Mechanical property anisotropy in textured silicon nitride

Several prior investigations have documented the deformation-induced rotation of ;Fracture toughness anisotropy is observed for these materials and is primarily due to crack deflection along oriented grain boundaries. Modeling is used to predict crack path in anisotropic materials by equating an orientation dependent fracture toughness with crack deflection mechanisms. Results from this modeling approach are in reasonable agreement with experimental observations of crack deflection in Vickers indentation and three-point bending, however, this approach only considers mode I of a mixed mode loading.;Hertzian contact tests were conducted on fine and coarse grain materials. A definite trend from cone cracking behavior to a shear microcracking mechanism was observed with increasing grain size. However, from observation, cone cracking initiates before the microcracking at all grain sizes, but is impeded in cases where the grain size is finite relative to the contact diameter. Direct measurement of damage associated with indentations was obtained through surface profilometry, allowing for analysis of contact behavior. Hertzian contacts in textured materials result in non-circular cone cracking behavior. This is attributed to the observed fracture toughness anisotropy. Implications regarding enhanced contact properties were demonstrated through sliding ball wear tests which showed dramatic effects of orientation on crack initiation.