共查询到20条相似文献,搜索用时 31 毫秒
1.
Wubian Tian ZhengMing Sun Hitoshi Hashimoto Yulei Du 《Journal of Materials Science》2009,44(1):102-107
The compressive properties of ternary compound Cr2AlC at different temperatures and strain rates were studied. When tested at a strain rate of 5.6 × 10−4 s−1, the compressive strength decreases continuously from 997 ± 29 MPa at room temperature to 523 ± 7 MPa at 900 °C. The ductile-to-brittle
transition temperature is measured to be in the range of 700 to 800 °C. When tested in the strain rate range of 5.6 × 10−5 to 5.6 × 10−3 s−1, Cr2AlC fails in a brittle mode at room temperature, whereas the deformation mode changes from a brittle to a ductile as the strain
rate is lower than 5.6 × 10−4 s−1 when compressed at 800 °C. The compressive strength increases slightly with increasing strain rate at room temperature and
it is less dependent on strain rate when tested at 800 °C. The plastic deformation mechanism of Cr2AlC was discussed in terms of dislocation-related activities, such as kink band formation, delamination, decohesion of grain
boundary, and microcrack formation. 相似文献
2.
A Ray P Barat P Mukherjee A Sarkar S K Bandyopadhyay 《Bulletin of Materials Science》2007,30(1):69-71
Plastic flow behaviour of low carbon steel has been studied at room temperature during tensile deformation by varying the
initial strain rate of 3·3 × 10−4s−1 to a final strain rate ranging from 1·33 × 10−3s−1 to 2 × 10−3s−1 at a fixed engineering strain of 12%. Haasen plot revealed that the mobile dislocation density remained almost invariant
at the juncture where there was a sudden increase in stress with a change in strain rate and the plastic flow was solely dependent
on the velocity of mobile dislocations. In that critical regime, the variation of stress with time was fitted with a Boltzmann
type Sigmoid function. The increase in stress was found to increase with final strain rate and the time elapsed in attaining
these stress values showed a decreasing trend. Both of these parameters saturated asymptotically at a higher final strain
rate. 相似文献
3.
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
4.
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
5.
Marco Antonio García-Bernal David Hernandez-Silva Victor Sauce-Rangel 《Journal of Materials Science》2007,42(11):3958-3963
In the present study, the superplastic behavior of five Al–Mg–Zn alloys in coarse grain size condition has been studied. The
alloys were melted, cast into ingots and hot rolled. The grain size of the rolled samples was 69, 45, 40, 30 and 35 μm. Tensile
test specimens were machined from the hot rolled plate in the rolling direction. Strain-rate-change (SCR) tests at temperatures
between 300 and 450 °C and strain rates between 1 × 10−4 and 1 × 10−1 s−1 were carried out to determine the strain rate sensitivity of the flow stress. Finally, elongation-to-failure tests were conducted
at those temperatures and strain rates, where the alloys showed high strain rate sensitivity. A maximal elongation of 400%
was obtained for the 3.89 wt.% Zn alloy. The results are explained in terms of solute drag creep as the principal deformation
mechanism. 相似文献
6.
The high temperature deformation characteristics of a commercial β -titanium alloy Ti-3Al-8V-6Cr-4Mo-4Zr have been studied
in the temperature range 830–925∘C. The alloy exhibited superplasticity in a narrow temperature and strain rate range i.e.
850–865∘C and 5× 10− 5–3× 10− 3 s− 1 respectively, with a maximum elongation of 634% at 855∘C. The superplastic behaviour in the alloy is considered to arise
as a result of subgrain formation at the higher strain rates (region III) which enhances diffusional creep at lower strain
rates (region II). The activation energy values for regions II and III were found to be close to the lower of the two activation
energy values (129.2 KJ/mole) proposed to describe self diffusion in β -phase suggesting that the rate controlling mechanism
during high temperature deformation of the alloy was that for lattice diffusion. 相似文献
7.
We have established that the preliminary plastic deformation of 12Kh18N12T austenitic steel causes cold-work hardening, which
depends on the strain rate. With increase in the strain rate of specimens from 8∙10−4 to 417∙10−4 sec−1, both strength (ultimate strength) and plasticity (percentage elongation) characteristics of 12Kh18N12T steel decrease. After
holding of the preliminarily work-hardened steel at a temperature of 650°C, its strength increases, and its plasticity decreases.
