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1.
Ageing characteristics of cast Zn-Al based alloy (ZnAl7Cu3) 总被引:1,自引:0,他引:1
Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich phase and four phase transformation, + T + , were detected during ageing at 150°C. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich and phases. 相似文献
2.
Summary The hypersonic small-disturbance theory is reexamined in this study. A systematic and rigorous approach is proposed to obtain the nonlinear asymptotic equation from the Taylor-Maccoll equation for hypersonic flow past a circular cone. Using this approach, consideration is made of a general asymptotic expansion of the unified supersonic-hypersonic similarity parameter together with the stretched coordinate. Moreover, the successive approximate solutions of the nonlinear hypersonic smalldisturbance equation are solved by iteration. Both of these approximations provide a closed-form solution, which is suitable for the analysis of various related flow problems. Besides the velocity components, the shock location and other thermodynamic properties are presented. Comparisons are also made of the zeroth-order with first-order approximations for shock location and pressure coefficient on the cone surface, respectively. The latter (including the nonlinear effects) demonstrates better correlation with exact solution than the zeroth-order approximation. This approach offers further insight into the fundamental features of hypersonic small-disturbance theory.Notation
a
speed of sound
-
H
unified supersonic-hypersonic similarity parameter,
-
K
hypersonic similarity parameter, M
- M
freestream Mach number
-
P
pressure
-
T
temperature
-
S
entropy
-
u, v
radial, polar velocities
-
V
freestream velocity
-
shock angle
-
cone angle
-
density
-
density ratio, /()
-
ratio of specific heats
-
polar angle
-
stretched polar angle, /
- (), (), ()
gage functions 相似文献
3.
Two casts of type 316L(N) austenitic stainless steel have been solution treated for 1 h at 1070 C, air-cooled, then aged for up to 20 000 h at temperatures between 550 C and 750 C. Grain boundary precipitation of the M23C6 phase occurs, and the Cr composition profile normal to the grain boundaries has been determined at high resolution by an analytical electron microscope. The data have been fitted firstly to collector plate models, which indicated that some of the material was in the process of desensitization, or healing, indicated by a rise in the boundary Cr content. The data were then fitted to a model of the Cr profile as a function of ageing treatment in the healing regime, and a good correlation was obtained. 相似文献
4.
High temperature oxidation behavior of Ti-Al-Nb ternary alloys 总被引:1,自引:0,他引:1
Yong Shen Xiaofei Ding Fugang Wang Y. Tan J.-M. Yang 《Journal of Materials Science》2004,39(21):6583-6589
The oxidation behavior of four Ti-Al-Nb ternary alloys with different microstructures were investigated at 1000°C using interrupted oxidation test in air. Alloys with single-phase -TiAl, two-phase -TiAl + 2-Ti3Al, multi-phase -TiAl + 2-Ti3Al + Nb2Al and two-phase 2-Ti3Al + Nb2Al were prepared. The oxidation resistance of the Ti-Al-Nb ternary alloy at high temperature was found to be better than that of the binary Ti-Al alloy. Among the four Ti-Al-Nb ternary alloys, the + 2 two-phase alloy has the best oxidation resistance. The presence of Nb-enriched phase such as Nb2Al and Nb3Al decrease the oxidation resistance at elevated temperature presumably due to the formation of Nb2O5, which would accelerate the exfoliation of oxide. 相似文献
5.
A. F. Kugaevskii 《Measurement Techniques》1963,6(11):949-952
Conclusions It is possible by means of the above resonator, according to our analysis and in the absence of air gaps between the sample and the line, to evaluate the real components and of permeability and permittivity respectively in the range of 2 to 100 with an error between ±3% and ±10% in the temperature range from room temperature to +400°C, and the imaginary components and (for tan and tan in the range of 0.001 to 2) with an error of 7 to 20% over the same temperature range. 相似文献
6.
The dielectric constants and loss factors,, for pure single-crystal MgO and for Fe-and Cr-doped crystals have been measured at frequencies, , from 500 Hz to 500 kHz at room temperature. For pure MgO at 1 kHz the values of and the loss tangent, tan , (9.62 and 2.16×10–3, respectively) agree well with the data of Von Hippel; the conductivity, , varies as
n
withn=0.98±0.02. In Fe-doped crystals increases with Fe-concentration (at any given frequency); for a crystal doped with 12800 ppm Fe, was about four times the value for pure MgO. At all concentrations the variation of log with log was linear andn=0.98±0.02. A decrease in with increasing Fe-concentration was also observed. A similar, although less pronounced, behaviour was found in Cr-doped crystals. The effects are discussed in terms of hopping mechanisms. 相似文献
7.
