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1.
Electron beam was used to join TC4 alloy to Ti3Al-based alloy. The composition of the weld was analysed by XRD and TEM and the results showed that the weld mainly composed
of α′ martensites. The change of heat input had little influence on the composition of the weld but can make the grain size
increasing. The fracture path of the joints was mainly decided by the microstructure of the weld and started from coarse grain
zone to HAZ and base metal of Ti3Al alloy. 相似文献
2.
The site preference of Zr atoms in Ti
3Al and the phase stability of Ti2ZrAl are examined using first-principles electronic structure total energy calculations.
Of the sixteen possible ways in which Ti, Zr and Al atoms can be arranged, in the lattice sites corresponding to D019 structure of Ti3Al, to obtain Ti2ZrAl, it is shown that Zr atoms prefer to get substituted at the Ti sites. It is further shown that among the seven crystal
structures considered, D019-like and L12-like are the competing ground-state structures of Ti2ZrAl. The above results are in agreement with the experimental results reported in the literature. Calculated values of equilibrium
lattice parameters, heat of formation and bulk modulus of Ti2ZrAl are presented. The basis for the structural stability and bonding are analysed in terms of the density of states. Between
the two possibleB2-like structures, Ti2ZrAl shows enhanced stability for the one where Zr is substituted in the Ti sublattice, which again is in agreement with the
experimental observation. 相似文献
3.
Caixuan Xu Anming Hu Naomichi Sakai Izumi Hirabayashi Mitsuru Izumi 《Journal of Superconductivity and Novel Magnetism》2007,20(4):309-314
Single domain GdBa2Cu7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed
Gd123 was successfully enhanced by addition of both BaCO3 and BaCuO2−x
, which suppress the formation of Gd1+x
Ba2−x
Cu3O7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO3 and 0.05 to 0.1, M BaCuO2−x
per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band
formed by Gd2BaCuO5 particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and
8, mm in thickness and a high critical current density J
c up to 91,200, A/cm2 was achieved at 77, K under self-field. 相似文献
4.
M. Bleiweiss J. Amirzadeh M. Yin A. Lungu T. Datta 《Journal of Superconductivity and Novel Magnetism》2005,18(4):567-572
Synthesis and optical transmission of MgB2 thin films on optically transparent glass are reported. In the 400–1000 nm regime as deposited films show high metallic reflectivity
and very little transmission. After deposition, the films were annealedex situ and rendered superconducting withT
c of 38 K, approaching that of the bulk material. The reaction conditions where quite soft ∼ 10 min at 550°C. The optical absorption
coefficient,α and photon energy,E followed a Tauc-type behavior, (αE)1/2=β
T(E −E
g). The band gap (E
g) was observed to peak at 2.5 eV; but, the slope parameterβ
Tbehaved monotonically with reaction temperature. Our results indicate that an intermediate semiconducting phase is produced
before the formation of the superconducting phase; also optical measurements provide valuable information in monitoring the
synthesis of MgB2 from its metallic constituents. In addition these films have interesting optical properties that may be integrated into optoelectronics. 相似文献
5.
K. P. Singh V. P. S. Awana S. Balamurugan M. Shahabuddin H. K. Singh M. Husain H. Kishan E. R. Bauminger I. Felner 《Journal of Superconductivity and Novel Magnetism》2008,21(1):39-44
Nano particle of Fe3O4 (nFe3O4) up to 6 at% were doped in the superconducting MgB2 samples. Despite the strong ferromagnetic nature of Fe3O4, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe3O4, T
c
=38 K is not changed, whereas for 6% T
c
decreases by 6 K. This indicates that a low concentration of Fe does not substitute either the Mg or B sites and probably
occupies the intergrain spaces. For 0.5% doped Fe3O4, an increase in J
c
with respect to the pure MgB2 samples is observed in the lower field and temperature regions (H<2 T and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic
dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at H>2 T, J
c
of the doped samples is always less than that of MgB2, and the activation is dominant in comparison with the effective pinning potential provided by the doping. Flux jumps are
observed in lower T and H regions for the samples doped up to 1% nFe3O4 only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for
the higher (4, 6 at%) nFe3O4 doped MgB2 samples show that at RT, the hyperfine field for both samples is ∼100 kOe and ∼120 kOe at 90 K. This means that the nFe3O4 particles decompose and form possibly an intermetallic Fe-B phase in the matrix. 相似文献
6.
