Microstructure and mechanical properties of silicon nitride with tape cast tri-layer structures

Four kinds of silicon nitride samples with tri-laminate structures were prepared by stacking tapes with aligned β-Si₃N₄ whisker seeds. Three-point flexural strengths of the samples were measured at both room temperature and 1673 K. As the total thickness of the layers with the whisker seeds aligned parallel to tension was increased, the flexural strength was increased at both room temperature and at 1673 K. The flexural strength at 1673 K was more sensitive to orientations of the grains in the surface layer than that at room temperature. Observation of the fracture surface revealed that the grains growing from the neighboring whisker seeds were often broken such that they formed a single one grain. Extensive brittle fracture of the grains without much grain pull-out occurred even at 1673 K for the samples.