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1.
The influences of stabilizers on - and -Al2O3 phase formations in Li2O(MgO)-Na2O-Al2O3 systems were investigated. When stabilized with 4MgCO3Mg(OH)25H2O, most of the -Al2O3 phase formed below 1200°C and further - to -Al2O3 transformation with an increase of temperature was not observed. On the other hand, when stabilized with Li2CO3,-Al2O3 formation occurred by two steps. First, -Al2O3 was partly formed below 1200°C, and, second, noticeable transformation from -Al2O3 to -Al2O3 occurred at higher temperature ranges. It was shown that transient eutectic liquid in the Li2O-Na2O-Al2O3 system promoted the - to -Al2O3 transformation at higher temperatures. Uniform distribution of both Mg2+ and Li+ stabilizing ions enhanced -Al2O3 formation at low temperatures. In the Li-stabilized systems, however, homogeneous distribution of Li+ ions hindered both the formation of transient eutectic liquid and the second - to -Al2O3 phase transformation at high temperatures.  相似文献   

2.
The precipitate structure and matrix deformation were examined in a commercial Cu-11.55 at %-Be-0.23 at %-Co alloy by quantitative X-ray diffraction techniques. A model is proposed that is consistent with early electron microscopy results by Bonfield and Edwards [J. Mater. Sci. 9 (1974) 398] and recent advances by Khachaturyan and Laughlin [Acta Metall. Mater. 38 (1990) 1823]. Agreement was found for a precipitate model consisting of highly deformed versions of the equilibrium -phase. This is in accord with earlier results for and precipitates and is further generalized to include the GP zone for this alloy. Two states of deformation are required, i.e. one relatable to and the GP zone, with a second relatable to a continuous deformation which describes the rotation of the precipitate. The matrix becomes and remains severely deformed prior to and through the hardness maximum. Bragg-like matrix peaks become partitioned into three components: quasilines, static diffuse scattering and a residual Bragg peak. The so-called arrowhead scattering should be re-examined as a generalized form of Laue scattering, which includes a difference between the square of the scattering amplitudes for the precipitate and the matrix that it replaces.  相似文献   

3.
The effect of 2 F() shape dependence on several physical properties of superconductors is studied at various values of the strong coupling indexT c/ ln . Our results indicate that the degree of shape dependence of each property is sensitive to the value ofT c/ ln . Generally, for the region we examine, 0.25T c/ ln 1.3, the dependence on shape is found to be higher than in the conventional strong coupling regimeT c/ ln 0.2. However, with the exception of the mass enhancement parameter , the amount of shape dependence does not increase steadily withT c/ ln and there appears to be regions of maximum shape sensitivity.  相似文献   

4.
The objective of this paper is to develop the load separation method for evaluating the pl and pl CMOD plastic factors used in the J estimation approach based on load versus displacement records. Appropriate forms for the geometry and deformation functions have been suggested from the EPRI Handbook solutions to produce the separable form for the load. The obtained functions are applied to evaluate the pl and pl CMOD plastic factors for center cracked tension specimen. The present load separation method gave results which are somewhat different from the estimated values of pl given in the literature. For shallow cracks, the pl and CMOD pl plastic factors show considerable variation with crack size and the strain hardening exponent. For a deeply cracked CCT specimen, the CMOD pl factor tends to the pl factor and equals approximately unity. Abbreviations: CCT – center cracked specimen; CMOD – Crack Mouth Opening Displacement; EPRI – Electric Power Research Institute; FEM – Finite Element Method; LLD – Load Line Displacement.  相似文献   

5.
Ductile L20-type wires and+L12-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. y, f and p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in y and f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.  相似文献   

6.
The present work is a study of a series of Ti-7.5Mo-xCr alloys with the focus on the effect of chromium content on the structure and mechanical properties of the alloys. Experimental results show that low hardness, strength and modulus binary Ti-7.5Mo alloy is comprised primarily of fine, acicular martensitic phase. When 1 wt % Cr is added, a small amount of phase is retained. With 2 wt % or more chromium added, the entire alloy becomes equi-axed phase with bcc crystal structure. The average grain size decreases with Cr content. When the alloy contains about 2–4 wt % Cr, a metastable phase is present. In Ti-7.5Mo-2Cr alloy appears the highest intensity accompanied with high microhardness, bending strength and modulus. The -induced embrittling effect is most profound in Ti-7.5Mo-2Cr alloy that exhibits a terrace type fracture surface covered with numerous micron-sized dimples. The alloys with higher Cr contents show normal ductile type fractography with much larger deformation dimples. The present results indicate that Ti-7.5Mo-(4–6)Cr alloys seem to be potential candidates for implant application.  相似文献   