K K Saini C P Sharma S N Ekbote Pavas Asthana D K Suri Kant Chander S A Agnihotry Subhas Chandra 《Bulletin of Materials Science》1991,14(2):235-239
EnhancedT
c in calcium-free Tl compounds of the series Tl
m
Ba2Ca
n−1Cu
n
O
x
(2201) has been reported. Three different starting compositions (2201, 1201 and 2202) were studied extensively with varying
conditions of preparation. Under optimized conditions (sintering temperature 970°C and duration 3–10 min) the highestT
c(onset) ranges from 103 K to ∼ 115 K andT
c (zero) ∼ 95 K was found. XRD studies showed the transformation of all the three nominal compositions into 2201 phase with
differentT
cs. 相似文献
7.
A. V. Semeno A. A. Pronin N. E. Sluchanko N. A. Samarin A. V. Kuznetsov S. V. Demishev 《Journal of Superconductivity and Novel Magnetism》2007,20(2):109-112
Electron spin resonance of a single crystal of CuGeO3 doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu2+ chains and from Co2+ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu2+ (χCu ∼ C
Cu/(T + Θ), with Θ = 92 K) and Curie for Co2+ (χCo ∼ C
Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on
polarization of oscillating magnetic field was discovered for Co2+ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented. 相似文献
8.
The behavior of the superconducting transition temperature T
c
and that of the jump of electron heat capacity (C
S
−C
N
)/C
N
of the compound MgB2 at T=T
c
with substitution of boron and magnesium atoms by other atoms from the periodic table of the elements, corresponding to introduction
of additional electrons or holes in this compound are researched. The microscopic superconductivity theory in MgB2 systems in the magnetic field parallel to the crystallographic axis (H
‖
c) is built. The magnitude of the upper critical field H
c2 is determined and its temperature dependence in two-band systems with different and identical topologies of Fermi surface
cavities of the corresponding bands is studied. The obtained results and their comparisons with the experimental data demonstrate
that all kinds of anomalies of the physical properties of the compound MgB2 are effectively described by the two-band model. 相似文献
9.
A. T. M. K. Jamil H. Noguchi K. Shiratori T. Kondo H. Munekata 《Journal of Superconductivity and Novel Magnetism》2005,18(3):321-324
Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of
[100-nm GaAs/50-nm Fe3Ga2−
x
As
x
/100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals
the formation of metamagnetic Fe3Ga4 grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with
the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T
N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition
with the enhancement due to the light-induced heating. 相似文献
10.
Fangli Yu Jianfeng Yang Yaohui Xue Jun Du Yuan Lu Jiqiang Gao 《Bulletin of Materials Science》2009,32(2):177-181
Porous Si3N4 ceramics were successfully synthesized using cheaper talc and clay as sintering additives by pressureless sintering technology
and the microstructure and mechanical properties of the ceramics were also investigated. The results indicated that the ceramics
consisted of elongated β-Si3N4 and small Si2N2O grains. Fibrous β-Si3N4 grains developed in the porous microstructure, and the grain morphology and size were affected by different sintering conditions.
Adding 20% talc and clay sintered at 1700°C for 2 h, the porous Si3N4 ceramics were obtained with excellent properties. The final mechanical properties of the Si3N4 ceramics were as follows: porosity, P
0 = 45·39%; density, ρ = 1·663·g·cm−3; flexural strength, σ
b (average) = 131·59 MPa; Weibull modulus, m = 16·20. 相似文献
11.
