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1.
Daisuke Watanabe Keishi Nishio Yoshio Sakka Masataka Ohgaki Ian J. Davies Tomohiro Umeda Seiichiro Koda Kiyoshi Itatani 《Journal of Materials Science》2011,46(6):1956-1962
High-density β-calcium orthophosphate (β-Ca3(PO4)2, also called β-tricalcium phosphate: β-TCP) ceramics with submicrometer-sized grains were fabricated using a pulse-current
pressure firing route. The maximum relative density of the β-TCP compacts was 98.7% at 1050 °C and this was accompanied by
a translucent appearance. The mean grain size of the β-TCP compacts increased slightly with temperature to reach 0.78 μm at 1000 °C. However, upon further increasing the firing
temperature to 1050 °C the mean grain size increased significantly to 1.6 μm. The extent of plastic deformation during tensile
testing was examined at temperatures between 900 and 1100 °C using a strain rate in the range 9.26 × 10−5 to 4.44 × 10−4 s−1. The maximum tensile strain achieved was 145% for a test temperature of 1000 °C and strain rate of 1.48 × 10−4 s−1 and this was attributed to the relatively high density and small grain size. 相似文献
2.
The isothermal oxidation behavior of Cr2AlC ceramics oxidized in air at 1,100 and 1,250 °C for 20 h was studied. The phase compositions and microstructure of the
oxidized surface were identified and observed by XRD and electron probe microanalysis (EMPA), respectively, while the cross
sections of oxidized samples were also examined by EMPA equipped with energy dispersive spectrum capabilities. The results
indicated that the oxidation of Cr2AlC samples was carried out by the outward diffusion of Al, together with small amounts of Cr, and the inward diffusion of
O to form a surface layer of α-Al2O3, while carbides (Cr7C3 and Cr3C2), rather than oxides (Cr2O3), were formed in a layer under the surface. The mass gain per unit surface area of oxidized Cr2AlC followed a parabolic relation with oxidation time, and the parabolic rates, k
p, for oxidation at 1,100 and 1,250 °C were 1.1 × 10−12 and 7.1 × 10−10 kg2 m4 s−1, respectively. 相似文献
3.
J.?S.?Almeida T.?S.?M.?Fernandes A.?J.?M.?Sales M.?A.?S.?Silva G.?F.?M.?P.?Júnior H.?O.?Rodrigues A.?S.?B.?Sombra
In this paper, the structural and dielectric properties of BNO (BiNbO4) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional
mixed oxide method and doped with 3, 5 and 10 wt. % Bi2O3–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the
triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of
dielectric permittivity (ε′
r
) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi2O3) and BNO5Pb (5 wt. % PbO) with values ε′
r
~ 59.54 and ε′
r
~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with
values tan δ ~ 5.71 × 10−4 and tan δ ~ 2.19 × 10−4, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples,
obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about ε′
r
~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at
temperature 80 °C, with about tan δ ~ 5.4 × 10−3. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C)
to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude
that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C,
which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H)
obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be
studied seeking the development ceramic capacitors for applications in radio frequency devices. 相似文献
4.
The dielectric, piezoelectric and elastic coefficients, as well as the electromechanical coupling factors, of NaNbO3 submicron-structured ceramics have been obtained by an automatic iterative method from impedance measurements at resonance.
Poled thin discs were measured from room temperature up to the depoling one, close to 300 °C. Dielectric thermal behaviour
was determined also for unpoled ceramics up to the highest phase transition temperature. Ceramics were processed by hot-pressing
from mechanically activated precursors. Microstructural effects on the properties are discussed. The suppression of the classical
maximum in dielectric permittivity in unpoled ceramics at the phase transition at 370 °C was found when a bimodal distribution
of grain sizes, with a population of average grain size of 110 nm in between much coarser grains, is observed. The appearance
of a phase transition at 150 °C took place when Na vacancies are minimised. The occurrence of a non-centrosymmetric, ferroelectric
phase, in the unpoled ceramic from room temperature to ~300 °C, highly polarisable resulting in high ferro–piezoelectric properties
was also observed in the ceramic which presents grain size below 160 nm. Maximum values of k
p = 14%, d
31 = −8.7 × 10−12 C N−1 and N
p = 3772 Hz m at room temperature, and k
p = 18%, d
31 = −25.4 × 10−12 C N−1 and N
p = 3722 Hz m at 295 °C were achieved in the best processing conditions of the ceramics. 相似文献
5.
