Mechanical Performance of Various INCONEL^® 740/740H Alloy Compositions for Use in A-USC Castings

The use of Ni-based superalloys as structural components of advanced ultra-supercritical steam and CO₂ turbines is becoming necessary due to the increasing performance requirements of future power plant designs. Although numerous Ni-based superalloys can respond to the demanding mechanical performance, very few present a combination of high-strength and creep resistance while maintaining good ductility and weldability. Furthermore, the improved performance is often associated with wrought alloys while the fabrication of large castings is the primary target for those applications. With the comparatively lower mechanical properties of cast alloys, new designs based on compositional changes are necessary to allow for the use of Ni-based superalloys in A-USC castings. This lack of performance is primarily associated with the large and inhomogeneous grain size as well as elemental segregation and other casting anomalies. This investigation presents various alloys with compositions within the range of INCONEL^® 740/740H designed to overcome the issues associated with the use of Ni-based superalloys in A-USC castings. Modifications to the chemistry were based on thermodynamic simulations and experimental results. Particular attention was given to reactive element additions, element partitioning, γʹ precipitate phase promoting elements and grain boundary carbides. The effects of the various compositional changes on the tensile and creep properties of INCONEL^® 740/740H will be discussed.