Z. Liu S. F. Wang S. Q. Zhao Y. L. Zhou 《Journal of Superconductivity and Novel Magnetism》2005,18(4):537-540
CeO2/YSZ/CeO2 buffer layers were deposited on textured Ni substrates byin situ pulsed laser deposition. The out-of-plane texture and in-plane texture of the buffer layers were characterized by X-ray diffraction
ω-scans and ϕ-scans. Using this CeO2/YSZ/CeO2 architecture as the buffer layers, high quality YBCO films with a zero-resistanceT
c about 90 K and a self-field critical current densitiesJ
c above 106 A/cm2 at 77 K can be obtained on Ni substrates. 相似文献
12.
The growth of mixed crystals of Ba
x
Ca1−x
(IO3)4 were carried out with simple gel method. The effect of various parameters such as pH of gel solution, gel concentration,
gel setting time, concentration of reactants on the growth was studied. Crystals having different morphologies and habits
were obtained. The grown crystals were characterized by XRD, FT-IR, EDAX, TGA, DTA and DSC. 相似文献
13.
Specific heats were measured on two samples of HoBa2Cu3O7−δ
in the temperature range 1·7 K to 10 K. In addition to the known Schottky behaviour, a peak in the specific heat curve was
observed near 7·9 K in both the samples. This peak is probably due to impurity contribution and the specific heat measurements
were undertaken in holmium oxide (Ho2O3), which was the suspected impurity. However, no peak was observed in the specific heat curve of holmium oxide 相似文献
14.
The effect of heating rate on the structural and magnetic properties of the nanocrystalline Fe81Si4B12P2Cu1 alloy has been investigated. Amorphous Fe81Si4B12P2Cu1 alloy was annealed at 753 K for 180 s at different heating rates ranging from 0.05 to 5 K/s in protective argon atmosphere.
The structural and magnetic properties of the as-quenched and annealed alloys were studied using X-ray diffractometer (XRD),
differential scanning calorimeter (DSC), vibrating sample magnetometer (VSM), and B–H loop tracer, respectively. Amorphous
precursor prepared by industry-grade raw materials is obtained. The increase of heating rate is found to be significantly
effective in decreasing the grain size of α-Fe(Si) phase, but the grain size increases at higher heating rate. The volume
fraction of α-Fe(Si) phase shows a monotonic decrease with the increase of the heating rate. The coercivity H
c markedly decreases with increasing heating rate and exhibits a minimum at the heating rate of 0.5 K/s, while the saturation
magnetization, M
s, shows a slight decrease. These results suggest that the effect of heating rate on H
c and M
s is originated from the changes of grain size and the volume fraction of α-Fe(Si) phase. 相似文献
15.
The nano particles of phase pure rare earth titanates, synthesized by the SHS technique, get well sintered at lower temperatures
compared to the compounds formed by the solid-state method. These dielectrics are highly stable and can be used in the microwave
frequency range. We report here a modified SHS method to synthesize phase pure monoclinic RE2Ti2O7 at 350°C through the oxide/nitrate precursors using an inorganic compound, ammonium acetate, in place of the general type
of organic activators such as urea, alanine etc. The nanopowders of La2Ti2O7, Pr2Ti2O7 and Nd2Ti2O7 on heating exhibit an exothermic behaviour with a broad maxima in the range 267–284°C and become endothermic with maxima
in the range 1043–1220°C; interestingly, the phase pure crystalline material is formed at the temperature of exothermic maxima,
as confirmed by XRD. 相似文献
16.
Abhijit Kar Sudipta Mandal Rabindra N. Ghosh Tamal K. Ghosh Ajoy Kumar Ray 《Journal of Materials Science》2007,42(14):5556-5561
Diffusivities of Ti, Cu, Al and Ag in the interface of Al2O3–Al2O3 braze joints using Ag–Cu–Ti active filler alloy, have been calculated by Matano–Boltzman method. The Matano plane has been
identified for each elemental diffusion at various brazing temperatures. The diffusivities of Ag, Cu and Al are almost insignificant
on formation of interface during brazing, whereas the diffusivity of Ti changes significantly with the brazing temperature
and controls the formation of different reaction product in the interface. Presence of TiO and Ti3Cu3O phases in the interface has been confirmed by transmission electron microscopy (TEM). 相似文献
17.
