| A theoretical model is suggested which describes plastic flow in amorphous covalent solids and amorphous intergranular boundaries in nanoceramics. On the basis of computer simulations (M.J. Demkowicz, A.S. Argon // Phys. Rev. Lett. 93 (2004) 025505), it is supposed that plastic flow in these amorphous structures is carried by liquid-like phase nuclei which form and grow in size within solid-like matrix phase. The nuclei suffer plastic shears modeled as glide dislocation loops. Energetics of formation and growth of the nuclei is examined in bulk amorphous silicon, silicon nitride and nanocomposite nc-TiC/a-Si3N4 ceramics. Within the model, it is shown that plastic flow in amorphous covalent solids tends to be localized at high stresses and low temperatures. Also, it is revealed that plastic flow within intergranular amorphous layers of a-Si3N4 in nanocomposite nc-TiC/a-Si3N4 can initiate cracks whose equilibrium and critical (Griffith) lengths depend on grain size and temperature. |
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