Creep Mechanisms in Commercial Grades of Silicon Nitride

Creep Mechanisms in Commercial Grades of Silicon Nitride 

Ceramics Science and Tedmoit Volume Z Properties. Edited by Ralf Riedel and I-Wel Chen Copyri t 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31156-9 

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I 13 Creep Mechanisms in Commercial Grades of Silicon Nitride... 

In this section, the mechanisms of deformation that are active in two-phase materials such as silicon nitride are summarized. The grains are assumed to be completely surrounded by the secondary phase conservative creep deformation of the material -that is, no change in volume - may then occur either as a consequence of deformation of the secondary phase, or by deformation of the silicon nitride particles themselves. If the volume is not conserved - as when cavities are formed - then other mechanisms can occur. Hence, the types of deformation that can occur in the above-mentioned commercial grades of silicon nitride will be briefly discussed. 

During recent decades, extensive efforts have been made to control the grain boundary phase and to improve the heat resistance of silicon nitride, and this has led to significant improvements in high-temperature mechanical reliability. For example, some grades of commercial silicon nitrides have shown excellent creep resistance, even at temperatures above 1400 °C (45, 46]. Subsequent XRD analyses of these materials have revealed Lu2Si207 and Lu4Si2N207 as secondary phases. 

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