At the same time, the isothermal influence for 1 and 10 h does not facilitate intercrystalline corrosion of the steel during
its holding in a corrosive medium for 24 h. 相似文献
8.
Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural,
optical and electrical properties were studied under different preparation conditions like substrate temperature, solution
flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10−2 ω-cm to 3.57 × 10−3 ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range
1.2 × 10−1 to 1.69 × 10−2 ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration
of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film
was found to be 7.74 × 10−4 ω-cm, which was deposited at 350°C with 0.26 g of SbCl3 and 4 g of SnCl4 (SbCl3/SnCl4 = 0.065).
Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at
substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM. 相似文献
9.
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
10.
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
11.
Seiji Motojima Noriyuki Iwamori Tatsuhiko Hattori 《Journal of Materials Science》1986,21(11):3836-3842
Si3N4 layers were obtained on a quartz substrate from a gas mixture of Si2Cl6, NH3 and H2 under a reduced pressure in a temperature range of 800 to 1300‡ C. Amorphous Si3N4 layers that were dense and adherent to the substrate were obtained in a temperature range of 800 to 1100‡ C. On the other
hand,α-Si3N4 layers were obtained at 1200‡ C and a source-gas ratio (N/Si) of 1.33 to 1.77. The lowest deposition temperature of amorphous
Si3N4 was considered to be about 700‡ C. The microhardness of amorphous Si3N4 obtained in a temperature range of 800 to 1100‡ C was 2400 to 2600 kg mm−2 (load: 50 g), and that ofα-Si3N4 obtained at 1200‡ C was 3400 kg mm−2. Chlorine contents in the Si3N4 layer decreased with increasing deposition temperature and source-gas ratio (N/Si), and with decreasing total pressure. 相似文献
12.
Creep behavior of AZ31 magnesium alloy in low temperature range between 423 K and 473 K 总被引:1,自引:0,他引:1
The deformation behavior of coarse-grained AZ31 magnesium alloy was examined in creep at low temperatures below 0.5 T
m and low strain rates below 5 × 10−4 s−1. The creep test was conducted in the temperature range between 423 and 473 K (0.46–0.51 T
m) under various constant stresses covering the strain rate range 5 × 10−8 s−1–5 × 10−4 s−1. All of the creep curves exhibited two types depending on stress level. At low stress (σ/G < 4 × 103), the creep curve was typical of class I behavior. However, at high stresses (σ/G > 4 × 103), the creep curve was typical of class II. At the low stress level, deformation could be well described by solute drag creep
whereas at the high stress level, deformation could be well described by dislocation climb creep associated with pipe diffusion
or lattice diffusion. The transition of deformation mechanism from solute drag creep to dislocation climb creep, on the other
hand, could be explained in terms of solute-atmosphere-breakaway concept. 相似文献
13.
Transparent and conducting SnO2 films are prepared at 500°C on quartz substrates by chemical vapour deposition technique, involving oxidation of SnCl2. The effect of oxygen gas flow rate on the properties of SnO2 films is reported. Oxygen with a flow rate from 0·8–1·35 lmin−1 was used as both carrier and oxidizing gas. Electrical and optical properties are studied for 150 nm thick films. The films
obtained have a resistivity between 1·72 × 10−3 and 4·95 × 10−3 ohm cm and the average transmission in the visible region ranges 86–90%. The performance of these films was checked and the
maximum figure of merit value of 2·03 × 10−3 ohm−1 was obtained with the films deposited at the flow rate of 1·16 lmin−1. 相似文献
14.
Room temperature tensile test results of solution annealed 304 stainless steel at strain rates ranging between 5 × 10−4 and 1 × 10−1 s−1 reveal that with increase in strain rate yield strength increases and tensile strength decreases, both maintaining power–law
relationships with strain rate. The decrease in tensile strength with increasing strain rate is attributed to the lesser amount
of deformation-induced martensite formation and greater role of thermal softening over work hardening at higher strain rates.
