Layered microstructures mechanical properties

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

Accurate control of microstructure on nanometric scale makes it possible to control magnetic and mechanical properties to a hitherto unattainable degree. In particular, magnetic nanostructures have recently become the subject of an increasing number of experimental and theoretical studies. The materials are made of alternating layers, around 10 A thick, of magnetic (e.g., cobalt) and nonmagnetic metals (e.g., copper). 

In this chapter, we describe the synthesis and characterisation of the microstructure and properties of layered-graded alumina-matrix composites through liquid infiltration. This approach is relatively simple and offers excellent control over the depth of the graded layer. The presence of a graded dispersion of reinforced particles in the alumina matrix has a profound influence on the physical and mechanical properties of the composites. An overview of the infiltration kinetics and the use of the infiltration process as a new philosophy for tailoring novel graded ceramic systems are also presented. 

In the literature, there has been no report about production of functionally graded SiAION ceramics by tape casting. The main advantage of this method with respect to others is that continuous change in composition, microstructure and mechanical properties can be obtained by stacking controlled layer thicknesses of different tape compositions. 

The purpose of the present study is to establish the technique for fabricating two kinds of FGMs, i.e. Zr02/Ni with 10 layers and Zr02/Al203 systems with 5 layers, by using the underwater-shock consolidation technique mentioned above and to investigate microstructures and thermo-mechanical properties. 

The morphology of the metal-ceramic interface depends upon the type of interaction that has occurred. If only physical interaction has occurred, the structure of the metal and ceramic is unchanged. However, if a chanical reaction occurs, the morphology is affected depending upon whether solid-solid or solid-liquid reactions occur and if new interfacial phases are formed. The formation of new interfacial phases alters not only the microstructure but also the physical and mechanical properties. These interfacial phases or reaction product layers are a consequence of the reactions needed to cause wetting of the ceramic. One can consider the reaction product layers as chemical bridges between the metal and ceramic. 

Films and substrates are held together by very short range forces, the bonds between one atom and the next. The mechanical properties of the films, including their intrinsic stress, are ultimately determined by these same bonds and their interaction with the microstructure. Their behaviour at surfaces can be greatly modified by minute quantities of impurity and they can be blocked completely by one molecular layer of contaminant. Adsorption is a particularly important process in thin films which must also be understood on an atomic scale. 

TABLE 1. Selected mechanical properties and area of application of some glass-containing composite systems with interpenetrating, graded or layered microstructure and hybrid composites. (The fracture strength values quoted are flexural strength data unless otherwise stated). 

In general, compared with solid state sintering, liquid phase sintering allows easy control of microstructure and reduction in processing cost, but degrades some important properties, for example, mechanical properties. In contrast, many specific products utilize properties of the grain boundary phase and, hence, need to be sintered in the presence of a liquid phase. Zinc oxide varistors and SrTiOs based boundary layer capacitors are two examples. In these cases, the composition and amount of liquid phase are of prime importance in controUing the sintered microstructure and properties. 

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