Effects of Long-Term Aging on the Microstructures and Tensile Properties of Ni-Based Single Crystal Superalloy

The microstructure evolution and the tensile properties of the second generation single crystal superalloy DD6 were investigated after full heat treatment and aging process at 980–1200 °C. The results indicate that the morphological instability occurs at relatively high temperature, and the γ' phase gradually connects and rafts after aged for 800 h at 1050 °C. After aged for 100 h at 1200 °C, the γ/γ' microstructure cubicity gradually becomes weaker and transforms into spherical boundary, accompanied with a few finer matrix phase embedded into strengthening phases. Whereas the dislocation lines are homogeneously distributed in the γ/γ' interface area, and dislocation motions are also strengthened with increasing of aging time and temperature. After aged at 1050 °C for 1000 h, the precipitation phase in the form of blocky appears in the enrichment areas of solution strengthening elements and its brittle characteristics will pile up dislocation motions at lower temperature. The ultimate tensile strength, yield strength and elongation percentage decrease with increasing of aging time, while a fluctuation of contraction area will occur at 760 °C