Tensile deformation of the steel is found to occur in three stages. The deformation transition strains are found to depend
on strain rate in such a manner that Stage-I deformation (planar slip) is favoured at lower strain rate. A continuously decreasing
linear function of strain rate sensitivity with true strain has been observed. Reasonably good estimation for the stress exponent
relating dislocation velocity and stress has been made. The linear plot of reciprocal of strain rate sensitivity with true
strain suggests that after some critical amount of deformation the increased dislocation density in austenite due to the formation
of some critical amount of deformation-induced martensite plays important role in carrying out the imposed strain rate. 相似文献
15.
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
16.
V. S. Shiryaev V. G. Pimenov M. M. Lipatova I. I. Evdokimov M. F. Churbanov Yu. P. Kirillov V. N. Kornoukhov 《Inorganic Materials》2010,46(3):314-317
We have studied the behavior of barium impurities in the form of BaF2 and BaO during vacuum distillation of selenium. The effective Ba partition coefficient is shown to depend on the impurity
concentration and evaporation rate. At initial barium contents in the range 3 × 10−3 to 2 × 10−5 wt %, the effective Ba partition coefficient is 600 and 1.5 at distillation rates of 4.7 × 10−6 and 1.5 × 10−3 cm3/(cm2 s), respectively. The chemical form of barium has no significant effect on its partition coefficient. Using a Rayleigh distillation
equation, we have determined the equilibrium partition coefficient and the thickness of the diffusion boundary layer in the
system. 相似文献
17.
Kittichai Sopunna Titipun Thongtem Michael McNallan Somchai Thongtem 《Journal of Materials Science》2006,41(14):4654-4662
Two alloys, Ti-47Al-2Nb-2Cr (MJ12) and Ti-47Al-2Nb-2Mn + 0.8TiB2 (MJ47), were nitrided in purified ammonia for 3.6 × 103–3.6 × 104 s (1–10 h) at a temperature range of 800–1,000 °C. The nitridation process can successfully improve alloy hardness which increased with an increase of the nitridation temperature and time. Hardness values of MJ12 and MJ47 with 1,000 °C nitridation for 3.6 × 104 s were the highest at 700.5 ± 9.0 and 694.7 ± 21.8 kg mm−2, respectively. The wear rate and friction coefficient were significantly reduced by the nitridation process. Wear resistance of both alloys increased by two orders of magnitude after nitridation compared to the corresponding alloys without nitridation. In addition, the alloys were analyzed using XRD, SEM, EDX and an optical microscope. 相似文献
18.
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
19.
Polycrystalline thin films of Ti-doped indium oxide (indium–titanium-oxide, ITiO) were prepared by d.c. magnetron sputtering and their electrical and optical properties were investigated. Doping of Ti was effective in improvement of the electroconductivity of the indium oxide: the electrical resistivity of 1.7 × 10−3 Ω cm of non-doping decreased to minimum value of 1.8 × 10−4 Ω cm at 2.4 at.% Ti-doping when the films were deposited at 300 °C. The polycrystalline ITiO films of 0.8–1.6 at. % Ti-doping showed the high Hall mobilitiy (82–90 cm2 V−1 s−1) and the relatively low carrier density (2.4–3.5 × 1020 cm−3) resulting in characteristics of both low resistivity (2.1–3.0 × 10−4 Ω cm) and high transmittance in the near-infrared region (over 80% at 1550 nm), which cannot be shown in the conventional Sn-doped indium oxide (ITO) films. 相似文献
20.
Perovskite oxides of the general formula, La0.9Sr0.1Ga0.8M0.2O3-δ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities
(σ R∼ 10−2 S/cm at 800°C) comparable to that of the best perovskite oxide ion conductor, La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) (σ ∼ 8 × 10−2 S/cm at 800°C). While M = Mn, Co, Ni, Cu members appear to be mixed conductors with a variable electronic contribution to
the conductivity, especially at high oxygen partial pressures (pO2 ≥1 atm), arising from mixed-valency of the transition metals, the M = Zn(II) phase is a pure oxide ion conductor exhibiting
a conductivity (σ ∼ 1.5 × 10−2 S/cm at 800°C) that is slightly lower than that of LSGM. The lower conductivity of the M = Zn(II) derivative could be due
to the preference of Zn(II) for a tetrahedral oxygen coordination. 相似文献