Local textures

Transmission electron microscopes (TEM) with their variants (scanning transmission microscopes, analytical microscopes, high-resolution microscopes, high-voltage microscopes) are now crucial tools in the study of materials crystal defects of all kinds, radiation damage, ofif-stoichiometric compounds, features of atomic order, polyphase microstructures, stages in phase transformations, orientation relationships between phases, recrystallisation, local textures, compositions of phases... there is no end to the features that are today studied by TEM. Newbury and Williams (2000) have surveyed the place of the electron microscope as the materials characterisation tool of the millennium . 

The DCG bands near the source, for the sample tested at the low stress of 17.2 MPa, are shown in greater detail in Fig. 41 a. The bands, with a spacing of the order of 100-200 pm, increase in size as the crack extends inward and they run continuously from one surface to another. These, and the gradations in void size and local texture across the width of each band, are characteristic of DCG bands At high magnifica-... 

T.W. Nelson, B. Hunsaker, and D.P. Field, Local Texture Characterization of Friction Stir Welds in IKX) Aluminum, Proceedings of the First International Conference on Friction Stir Welding, June 14—16, 1999 (Thousand Oaks, CA), TWI, paper on CD... 

The trend in this field of texture analysis is now to combine information on global textures (obtained from statistical diffraction data) and local textures (obtained from individual orientation measurements in electron microscopy). This allows the determination of the ODFs as well as functions which describe the orientation relationships between the grains. Such studies will very likely improve the understanding of the behavior of polycrystalline materials and will therefore lead to the optimization of their properties. 

This phenomenon (see the report of Merino, these lectures) has been modeled using equations of pressure solution coupled to the transport of solute species along intergrain boundaries [ 6, ] The central approach was to consider any given crystal to evolve in an average environment specified by the local texture. Consider a crystal of ijineral i of volume L (r,t) and located in the vicinity of point r L is taken to evolve according to... 

Henequen. Agavefourcroydes grows ia Mexico where it was first cultivated by the Mayans ia the Yucatan (Yucatan Sisal). The plant produces for 20—30 years. The lower bottom leaves, which are up to 2 m long and 10—15 cm wide, are cut, machine decorticated, and cleaned. Henequen fibers are white to yellowish red and are inferior to sisal ia strength, cleanliness, texture, and length, the other grading criteria. Henequen is grown for local use ia Cuba (Cuban Sisal) and El Salvador. Twiae, small ropes, coarse mgs, and sacks are made commercially from henequen. 

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. 

Where Jo and S are the current density of the primary beam and the area of the irradiated sample, Z is the wave length, Ohki the structure factor amplitude, Q the volume cell, Z a factor that takes the microstructure of sample into account (Zm - for a mosaic single crystalline film, Zt - for a texture film), t is the sample thickness, dhu the interplanar spacing, a represents the mean angular distribution of the microcrystallites in the film, p is a multiplicity factor (accounts for the number of reflections of coincidence), R is a horizontal coordinate of a particular reflection in DP from textures and (p is the tilt angle of the sample. In the case of polycrystalline films, a local intensity is usually measured and the corresponding relation is ... 

Evidence from drill core and microstructure studies indicate that euhedral, zoned arsenopyrite grains tend to be clustered, and mantled by pyrite (Fig. 4), and their distribution is structurally controlled. These textures are interpreted to represent pressure solution as the main deformation mechanism during Di. This interpretation is supported by serrated pyrite boundaries (Fig. 4) and pyrite-bearing veins. However, locally unstrained euhedral pyrite porphyroblasts overprint Di and D2 structures, implying a late-stage post-D2 growth (Fig. 4). 

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