Improving the Stress Rupture and Creep of Silicon Nitride.
AVCO SYSTEMS DIV WILMINGTON MA
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Yttria-stabilized zirconium oxide Zyttrite additions to purified silicon nitride were found to improve the high temperature strength, stress rupture and creep properties of hot pressed samples very markedly. Room temperature bend strengths, however, of four compositions evaluated were each about one-third lower that Norton Companys NC-132 silicon nitride composition. This difference decreased with increasing temperature until at 1200 C, there was reasonable equivalence between most of the zyttrite containing compositions and NC-132 in terms of short time bend strength measurements. At 1370 C, the 10 and 20 wt. containing zyttrite compositions showed bend strengths as much as double the NC-132 material. Bend stress rupture fesults for 10 and 20 wt. zyttrite containing compositions showed a strong stress sensitivity at the 276 MNm2 40 Kpsi level above 1200 C. Creep in bending measurements showed that at 1370 C and 1450 C, zyttrite containing compositions exhibited creep rates that were about 2 orders of magnitude lower that NC-132 material samples. All compositions appeared to follow deformation kinetics related to a visco-elastic mechanism, i.e., glassy phase diffusional creep or grain boundary sliding. Author
- Ceramics, Refractories and Glass