Measurement of local elastic strains in the single-crystal nickel-based superalloy CMSX-6 by convergent-beam electron diffraction

Abstract

Abstract High spatial resolution convergent beam electron diffraction (CBED) was used in this study as a powerful tool to investigate the local lattice parameters (and elastic strains) in the γ and γ′ phases of the single-crystal nickel-based superalloy CMSX-6 at room temperature, before and after high-temperature creep deformation in tension. With the aid of a newly implemented improved fast evaluation procedure, it was possible to determine the elastic strains in a large number of positions in the microstructure. The experimental results are in global agreement with earlier work but more specific with regard to details. Thus, it is confirmed that compressive elastic stresses exist in both horizontal and vertical γ channels in the initial state and that, after tensile creep at 980°C, in agreement with an earlier dislocation model, the elastic strains in the horizontal γ channels change from the compressive to a tensile state, acting perpendicular to the deformation axis, while the strain state in the vertical channels is only modified quantitatively. As a new result, it is noted that while the elastic strain in γ′ particles is initially homogeneous, an inhomogeneous distribution of the elastic strains in the γ′ phase is observed after high-temperature creep. The findings reported demonstrate the capability of the improved time-saving CBED evaluation procedure with respect to the reliable determination of local lattice parameters in fine-scale microstructures.