常圧焼結アルミナ平滑材の回転曲げ疲労挙動に及ぼす粒径の影響

抄録

A rotary bending test was carried out on sintered Al₂O₃ at room temperature to study the effect of grain size on the fatigue behavior. The plain specimens with three kinds of grain size were prepared by controlling the sintering temperature. The fatigue test was performed within the range of 10⁴ to 10⁹ stress-cycles using an Ono's rotary bending fatigue testing machine (3420rpm). The test results were compared with the static bending strength measured by the non-rotating fatigue machine. The fractured surfaces after the two tests were also examined by SEM. It became clear that the fatigue strength of the finer grain material was higher than that of the larger grain one. The life of each material increased remarkably as the stress amplitude decreased, and the knee seemed to exist at a cyclic number more than 10⁸. The ratio of the assumed fatigue limit to the static bending strength decreased as the grain size increased. Each S-N curve, including the static strength, could be represented by a straight line up to about 10⁸ stress-cycles and could be expressed by the formula, σⁿN=constant. The exponent n for the finer grain material was higher than that for the larger grain one. It was considered that the fatigue crack growth behavior was different due to the grain size. Mirrors were not revealed clearly on the fractured surfaces and microscopic observations on the fractured surface of the finer grain material were similar to those of the larger grain one. The fracture features after both fatigue and static tests could not be distinguished, and the fatigue fractured morphology could not be found.