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• β-NiAl phase precipitates in a novel high Ru-containing Ni-SC. • Ru element is found to be obviously biased in β-NiAl phase. • The partition of Ru assists nucleation of β-NiAl phase during solidification. • Studies based on the solidification path of experimental alloy were carried out. The precipitation of β-NiAl phase in a high Ru-containing Ni-based single crystal superalloys was investigated. The β-NiAl phase is mainly distributed in the interdendritic region of the as-cast structure. And it was found parts of Ru elements were polarized in β-NiAl phase as the existence of strong bonds between Ru atoms and Al atoms. In addition, the solidification path of the experimental alloy passes through the region of the L → L 1 + γ → L 2 + γ + β-NiAl → L 3 + γ + β-NiAl + precipitated γ′ → γ + β-NiAl + precipitated γ′ + γ/γ′ eutectics. It provides experimental data and theoretical guidance for the composition design of the novel Ru-containing high-generation Ni-SCs. [ABSTRACT FROM AUTHOR]

The important factors limiting the fourth-generation Ni-based single-crystal superalloys (Ni-SXs) are the increases in cost and density. A cheaper and lighter potential alternative element of Ru, Co's comprehensive effects were studied. The effects of Co and inhomogeneity between dendrite core (DC) and interdendritic region (ID) on creep performance at 1100 °C and 137 MPa in a 4th generation Ni-SXs were systematically investigated. The results show that the Ni-SXs with 9 wt% Co has the longest creep lifetime. Co additions alleviate the overall element segregations between DC and ID, especially Re, Cr, and W. And reverse partitioning behavior of Co also changes the partitioning ratio of elements between γ and γ′ phases, resulting in the inhibition of TCP phases precipitation for most creep time to avoid excessive consumption of solid solution strengthening elements and local stress concentration. The decrease of the lattice constant of γ reduces lattice misfit between γ and γ′ with the addition of Co, leading to the enlargement of dislocation network spacing and less resistance for movement or shearing of dislocation. The decrease of γ′ solvus temperature with Co addition promotes the dissolution of γ′ at high working temperature, resulting in severe topological inversion of γ/γ′ microstructures at ID. In addition, the main creep cracks of all Ni-SXs appear at ID, so the inhomogeneity between DC and ID is concerned. • The precipitation of TCP phases are inhibited with Co addition, which is a basis of low-cost and low-density alloy design. • The comprehensive effects of Co on high temperature creep properties are investigated and an optimal Co content exists. • The increase of Co affected the γ′ phase content, lattice mismatch, element distribution and TCP phase. • The effect of Co on microstructures evolution varies at different creep stages. • The inhomogeneity between dendrite core and interdendritic region causes creep cracks originate from interdendritic region. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • The thermodynamic and dynamic factors influencing the nucleation and growth of topologically close-packed (TCP) phases are summarized in detail. • The possible mechanism of the interface structure affecting TCP phase growth is discussed. • The corresponding research directions of TCP phase precipitation and alloy design are proposed. The nucleation and growth of topologically close-packed (TCP) phases in Ni-based single crystal superalloys (SCs) are controlled by composition, temperature, time, interface structure and stress. The formation of TCP phases causes detrimental effects on the mechanical properties of SCs. Therefore, it is crucial to study the formation mechanism and control factors of TCP phases to develop new-generation Ni-based SCs. Different alloying elements influence the TCP phase nucleation by adjusting the chemical driving force. The interface structure determined by interface energy and strain energy mainly affects the growth mechanism and morphology of the TCP phase. Various temperature determines the driving force for TCP nucleation and diffusion rates of elements during TCP phase growth. Holding time is also crucial to the growth and evolution of TCP phases. Applied stress also has an impact on the precipitation of TCP phases. Evolution between different types of TCP phases depends on the temperature, composition and crystal structure of TCP phases. TCP phases damage the mechanical properties mainly by causing stress concentration and weak interface strength. The review aims to establish a link among TCP phase formation, alloy design and microstructure from the macroscopic view to the microscopic view, providing some perspectives for future research. [ABSTRACT FROM AUTHOR]