Materials science and engineering a-structural materials properties microstructure and processing vol:202 issue:1-2 pages:157-171
Quantitative texture data have been measured by X-ray diffraction on Bi2223 powders, cold-pressed to different pellet strains. Comparisons of Bi2223 aggregates and geological phyllosilicate fabrics show that both materials, characterized by a platy grain morphology, exhibit a similar texture development. This texture development is best explained by grain-shape-induced rotation processes, which are eventually limited by grain-on-grain impingements of the relatively rigid particles. With increasing compaction, the degree of preferred orientation of platelets levels off at (001) pole densities of five to six multiples of a random distribution (m.r.d.). By contrast, intracrystalline slip mechanisms would produce much stronger textures at equivalent strains. From analogy with phyllosilicate fabrics it is suggested that textures in Bi2223 compacts could be improved by hot-pressing rather than cold-pressing to alleviate incompatibilities at grain boundaries. Pole densities of 20 m.r.d. have been produced in experiments and observed in naturally deformed argillaceous rocks. Such processing would also improve grain contacts. Of secondary importance is the size of the rigid, equiaxed, second-phase particles, which needs to be reduced to obtain stronger crystallite alignment.