Morphology and chemical composition of [gamma]/[gamma]' phases in Re-containing Ni-based single crystal superalloy during two-step aging

The [gamma]/[gamma]' microstructure of a Re-containing Ni-based single crystal super alloy after a two-step aging was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The crystals were grown by the floating zone (FZ) method. Both cuboidal and spherical [gamma]' precipitates were formed after a two-step aging. The size of the cuboidal [gamma]' phases first increased and then decreased with the extension of the second-step aging time. Re, Co and Cr strongly concentrated in the [gamma] phase whereas Ni and Al enriched in the [gamma]' phase. Thermodynamic calculation by JMatPro was performed to explain the experimental observations.