Ageing characteristics of an extruded eutectoid Zn-Al based alloy were investigated using X-ray diffraction and scanning electron microscopy techniques. The extruded alloy consisted of Al rich phase and Zn rich E and phases. The original cast eutectoid Zn-Al alloy was extruded at 250 °C. Both supersaturated s and s phase decomposed during extrusion and appeared as fine and coarse lamellar structures. The E and phases particles formed in the original interdendritic region. It was found that two Zn rich phases E and decomposed sequentially during ageing at 170, 140 °C. The decomposition of the E phase occurred as a discontinuous precipitation in the early stage of ageing and the decomposition of the phase took place in a four phase transformation: + T + in the prolonged ageing. Two typical morphologies of the decomposition of the Zn rich phases E and were distinctive in back-scattered scanning electron microscopy. 相似文献
8.
Measurements of the average thermal conductivity exp hQ/T and of the thermal relaxation time to reach steady-state equilibrium conditions are reported in the superfluid phase for dilute mixtures of3He in4He. Hereh is the cell height,Q is the heat flux, andT is the temperature difference across the fluid layer. The measurements were made over the impurity range 2×10–9<X(3He)<3×10–2 and with heat fluxes 0.3<Q<160 µW/cm2. Assuming the boundary resistanceR
b
, measured forX<10–5, to be independent ofX over the whole range ofX, a calculation is given for exp. ForQ smaller than a well-defined critical heat fluxQ
c
(X) X
0.9, exp is independent of Q and can be identified with the local conductivity eff, which is found to be independent of the reduced temperature = (T–T)/T for –10–2. Its extrapolated value at T is found to depart forX10–3 from the prediction X
–1
, tending instead to a weaker divergence X
–a
witha0.08. A finite conductivity asX tends to zero is not excluded by the data, however. ForQ >Q
c
(X), a nonlinear regime is entered. ForX10–6, the measurements with the available temperature resolution are limited to the nonlinear conditions, but can be extrapolated into the linear regime forX2×10–7. The results for exp(Q),Q
c
(X), and eff(XX) are found to be internally consistent, as shown by comparison with a theory by Behringer based on Khalatnikov's transport equations. Furthermore, the observed relaxation times (X) in the linear regime are found to be consistent forX>10–5 with the hydrodynamic calculations using the measured eff(X). ForX<10–5, a faster relaxation mechanism than predicted seems to dominate. The transport properties in the nonlinear regimes are presented and unexplained observations are discussed. 相似文献
9.
The effect of antimony on the creep behaviour (dislocation creep) of a 25 wt% Cr-20 wt% Ni stainless steel with ~ 0.005 wt% C was studied with a view to assessing the segregation effect. The antimony content of the steel was varied up to 4000 ppm. The test temperature range was 1153 to 1193 K, the stress range, 9.8 to 49.0 MPa, and the grain-size range, 40 to 600m. The steady state creep rate,
, decreases with increasing antimony content, especially in the range of intermediate grain sizes (100 to 300m). Stress drop tests were performed in the secondary creep stages and the results indicate that antimony causes dislocations in the substructure to be immobile, probably by segregating to them, reducing the driving stress for creep.Nomenclature
a
Creep stress in a constant load creep test without stress-drop
-
A
Initial applied stress in stress-drop tests
-
Stress decrement
- (
A-)
Applied stress after a stress decrement,
- t
i
Incubation time after stress drop (by the positive creep)
-
C
Strain-arrest stress
-
i
Internal stress
-
s
s-component (=
i-
c)
-
Steady state creep rate (average value) in a constant load creep test
-
Strain rate at time,t, in a constant load creep test
-
New steady state creep rate (average value) after stress drop from
A to (
A-)
-
Strain rate at time,t, after stress drop. 相似文献
10.
