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To model the centrifugal loads and complex geometries experienced by turbine blades during service, the nickel-based single crystal superalloy DD6 samples with a groove structure are designed and tested under the coupling conditions of high-speed rotating of 20,000 r/min and high temperature of 980 ℃. Scanning electron microscopy and transmission electron microscopy are used to analyze the microstructural evolution of γ-γ' phases and dislocation morphologies of 400 h and 1000 h samples. The results indicate that microstructural degradation of the γ-γ' phase attributes to the larger centrifugal tensile stress S 11 in the applied physical stress compositions until deformation occurs. Our observations suggest that a/2 < 101 > -type dislocations initiate plastic deformation by slipping within the γ phase. However, their movement is constrained at the interface between the γ and γ' phases, resulting in their tendency to aggregate at this boundary. After the formation of stable interfacial dislocation networks, these dislocations then react to generate either a< 010 > -type dislocations or a/2 < 112 > -type dislocations, which cut into the γ' phase. However, under high stress conditions, the a/2 < 101 > -type dislocations are primarily cut directly in the form of dislocation pairs. • The γ-γ' phase degradation and dislocation evolution of DD6 superalloy was investigated. • Creep tests are conducted under high-speed rotating and high temperature condition. • Microstructural degradation of the γ-γ' phase attributes to the larger centrifugal tensile stress S 11. • Interfacial dislocation networks and superdislocations accelerate the separation and disappearance of the γ phase. [ABSTRACT FROM AUTHOR]

Here, we investigate a new type of kink structure that is found at γ/γ′ interfaces in nickel-based single crystal superalloys. We studied these structures at the atomic and elemental level using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The core of the dislocation absorbs high-Z elements (i.e., Co and Re) that adopt hexagonal arrangements, and it extrudes elements (i.e., Ni and Al) that adopt face centered cubic (fcc) structures. High-Z elements (i.e., Ta and W) and Cr, which is a low-Z element, are stabilized in body centered cubic (bcc) arrangements; Cr tends to behave like Re. High-Z elements, which migrate and adopt a hexagonal structure, induce kink formation at γ/γ′ interfaces. This process must be analyzed to fully understand the kinetics and dynamics of creep in nickel-based single crystal superalloys. [ABSTRACT FROM AUTHOR]

It is important and necessary to understand the micro-mechanism of rhenium (Re) effect in the deformation process. The in-situ tensile experiments of Ni–Al and Ni–Al-Re model single crystal superalloys have been carried out in scanning electron microscope at 750 °C. It is found that Re can promote the complex stacking fault (CSF) formation, which is similar to the previous results after tensile experiments at room temperature. The micro-mechanism of Re promoting the CSF formation has been investigated by means of advanced probe-corrected scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. The local high concentration of Re is observed at CSF regions after tensile experiments both at room temperature and 750 °C. The first principles calculation results further indicate that low concentration of Re increases CSF energy, while high concentration of Re decreases CSF energy, which is consistent with the experimental results. • In-situ tensile experiments of model single crystal superalloys are carried out. • Re can promote the complex stacking fault (CSF) formation. • High concentration of Re is observed in local region along CSF. • The calculation results show high concentration of Re decreases CSF energy. [ABSTRACT FROM AUTHOR]

L1 2 structured γ′ phase is the main strengthening phase of Ni-base superalloys, which contain multiple alloying elements. Locations of these elements in the lattice are crucial for understanding the mechanical/physical properties of γ′ phases. Here, we reveal the site occupancy of various elements in γ′ phases of two multi-component Ni-base single crystal superalloys by using advanced scanning transmission electron microscopy and energy disperse spectroscopy. Cr, Mo, Re, Ta, W and Ti atoms preferentially locate at Al sublattices, and Co and Ru atoms prefer Ni sublattices. Moreover, the addition of Ru does not affect the site occupancy of other alloying elements. Image 1 • EDS mapping directly shows atomic distribution of all elements in the γ′ phases. • Cr, Mo, Re, Ta, W and Ti atoms preferentially occupy Al sublattices. • Co and Ru atoms prefer Ni sublattices. • Ru has limited effect on site occupancy of other alloying elements in γ′ phase. [ABSTRACT FROM AUTHOR]