Time-Temperature Effects in Nitride and Carbide Ceramics

Abstract

High-performance ceramics based on the nitrides and carbides of silicon are being actively evaluated in a large number of heat engine and industrial heat exchanger demonstration programs (1–4). In most of these applications the ceramic components will be exposed to high temperatures, in oxidizing environments, for times ranging from a few thousand to several tens of thousands of hours. For successful application, it is essential that the designer have a full understanding of the time, temperature, and stress dependence of the strength (and/or retained strength after environmental exposure) for these materials. Unfortunately, in the 1975–1977 time period when the preliminary design studies for many of today’s engine demonstration programs were initiated, the available data on silicon nitride and carbide ceramics were very sparse. Recognizing the need for a more extensive data base in this important area, the U. S. Department of Energy funded our laboratory and others to address the problem. This paper presents the methodology used and some of the principal results obtained by our laboratory during the past four years. More detailed results are presented in references 5 through 8.