Giichi Terui 《Journal of Low Temperature Physics》1976,25(5-6):645-670
From the second-sound velocityU
2
near the superfluid transition point, the superfluid densities in3He-4He mixtures,
s
(X) and
s
(), were deduced along the paths of constant3He concentrationX and of constant chemical potential difference of3He and4He. The following critical exponents of
s
are determined: (a) =XX for
s
(X) in the(X, T) plane,(b) X for
s
(X) in the(, T) plane, and(c) for
s
() in the(, T) plane. It is found that and X
change by about 4–6% relative to with increasing3He concentration up toX=0.4 and by 8–10% up toX=0.53. It seems that, belowX=0.53, universality hold for . Values of have been found to be in good agreement with the critical exponent of
s
in pure4He under constant pressure. The values of and X
forX0.53 are also found to be consistent with the scaling relations in the (,T) plane of3He-4He mixture.Work performed in part while at the Electrotechnical Laboratory. 相似文献
11.
V. S. Sidorov 《Journal of Engineering Physics and Thermophysics》1981,41(3):1032-1035
An analytical solution of the thermal conductivity problem with boundary conditions of the third kind and arbitrary coordinate and time dependence of the Biot number is found in the form of a converging series of quadratures.Notation , z
dimensionless coordinates
-
dimensionless temperature
- Q
dimensionless volume heat-liberation density per unit time
- Fo=/2
Fourier number
- Bi1(, Fo)=(, Fo) · /
Biot number
-
thermal diffusivity coefficient
-
plate thickness
-
time
- (, Fo)
heat-liberation coefficient
-
thermal conductivity coefficient
- i
summation index
- Jo
zero order Bessel function of the first kind
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 536–540, September, 1981. 相似文献
12.
We present data on the copper isotope effect (63Cu-65Cu), Cu =-nTc/nmCu, for two isotopic pairs of oxygen-deficient YBa2Cu3O7–, where varies between 0.06 and 0.52. Cu is below 0.01 at =0.06 (fully oxygenated), it takes values between –0.14 and –0.34 in the 60 K plateau. Larger negative values of Cu are observed away from the plateau. The dependence of Cu is similar to that of the pressure effect dnTc/dP. 相似文献
13.
S. I. Moukhin 《Journal of Low Temperature Physics》1979,37(1-2):219-230
For a spin-glass with nonmagnetic defects (n
m
1/3l 1, where n
m is the magnetic impurity concentration and l is the mean free path) an absorption function () is derived. Three ranges of temperature and external magnetic field are considered. In the vicinity of the transition the value of () d is estimated as a function of temperature and field. 相似文献
14.
V. M. Baboshin Yu. A. Buevich A. K. Ivonin I. V. Kirnos B. G. Kukui 《Journal of Engineering Physics and Thermophysics》1984,47(1):821-826
Experiments are described and a model is evaluated for the process of production of superpure hydrogen from mixtures with ammonia and nitrogen by selective diffusion through thin metallic membranes.Notation jH, jC
molar fluxes of hydrogen and ballast gas
- k
effective permeability coefficient (product of hydrogen solubility coefficient times diffusion coefficient, divided by membrane thickness)
-
l, L
coordinate measured along supply channel and maximum value thereof (channel length)
- M
molecular weight of hydrogen
- P
working perimeter of diffusion cell
- p, p
pressure in supply and output channels
- Q, QH
mixture flow rate and hydrogen output for one cell or entire unit
- S
area of working section of supply channel
- v
velocity in output channel
- x, xo
molar fraction of hydrogen in mixture and value thereof at inlet
- z, Z
dimensionless coordinate and length of apparatus
- ,
dimensional and dimensionless hydraulic resistance coefficients
- , *
dimensionless pressure in output channel and value thereof at outlet
-
dimensionless pressure (concentration) of hydrogen in supply channel
-
hydrogen density in output channel
-
relative output
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 100–108, July, 1984. 相似文献
15.
Simultaneous measurements of () and of the molar volume are reported for liquid mixtures of 3He in 4He over the temperature range between 0.5 and 2.5 K. Here is the shear viscosity and is the mass density. In the superfluid phase, the product of the normal components,
n
and
n
, is measured. The mixtures with 3He molefractions 0.30 < X < 0.80 are studied with emphasis on the region near the superfluid transition T
and near the phase-separation curve. Along the latter, they are compared with data by Lai and Kitchens. For X > 0.5, the viscosity singularity near T
becomes a faint peak, which however fades into the temperature-dependent background viscosity as X tends to the tricritical concentration X
t. Likewise, no singularity in is apparent when T
t is approached along the phase separation branches – and +. Furthermore, viscosity data are reported for 3He and compared with previous work. Finally, for dilute mixtures with 0.01 X 0.05, the results for are compared with previous data and with predictions. 相似文献
16.
