Abstract
Abstract Crack deflection is a potential mechanism for toughening essentially brittle materials. Deflection generally occurs along grain boundaries and is enhanced by particles with high aspect ratios. Si 3 N 4 /SiC ceramic/ceramic composites contain elongated β Si 3 N 4 grains as a major phase and provide a good illustration for this mechanism. As a result, such materials demonstrate a relatively good fracture toughness. It is shown in this study, using transmission electron microscopy (TEM), that transgranular cracks, which develop at low temperatures and/or high deformation rates (present case), may also be deflected by intragranular SiC inclusions. Cracks use the 100 planes and propagate along the 〈100〉 directions of the silicon nitride hexagonal lattice. Further, after large plastic deformations at high temperature, slip defects are observed in silicon nitride grains, with many step-like deviations (‘cross’ slip), and the slip system is found to be [001] {100}.
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