High temperature dynamic fatigue performance of a hot isostatically pressed silicon nitride

The dynamic fatigue performance of an injection molded, hot-isostatically pressed silicon nitride containing 6 wt.% yttrium oxide as a sintering aid was examined at 1000, 1200, and 1400 °C, in four-point flexure in ambient air and argon. This material was more susceptible to slow crack growth, as reflected by the slopes of the flexure strength vs. stressing rate curves, as the test temperature was increased in both environments. At the same temperature, this material was much more susceptible to slow crack growth in ambient air than in argon. Stress-corrosion cracking (and not creep damage) was the dominant damage mechanism, although the material crept at the slower stressing rates in both environments. Stress-corrosion cracking ultimately caused a reduction in strength.