Abstract
The flexural strength of yttria-doped sintered silicon nitride was evaluated as a function of temperature (20 to 1300 ‡C in air environment), applied stress and time. Two mechanistic regimes were manifest in the temperature dependence of the fracture stress. A temperature-independent region of fast fracture (catastrophic crack extension) existed up to 900 ‡ C, in which the mode of crack propagation was primarily transgranular. Above 1000 ‡ C, the strength (fracture stress) decreased considerably due to the presence of subcritical or slow crack growth which occurred intergranularly. This material did not show a static oxidation problem in short-term (≤100 h) tests in the low-temperature regime (600 to 1000 ‡ C) as has been observed in other yttria-doped silicon nitrides. Flexural-stress rupture testing in the temperature range 800 to 1200 ‡ C in air indicated the material's susceptibility to time-dependent failure, and outlines safe applied stress levels for a given temperature.
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