A High-Resolution Method to Map Out the γ/γ' Lattice Misfit in Ni-Based Superalloys

Abstract

Lattice misfit is an essential parameter/property that affects the mechanical behavior of two-phase superalloys. Here we report a new method to use sub-micrometer-focused synchrotron X-ray beam to directly measure the γ/γ′ misfit in Ni-based superalloys. By combining polychromatic X-ray Laue diffraction and monochromatic energy scan, the lattice constants of both phases and the lattice misfit are mapped out at high spatial resolution, which is only limited by the X-ray beam size and scanning step size. We also developed data analysis algorithms to elevate the reliability of peak fitting and the precision and accuracy of lattice constants/misfit measurements. The success of our method is illustrated by uncovering the pronounced variations and non-monotonic profiles of the misfit and phase fractions throughout the heat affected zone in a laser 3D-printed Ni-based superalloy. The nano-hardness distribution in the transition region from the base metal to the cladding layers is empirically correlated with the phase fractions that are reflected by the diffraction peak intensities.