As-fired strength of sintered silicon nitride ceramics

• Published in: Ceramics international Vol. 26; no. 2; pp. 197 - 202
• Main Authors: Tseng, Wenjea J., Kita, Hideki
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-03-2000; Elsevier Science
• Subjects: Applied sciences; As-fired strength; Building materials. Ceramics. Glasses; C. Fracture; Ceramic industries; Chemical industry and chemicals; D. Silicon nitride; Defect size density; Exact sciences and technology; Structural ceramics; Technical ceramics; As-fired strength; Defect size density; D. Silicon nitride; C. Fracture; Bending strength; Fracture mechanics; Silicon Nitrides; Mechanical properties; Experimental study; Microstructure; Modeling; Non oxide ceramics; Structural ceramic; Surface structure
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/S0272-8842(99)00040-1

An increased machined, bulk strength is seen to lead to an improved as-fired strength. Silicon nitride with an as-fired strength as high as 750 MPa can be obtained, sufficient for most structural applications. Microstructural examinations reveal that the reduction of surface and subsurface pores (or equivalent, may be treated as cracks) both in size and occurrence frequency is the primary reason for the strength increase observed. A linear elastic fracture mechanics model correlates the as-fired and bulk strength properties, and predicts that subsurface flaws located in a reasonably deep site underneath the surface would dominate the flexural strength if their length exceeds 2.3–2.8 times of the length of surface defects. The subsurface flaws very close to the surface are the most damaging and should be avoided by process optimizations.