Preparation and properties of SiAlON ceramics by gel casting and pressureless sintering

J. Li, C. F. Zhang, W. H. Zhang, School of Metallurgy and Environment, Central South University, Changsha, China. R. M. Yin, College of Metallurgical Engineering, Hunan University of Technology, Zhuzhou, China. Corresponding author: J. Li, e-mail: 133501020@csu.edu.cn. This study employed a low-toxicity N, N-dimethylacrylamide/N, N-methylene acrylamide (DMAA /MBAM) gel system to near net shape SiAlON ceramics from aqueous slurries with a solid loading of 40 wt.% Si3N4, Al2O3, Y2O3, AlN, and Ce2O3 powder mixtures. The green bodies were sintered by oneand three-step pressureless sintering. Results showed that green bodies had a homogeneous microstructure with a high density of 1,9 g/cm3 and high flexural strength of 28,6 Mpa. Equiaxed α-SiAlON was prepared by one-step pressureless sintering, whereas β-Si4Al2O2N6 with an elongated morphology was fabricated by three-step pressureless sintering. Therefore, a lowtemperature heat preservation stage reduces the nucleation rate, which is favorable for the development of elongated β-SiAlON grains.