Microstructural characterization and high-temperature strength of hot-pressed silicon nitride ceramics with Lu2O3 additives

• Published in: Philosophical magazine letters Vol. 83; no. 6; pp. 357 - 365
• Main Authors: Guo, Shuqi, Hirosaki, Naoto, Yamamoto, Yoshinobu, Nishimura, Toshiyuki, Kitami, Yoshizo, Mitomo, Mamoru
• Format: Journal Article
• Language: English
• Published: London Taylor & Francis Group 01-06-2003; Taylor & Francis
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; General studies; Technical ceramics; Stress strain relation; Silicon nitride; Experimental study; Inorganic compound; Grain boundary; Bending strength; Lutetium oxides; Hot pressing; Transmission electron microscopy; Transition metal compounds; Sintering; Chemical composition; Microstructure; Ceramic materials; Bending test
• ISSN: 0950-0839; 1362-3036
• DOI: 10.1080/0950083031000119172

The microstructures of two hot-pressed Si
3
N
4
ceramics, with 3.33 and 12.51 wt% Lu
2
O
3
additive, have been characterized using transmission electron microscopy. The microstructures of both samples consisted of elongated β-Si
3
N
4
grains and a secondary phase, contained in pockets surrounded by the grains, with a crystalline or amorphous form. In the 3.33 wt% Lu
2
O
3
-containing Si
3
N
4
ceramic, all the multiple-grain junctions were completely crystalline while, in the 12.51 wt% Lu
2
O
3
-containing Si
3
N
4
ceramic, approximately half the junctions were devitrified. A thin intergranular amorphous film present between the two-grain boundary was common; however, a film-free grain boundary was observed in the 12.51 wt% Lu
2
O
3
sample. The film-free grain boundary was determined to be approximately 35%. Both ceramics fractured in four-point flexure between 1200 and 1600°C. Their high-temperature strength is closely associated with the nature of the grain-boundary phase formed during the sintering process.