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1.
An Al-Zn-Mg alloy (7010) was cold-rolled and annealed to produce a small recrystallized grain size, and superplastically deformed in the temperature range 475 to 520° C at strain rates
to 2.8×10–3 sec–1. At 500° C and
sec–1 superplastic elongations up to 350% were obtained, but above about 60% elongation the residual room-temperature tensile properties after heat treatment decreased due to increasing grain-boundary cavitation. Grain growth rates were increased by superplastic strain. 相似文献
2.
The solubility of Nd at the Ba sites and the superconductivity of YBa2–x
Nd
x
Cu3O
y
were investigated by X-ray powder diffraction and measurements of the electrical resistance and ac susceptibility. The single Re123 phase was obtained for x0.30. The onset transition temperature
is insensitive to the Nd content x in the region of x0.40. All are higher than 95 K. The zero resistance transition temperatures
, however, exhibits two-step variation with the increase of x. For x0.25,
are all above 92 K. The highest
of 94 K was obtained for x=0.25. For x0.3
drops sharply to about 84 K. Finally
falls to 30 K and
is below 10 K for x=0.5. The two-step variation of T
c might be an indication of the existence of two trap levels for holes. 相似文献
3.
The influence of specimen width on fracture parameters has been investigated. The range examined was sufficiently large to obtain ductile and brittle fractures. With reference to previously published work, the phenomenology has been analysed by combining BCS model and Carpinteri's brittleness number approach.Nomenclature
a
crack length
-
f(a/W)
shape function according to ASTM specification [16]
-
F(a/W)
shape function according to Tada Paris notation [21]
-
E
elastic modulus
-
K
IC
plane strain fracture toughness
-
K
IC
f
fictitious plane strain fracture toughness
-
K
IC2
plane stress fracture toughness
-
J
IC
f
J-integral at maximum load
-
L
span
-
weight average molecular weight
-
number average molecular weight
-
polydispersity
-
P
M
maximum load
-
P
F
load of brittle fracture
-
p
P
load of plastic collapse
-
s
brittleness number
-
V
machine cross speed
-
W
specimen width
-
y
yield stress
-
strain rate 相似文献
4.
Shouhua Feng Hongming Yuan Zhan Shi Yan Chen Yongwei Wang Keke Huang Changmin Hou Jixue Li Guangsheng Pang Ying Hou 《Journal of Materials Science》2008,43(7):2131-2137
Perovskite oxides have provided magical structural models for superconducting and colossal magnetoresistance, and the search
for nano-scale and/or atomic-scale devices with particular property by specific preparations in the same systems has been
extensively conducted. We present here the three oxidation states of manganese (Mn3+, Mn4+, Mn5+) in the perovskite oxide, La0.66Ca0.29K0.05MnO3, which most interestingly shows the rectifying effect as atomic-scale p–n junctions (namely FY-Junctions) of single crystals and films. The family of cubic perovskite oxides were synthesised by the
so-called hydrothermal disproportionation reaction of MnO2 under the condition of strong alkali media. The new concept of the atomic-scale p–n junctions, based on the ideal rectification characteristic of the p–n junctions in the single crystal, basically originates from the structural linkages of [Mn3+–O–Mn4+–O–Mn5+], where Mn3+
and Mn5+
in octahedral symmetry serve as a donor and an acceptor, respectively, corresponding to the localized Mn4+
. 相似文献
5.
The rigid body translation accompanying a (
11) twin boundary in silicon has been studied by transmission electron microscopy. From a detailed analysis of theα-type fringe systems in the 111, 311 and 2
0 common reflections, the following translation vector is deduced:
[011], which is equivalent to
[411] in the other crystal element. A slight deviation of this orientation is possible. 相似文献
6.
