Abstract
High-temperature creep rupture of polycrystalline materials involves a number of physical mechanisms, such as the nucleation and diffusive growth of grain boundary cavities and grain boundary sliding, which act at different length scales in the material. This paper uses a micromechanical model to explore how random variations in the microstructure of the material affect its lifetime. The model involves a chain of size scale transitions and two size scales are considered in particular: the size scale of individual cavities and the scale of aggregates of grains. Emphasis is put on geometrical variations in the microstructure, i.e. random variations in size and shape of grains in an aggregate. The role of grain boundary sliding, and the competition between creep flow and grain boundary diffusion are highlighted. Wherever possible, regimes are indicated where such microstructural variations can be safely neglected or where they are critical in determining the lifetime.
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