Abstract
A dislocation based criterion is proposed for describing the raft formation in single crystals of nickel-based superalloys subject to creep at high temperature. Those of the precipitate faces exhibiting dislocations after the onset of creep are thought to expand by directional coarsening of γ′ precipitates. The proposed criterion predicts correctly the raft morphology for creep along cristallographic directions of high and low symmetry for alloys exhibiting a positive or a negative misfit. A diffusional mechanism based on the effect of creep dislocations on the local γ phase chemical composition is suggested to account for the observed relationship between dislocation activity and directional coarsening of precipitates.
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