Model of diffusion coarsening of the raft structure in single crystals of nickel-base superalloys

The creep resistance of nickel-base superalloy single crystals is determined by the stability of the raft structure that forms at elevated temperatures under applied tensile stresses. This paper proposes a mechanism of stabilization and coarsening of the raft structure, based on the analysis of the balance between the elastic energy and the γ-γ′ interphase energy. An abrupt coarsening of the raft structure, observed at the final stage of a creep test, is caused by unlimited diffusion-controlled growth of hole-like macrodefects in γ′ layers of the structure. Based on this model, numerical estimations of the coarsening kinetics have been made, using structural and energetic characteristics of a commercial superalloy. The results are consistent with typical creep test results for nickel-base superalloys.