Effect of Grain Growth on the Flexural Strength and Fracture Toughness of Gas Pressures Sintered Silicon Nitride

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J. Korean Ceram. Soc. > Volume 33(11); 1996 > Article

Journal of the Korean Ceramic Society 1996;33(11): 1187.

가스압 소결한 질화규소에서 입자성장이 강도와 파괴인성에 주는 영향

최헌진, 이준근, 김영옥¹

KIST 세라믹스부
¹서울시립대학교재료공학과

Effect of Grain Growth on the Flexural Strength and Fracture Toughness of Gas Pressures Sintered Silicon Nitride

ABSTRACT

Silicon nitride containing 2 w/o Y2O3 and 1 w/o Al2O3 as sintering additives was fabricated by gas pressure sintering and the effect of grain growth onthe flexural strength and fracture toughness was investigated. Duplex microstructure consisting of the large grains and the matrix of small grains was obtained by the two step gas pressure sintering : 180$0^{circ}C$ for 2 h in a N2 atmosphere of 2 MPa followed by 190$0^{circ}C$ for 0 to 8 h in a N2 atmosphere of 8 MPa. The average diameter and aspect ratio of the matrix grains were not changed with the second step sintering time, The flexural strength and fracture toughness were dominated by the large grains. The flexural strength was decreased with sintering time due to increasing the size of large grains which was acted as a fracture origin. The fracture toughness was increased with sintering time due to increasing the diameter and aspect ratio of the large grains and then decreased when the sintering was performed more than 4 h due to the transgranu-lar fracture of the large grains which have a diameter of >~2 ${mu}{textrm}{m}$

Key words: Silicon nitride, Duplex microstructure, Grain growth, Flexural strength, Fracture toughness