Strength and dynamic fatigue of silicon nitride at intermediate temperatures

A. A. Wereszczak, H. T. Lin, T. P. Kirkland, M. J. Andrews, S. K. Lee

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

The flexure strength distributions and dynamic fatigue of GS44, NT551, and NT154 silicon nitrides were determined at intermediate temperatures (≤850°C) in ambient air. GS44 and NT551 were fabricated by gas pressure sintering and had a larger volume fraction of secondary phase than the hot-isostatically pressed NT154. The inert characteristic strength for the GS44 and NT551 decreased with temperature while that for the NT154 was statistically independent of temperature. The slow crack growth exponent, N, for the GS44 and NT551 exhibited a 70-80% decrease between 700 and 850°C while the strength of NT154 was comparatively independent of stressing rate at 850°C. Associated with those changes in mechanical performances, the coefficient of thermal expansion (CTE) for the GS44 and NT551 sharply increased between 700 and 850°C while that for the NT154 did not. Although the observed change in CTE (and the temperature range where it occurred) did not have any obvious correlation with a change in inert strength at these intermediate temperatures, its presence was an indicator of a threshold temperature where dynamic fatigue resistance was compromised if the temperature exceeded it. The change in material state (and the associated temperature region for which it occurs) is linked to the equilibrium state of the secondary phase in the silicon nitride.

Original languageEnglish
Pages (from-to)2669-2684
Number of pages16
JournalJournal of Materials Science
Volume37
Issue number13
DOIs
StatePublished - Jul 1 2002
Externally publishedYes

Funding

Research was sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the Heavy Vehicle Propulsion System Materials Program, under Contract DE-AC05-00OR22725, managed by UT-Battelle, LLC. The authors wish to thank G. Gilde and J. Swab for reviewing the manuscript and for their helpful comments, and C. J. Rawn for performing the XRD experiments.

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