Direct measurement of residual stresses and their effects on the microstructure and mechanical properties of heat-treated Si3N4 ceramics II: With CeO2 as a single additive
✍ Scribed by Gang Feng Guo; Jianbao Li; Xiang Yang Kong; Hong Lin; Long Liang; Mingsheng He; Liu Yang; Jiang Wu; Bai Cui
- Publisher
- Elsevier Science
- Year
- 2007
- Tongue
- English
- Weight
- 855 KB
- Volume
- 55
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
The heat treatment of silicon nitride ceramics with only CeO 2 as a sintering additive was carried out at different temperatures. Large residual stress was induced only by the non-relaxed volume changes and not by the relaxed volume changes (i.e. the crystallized phases with cavities or microcracks). The fact that the liquid formation temperature of the Si-Ce-O-N system ($1470 °C) is much lower than that of the Si-Yb-O-N system ($1650 °C) is the reason why the residual stress is comparable almost to each other in CeO 2 -doped Si 3 N 4 , but increases steadily with heat-treatment temperature in Yb 2 O 3 -doped Si 3 N 4 . The large residual stress and the induced cavities and microcracks are the dominant factors for the reduction in room-temperature strength of the heat-treated samples. The defects in b-Si 3 N 4 grains of heat-treated samples were caused by the large residual stress, and may lead to the reduction of both room-and high-temperature strengths. These results significantly extends our previous study (Guo GF, Li JB,