Influence of microstructural variations on steady state creep and facet stresses in 2-D freely sliding polycrystals

Abstract

At elevated temperatures, creep in polycrystalline aggregates is often accompanied by free grain boundary sliding, which tends to enhance the macroscopic creep rate and the transverse facet stresses. This paper deals with the influence on these phenomena of variations in the microstructure, in terms of variations in the size and shape of grains in an aggregate. Numerical results for two-dimensional cell analyses involving many grains are presented which demonstrate that random microstructural variations relative to an array of regular hexagonal grains invariably lead to an increase of the creep rate enhancement due to sliding. For power-law creeping grains and for the variations considered here, the effects amount to up to a 60% increase. Moreover, it is shown that microstructural variations lead to a wider distribution of transverse facet stress levels with a considerably higher average than for regular hexagonal grains. Both effects are of significance for creep rupture life time estimates.