Improved creep properties of a Ni-based single crystal superalloy by optimized solid solution treatments

This work investigates the effects of solid solution treatment procedures on microstructures and creep properties of a second-generation Ni-based single crystal superalloy. The microstructure features vary with the adjustment of solid solution treatments, including segregation degree and volume fraction, size, and density of H-pores. With the reduction of element segregation, the volume fraction, size and density of H-pores all increase. After the microstructure becomes completely homogenized, the volume fraction of H-pores remains constant, while the size of H-pores still increases, corresponding to the decreasing density. A bimodal relationship between full cycle creep life and solid solution treatment was observed, with two peaks appearing in the creep life. The two maximum creep lives under 1100 °C and 137 MPa conditions are 186 h and 192 h, with a maximum increase of 67 % compared to the sample after initial heat treatment. The segregation degree affects the precipitation of TCP phases and the H-pore features affect the formation of creep cavities during creep. The coupling effects of these two factors are the reason for the two peaks in the creep life.