Polycrystalline mechanical properties

The behavior of polycrystalline materials is often dominated by the boundaries between the crystallites, called grain boundaries. In metals, grain boundaries prevent dislocation motion and reduce the ductility, leading to hard and brittle mechanical properties. Grain boundaries are invariably weaker than the crystal matrix, and... 

Stem, L.A. Kirby, S.H. Durham, W.B. (1998). Polycrystalline Methane Hydrate Synthesis from Superheated Ice, and Low-Temperature Mechanical Properties. Energy and Fuels, 12 (2), 201 -211. 

The mechanical properties of materials are of enormous influence on the way these can be processed. After a molten metal has cooled to a solid, the solid metal is mechanically moulded into the desired form. The way of cooling and the final shape to a large extent determine the properties of the product. By means of a heat treatment it is possible to alter the properties of some metals. In this process the polycrystalline material is converted to a less polycrystalline form and eventually a state is reached which comes close the the ideal state, i.e. the metal is nearlv monocrvstalline (figure 10.10). 

Yashar, P.C. and Barnett, S.A. (1999), Deposition and mechanical properties of polycrystalline Y203/Zr02 superlattices , Journal of Materials Research, 14, 3614— 3622. 

Thin metal Hlms (Pt, Pd) have been used for the adsorption and detection of gases such as H2 and NH3 [138,139]. While the interaction mechanisms for these sensors were not specified, it is well known that H2 dissolves to a significant extent in Pd, with concomitant changes in the density, electrical conductivity, and mechanical properties of the fllm. The H2/Pt interaction as well as the interaction of NHa with both Pd and Pt undoubtedly involves chemisorption on surface sites. Metal thin films deposited by nearly all techniques are polycrystalline chemisorption along grain boundaries can often lead to a response that is considerably larger than predicted from the properties of metal single crystals. 

Ionic conductivity (although somewhat lower) is reasonably isotropic in polycrystalline ceramic materials, which can be fabricated economically with excellent mechanical properties. 

In the past there have been several attempts to investigate the relationship between structure and mechanical properties in polyethylene. It has proved possible to produce samples of the polymer with a single-crystal texture ( ) but they are still polycrystalline and certain ambiguities remain concerning the detailed deformation mechanisms in such samples (9 ). There have also been reports of studies of the deformation of single crystals of polyethylene on extensible substrates (10,11). Because the polymer... 

The mechanical properties of tungsten are only intrinsic as long as highly pure single crystals are Considered. Polycrystalline tungsten, from a technical standpoint, is the most important form and, by far, the biggest amount of the metal used. These properties are also strongly influenced by two main factors ... 

Solute and impurity segregation to grain boundaries in polycrystalline solids is known to affect mechanical properties and engineering performances of these materials. 

As is well known that mechanical properties of chromium are essentially depend on its purity [4], At the same time the grains size decrease to nanocrystalline size in polycrystalline materials leads to increase 3-5 times in hardness and yield point [5], Thus, extremely high values of... 

The discovery of the new high Tc, superconducting ceramics has generated excitement among physicists and material scientists alike. It is important to recognize that these materials are very similar to other advanced ceramics in that they are prepared from oxide powders which are pressed and sintered. They are polycrystalline materials whose electrical, magnetic, and mechanical properties will be critically dependent on their... 

Diamond has been well-known for long for its outstanding mechanical properties like great hardness and low frictional coeffident Therefore, it was self-suggesting to examine the respective characteristics of diamond films as well. Actually the results are found to vary depending on the morphology of the film and, for polycrystalline materials, on the particle size. 

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