Morphology Evolution of γ′ Precipitates during Isothermal Exposure in Wrought Ni-Based Superalloy Inconel X-750

The morphological evolution of gamma' precipitates and lattice misfit with isothermal aging were closely investigated in wrought Ni-based superalloy Inconel X-750. The gamma' morphology dramatically changes in terms of shape, distribution, coalescence and coherency at the gamma/gamma' interface. These processes and their dependence on temperature are summarized as a gamma' morphology map together with a time-temperature-precipitation (TTP) diagram through quantifying relevant morphological parameters. The lattice misfit was measured by X-ray diffraction and is positive; it decreases from 0.6% at room temperature to 0.1% at the aging temperature. These results suggest that the morphological changes of the gamma' precipitates are attributable to very low lattice misfit, the interaction of the elastic field, the volume fraction of the precipitates and incoherence in gamma/gamma' interface.