Optimizing Local Phase Transformation in Ni-Based Superalloys Utilizing Thermodynamically Driven Design Framework and Multiscale Characterization

SuperalloysSuperalloys are inherently complex alloys to designDesign due to their multicomponent nature; designing alloys to take advantage of the newly discovered Local Phase TransformationLocal phase transformation (LPT) strengthening creates constraints on alloy composition beyond the conventional considerations for polycrystalline, precipitatePrecipitates-strengthened microstructuresMicrostructure. The basis for designDesign is precipitationPrecipitation of χ/η on superlattice stacking faultsStacking faults and microtwinsMicrotwin while remaining thermodynamically inaccessible to form in bulk. This approach to LPT strengthening has now been demonstrated by optimizing η-LPT in an empirically designed alloy, NA1, the performance of which is shown here by testing [001] oriented single crystalsSingle crystal at several conditions. Computationally designed alloy, NA6, in polycrystalline form, was shown to perform similarly to single crystalline NA1 at 760 °C 552 MPa and outperform single crystalSingle crystal CMSX-4CMSX-4 as well as all LPT-strengthened polycrystalline alloys at this temperature. The deformation substructure of NA6 was investigated via HR-STEM, showing both η-LPT at SESFSuperlattice Extrinsic Stacking Faults (SESF) and χ-LPT at microtwinsMicrotwin. 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.