Direct measurement of residual stresses and their effects on the microstructure and mechanical properties of heat-treated Si sub(3)N sub(4) ceramics II: With CeO sub(2) as a single additive

• Published in: Acta materialia Vol. 55; no. 9; pp. 3245 - 3251
• Main Authors: Guo, G F, Li, J, Kong, X Y, Lin, H, Liang, L, He, M, Yang, L, Wu, J, Cui, B
• Format: Journal Article
• Language: English
• Published: 01.05.2007
• Subjects: Additives; Ceramics; Heat treatment; Microcracks; Reduction; Residual stress; Silicon nitride; Sintering
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2007.01.023

The heat treatment of silicon nitride ceramics with only CeO sub(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 super(o)C) is much lower than that of the Si-Yb-O-N system (~1650 super(o)C) is the reason why the residual stress is comparable almost to each other in CeO sub(2)-doped Si sub(3)N sub(4), but increases steadily with heat-treatment temperature in Yb sub(2)O sub(3)-doped Si sub(3)N sub(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 sub(3)N sub(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, Yang XZ, Lin H, Liang L, He MS, Tong XG, Yang J. Acta Mater 2006; 54:2311) on heat-treated Si sub(3)N sub(4) ceramics with only Yb sub(2)O sub(3) (one of the heavier lanthanide oxides) as a sintering additive.