Ada López Mariana G. da Silva Elisa Baggio-Saitovitch Alexandre R. Camara Raimundo N. SilveiraJr. Raul José Mauricio da Fonseca 《Journal of Materials Science》2008,43(2):464-468
Samples of SrAl2O4 and SrAl2O4:Cr3+ were prepared by mixing the powder materials SrCO3, Al2O3, and Cr2O3. The crystal structures of the undoped and doped samples were analyzed by X-ray diffraction (XRD) measurements. The diffraction
patterns reveal a dominant phase, characteristic of the monoclinic SrAl2O4 compound and another unknown secondary phase, in small amount, for doped samples. The data were fitted using the Rietveld
method for structural refinements and lattice parameter constants (a, b, c, and β) were determined. Luminescence of Cr3+ ions in this host is investigated for the first time by excitation and emission spectroscopy at room temperature. Emission
spectra present a larger band and a smaller structure associated to the
and electronic transitions, respectively. The obtained results are analyzed by crystal-field theory and the crystal-field parameter,
Dq, and Racah parameters, B and C, are determined from the excitation measurements. 相似文献
7.
An isothermal section of the phase diagram of the system Co-Sb-O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. The following galvanic cells were designed to measure the Gibbs energies of formation of the three ternary oxides namely CoSb2O4, Co7Sb2O12 and CoSb2O6 present in the system.
where 15 CSZ stands for ZrO2 stabilized by 15 mol % CaO. The reversible emfs obtained could be represented by the following expressions.
The standard Gibbs energies of formation of CoSb2O4, Co7Sb2O12 and CoSb2O6 were computed from the emf expressions:
The reasonability of the above data were assessed by computing the entropy change for the solid-solid reactions leading to the formation of ternary oxides from the respective pairs of constituent binary oxides. 相似文献
8.
The interface structure of an Al2O3/Nb/Al2O3 sandwich produced by solid-state diffusion bonding was investigated in detail by various transmission electron microscopy (TEM) methods. The joint possessed at one interface a
,
, and on the other interface a
and
orientation relationship. At both interfaces, misfit dislocations formed to compensate the lattice mismatch as found by high-resolution transmission electron microscopy (HRTEM). Electron energy-loss near edge structure (ELNES) studies revealed that the interface is terminating with an Al layer resulting in Al–Nb bonds. Identical sandwiches were investigated on the meso- and macroscopic scale by performing compression tests and simultaneously monitoring the strain development at (001)Nb and crystal faces. The full-field optical strain measurements (FFOM) revealed that the strain is localized at the interfaces when observed at the (001)Nb face while it is along the maximum shear directions of 36–54° inclined to the interface when observed at the face. The strain localization along a specific maximum shear direction results in the cleavage of Al2O3, always initiating from the interface possessing the
and
orientation relationship. 相似文献
9.
Single-phase nickel manganite spinels, Ni
x
Mn3–x
O4, with 0.5 x 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni2+ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni2+ ions (forx>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni2+ in A sites =P = – 82.1x
2+192.4x–81.5 and thus the general formula for cation distribution is
相似文献
10.
Harue Wada 《Journal of Materials Science》1991,26(10):2590-2594
Formation of silicon oxynitride was observed during silicon nitride whisker synthesis from silica, carbon and nitrogen. The
silicon oxynitride formation was limited to a bottom area of the charged powders and found both in whisker and powder. The
possible reason for this localized Si2N2O formation is analysed, based on the effect of gas phase composition on the phase stability among β-Si3N4, β-SiC and Si2N2O. The phase stability is closely related to the
ratio in the gas phase. To suppress Si2N2O formation, the
ratio must be lower than that of the phase boundary in the Si2N4/Si2N2O equilibrium, whereas it must be higher than that of the phase boundary in the SiC/Si2N2O equilibrium. The formation of silicon oxynitride during silicon nitride whisker formation was caused most likely by fluctuation
in the
ratio in the gas phase surrounding the lower area. 相似文献
11.
The objective of this work was to characterize the interfacial reaction zone in the metal matrix composite system-Al2O3(FP)/Mg (ZE41A). The composite was fabricated by liquid infiltration method. The reaction zone, a result of the reaction between magnesium in the alloy and the alumina fibres, was analysed for its morphology, chemistry, and crystallographic orientation using transmission electron microscopy. The results of this study showed the reaction zone to be, on average, 100nm wide and composed of MgO. The grains of the reaction zone ranged from less than 10 nm at the fibre/reaction zone interface to greater than 100nm at the matrix/reaction zone interface. It is proposed that the growth of the reaction zone was controlled by a seepage mechanism involving infiltration of liquid magnesium between MgO crystalS. Finally, it was observed that the MgO grains have the following crystallographic orientation relationship with the alumina grains from which they grew:
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