Development of Next Generation Ni-base Single Crystal Superalloys Containing Ruthenium

Abstract

A single crystal superalloy with a superiority in creep strength to the fourth generation single crystal (SC) superalloys has been developed. Following the guideline given by our alloy design program, Mo was added to one of our fourth generation SC superalloy, TMS-138, to change its lattice misfit toward larger negative (aγ >aγ′). In a superalloy with larger negative lattice misfit, enhancement of rafting and formation of finer dislocation network at the γ/γ′ interface is expected. Ru was also added to suppress the formation of TCP phases which is expected with the Mo addition. The designed superalloy, TMS-162, was cast to SC bars, solution and aging heat-treated, and tested in terms of creep at 137 MPa and at 1100°C. The temperature capability of the creep rupture strength in the TMS-162 was found to be about 20°C higher than that of our fourth generation SC alloy, TMS-138. It was confirmed by transmission electron microscope observation that the misfit dislocation network generated on the γ/γ′ interface in the rafted structure was finer in the new generation SC alloy, TMS-162, than in the fourth generation SC alloy, TMS-138, as designed. We concluded that the finer dislocation network increases the stress required to for dislocations to cut into γ′ phases and makes the creep strength higher.