Creep deformation of γ - γ' based superalloys involves creation of high density of planar defects in the microstructure. The type of induced defects, such as stacking faults, antiphase boundaries and twins depends on the alloy chemistry, temperature and the applied stress. Recent investigations reveal, these defects are not only structurally distinct from the surrounding lattice but also possess different chemical nature that shows evidence of local reordering and solute diffusion phenomena occurring during deformation. However, till now there no experimental evidences on the mechanism of local diffusional process. Additionally, these studies were limited only to energy dispersive spectroscopy (EDS) attached to transmission electron microscope (TEM) in Scanning TEM mode.
In this work, A unique correlative approach combining controlled electron channeling contrast imaging (cECCI), conventional and high-resolution scanning transmission electron microscopy (HR-(S)TEM) and atom probe tomography (APT) was used to explore the full nature of planar defects formed during creep of new CoNi-based single crystal superalloys. These alloys show, at 900°C, creep properties comparable to 1st generation Ni based superalloys. The atomic structure, solute partitioning to these defects and the chemical gradients in their vicinity led us to propose new diffusive phase transformation mechanisms operating under stress at high temperatures during shearing of γ' ordered phase in these alloys.