SUMMARY

Nickel superalloys exhibit rich diversity of microstructures with different size and shape distributions of γ' precipitates embedded within γ parent matrix. The γ-γ' microstructure is controlled by cooling rates and governs the mechanical properties. Naturally, there is a need for better understanding of process-structure-property (PSP) relationships in nickel superalloys. More specifically, there is considerable interest in PSP linkages at the grain-scale where the mechanical response is determined by the γ' precipitates without the influence of grain boundaries; this is because the dominant strengthening mechanism in nickel superalloys is precipitate hardening. However, there are two main challenges: 1) there is a lack of reliable digital protocols for characterizing and quantifying microstructure at the grain scale, and 2) mechanical tests at the grain scale (e.g., micro-tensile or micro-pillar) are incredibly difficult and low-throughput. In this study, a Jominy end-quench approach will be used to make a sample prototype library with controlled gradients in the cooling rates. Automated digital protocols will be developed and used to characterize and quantify the local microstructures in the Jominy specimen. Spherical nanoindentation will be used to collect local mechanical responses at the scale of individual grains, whose lattice orientations will be measured by electron backscatter diffraction. The nanoindentation results, along with the crystal orientations, will be used to extract intrinsic grain-scale properties, i.e., the single crystal elastic constants and the CRSS values. All the collected data will be used to establish the PSP linkage at the grain-scale.