7.
The theory of autopoiesis, i.e., self-referentiality in the operation of the system, provides us with a production rule for change in the structure of the network. Using information theory, a model system is developed to study the relative likelihood of dynamic transitions: various senses of irreversibility (emergence, and path dependency) are disinguished. A test for path dependency is applied to two sets of empirical data which supposedly reflect historical discontinuities: the budget of theFraunhofer Gesellschaft, and the citation network among AIDS research related journals. The model for the interaction between self-referential developments and goal-referential boundary conditions is further specified, using the example of technological trajectories and selection environments.  相似文献   

8.
The crystallization of Li,Mg-aluminosilicate solid solutions in lithium-bearing zircon and/or cordierite-based ceramics is studied as a function of firing temperature up to 1500 C. X-ray diffraction, electron microprobe analysis and microscopic techniques were used for the identification of the studied phases. Keatite solid solution (ss) coexists with zircon and/or cordierite at temperatures up to 1300 C. On raising the temperature to 1400–1500 C,-quartz ss is crystallized at the expense of both keatite and cordierite with the precipitation of spinel on cooling from such high temperatures. In bodies containing zircon, the dissociation of zircon at 1400–1500 C into its constituents epitaxially enhances the nucleation of-quartz ss crystallization.  相似文献   

9.
The corrosion-induced material loss in crude oil carrying steel pipelines was originally studied by making use of the backscatter X-ray technique. The steel thickness can be determined by studying the density profile of the backscatter intensity vs. the depth location of a voxel. There are, however, some practical limitations to the above method, and a new method for evaluating steel thickness, namely, the transcatter technique is described. This technique uses the intensity of the beam which is transmitted by the pipe wall and subsequently scattered by the hydrocarbon inside the pipeline. The thickness is evaluated using three techniques, namely, the sequential technique, the dual angle technique, and the reference technique. Of the three techniques, the sequential technique has been studied in detail. The mathematical equations and experimental results related to the transcatter technique show that the thickness can be measured with an accuracy of better than 10% for a nominal steel thickness of 8 mm with a measurement time of several minutes.  相似文献   

10.
We propose a 1-t1-2 pulse-NMR experiment to detect the spin-diffusion anisotropy, =D-D, in degenerate spin-polarized3He-4He mixtures, where D and dare the transverse and longitudinal spin diffusion coefficients. In such an experiment the nonlinearity of the dynamics produces multiple spin echoes (MSE). At the 3He concentration x3 4% the spinrotation parameter vanishes (M 0), so that the nonlinearity of the equations of motion is entirely due to the anisotropy. In this situation, detection of MSE amounts to observation of D. For slight anisotropy, i.e. D/D 0.25, we use a perturbation scheme similiar to that developed by Einzel et al. (in that case, for small M and small demagnetizing field) to calculate the second and third echo heights. For larger anisotropy we numerically calculate the echo heights. We find that for D/D = 0.5 the heights are 2 % of the first echo, and should be detectable. The (1, 2) tip-angle dependence of the D echoes is different from that of the M and demagnetization echoes, and furthermore, they occur at right angles to these echoes (in spin space). Thus, even when small spin-rotation and demagnetization effects are present, the 1-t1-2 experiment provides a sensitive means of detecting the anisotropy.  相似文献   

11.
The diffusible hydrogen in Cr-Mo steels are observed with autoradiography technique. Specimens with the diffusible hydrogen are prepared by an electrochemical cathodic charging method and those without the diffusible hydrogen by annealing at 373 K after charging hydrogen. TEM autoradiographs suggests, by the developed silver grains, that the hydrogen trapping sites are the grain boundary and internal interface of ferrite-cementite and ferrite-lath structure. After keeping the sample at 373 K, the silver grains disappeared. Most of hydrogen trapping sites release almost all the hydrogen at 373 K. It is clear that these sites of high-strength steels supplies the diffusible hydrogen. Hydrogen absorption characteristics of quench hardening tempering Cr-Mo steels have been evaluated by thermal desorption spectrometry (TDS). From tritium electron microscopic autoradiography and TDS analysis, the lower temperature (360 K–370 K) peaks show the diffusing hydrogen which is released a few days. The diffusible hydrogen from trapping sites such as the internal interface of ferrite-cementite or ferrite-lath structure are distinguished to the diffusing hydrogen.  相似文献   

12.
The birefringence topography of a Bi12GeO20 single crystal which has a strong natural optical activity is presented. The natural optical activity of the crystal may be completely compensated by reflection polarised light microscopy so that the birefringence images of dislocations and subboundaries are observed. The Burgers' vectors of dislocations were found to be of the types 1/2 1 1 1, 1 0 0 and 1 1 0 and dislocations which form subboundaries are also of these types.  相似文献   

