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The phase partition and site preference of Re atoms in a ternary Ni–Al–Re model alloy, including the electronic structure of different Re configurations, are investigated with first-principles calculations and atom probe tomography. The Re distribution of single, nearest neighbor (NN), next-nearest neighbor (NNN), and cluster configurations are respectively designed in the models with γ and γ′ phases. The results show that the Re atoms tend to entering γ′ phase and the Re atoms prefer to occupy the Al sites in γ′ phase. The Re cluster with a combination of NN and NNN Re–Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys, and the configuration with isolated Re atom is more preferred in the system. Especially, the electronic states are analyzed and the energetic parameters are calculated. The electronic structure analyses show there exists strong Ni–Re electronic interaction and it is mainly contributed by the d–d hybridization. The characteristic features of the electronic states of the Re doping effects are also given. It is also found that Re atoms prefer the Al sites in γ′ side at the interface. The density of states at or near the Fermi level and the d–d hybridizations of NN Ni–Re are found to be important in the systems. [ABSTRACT FROM AUTHOR]

The influence of refractory additions on tensile deformation behavior has been studied at an intermediate temperature (760°C) using scanning and transmission electron microscopy. Tensile experiments revealed that elemental additions of tantalum (Ta), tungsten (W), and rhenium (Re) could improve the yield strength (YS) of the model alloys with an order of YS(Ni–Al–W) > YS(Ni–Al–Ta) > YS(Ni–Al-Re) > YS(Ni–Al). During the plastic deformation of model alloys at the intermediate temperature, the deformation via Orowan bypassing and shear could be activated synergistically. The changes of anti-phase boundary (APB) energies on {001} and {111} planes are related to the cross-slip driving force, critical resolved shear stress and stage II work hardening rate in γ' precipitates. The effects of γ' size and refractory additions (Ta, W, and Re) on the yield strength of model alloys at intermediate temperature are also discussed, which can provide qualitative reference for alloy design. • The effect of Re on the yield strength and plasticity is less than that of Ta and W. • The lattice distortion related with changes in APB energies and order strengthening. • There is a positive correlation between cross-slip driving force and stage II WHR. • At medium temperature, Orowan bypassing and γ' shearing are activated synergistically. • W and Ta are two promising candidates for replacing precious Re element. [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]

Creep rupture life is a key material parameter for service life and mechanical properties of Ni-based single crystal superalloy materials. Therefore, it is of much practical significance to accurately and efficiently predict creep life. Here, we develop a divide-and-conquer self-adaptive (DCSA) learning method incorporating multiple material descriptors for rational and accelerated prediction of the creep rupture life. We characterize a high-quality creep dataset of 266 alloy samples with such features as alloy composition, test temperature, test stress, and heat treatment process. In addition, five microstructural parameters related to creep process, including stacking fault energy, lattice parameter, mole fraction of the γ' phase, diffusion coefficient and shear modulus, are calculated and introduced by the CALPHAD (CALculation of PHAse Diagrams) method and basic materials structure-property relationships, that enables us to reveal the effect of microstructure on creep properties. The machine learning explorations conducted on the creep dataset demonstrate the potential of the approach to achieve higher prediction accuracy with RMSE, MAPE and R 2 of 0.3839, 0.0003 and 0.9176 than five alternative state-of-the-art machine learning models. On the newly collected 8 alloy samples, the error between the predicted creep life value and the experimental measured value is within the acceptable range (6.4486 h–40.7159 h), further confirming the validity of our DCSA model. Essentially, our method can establish accurate structure-property relationship mapping for the creep rupture life in a faster and cheaper manner than experiments and is expected to serve for inverse design of alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Partitioning and diffusion of transition metal solutes can significantly affect the coarsening rate of γ′ precipitates in Ni-based single crystal superalloys. Using first-principles density-functional calculations and atom probe tomography, we investigated the partitioning coefficient and diffusion rate of 3d (Ti Ni), 4d (Zr Pd), and 5d (Hf Pt) transition metal solutes. For ternary model Ni-based single crystal superalloys, the 3d solutes (except Ti) partition to the matrix phase, whereas 4d and 5d solutes (except Ru, Rh, and Ir) prefer γ′ precipitates. The existing atom probe tomography results are consistent with the calculation results. Across the periodic table, middle-row elements have a higher (lower) diffusion activation energy (diffusion rate) than early and late row elements. The band-filling effect that is coupled with electronic structure analysis can explain the parabolic behavior of energetics that involves bond breaking. To minimize the coarsening rate, we have screened alloying elements that both have a low diffusion rate in the γ matrix and partition to the γ′ phase. These alloying elements will suppress the coarsening behavior of the precipitates and are expected to contribute to the stability of precipitates at elevated temperature. [ABSTRACT FROM AUTHOR]

The effect of elemental interactions between solute elements on diffusion in Ni X Y (X, Y: Al, Ti, Nb, Ta, Cr, Co, Mo, W, Re, Ru) systems and γ′-coarsening in model Ni-based superalloys are investigated by performing first-principles calculations and high-temperature thermal exposure experiments. The ternary interactions are important for the diffusion barrier of a solute in Ni X Y and the coarsening rate of precipitates. These results are related not only to the electronic structure but also to chemical bonding. [ABSTRACT FROM AUTHOR]