A. Talapatra S. K. Bandyopadhyay Pintu Sen A. Sarkar P. Barat 《Bulletin of Materials Science》2004,27(5):429-432
MgB2 superconductor has been synthesized using a simple technique at ambient pressure. The synthesis was carried out in helium
atmosphere over a wide range of temperatures. Magnesium was employed in excess to the stoichiometry to prevent the decomposition
of MgB2. Samples of MgB2 thus prepared have been almost free from MgO as compared to other methods. Resistivities of the samples are quite low with
residual resistivity ratio (RRR) of around 3.T
c
(R = 0) is 38.2-38.5 K with ΔT
C of 0.6–1.0 K. Comparative studies of various methods of low pressure synthesis have been presented. 相似文献
18.
The present study was concerned with the effects of over-aging on damping property and fracture toughness in Ti–6Al–4V alloy. Damping property and toughness become important factors for titanium implants, which have big modulus difference between bone and implant, and need high damping capacity for bone-implant compatability. Widmanstätten, equiaxed, and bimodal microstructures containing fine α2 (Ti3Al) particles were obtained by over-aging a Ti–6Al–4V alloy. Over-aging heat treatment was conducted for 200 h at 545 °C. Fracture toughness, Charpy impact, and bending vibration tests were conducted on the unaged and the over-aged six microstructures, respectively. Charpy absorption energy and apparent fracture toughness decreased as over-aging was done, even if the materials were strengthened by precipitation of very fine and strong α2-Ti3Al particles. On the other hand, damping properties were enhanced by over-aging in Widmanstätten and equiaxed microstructures, but was weakened in bimodal microstructure due to the softening of tempered martensite and the decreasing of elastic difference between tempered martensite and α phase contained α2 particles, etc. These data can provide effective information to future work about internal damping and fracture properties of Ti–6Al–4V alloy. 相似文献
19.
The oxidation behaviours of bulk Ti3Si(1−x)Al
x
C2 prepared by hot pressing were investigated. The results showed that the isothermal oxidation behaviour of Ti3SiC2 obeyed a parabolic law between 900 and 1100°C, and followed a two-step parabolic rate law between 1200°C and 1300°C. The
cyclic oxidation behaviour of material is assumed to obey a three-step parabolic rate law at 1100°C and 1200°C. The calculated
activation energy of isothermal oxidation is 101·43 kJ·mol−1. The oxide layers consisted of a mass of α-Al2O3 and little TiO2 and SiO2 are observed on Ti3SiC2 as a dense and adhesive protect scale. The oxidation mechanism varies with the additive aluminum that greatly improves the
oxidation resistance of Ti3SiC2. 相似文献
20.
Based on the structure characteristic of Ti3AlC2 and the easy formation of Ti3Al1 − x
Si
x
C2 solid solution, a Si interlayer was selected to join Ti3AlC2 layered ceramic by diffusion bonding method. Joining was performed at 1,300–1,400 °C for 120 min under 5 MPa load in an Ar
atmosphere. The phase composition and interface microstructure of the joints were investigated by XRD, SEM and EPMA. The results
revealed that Ti3Al(Si)C2 solid solution formed at the interface. The mechanism of bonding is attributed to silicon diffusing inward the Ti3AlC2. The strength of joints was evaluated by a 3-point bending test. The jointed specimens exhibit a high flexural strength of
285 ± 11 MPa, which is about 80% of that of the Ti3AlC2; and retain this strength up to 1,000 °C. The high mechanical performance of the joints indicates that diffusion bonding
via a Si interlayer is effective to bond Ti3AlC2 ceramic. 相似文献