The study of superalloys and their processing has extensively correlated to the development of aerospace industry. The technology of single crystal in superalloy is regarded as a crucial factor for the promotion of the engine efficiency and performance. The objectives of this paper are to study the room temperature and 899℃ tensile and 760℃/735 MPa creep properties of single crystal and polycrystal cast Mar-M247 superalloy, and to explore the factors responsible for its hgh temperature brittleness. The present results show that the yield and tensile strength of single crystal are identical to those of polycrystal at both room temperature and 899℃. However, elongation of single crystal is apparently greater than polycrystal (room temperature elongation of single crystal is 2 to 3 times greater, and about 4 times at 899℃). Creep life and rupture elongation of single crystal tested under 760℃/735 MPa are larger than polycrystal (creep life of single crystal is 7 times larger than polycrystal, elongation is 8 to 10 times greater). Single crystal has an obvious 3-stage creepprocedure, however, polycrystal is fractured during 2nd stage of creep. Steady state creep rate in single crystal is approximately same with the polycrystal. The results of fractogaphic analysis show that the fracture mode of polycrystal is a typical intergranular fracture, and the fracture originating at grain boundary is the controlling factor leading to lower creep life and elongation. Efforts associated with enhancing the strength and ductility of grain boundary in Mar-M247 superalloy should be made to improve the reliability and safety of Mar-M247 superalloy operated at high temperature.
Mar-M247 superalloy Creep Elongation