Size effect of raw Si powder on microstructures and mechanical properties of RBSN and GPSed-RBSN bodies

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 333; no. 1; pp. 306 - 313
• Main Authors: Lee, Byong-Taek, Yoo, Jeong-Ho, Kim, Hai-Doo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2002; Elsevier
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Gas pressure sintering; Microstructures; Reaction-bonded Si 3N 4; Silicon nitride; Structural ceramics; Technical ceramics; Gas pressure sintering; Microstructures; Reaction-bonded Si 3N 4; Silicon nitride; Reaction sintering; Hot pressing; Silicon Nitrides; Size effect; Mechanical properties; Silicon; Manufacturing; Experimental study; Microstructure; Powder; Non oxide ceramics; Structural ceramic
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(01)01855-X

Size effect of raw Si powder on microstructures and mechanical properties of reaction-bonded Si 3N 4 (RBSN) and of GPSed-RBSN bodies was investigated using Si powder of 2 and 7 μm in average size. The percent nitridation of RBSN body at 1410 °C using 2 μm Si powder was 80.5%, which was lower than that of using 7 μm Si powder (94.2%). In the GPSed-RBSN body sintered at 1850 °C for 3.5 h using 7 μm Si powder, many large, rod-like Si 3N 4 grains were formed relative to the specimen using 2 μm Si powder. This was caused by the heterogeneous distribution of liquid phase as increasing the size of raw Si powder. The fracture strength and fracture toughness of GPSed-RBSN body using 7 μm Si powder were, respectively, 865 MPa and 6.5 MPa m 1/2, which were higher than those of using 2 μm Si powder with 633 MPa and 4.8 MPa m 1/2. The main reason for the increase in mechanical properties of GPSed-RBSN body using 7 μm Si powder was due to the formation of large, rod-like Si 3N 4 grains, which promoted the remarkable crack bridging and crack deflection on the fracture surfaces.