Behavior of electrical resistance was examined in room temperature and elevated temperatures up to 1000 °C for two types of
SiCCVD fibers with diameters of 140 and 70 μm, respectively. The results showed that electrical resistance showed a good linear
relationship with the length of fibers. Electrical resistance decreased as temperature increased, besides, temperature coefficient
of electrical resistance was a minus constant, −5.2 × 10−4 °C−1 except that in the first heating. In the first heating, electrical resistance and temperature coefficient increased and had
a peak in the range of 550–700 °C owing to the burning of the carbon-rich layer on the fiber surface. It suggested that behavior
of electrical resistance of the fibers depended mainly on the carbon core and the carbon-rich layer. It was confirmed that
SiCCVD fiber could be used as heating elements for micro-heater and finally a micro-heater using SiCCVD fiber as heating elements was developed. 相似文献
6.
Kaixuan Wang Weidong Zeng Yongqing Zhao Yunjin Lai Yigang Zhou 《Journal of Materials Science》2010,45(21):5883-5891
Isothermal compression of Ti-17 titanium alloy with lamellar starting structure at the deformation temperatures ranging from
780 °C to 860 °C, the strain rates ranging from 0.001 to 10 s−1, and the height reductions ranging from 15% to 75% with an interval 15% were carried out. Based on experimental results,
3-D processing maps including strain were developed and used to identify various microstructural mechanisms and distinguish
the safe and unsafe domains. The processing maps exhibit two maximum power dissipation efficiency domains and dynamic globularization
takes place in this two domains. The first domain occurs at 800–860 °C and at strain rates lower than 0.01 s−1, and the second occurs at 780–800 °C and at strain rates lower than 0.01 s−1. With the increasing of the strains, the values of maximum power dissipation efficiency in this two domains increase. One
flow instability domain due to adiabatic shear bands and lamellar kinking occurs at strain rates higher than 0.487 s−1, lower temperature, and higher strain above 0.2. The instability deformation region increases with increasing strain, strain
rate, and decreasing temperature. 相似文献
7.
In this study, polycrystalline AgGaS2 thin films were deposited by the sequential evaporation of AgGaS2 and Ag sources with thermal evaporation technique. Thermal treatment in nitrogen atmosphere for 5 min up to 700 °C was applied
to the deposited thin films and that resulted in the mono phase AgGaS2 thin films without the participation of any other minor phase. Structural and compositional analyses showed the structure
of the films completely changes with annealing process. The measurements of transmittance and reflectance allowed us to calculate
the band gap of films lying in 2.65 and 2.79 eV depending on annealing temperature. The changes in the structure with annealing
process also modify the electrical properties of the films. The resistivity of the samples varied in between 2 × 103 and 9 × 106 (Ω-cm). The room temperature mobility depending on the increasing annealing temperature was in the range of 6.7–37 (cm2 V−1 s−1) with the changes in carrier concentrations lying in 5.7 × 1013–2.5 × 1010 cm−3. Mobility-temperature dependence was also analyzed to determine the scattering mechanisms in the studied temperature range
with annealing. The variations in the electrical parameters of the films were discussed in terms of their structural changes. 相似文献
8.
Liang Fang Zhao Yang Hui Zhang Chunchun Li Xiyang Peng Changzheng Hu Dongjin Chu 《Journal of Materials Science: Materials in Electronics》2011,22(9):1208-1212
Polycrystalline samples of Ba4Ln2Fe2Ta8O30 (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric
and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal
tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional
temperature stability, a relatively small temperature coefficient of dielectric constant (τ
ε
) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10−3 and 2.8 × 10−3 (at 1 MHz) for Ba4La2Fe2Ta8O30 and Ba4Nd2Fe2Ta8O30, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication
of discrete multilayer capacitors in microelectronic technology. 相似文献
9.
