Atomic arrangement and formation of planar defects in the μ phase of Ni-base single crystal superalloys

The internal characteristics of the μ phase in Ni-base single crystal superalloys aged at 1100 °C for 1000 h were investigated via spherical aberration-corrected transmission electron microscopy. There were a large number of planar defects on the (001) plane at the growth tip of the μ phase. HAADF-STEM results show that these planar defects were mainly of two types. 1) A twin structure with a mirror plane of the middle atomic planes of the Zr₄Al₃ sheet, which was generated by shearing of atoms in the MgCu₂ sheet along the [1-10] direction. 2) A mirror-symmetrical stacking fault of two Zr₄Al₃ sheets, which was formed by the pulling out of a single MgCu₂ sheet. The planar defects were mainly caused by coordination of the distortions of the μ phase and the matrix. Segregation of Mo, Cr, and Re elements occurred near stacking faults, rather than twin structures.