Ni-Based Superalloys Utilizing Thermodynamically Driven Design Framework and Multiscale Characterization

Superalloys are inherently complex alloys to design due to their multicomponent nature; designing alloys to take advantage of the newly discovered Local Phase Transformation (LPT) strengthening creates constraints on alloy composition beyond the conventional considerations for polycrystalline, precipitate-strengthened microstructures. The basis for design is precipitation of chi/eta on superlattice stacking faults and microtwins while remaining thermodynamically inaccessible to form in bulk. This approach to LPT strengthening has now been demonstrated by optimizing eta-LPT in an empirically designed alloy, NA1, the performance of which is shown here by testing [001] oriented single crystals at several conditions. Computationally designed alloy, NA6, in polycrystalline form, was shown to perform similarly to single crystalline NA1 at 760 degrees C 552 MPa and outperform single crystal CMSX-4 as well as all LPT-strengthened polycrystalline alloys at this temperature. The deformation substructure of NA6 was investigated via HR-STEM, showing both eta-LPT at SESF and chi-LPT at microtwins. Compositions of these LPT were elucidated using atomic resolution energy dispersive X-ray spectroscopy and compared to LPT compositions in relevant alloys and discussed considering recent studies on fault propagation velocities.