Direct Lattice Parameter Measurements Using HAADF-STEM

Lattice strain is generated in crystal structures as a result of atomic size differences between host atom and solute elements during substitutional alloying. Extensive work has been performed to study lattice parameter variation with alloying elements, primarily using diffraction methods. The global information provided by reciprocal space analysis, however, limits access to local structural details. In contrast, atomic resolution STEM enables direct imaging of the crystal structure, but drift distortion currently limits capabilities to measure lattice parameters. This is particularly relevant for Ni-based superalloys as the microstructure consists of cuboidal intermetallic γ’ phase precipitate (L12 structure) within a γ phase matrix (FCC structure). As the coherent γ/ γ ’ interface is responsible for limiting dislocation motion [1], direct measurement of lattice parameters and strain provides critical information to further next generation alloy design.