Xibao Li Gangqin Shao Xiaohua Yu Jian Wang Hongxing Gu 《Journal of Materials Science: Materials in Electronics》2011,22(2):189-192
Ce0.8Sm0.2O1.9 (SDC) powder was synthesized by spray pyrolysis at 650 °C. XRD results showed that phase-pure SDC powder with an average
crystallite size of 11 nm was synthesized. SDC electrolyte film was prepared by tape casting and sintered at different temperatures
of 1,300, 1,400 and 1,500 °C for 2 h, respectively. The SDC electrolyte film was relatively denser and showed finer microstructure
at relatively lower temperature of 1,400 °C, which might be due to the high sintering activity of the spray pyrolysis SDC
powder. The ionic conductivity of the SDC electrolyte film sintered at 1,400 °C reached a maximum value of 9.5 × 10−3 S cm−1 (tested at 600 °C) with an activation energy for conduction of 0.90 eV. 相似文献
10.
Compressive experiments on three types of rigid polyurethane foams were conducted by employing modified split Hopkinson pressure
bars (SHPBs). The foam materials, which were based on polymethylene diisocyanate (PMDI), varied only in density (0.31 × 103, 0.41 × 103, and 0.55 × 103 kg/m3) and were compressed at strain rates as high as 3 × 103 s−1. Dynamic experiments were also performed on these three foam materials at temperatures ranging from 219 to 347 K, while maintaining
a fixed high strain rate of ~3 × 103 s−1. In addition, an MTS materials testing frame was used to characterize the low-strain-rate compressive response of these three
foam materials at room temperature (295 K). Our study determined the effects of density, strain rate, and temperature on the
compressive response of the foam materials, resulting in a compressive stress–strain curve for each material. 相似文献
11.
Z. L. Ning G. J. Wang F. Y. Cao J. F. Sun J. F. Du 《Journal of Materials Science》2009,44(16):4264-4269
The engineering stress versus engineering strain curves for a Mg–2.54Nd–0.26Zn–0.32Zr cast alloy were measured by Gleeble-1500D
thermo-simulation machine in the temperature range of room temperature to 400 °C at initial strain rates of 10−4–10−2 s−1. The effects of strain rate on stress, elongation to facture, and section shrinkage were analyzed. The fractograph morphologies
were investigated by using SEM. It was found that strain rate has little effect on engineering stress for the Mg–2.54Nd–0.26Zn–0.32Zr
alloy when tested at below 250 °C. When tested at above 250 °C, low strain rate resulted in decreased engineering stress,
increased elongation to fracture, and section shrinkage. The fracture mode is cleavage fracture with elongated dimple below
250 °C and changes to typical ductile failure when tested above 250 °C. 相似文献
12.
Ternary compound Cr2AlC was synthesized by a reactive sintering process and its mechanical properties in the 25-1000 °C temperature range were studied by 4-point bending tests. The flexural strength of Cr2AlC decreases continuously from 555 ± 11 MPa at room temperature down to 100 ± 4 MPa at 1000 °C and this strength decreasing tendency is more obvious as the testing temperature is higher than 900 °C. The ductile-to-brittle transition temperature of Cr2AlC locates in the range of 800-900 °C. The macro-plastic deformation of Cr2AlC is mainly attributed to the initiation and propagation of large number of microcracks. 相似文献
13.
Woei-Shyan Lee Chi-Feng Lin Tao-Hsing Chen Hsin-Hwa Hwang 《Journal of Materials Science》2008,43(5):1568-1575
A compressive split-Hopkinson pressure bar apparatus and transmission electron microscopy (TEM) are used to investigate the
deformation behaviour and microstructural evolution of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8 × 102 s−1 to 8 × 103 s−1 and temperatures between 25 °C and 900 °C. In general, it is observed that the flow stress increases with increasing strain
rate, but decreases with increasing temperature. The microstructural observations reveal that the strengthening effect evident
in the deformed alloy is a result, primarily, of dislocations and the formation of α phase. The dislocation density increases
with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density
varies linearly with the flow stress. The amount of α phase increases with increasing temperature below the β transus temperature.
The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current
loading conditions. 相似文献
14.
