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731.
Mami Tanabe Junichi Tatami Motoyuki Iijima Tsukaho Yahagi Takuma Takahashi Hiromi Nakano Tatsuki Ohji 《Journal of the American Ceramic Society》2023,106(9):5431-5439
In this study, the yield stress and fracture strength of -Si3N4 single crystals were directly measured by bending tests of microcantilever beam specimens that were prepared by a focused ion beam method. The -Si3N4 single crystals were plastically deformed at room temperature under high bending stress, and the yield stress depended on the crystal orientation. Transmission electron microscopy observation of the specimens after bending tests indicates that the plastic deformation resulted from dislocations in the primary slip system <0001>, and the critical resolved shear stress of this slip system determined from the yield stress was 1.34 GPa. The fracture strength of -Si3N4 single crystals ranged approximately up to 20 GPa, depending on the crystal orientation as with the yield stress. The fracture behavior of -Si3N4 single crystals was discussed in terms of the accumulation of dislocations. 相似文献
732.
Yuki Nakashima You Zhou Keisuke Tanabe Souhei Arima Teruhisa Okuno Kiyoshi Hirao Tatsuki Ohji Manabu Fukushima 《International Journal of Applied Ceramic Technology》2023,20(6):3376-3384
We prepared sintered reaction-bonded silicon nitride ceramics by using yttria and magnesia as sintering additives and evaluated the effects of nitrogen pressure (0.1–1.0 MPa) on their microstructure, bending strength, fracture toughness, and thermal conductivity. The ratio of β phase in the nitrided compacts varied with the pressure and increased with increasing it. Since many β grains in the nitrided compacts were formed and interlocked each other with a stable three-dimensional structure which restricted the shrinkage during the sintering procedure, many pores remained in the sintered body. Under the middle pressure (0.3–0.5 MPa), the grains grew large because the number of formed nuclei was small. On the other hand, under the high pressures (0.8–1.0 MPa), the grains were relatively fine and uniform because of a large number of nuclei. Since the porosity and grain length depended on the nitridation mechanism, which was affected by the nitrogen pressure, the properties largely varied accordingly. The nitridation at 0.1 MPa gave the best properties in this study. 相似文献