J. Korean Ceram. Soc. > Volume 49(4); 2012 > Article
 Journal of the Korean Ceramic Society 2012;49(4): 318. doi: https://doi.org/10.4191/kcers.2012.49.4.318
 Sintered-reaction Bonded Silicon Nitride Densified by a Gas Pressure Sintering Process - Effects of Rare Earth Oxide Sintering Additives Sea-Hoon Lee, Jae-Woong Ko, Young-Jo Park, Hai-Doo Kim, Hua-Tay Lin1, Paul Becher1 Engineering Ceramics Research Group, Korea Institute of Materials Science1Materials Science and Technology Division, Oak Ridge National Laboratory ABSTRACT Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, $Lu_2O_3-SiO_2$ (US), $La_2O_3$-MgO (AM) and $Y_2O_3-Al_2O_3$ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the $La_2O_3$-MgO system. Since the $Lu_2O_3-SiO_2$ system has the highest melting temperature, full densification could not be achieved after sintering at $1950^{circ}C$. However, the system had a reasonably high bending strength of 527 MPa at $1200^{circ}C$ in air and a high fracture toughness of 9.2 $MPa{cdot}m^{1/2}$. The $Y_2O_3-Al_2O_3$ system had the highest room temperature bending strength of 1.2 GPa. Key words: $Si_3N_4$, RBSN, Rare earth oxide, Strength, Toughness
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