WCP-reinforced ferrous matrix composites were processed by direct addition of WCP (100–150 μm) and the melt of the matrix alloy to a rotating mold at 1000 rpm. Dry sliding wear behaviors of the composites
containing about 80 vol.% of WCP and high-speed steel counterpart were investigated at room temperature and 400 °C against a rotating die steel ring. And
wear experiments were performed under loads of 50, 100, and 150 N and a fixed sliding velocity of 30 m/s. Results show that
at room temperature, both materials exhibited a marked increase in wear rate with load applied. Wear rates of the composites
and high-speed steel under loads of 50, 100, and 150 N at room temperature achieved 1.61 × 10−6, 2.14 × 10−6, 3.56 × 10−6, and 3.11 × 10−6, 23.08 × 10−6, 57.39 × 10−6 g/m, respectively. At a testing temperature of 400 °C, the composites exhibited a marked increase in wear rates and high-speed
steel exhibited mild wear (characterized by extremely low wear rates) over the range of loads considered in these experiments.
Wear rates of both the composites and high-speed steel at 400 °C achieved 2.42 × 10−6, 5.19 × 10−6, 6.64 × 10−6, and 4.1 × 10−6, 8.92 × 10−6, 26.02 × 10−6 g/m, respectively, under different loads. Finally, the wear-mechanism was discussed in this article. 相似文献
15.
An as-received reactor pressure vessel (RPV) steel SA508 class 3 (SA508 Cl.3) has been subjected to uniaxial tension tests
in the strain-rate range of 6.67 × 10−5 s−1 to 1.2 × 10−2 s−1 and the temperature range of 298 K to 673 K to investigate the effects of temperature and strain rate on its mechanical properties.
It was found that the region of dynamic strain aging (DSA) was in the temperature range of 523–623 K at a strain rate of 1.2 × 10−3 s−1, 473–573 K at 1.2 × 10−4 s−1, and 473–573 K at 6.67 × 10−5 s−1, respectively. Serrated stress–strain behaviors, predominately consisting of type A, B, and C, have been observed in these
temperatures and strain-rate ranges. The solutes responsible for DSA have been identified to be carbon and nitrogen, and nitrogen
atoms play a more important role. The relative DSA mechanisms for this RPV steel are discussed. 相似文献
16.
Z. Nagamedianova E. Sánchez 《Journal of Materials Science: Materials in Electronics》2007,18(5):547-552
There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses based on Li2S-P2S5-Sb2S3 system have been synthesized by a classical quenching technique. A summary of thermal and structural characterization is
presented. Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The compositions of low
lithium content (below 20% mol) have presented low electronic conductivities close to 10−8 S/cm at room temperature. The compositions of medium lithium content (30–50% mol) have presented mixed ionic-electronic behavior
with predominant on ionic conductivity with a maximum values around 10−6 S/cm for samples up to 50% Li2S at room temperature. Arrhenius behavior is verified between 25°C and Tg for all glasses with activation energies about 0.55–0.64 eV. A comparative study of conductivities with glasses belonging
to the other chalcogenide systems has been undertaken. 相似文献
17.
The hot deformation behavior of Al 2024 was studied by isothermal hot compression tests in the temperature range of 250–500 °C
and strain rate range of 10−3 to 102 s−1 in a computer-controlled 50 kN servo-hydraulic universal testing machine (UTM). The results show that the flow stress of
Al 2024 alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization.
The processing map exhibits two domains of optimum efficiency for hot deformation at different strains, including the low
strain rate domain at 500 °C and between 10−2 and 10−1 s−1 and the high strain rate domain in 250 and 300 °C in the strain rate range of 101 to 102 s−1. An attempt has been made in this article to generate a new hybrid 4D process map which illustrates contours of power dissipation
and instability in the 3D space of strain rate, temperature, and strain. 相似文献
18.
Guo-Hua Chen 《Journal of Materials Science》2007,42(17):7239-7244
The effects of replacement of MgO by CaO on the sintering and crystallization behavior of MgO–Al2O3–SiO2 system glass-ceramics were investigated. The results show that with increasing CaO content, the glass transition temperature
firstly increased and then decreased, the melting temperature was lowered and the crystallization temperature of the glass-ceramics
shifted clearly towards higher temperatures. With the replacement of MgO by less than 3 wt.% CaO, the predominant crystalline
phase in the glass-ceramics fired at 900 °C was found to be α-cordierite and the secondary crystalline phase to be μ-cordierite.
