Gamma prime coarsening in a nickel base single crystal superalloy

Abstract

The γ′ morphological evolution and coarsening kinetics have been investigated in a nickel base single crystal superalloy during thermal exposure at 900°C. The γ′ precipitates coarsen both in the dendrite arms (DAs) and the interdendritic regions (IRs) with the exposure time. However, an anomalous coarsening behavior has been found, i.e., the average particle size in the DAs is always larger than that in the IRs after exposure for 100h. The cube rate law gives a much better fit for the IRs than for the DAs owing to apparent coalescence phenomenon in the DAs compared to that in the IRs. The particle size distribution (PSD) results indicate that obvious coalescence in the DAs may be partially attributed to the initial size inhomogeneity while γ′ particles always maintain cubic in the IRs during thermal exposure.