Effect of Sintering Variables on the Microstructure and Mechanical Properties of the Gas Pressure Sintered <TEX>$Si_3N_4$</TEX>

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J. Korean Ceram. Soc. > Volume 31(2); 1994 > Article

Journal of the Korean Ceramic Society 1994;31(2): 129.

$Si_3N_4$ 가스압 소결체의 미세조직과 기계적 성질에 미치는 공정변수의 영향

박동수, 김해두, 정중희¹

한국기계연구원 요업재료실
¹주식회사 신서

Effect of Sintering Variables on the Microstructure and Mechanical Properties of the Gas Pressure Sintered $Si_3N_4$

ABSTRACT

Si3N4 with 6w/o Y2O3 and 1.5w/o Al2O3 has been gas pressure sintered and its densification behavior and the effect of the sintering variables on the microstructure and mechanical properties were investigated. Densification rate was higher at temperature below 1775$^{circ}C$ and between 187$0^{circ}C$ and 195$0^{circ}C$ than between 1775$^{circ}C$ and 187$0^{circ}C$. The faster densification at temperature between 187$0^{circ}C$ and 195$0^{circ}C$ was thought to be due to the increased amount of liquid phase resulting from the increased amount of Si3N4 dissolving in the liquid. $beta$-Si3N4 and Y-disilicate at temperatures below 1775$^{circ}C$, and only $beta$-Si3N4 at 187$0^{circ}C$ and above were detected by XRD analysis. Three different two-step schedules were employed to obtain sintered body with above 99% theoretical density and to investigate the effect of the sintering variables on the density, the microstructure and the mechanical properties of the sintered body. The sintered density did not change with the heating rate, and the microstructure became coarser as the temperature increased. The strength decreased with the width of $beta$-Si3N4 grain, while the fracture toughness increased with the square root of it. A ceramic cutting tool made of the sintered body showed an uniform flank wear after the cutting test.