Jeffrey M. Harris K. Krishana N. P. Ong R. Gagnont L. Taillefer 《Journal of Low Temperature Physics》1996,105(3-4):877-886
The washboard frequency of the moving vortex lattice in untwinned YBa2 Cu3 O6.93 may be observed through mode-locking to an externally applied ac current of frequency ext. The interference between and ext results in jumps in the dc current-voltage characteristics when and ext are harmonically related1. The interference effect disappears in the vortex liquid state. The Hall conductivity xy below Tc in YBCO contains contributions2 from a positive quasiparticle (qp) term (H) and a negative vortex term (1/H). The qp term is surprisingly large well below Tc and implies a large gap anisotropy and a long qp mean free path (mfp). The thermal Hall effect3 xy is closely related to the qp xy; xy is produced by asymmetric scattering of qp by pinned vortices. The qp mfp at H = 0, extracted from xy and extended to low T by xy, increases remarkably from 90 Å at Tc to more than 0.5m at 22 K. 相似文献
17.
J. H. Merkin 《Journal of Engineering Mathematics》1985,19(3):189-201
Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x
and when the (non-dimensional) surface heat flux is –x
are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value 0, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >0, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as 0 and as –1, and the natures of these singularities are discussed. 相似文献
18.
Yu. A. Kirichenko S. M. Kozlov K. V. Rusanov E. G. Tyurina 《Journal of Engineering Physics and Thermophysics》1982,42(1):1-6
The effect of pressure and underheating on the position of the boundary between heat-transfer regimes in liquid helium and hydrogen is investigated.Notation q
heat flux
- p
pressure
- =Ts–T
underheating
- Ts
saturation temperature
- T
temperature of liquid
- T=Twa – T
Ts=Twa – Ts
- Twa
temperature of heat-emitting surface
- A,a, B, b, C
constants
- m, n
indices
- Nu
Nusselt number
- Ra
Rayleigh number
-
thermal conductivity
-
coefficient of cubical expansion
-
kinematic viscosity
- g
acceleration
-
standard deviation
Indices 01
conditions of convection-boiling transition
- 02
conditions of boiling-convection transition
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 5–11, January, 1982. 相似文献
19.
The problem of freezing of pure water in a round pipe is treated with due regard for convection under asymmetric thermal boundary conditions in the absence of motion along the pipe. The problem is solved numerically using the control volume approach, SIMPLER algorithm, and the enthalpy method. Results are obtained for three Grashof (Gr) and six Biot (Bi) numbers: Gr = 1.55 × 106, Bi = 0.305 (0 < ), Bi = 0.044 ( < 2); Gr = 1.24 × 107, Bi = 0.610 (0 < ), Bi = 0.087 ( < 2); Gr = 9.89 × 107, Bi = 1.220 (0 < ), Bi = 0.174 ( < 2). The correctness of calculation of the problem disregarding free-convection flows is analyzed. 相似文献
20.
Based on a theoretical model developed previously by the authors in Part II of this series for a single fibre pull-out test, a methodology for the evaluation of interfacial properties of fibre-matrix composites is presented to determine the interfacial fracture toughness G
c, the friction coefficient , the radial residual clamping stress q
o and the critical bonded fibre length z
max. An important parameter, the stress drop , which is defined as the difference between the maximum debond stress
d
*
and the initial frictional pull-out stress fr, is introduced to characterize the interfacial debonding and fibre pull-out behaviour. The maximum logarithmic stress drop, In(), is obtained when the embedded fibre length L is equal to the critical bonded fibre length z
max. The slope of the In()-L curve for L bigger than z
max is found to be a constant that is related to the interfacial friction coefficient . The effect of fibre anisotropy on fibre debonding and fibre pull-out is also included in this analysis. Published experimental data for several fibre-matrix composites are chosen to evaluate their interfacial properties by using the present methodology.On leave at the Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong. 相似文献