Ceramics are assuming an important role for use in power generation. One of the road blocks is a complete characterization of the deformation and life of advanced ceramics at elevated temperatures. Substantial high temperature creep testing has been conducted in recent years. Most commonly, Norton’s law for deformation and the Monkman-Grant relationship for failure have been used to correlate test data.

In this paper, internal variable modeling is discussed as an alternative to Norton’s Law/Monkman-Grant. Through the use of internal variables, micromodeling of the important mechanisms can be extended to the macroscopic behavior. Also, the effects of simultaneous or competing phenomena can be considered. An example is the growth of lenticular cavities on the two grain boundaries of certain silicon nitrides while the grain boundaries are crystallizing. The results of a preliminary internal variable model for HIPed silicon nitride is presented and compared with tensile creep experiments.

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