Abstract: The γ/γ' microstructural evolution in a nickel based single crystal superalloy during load-free thermal exposure at 900?°C has been further investigated in this paper. The growth characteristics of γ′ precipitates were discussed in detail. The generation of interfacial dislocations would accelerate the rate of coalescence in the dendrite arms. The average sizes of precipitates were used to compare interface with diffusion controlled growth mechanism and no mechanism seems obviously dominant, although the square rate law gives slightly better fit. The coarsening behavior may be controlled by diffusion through the ragged interface between the γ′ precipitate and the γ matrix.

Key words: Single crystal superalloy, Coarsening, Interfacial dislocations, Rate controlling mechanism