Si_3N_4及びSiCウイスカー/Si_3N_4ホットプレス体の破壊靱性異方性の評価法依存性

概要

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In our previous report on hot-pressed Si_3N_4 monolith and SiC whisker (SiC(w))/Si_3N_4 composite compacts, it wa clarifed that the fracture tougness (K_<IC>) measured by CSF method (the shape of pre-crack is semi-ellipse) were nearly the same for VV and PV specimens (VV specimen ; the tensile surface and longitudinal direction of the specimen are both vertical to hot-press direction (HD), PV specimen ; the tensile surface and longitudinal direction are parallel and vertical to HD, respectively) ; anisotropy of K_<IC> was not observed. This phenomenon was considered to be due to the fact that the average angel (θ) of the intersection or cutting direction of propagating crack to the longer axes of acicular Si_3N_4 grains and/or SiC(w) around the precrack is nearly the same (about 68°) for both specimens. Therefore, when SEPB method is used as a K_<IC> evaluating method where the shape of the pre-crack in the specimen is rectangle, VV and PV specimens are presumed to show different K_<IC> values, because the θ is different for both specimens (about 90° and 45°, respectively). In this study, this presumption was experimentally investigated. The result was in accordance with the presumption, and the fracture morphology (intergranular or transgranular fracture of acicular Si_3N_4 grain and/or SiC(w)) near the pre-crack supported the experimental results.
1995-04-01