Tensile Creep in an in Situ Reinforced Silicon Nitride

The tensile creep of an in situ reinforced silicon nitride is described in terms of the rheological behavior of the thin intergranular film present in this liquid-phase sintered silicon nitride. The high stress exponents and apparent activation energies (at constant stress) can be explained assuming non-Newtonian flow behavior of the film during grain boundary sliding. Time-to-failure is related to the minimum creep rate, even for samples which fail by slow crack growth. In addition, the primary creep region and the relaxation effects observed on unloading are described in terms of grain boundary sliding modified by the presence of a grain boundary phase with a lower elastic modulus than silicon nitride.