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991.
Transmission electron microscopy and selected area electron diffraction performances were used to characterise the microstructure of a multicomponent soda-lime silicate glass, the composition of which corresponds to the miscibility gap in the SiO2—Na2O system. It has been stated that phase separation already exists in as prepared specimens, and the Na2O-rich phase occurs in the form of nearly spherical droplets. The microstructure of these glasses was modified by high-temperature annealing in air and hydrogen, by irradiation with soft X- and gamma-irradiation and by mechanical stretching. In this way the quantity, size, shape and distribution of these particles was changed. A variety of induced changes affects the structure-sensitive properties of commercial soda lime silicate glasses, which can be potentially useful for new applications. 相似文献
992.
Nanostructured thin films were deposited by excimer laser ablation of silver targets in controlled atmospheres of He and Ar. The film structural properties were investigated by means of scanning electron microscope and transmission electron microscope imaging. The film growth mechanism was identified as the result of coalescence of nanometric clusters formed during plume flight. Cluster formation involves plume confinement as a consequence of the increased collisional rate among plasma species. Fast photography imaging of the laser-generated silver plasma allowed to identify plasma confinement, shock wave formation and plasma stopping. 相似文献
993.
994.
John Gavin Christopher Jennison 《Journal of computational and graphical statistics》2013,22(2):182-201
Abstract In statistical image reconstruction, data are often recorded on a regular grid of squares, known as pixels, and the reconstructed image is defined on the same pixel grid. Thus, the reconstruction of a continuous planar image is piecewise constant on pixels, and boundaries in the image consist of horizontal and vertical edges lying between pixels. This approximation to the true boundary can result in a loss of information that may be quite noticeable for small objects, only a few pixels in size. Increasing the resolution of the sensor may not be a practical alternative. If some prior assumptions are made about the true image, however, reconstruction to a greater accuracy than that of the recording sensor's pixel grid is possible. We adopt a Bayesian approach, incorporating prior information about the true image in a stochastic model that attaches higher probability to images with shorter total edge length. In reconstructions, pixels may be of a single color or split between two colors. The model is illustrated using both real and simulated data. 相似文献
995.
Microstructural study of as-grown Ti4AlN3 MAX phase has been performed by transmission electron microscopy. Dislocation walls, dislocation nucleation sites and stacking faults are described. In particular, diffraction contrast analysis combined with high-resolution images give a new insight into the nature of the stacking faults: contrarily to what is usually postulated, it is shown that the stacking faults possess a shear component in the basal plane. The stacking faults are created by the insertion of MX layers in the lattice via diffusion mechanisms. Their possible role on the deformation mechanism of MAX phases is discussed. 相似文献
996.
The deformation around a 500-nm deep Berkovich indent in a large grained Fe sample has been studied using high resolution electron back scatter diffraction (EBSD). EBSD patterns were obtained in a two-dimensional map around the indent on the free surface. A cross-correlation-based analysis of small shifts in many sub-regions of the EBSD patterns was used to determine the variation of elastic strain and lattice rotations across the map at a sensitivity of ~±10?4. Elastic strains were smaller than lattice rotations, with radial strains found to be compressive and hoop strains tensile as expected. Several analyses based on Nye's dislocation tensor were used to estimate the distribution of geometrically necessary dislocations (GNDs) around the indent. The results obtained using different assumed dislocation geometries, optimisation routines and different contributions from the measured lattice rotation and strain fields are compared. Our favoured approach is to seek a combination of GND types which support the six measurable (of a possible nine) gradients of the lattice rotations after correction for the 10 measurable elastic strain gradients, and minimise the total GND line energy using an L1 optimisation method. A lower bound estimate for the noise on the GND density determination is ~±1012 m?2 for a 200-nm step size, and near the indent densities as high as 1015 m?2 were measured. For comparison, a Hough-based analysis of the EBSD patterns has a much higher noise level of ~±1014m?2 for the GND density. 相似文献
997.
998.
We report on the glass-forming ability and devitrification behavior of Zr60Cu30Al10, Zr60Cu25Al10Fe5 and Zr62.5Cu22.5Al10Fe5 bulk glass-forming alloys on heating. The effect of Fe addition on the structure of Zr–Al–Cu alloys is also discussed. Crystallization kinetics and structural changes in the glassy alloys were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The results indicate that good glass-formers, such as Zr62.5Cu22.5Al10Fe5, are located somewhat beyond the equilibrium eutectic point. Possible phase separation in the supercooled liquid on heating and electron beam-induced in situ crystallization are observed and discussed. 相似文献
999.
The transformation mechanism of hexagonal delta phase from the disordered bcc gamma phase has not been reported before in the Zr-rich U–Zr alloy system. With the help of X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM analyses it was shown that the gamma to delta conversion takes place by the lattice collapse mechanism of omega transformation. It was also ascertained that a higher aging temperature or time promotes the growth of all four variants of the delta phase within a parent gamma grain. In addition, ab initio electronic structure calculations showed that the bcc to hexagonal transformation, involving partial ordering of the parent bcc phase followed by (111) plane collapse, is energetically favorable. 相似文献
1000.
Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi0.5Na0.5)TiO3–2.6%BaTiO3–12.0% (Bi0.5K0.5)TiO3 (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8?mol% Nb2O5 were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R?=?56.6: 28.4: 15.0?wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C?+?T)-phase mixture core. The T- and R-twin boundaries are determined to {111}T and {110}R, respectively, and the fault vector for T-APB to R?=?1/2?110]T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained. 相似文献