Delayed Failure of Hot Isostatic Pressed Silicon Nitride at High Temperatures
The static fatigue behaviour of three series of HIP Si3N4 materials has been studied. Two series were produced from powder supplied by KemaNord Industrikemi (Ljungaverk, Sweden), one was alloyed with 2.5 w/o Y2O3, and the other one with 2.5 w/o Y2O3 + 1 w/o Al2O3. A third serie, produced from Si3N4 powder supplied by UBE Industries (Tokyo, Japan), was alloyed with 4 w/o Y2O3. Static fatigue testing was performed at temperatures from 1100°C to 1400°C, using stress levels ranging from 20 to 75% of the appropriate fast fracture high temperature strength. The creep rate was found to be significantly higher for the KemaNord material containing alumina. The susceptibility for slow crack growth was also much larger for this material compared to the materials without alumina additions.
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