Effect of Low-Angle Boundaries on the Microstructures and Tensile Properties of the Third-Generation Single-Crystal Superalloy DD9

The microstructure of low-angle boundaries (LABs) of thethird-generation single-crystal superalloy DD9 and its effect on the tensile properties at 1100 degrees C were investigated. Double seed crystals techniques were used to obtain the specimens of DD9 alloy with LABs. The results show thatthe as-cast LABs of DD9 alloy are composed of strip-like and bulk gamma' phases with gamma matrix, while no gamma' phases were foundat the LABs after the heat treatment. The LABs had little effect on the tensile strength of DD9 alloy, but hadan obvious effect on the tensile plasticity, and the fracture surfaces of tensile-ruptured DD9 alloy with LABs of 3.7 degrees similar to 11.4 degrees exhibited intergranular fracture features at 1100 degrees C.