Hot deformation characteristics of a polycrystalline γ-γ′-δ ternary eutectic Ni-base superalloy

Nickel-base superalloys possess an unparalleled combination of mechanical and physical properties for elevated temperature applications and are likely to remain the first choice for structural components in turbine engine applications in the future. In order to keep pace with increasingly demanding design requirements associated with advanced gas turbine technologies, the properties of Ni-base superalloys can be greatly enhanced via thermo-mechanical and/or compositional changes. Recent studies have revealed that ternary eutectic γ-γ′-δ Ni-base superalloys exhibit promising high temperature mechanical properties that may potentially be superior to state-of-the-art polycrystalline Ni-base superalloys that are currently used in advanced gas turbines. As the properties of this novel class of alloys are largely dependent on microstructural strengthening mechanisms, both the composition and thermo-mechanical processing parameters need to be optimized concurrently. Deformation at temperatures and strain rates between 1040-1140 °C and 0.1-0.001/s resulted in a transition of dominant deformation mechanisms from dislocation based plasticity to grain boundary rotation and sliding. The governing deformation mechanism was found to influence the alignment of δ phase precipitates and the degree of anisotropy that occurs during hot deformation of γ-γ′-δ Ni-base superalloys. Coupling high deformation temperatures with low strain rates promotes grain boundary sliding and rotation leading to less internal cavitation damage and a more isotropic microstructure.