Compressive plastic deformation of polycrystalline Si3N4: considerations on the solution-reprecipitacion model and on the cavity-formation model

Compressive creep of silicon nitride has been studied in several commercial and experimental grades of creep-resistant Si3N4. The temperature range wa s 1400-1500 degreesC, and inert atmosphere was used to avoid long-term degr adation of the samples. The creep rates at a given temperature showed more than one order of magnitude of grade to grade variability. Microstructural analysis showed the presence of cavities after deformation. When analyzed b y a classic power-taw equation the creep parameters n=1 for all the grades, while Q varied from 444 to 951 kJ/mol. The activity of diffusional mechani sms is discussed. Alternatively, the results have been analyzed by means of the Luecke-Wiederhorn cavitation model.