Tensile creep performance of a developmental in-situ reinforced silicon nitride

The evaluation was done between 1300 and 1425 C in ambient air. Minimum creep rate was evaluated vs tensile stress and temperature, and measured tensile creep performances of two different specimen geometries (buttonhead and dogbone - machined from same billet) were compared. This Si nitride exhibited comparable or better creep resistance than other Si nitrides described in the literature. Measured creep response of the material and lifetime were observed to be geometry dependent; the smaller cross-sectioned dogbone samples exhibited faster creep rates and shorter lives, presumably due to faster oxidation-induced damage in this geometry. The tensile creep rates and lifetimes were found to be well represented by the Monkman- Grant relation between 1350 and 1425 C, with some evidence suggesting stratification of the data for the 1300 C tests and a change in dominant failure mode between 1300 and 1350 C. Lastly, values of the temperature-compensated stress exponent and activation energy for tensile creep were found to decrease by 80 and 75% in compression, respectively, illustrating anisotropic creep behavior in this Si nitride