When the replacement was increased to 10 wt.%, the predominant crystalline phase was found to be anorthite and the secondary
phase to be α-cordierite. Both thermal expansion coefficient (TCE) and dielectric constant of samples increases with the replacement
of MgO by CaO. The dielectric loss of sample with 5 wt.% CaO fired at 900 °C has the lowest value of 0.08%. Only the sample
containing 5 wt.% and10 wt.% CaO (abbreviated as sample C5 and C10) can be fully sintered before 900 °C. Therefore, a dense
and low dielectric loss glass-ceramic with predominant crystal phase of α-cordierite and some amount of anorthite was achieved
by using fine glass powders (D50 = 3 μm) fired at 875–900 °C. The as-sintered density approaches 98% theoretical density. The flexural strength of sample
C5 firstly increases and then decreases with sintering temperature, which closely corresponds to its relative density. The
TCE of sample C5 increases with increasing temperature. The dielectric property of sample C5 sintered at different temperatures
depends on not only its relative density but also its crystalline phases. The dense and crystallized glass-ceramic C5 exhibits
a low sintering temperature (≤900 °C), a fairly low dielectric constant (5.2–5.3), a low dielectric loss (≤10−3) at 1 MHz, a low TCE (4.0–4.25 × 10−6 K−1), very close to that of Si (∼3.5 × 10−6 K−1), and a higher flexural strength (≥134 MPa), suggesting that it would be a promising material in the electronic packaging
field. 相似文献
19.
R. Jovani Abril R. Eloirdi D. Bou?xière R. Malmbeck J. Spino 《Journal of Materials Science》2011,46(22):7247-7252
Nanocrystallites of UO2 with a size of 3–5 nm were studied in situ with high temperature X-ray diffraction (HT-XRD), thermogravimetry (TGA), and
differential thermal analysis. The evolution of the crystallite size, the lattice parameter, and the strain were determined
from ambient temperature up to 1200 °C. Below 700 °C, a weak effect on the crystallite size occurs and it remains below 10 nm,
while a strong expansion of the lattice parameter is measured. The strain decreases with temperature and is completely released
at 700 °C. Above this temperature, begins the sintering of the nanocrystallites reaching a size of about 80 nm at 1200 °C.
The weight loss curve observed in TGA is assigned to the desorption of water molecules and is correlated with the strain evolution
observed by HT-XRD. The linear thermal expansion and the thermal expansion coefficient at 800 °C are 1.3% and 16.9 × 10−6 °C−1, respectively. 相似文献
20.
Marina B. Ruggles-Wrenn Tufan Yeleser Geoff E. Fair Janet B. Davis 《Applied Composite Materials》2009,16(6):379-392
The tensile creep behavior of a N610™/LaPO4/Al2O3 composite was investigated at 1,100°C in laboratory air and in steam. The composite consists of a porous alumina matrix reinforced
with Nextel 610 fibers woven in an eight-harness satin weave fabric and coated with monazite. The tensile stress-strain behavior
was investigated and the tensile properties measured at 1,100°C. The addition of monazite coating resulted in ~33% improvement
in ultimate tensile strength (UTS) at 1,100°C. Tensile creep behavior was examined for creep stresses in the 32–72 MPa range.
Primary and secondary creep regimes were observed in all tests. Minimum creep rate was reached in all tests. In air, creep
strains remained below 0.8% and creep strain rates approached 2 × 10−8 s−1. Creep run-out defined as 100 h at creep stress was achieved in all tests conducted in air. The presence of steam accelerated
creep rates and significantly reduced creep lifetimes. In steam, creep strain reached 2.25%, and creep strain rate approached
2.6 × 10−6 s−1. In steam, creep run-out was not achieved. The retained strength and modulus of all specimens that achieved run-out were
characterized. Comparison with results obtained for N610™/Al2O3 (control) specimens revealed that the use of the monazite coating resulted in considerable improvement in creep resistance
at 1,100°C both in air and in steam. Composite microstructure, as well as damage and failure mechanisms were investigated. 相似文献