13.
The coarsening behavior of precipitates with a uniform size distribution and with a bimodal size distribution in a mechanically alloyed ODS Ni-base superalloy were investigated to clarify the effect of elastic interaction energy on the coarsening behavior of precipitates. The coarsening rate decreased with increasing size of precipitates with a uniform size distribution, contrary to the classical LSW theory, and the coarsening behavior of precipitates with a bimodal size distribution exhibited Ostwald ripening in which the larger precipitates grow at the expense of smaller precipitates. The driving force for coarsening of precipitates was analyzed based on the two-particle model, considering the effect of elastic interaction energy in addition to the effect of interfacial energy. The contribution of elastic interaction energy on the total energy was found to increase with increasing size of precipitates, and the decelerated coarsening of precipitates was attributed to the decrease in the driving force for coarsening with increasing size of precipitates.  相似文献   

14.
Using a push-rod dilatometer, we measured between 76 and 390 K the thermal expansion of a particle-reinforced-composite wrought plate obtained by powdermetallurgy methods. The particles, 30% by volume, consisted of monocrystals of -SiC with sizes near 10 m. The matrix consisted of a 6061 aluminum alloy with original particle sizes near 20 m. We found the perpendicular thermal expansivity, 3, higher by 26% than the in-plane thermal expansivity, 1-2. These values differ from a rule-of-mixture prediction by –3 and –23%, respectively. All three i, components lie outside the Rosen-Hashin bounds. Levin's isotropic model agrees within 10% with the 1-2-3 average. Both the anisotropy and the bounds violation result from microstructural nonhomogeneity arising from processing. Rosen and Hashin's transverse-isotropicsymmetry relationships account approximately for these effects by introducing the anisotropic elastic constants. Using neutron diffraction, we determined that the SiC particles are textureless.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.  相似文献   

15.
Far from the lambda transition the critical flow of superfluid 4 He through a small orifice is determined by thermal nucleation of quantized vortices. Between 300 mK and 2 K linearly decreasing critical flow velocity has been observed earlier. As the temperature approaches T the size of the vortex core increases and becomes comparable to that of the orifice. We report here measurements of the critical mass current in this temperature range. An array of 24 3×0.17 m holes in parallel with a macroscopic parallel path and flexible-diaphragm Helmholtz resonator have been used. The temperature range explored was from 80 mK to 20 K below T. Preliminary analysis of the data shows that for a reduced temperature t=(T–T)/T1·10 4 the critical current scales approximately as t 1.25 . Closer to T the critical phase difference across the array becomes comparable to 2 and the results have to be analyzed in terms of Josephson effect. The superfluid density has been measured at the same time as the critical current.  相似文献   

16.
Nucleate boiling     
The study deals with the effect of the surface conditions on the nucleate boiling curve. A relation is proposed which describes the complete nucleate boiling curve.Notation q thermal flux - q* thermal flux at which the liquid boils after one-phase convection - qc thermal flux during one-phase convection - qcr1, qcr2 first and the second critical thermal flux - T saturation temperature - T superheat of the heating surface relative to the saturation temperature - T* superheat prior to boiling of the liquid after one-phase convection - Tcr1 superheat during the first boiling crisis - Tcr3min minimum superheat at which the third boiling crisis can occur - P pressure - Pcr critical pressure - heat transfer coefficient during nucleate boiling - Rcr radius of a critical vapor forming nucleus - coefficient of surface tension - r latent heat of evaporation - thermal conductivity of the liquid - kinematic viscosity of the liquid - , densities of the liquid and the vapor - g gravitational constant - k Boltzmann constant - N Avogadro number - h Planck's constant Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 3, pp. 394–401, March, 1981.  相似文献   

17.
The influence of the temperature on the signaltonoise ratio in the optoelectronic recirculation circuit of an informationmeasuring system with an avalanche photodetector has been analyzed. It has been established that the temperature dependence of the pulse power of an injection laser has an influence on the width and position of the maximum in the temperature dependence of at the output of the photodetector in a recirculationtype system. The methods of maintenance of the avalanche multiplication factor of a photodetector at a given level have been proposed and their efficiency has been estimated.  相似文献   

18.
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   

19.
Several crystallographically non-equivalent structures of sodium disilicate are known to exist. Successive heat treatments of the sodium disilicate glasses show -, -, - and -Na2Si2O5 as the devitrification products, depending upon the nature of heat treatment. At higher temperatures and for longer treatment times, only -Na2Si2O5 is observed but for intermediate temperature and time, and forms of the polymorphs are produced. For shorter times, all the polymorphs are formed. The results are verified using magic angle spinning nuclear magnetic resonance as well as X-ray diffraction. A way of estimating the unknown Si–O–Si mean bond angle of the polymorphs, with the help of the known values of the angles, is also presented.  相似文献   

20.
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   

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