YANG Zhou ¹, LI Hongtao ², ZHANG Chunyan ¹, TIAN Zhongqing ¹, CAO Liangliang ¹, HUANG Fuxiang ¹, MENG Fancheng ¹
(1. School of Materials Science & Engineering, Chongqing University of Technology, Chongqing 400054, China; 2. Xingxin Areospace Advanced Materials (Shanghai) Co. Ltd, Shanghai 200333, China)

Abstract: Yb₂O₃ and Al₂O₃ are used as sintering aids to study the effects of single-step and two-step sintering process on microstructure and mechanical properties of Si₃N₄ ceramics. Single-step sintering for a long time can be used to reduce internal pores of the sample, but abnormal growth of β-Si₃N₄ grains is present, thus deteriorating mechanical properties to a certain degree. Relative density of the Si₃N₄ ceramics prepared by using two-step sintering could reach 98.25%, while the internal and external structures are uniform and no abnormal grain growth is observed. The sample has hardness of1478Hv, room temperature flexural strength of 832 MPa, high temperature (900 ℃) flexural strength of 646 MPa and fracture toughness of 7.3 MPa·m^1/2, while it also has excellent comprehensive mechanical properties. Therefore, the two-step sintering is an effective method to prepare Si₃N₄ ceramics with high density and high comprehensive mechanical properties.
Key words: silicon nitride; gas pressure; two-step sintering; mechanic properties; microstructure