The development of microstructures

In the case of optoelectronics, the aim is to utilise light in an analogous role to electrons. The optical equivalents to transistors are photonic crystals. These structures interact with light in controlled and predetermined ways. Many are based on 

Nanostructures exist at many levels, and as the example of opal suggests, many of these have been discovered in nature. For example, typical spider thread (there are many species of spider and many types of thread) is a polymeric material that has remarkable properties, that have been likened to the ability of a fishing net to capture a balhstic missile. These properties result from the nanostructure of the thread, which consists of interleaved crystalline and noncrystalline regions. 

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The development of processing strategies in which the interaction between fluid motion and microstructural conformation can be used for (a) the development of microstructured materials with desired macroscopic properties and (b) active control of the flow itself, as in drag reduction and fluidized bed stabilization. 

The relative magnitudes of the Tg values in the two-phase region should be related to the development of microstructure in mesophase pitch, as discussed earlier. Tg will also be a useful parameter in defining the maximum temperature at which fibres can be oxidized without molecular motion causing some decrease in extent of preferred orientation. 

The development of microstructure is considered in Section 7.4. The broad microstructures of pastes more than about 28 days old are similar to those of C3S pastes. Fig. 7.2 shows a typical backscattered electron image, obtained under conditions maximizing contrast from compositional differences. The following types of region are distinguishable by their differing grey levels and by their compositions determined by X-ray microanalysis. 

Drury, M. R., Humphreys, F. J. (1986). The development of microstructure in Al-5<7o Mg during high temperature deformation. Acta MetalL, 34,2259-71. 

Locat J. 1995. On the development of microstructure in collapsible soil. Genesis and Properties of Collapsible Soils. 1995 93-128. 

Polycrystalline films in a multilayered structure are observed to be more prone to the development of microstructural flaws than glass films during cosintering (53), so it is particularly important to minimize the presence of processing flaws in the polycrystalline layer during forming. When it does not lead to a deterioration in the properties of the multilayered system, the incorporation of a glassy second phase improves the stress relaxation in the polycrystalline film and can serve to alleviate the development of flaws. 

Figure 12.41 Schematic diagram illustrating the development of microstructural texturing during hot pressing.

The usual approach in analyzing complex ceramic—metal interfaces is to characterize experimentally the specific properties of the ceramic—metal interfaces that one wishes to understand and control. In this chapter, brazing of AIN is used as an example. The objective is for one to learn as much as possible about the reactions that occur at the interface in order to control processing and to optimize properties. In turn, one must understand the mechanisms of adhesion and the development of microstructure, recognizing that the information may be particular to the system studied. 

An Y, Holt JJ, Mitchell GR, Vaughan AS (2006) Influence of molecular composition on the development of microstructure from sheared polyethylene melts molecular and lamellar templating. Polymer 47 5643-5656... 

Transmutation processes result in the creation of new isotopes (via (n, y) reactions) or other chemical elements (via (n,o ), (n,p) or (n,P) reactions). In practice, the most important consideration in this context is the formation of atoms of inert gases, especially He (and H), which has been observed in a number of materials. The presence of these gases strongly affects defect interactions during irradiation at elevated temperatures as they readily diffuse at elevated temperatures, are barely soluble in the lattice, and are chemically inert, thus greatly affecting the development of microstructure within the material during irradiation. 

The understanding of phase diagrams for alloy systems is extremely important because there is a strong correlation between microstructnre and mechanical properties, and the development of microstructure of an alloy is related to the characteristics of its phase diagram. In addition, phase diagrams provide valuable information about melting, casting, crystallization, and other phenomena. 

At this point it is instructive to examine the development of microstructure that occurs for isomorphous alloys during solidification. We first treat the situation in which the cooling occurs very slowly, in that phase equilibrium is continuously maintained. 

Figure 9.4 Schematic representation of the development of microstructure during the equilibrium solidification of a 35 wt% Ni-65 wt% Cu alloy.

The development of microstructure in both single- and two-phase alloys typically involves some type of phase transformation—an alteration in the number and/or character of the phases. The first portion of this chapter is devoted to a brief discussion of some of the basic principles relating to transformations involving solid phases. Because most phase transformations do not occur instantaneously, consideration is given to the dependence of reaction progress on time, or the transformation rate. This is followed by a discussion of the development of two-phase microstructures for iron-carbon alloys. Modified phase diagrams are introduced that permit determination of the microstructure that results from a specific heat treatment. Finally, other microconstituents in addition to pearlite are presented and, for each, the mechanical properties are discussed. 

During a phase transformation, an alloy proceeds toward an equilibrium state that is characterized by the phase diagram in terms of the product phases and their compositions and relative amoimts. As Section 10.3 notes, most phase transformations require some finite time to go to completion, and the speed or rate is often important in the relationship between the heat treatment and the development of microstructure. One limitation of phase diagrams is their inabihty to indicate the time period required for the attainment of equilibrium. 

Some of the basic kinetic principles of sohd-state transformations are now extended and applied specifically to iron-carbon alloys in terms of the relationships among heat treatment, the development of microstructure, and mechanical properties. This system has been chosen because it is familiar and because a wide variety of microstructures and mechanical properties is possible for iron-carbon (or steel) alloys. 

In terms of heat treatment and the development of microstructure, what are two major limitations of the iron-iron carbide phase diagram ... 

When considering the development of microstructure we are concerned with heterogeneous equilibrium, I.e. equilibrium involving more than one phase. The free energy, G, of a component phase is defined ly... 

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