HIGH-TEMPERATURE DYNAMIC FATIGUE PERFORMANCE OF A HOT ISOSTATICALLY PRESSED SILICON-NITRIDE

The dynamic fatigue performance of an injection molded, hot-isostatica lly pressed silicon nitride containing 6 wt.% yttrium oxide as a sinte ring aid was examined at 1000, 1200, and 1400 degrees 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 streng th vs. stressing rate curves, as the test temperature was increased in both environments. At the same temperature, this material was much mo re susceptible to slow crack growth in ambient air than in argon. Stre ss-corrosion cracking (and not creep damage) was the dominant damage m echanism, although the material crept at the slower stressing rates in both environments. Stress-corrosion cracking ultimately caused a redu ction in strength.