Grain boundary engineering of superalloys for aerospace engine applications

Grain Boundary Engineering (GBE) involves microstructural optimization via the strategic application of thermo-mechanical metallurgical processing and fabrication steps that increase the fraction of special, low-energy, and degradation-resistant grain boundaries (i.e., structurally ordered low E grain boundaries) in the microstructure. By elevating the fraction of special grain boundaries in a metal or alloy either in the bulk or in the near-surface region, a commensurate improvement in the material properties is achieved owing to the intrinsic degradation-resistance (corrosion, sliding, cracking) of the "special" grain boundaries. Alloys that can benefit from this treatment include nickel-based superalloys that are used in the hot sections of gas turbine engines. Under increasingly demanding operating conditions, these materials can be vulnerable to grain boundary-related elevated-temperature degradation processes including creep, fatigue, solute segregation, precipitation embrittlement, and intergranular environmental attack. In this study, the benefits of GBE-processing on the reliability and durability of Inconel 718 superalloy are presented and discussed with emphasis on the improvement of its resistance to creep and crack growth.