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Detailed characterizations of interfacial dislocation networks in a nickel-base single crystal superalloy after creep loading for 85 h at 1100 °Cand 130 MPa were carried out at larger magnifications. The “square-like” dislocation network is formed by dislocation reaction including a[010], a/2[110], a / 2 [ 1 1 ¯ 0 ] dislocations and is different from square (and hexagonal) networks in formation mechanism and geometric structure. The atomic structure of core region of dislocations indicates their individual features and highlights the three-dimensional geometry of “square-like” dislocation network for the first time. [ABSTRACT FROM AUTHOR]

The partitioning behaviors of alloying elements Cr, Co, Al, Ta, etc. on the γ and γ′ phases of high Cr-containing (∼9wt.%) nickel-base single crystal superalloys have been investigated with and without the addition of 3wt.% Ru. The “reverse partitioning effect” occurs, which means that the addition of Ru causes the partition of Cr and Co into γ′ phase, while Al an Ta concentrate into γ matrix. However, Ru promotes the precipitation of topologically close-packed (TCP) phases, since the diffusion coefficient between the TCP phase and the matrix interface increases with the diffusion behaviors of refractory elements. For the coarsening and slightly rafting of γ′ phases, the increase of elemental diffusion plays much more important role in its kinetic process than the decrease of lattice misfit. [ABSTRACT FROM AUTHOR]

Abstract: 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 [001]γ//[11 ]σ, ( 20)γ//( 10)σ, ( 0)γ//(111)σ; [011]γ//[110]σ, (1 1)γ//(00 )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. [Copyright &y& Elsevier]

Abstract The internal characteristics of the μ phase in Ni-base single crystal superalloys aged at 1100 °C for 1000 h were investigated via spherical aberration-corrected transmission electron microscopy. There were a large number of planar defects on the (001) plane at the growth tip of the μ phase. HAADF-STEM results show that these planar defects were mainly of two types. 1) A twin structure with a mirror plane of the middle atomic planes of the Zr 4 Al 3 sheet, which was generated by shearing of atoms in the MgCu 2 sheet along the [1-10] direction. 2) A mirror-symmetrical stacking fault of two Zr 4 Al 3 sheets, which was formed by the pulling out of a single MgCu 2 sheet. The planar defects were mainly caused by coordination of the distortions of the μ phase and the matrix. Segregation of Mo, Cr, and Re elements occurred near stacking faults, rather than twin structures. Highlights • There are a large number of planar defects on the (001) plane at the growth tip of the lath-like μ phase. • The twin structure in μ phase is generated by shearing the atoms of MgCu 2 sheet along the [1−10] direction. • The stacking fault in μ phase is a mirror-symmetrical of two Zr 4 Al 3 sheets, which is formed by pulling out one MgCu 2 sheet. [ABSTRACT FROM AUTHOR]

Highlights: [•] Critical resolved shear stress for twinning in superalloy are calculated theoretically. [•] Finite element method analyzes the stress distribution around micropore near crack-tip. [•] Deformation twinning occurs due to the stress concentration. [ABSTRACT FROM AUTHOR]