported by the bonding density distribution. When solute atoms change from Ti（Zr, Hf） to V（Ta） then to Cr（Mo, W）, the bonding electron density between the central solute atom and its first neighbouring Nb atoms is increased and becomes more anisotropic, which indicates the strong interaction and thus enhances the elastic properties of Nb-Cr（Mo, W） alloys. Under uniaxial {100） tensile loading, alloyed elements with less （more） valence electrons decrease （increase） the ideal tensile strength.展开更多
The elastic limit of single-phase alloy Nb-2Mo-2Zr-1Ti is higher as recovered state in comparison with as cold-rolled or recrystallized one.For Nb-40Ti-5.5AI alloy of age-hardening type,the elastic limit is lower as c...The elastic limit of single-phase alloy Nb-2Mo-2Zr-1Ti is higher as recovered state in comparison with as cold-rolled or recrystallized one.For Nb-40Ti-5.5AI alloy of age-hardening type,the elastic limit is lower as cold-rolled state,but increases considerably after proper aging.However,its elastic modulus changes no more,so the stored-energy (σ_e^2/E)may raise significantly.The temperature dependence on elastic modulus for pure Nb as intensely cold-worked or recrystallized state is anomalous.This anomaly may disap- pear after recovered treatment of intensely cold-worked state at 600℃ for 4 h.and may change no more after that of recrystallized state.The anomalous behaviour of elasticity was also discussed on the non-magnetic Nb.展开更多
In order to investigate the effect of erbium （Er） on the microstructure of orthorhombic Ti2A1Nb-based alloys, four testing alloys were prepared by adding differ- ent contents of the rare earth metal Er to Ti-22A1-25...In order to investigate the effect of erbium （Er） on the microstructure of orthorhombic Ti2A1Nb-based alloys, four testing alloys were prepared by adding differ- ent contents of the rare earth metal Er to Ti-22A1-25Nb alloy and optical microscopy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, energy- dispersive spectrometry, and transmission electron microscopy were used. The results show that the addition of Er is capable of grain refining and the refinement effect is more obvious with increasing content of Er. The Er203 dispersoids formed by internal oxidation and A13Er com- pound particles are observed in Er-doped alloys and the number of Er precipitates is increased with increasing Er addition. It is likely that the solubility of Er in the Ti2A1Nb alloy is very low and Er precipitates tend to segregate at grain boundaries, which together with the surface activity of rare earth elements is supposed to decrease the prior B2 grain size of Ti-22A1-25Nb alloy effectively.展开更多
Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance a...Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.50771004)
文摘A first-principles density functional approach is used to study the electronic and the elastic properties of Nb15X （X = Ti, Zr, Hf, V, Ta, Cr, Mo, and W） alloys. The elastic constants cn and c12, the shear modulus CI, and the elastic modulus E（lOO） are found to exhibit similar tendencies, each as a function of valence electron number per atom （EPA）, while c44 seems unclear. Both cu and c12 of Nb15X alloys increase monotonically with the increase of EPA. The C/ and E000） also show similar tendencies. The elastic constants （except c44） increase slightly when alloying with neighbours of a higher d-transition series. Our results are supported by the bonding density distribution. When solute atoms change from Ti（Zr, Hf） to V（Ta） then to Cr（Mo, W）, the bonding electron density between the central solute atom and its first neighbouring Nb atoms is increased and becomes more anisotropic, which indicates the strong interaction and thus enhances the elastic properties of Nb-Cr（Mo, W） alloys. Under uniaxial {100） tensile loading, alloyed elements with less （more） valence electrons decrease （increase） the ideal tensile strength.
文摘The elastic limit of single-phase alloy Nb-2Mo-2Zr-1Ti is higher as recovered state in comparison with as cold-rolled or recrystallized one.For Nb-40Ti-5.5AI alloy of age-hardening type,the elastic limit is lower as cold-rolled state,but increases considerably after proper aging.However,its elastic modulus changes no more,so the stored-energy (σ_e^2/E)may raise significantly.The temperature dependence on elastic modulus for pure Nb as intensely cold-worked or recrystallized state is anomalous.This anomaly may disap- pear after recovered treatment of intensely cold-worked state at 600℃ for 4 h.and may change no more after that of recrystallized state.The anomalous behaviour of elasticity was also discussed on the non-magnetic Nb.
基金financially supported by the Science and Technology Ministry of China to the National High Technology "863" Project (No. 2012AA062302)
文摘In order to investigate the effect of erbium （Er） on the microstructure of orthorhombic Ti2A1Nb-based alloys, four testing alloys were prepared by adding differ- ent contents of the rare earth metal Er to Ti-22A1-25Nb alloy and optical microscopy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, energy- dispersive spectrometry, and transmission electron microscopy were used. The results show that the addition of Er is capable of grain refining and the refinement effect is more obvious with increasing content of Er. The Er203 dispersoids formed by internal oxidation and A13Er com- pound particles are observed in Er-doped alloys and the number of Er precipitates is increased with increasing Er addition. It is likely that the solubility of Er in the Ti2A1Nb alloy is very low and Er precipitates tend to segregate at grain boundaries, which together with the surface activity of rare earth elements is supposed to decrease the prior B2 grain size of Ti-22A1-25Nb alloy effectively.
基金Foundation item： National Natural Science Foundation of China （50671081）
文摘Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.
