High resolution transmission electron microscopy studies of σ phase in Ni-based single crystal superalloys

By means of high resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field image technique (HAADF), morphological of plate-shaped σ phase and interfacial characteristics between plate-shaped σ phase and γ phase in Ni-based single crystal superalloys have been studied. On the basis of HRTEM observations, an atomic structural interface between σ phase and γ phase with a step has been proposed. σ Phase has the relationship of [0 0 1]γ//[1 1 2¯]σ, (2¯ 2 0)γ//(1¯ 1 0)σ, (2¯2¯ 0)γ//(1 1 1)σ; [0 1 1]γ//[1 1 0]σ, (1 1¯ 1)γ//(0 0 1¯)σ with the γ phase. The compositional characteristics of the σ phase which are rich in more heavy elements, such as W, Re, Cr and Ru, has also been clearly revealed by the HAADF imaging technique and Energy Dispersive X-Ray Spectroscopy (EDS) mapping analysis.

(a) TEM micrograph of σ phase; (b) HRTEM image of σ/γ interface corresponding to the area of the white frame in (a); (c) an enlarged image of area from the white frame in (b). The combination of σ/γ interface appears very well, and a two-atomic-layer step is shown on the σ/γ interface. In addition, σ phase has the orientation relationship of [0 0 1]γ//[1 1 2¯]σ, (2¯ 2 0)γ//(1¯ 1 0)σ, (2¯2¯ 0)γ//(1 1 1)σ; [0 1 1]γ//[1 1 0]σ, (1 1¯ 1)γ//(0 0 1¯)σ with the γ phase.Figure optionsDownload as PowerPoint slideHighlights
► Elemental characteristic of σ phase is studied by HAADF techniques and EDS analysis.
► Interfacial characteristics of σ/γ interface are revealed by HRTEM.
► An atomic structural σ/γ interface with a two-atomic-layer step has been proposed.