Microstructure discontinuities

The second misconception involves the perception of what constitutes a defect. A defect is not simply a visually observable discontinuity such as a hole, lap, or seam in a component. Defects, from a failure-analysis standpoint, may also be such things as a high residual stress that may lead to cracking or unfavorable microstructures that can lead to either... 

Foam generated in porous media consists of a gas (or a liquid) dispersed in a second interconnected wetting liquid phase, usually an aqueous surfactant solution (1). Figure 1 shows a micrograph of foam flowing in a two-dimensional etched-glass porous medium micromodel (replicated from a Kuparuk sandstone, Prudhoe Bay, Alaska (2)). Observe that the dispersion microstructure is not that of bulk foam. Rather discontinuous... 

Ceramic oxide fibres, both continuous and discontinuous, have been commercially available since the 1970s, and processing and microstructure control are very important in obtaining the desired properties. Among the desirable characteristics in any ceramic fibre for structural applications are ... 

In the development of functionally graded materials, there are two approaches. One is to eliminate the boundary of laminated-type composites, thereby eliminating discontinuities in the properties at the boundary. The other option is to make non-uniform distributions of dispersoids in a homogeneous composite, thus creating multiple functions within the material.2 Therefore, continuous variation in composition, microstructure and so on, results in change in properties as a function of position in the component.6... 

Flexible foams are three-dimensional agglomerations of gas bubbles separated from each other by thin sections of polyurethanes and polyureas. The microstructures observed in TDI- and MDI-based flexible foams are different. In TDI foams monodentate urea segments form after 40% conversion, followed by a bidentate urea phase, which is insoluble in the soft segment. As the foam cures, annealing of the precipitated discontinuous urea phase... 

Freeze-fracture TEM combined with nuclear magnetic resonance and quasielastic light scattering was used to study the microstructure of surfactant-water systems and dynamics of o/w and bicontinuous ME systems [41], The authors reported a rather abrupt transition from a discontinuous droplet (o/w) to bicontinuous (oil-and-water) microstructure occurring at low surfactant concentration, close to a three-phase region in the constructed phase diagram of pentaethylene glycol dodecyl ether, water, and octane [41],... 

Phase I work revealed that a sufficient condition for obtaining spectra without the Christiansen eflFect distortion was that the deposited film has no areas bare of polymer. When such a continuous film was obtained, other microstructural features and even polymer type were of secondary importance and were possibly even unimportant in obtaining good quality spectra. It was possible to obtain undistorted spectra from discontinuous films. However, particle size range of the deposit appeared critical to the results. The diversities of polymer morphologies possible and their sensitivity to operating conditions meant that tailoring particle size would be very difficult. Deposition control to ensure continuous films appeared as a much more attainable objective and was pursued in Phase II. 

The above features of a sheared colloidal crystal appear to be similar in both BCC and FCC structures. However, there are differences in details, and perhaps even within a given symmetry the flow behavior might vary with particle concentration or charge density. For example, Chen et al. (1994) have shown that between the strained crystal and sliding-layer microstructures there can be a polycrystalline structure, the formation of which produces a discontinuous drop in shear stress (see Fig. 6-33). Ackerson and coworkers gave a detailed description of the fascinating shear-induced microstructures of these systems (Ackerson and Clark 1984 Ackerson et al. 1986 Chen et al. 1992, 1994). 

In terms of the process time control, CVD can be divided into three categories, namely continuous, discontinuous and pulsed CVD (P-CVD). Discontinuous CVD is used in most CVD processes, whereas continuous CVD is extensively used for fibre coating and high-volume production of semiconductor devices. In order to improve the coating thickness uniformity and its microstructure, P-CVD is commonly used. 

Figure 3 shows the results of EDX analyses of the two systems. Both the back electron images in (a) and Ka-line images of constitutional elements clearly indicate that the continuous compositional changes were achieved in each system. It is concluded that the FGM produced by the underwater-shock consolidation has fully densified microstructure ever3 here in an overall cross section without any discontinuity and defects. 

Key words Titanium in-situ composites, discontinuous reinforcement, silicide reinforcement, boride reinforcement, mixed silicide-boride reinforcement, ductile reinforcement, microstructure, a -phase, (3-phase, mechanical properties, fracture mechanisms. 

Key words Titanium discontinuous composites, microstructure, mechanical properties, plastic deformation. 

The titanium-based composites with discontinuous reinforcement are attractive materials for a wide range of applications because of their high specific strength and stiffness and good fracture-related properties. Mechanical behavior of these materials depends strongly on both composition and microstructure of matrix and type, size and volume fraction of reinforcing phase. Hot plastic deformation is a powerful tool enhancing mechanical properties of titanium alloys. 

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