Strength and Lattice Defects of Ceramics

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The aim of this research project is to promote the co-operative research activities on the strength of ceramics among the authorities in the various fields, and to achieve profound understandings about the strenght and mechanical properties of ceramics from the view points of lattice defects.The results obtained by this project are as follows: (1) Hardness and brittleness are th general properties of ceramic materials. They are attributed to high peierls stress and small number of slip systems, which are well understood by the crystal geometrical property (2) Strength at high temperatures of SiC, ZrO_2 and other ceramic single crystals were examined systematically, and the deformation mechanisms in them are understood on the basis of disiocation theory. (3) Direct observation technique of dislocations in lonic crystals using light scattering was estabiished and its resolution was improved greatly. (4) Plasticity of semi-conducting compounds was also investigated and photo-plstic effects was accounted for by a new model. (5) Grain bounderies in ceramics were observed by iattice images using high resolution electron microscopes and am amorphous layer was found at the boundery in some ceramics.These resuits provide good guides to improve the mechanical properties of ceramic materials.