Ground-state properties and relative stability between the L12 and DOa phases of Ni3Al by Nb substitution

Structural stability, elasticity, thermodynamics, and electronic structures of L12-type Ni3X (X = Al, Ti, V, Nb) phases under external pressure condition

In this paper, the effect of pressure on the structural stability, elasticity, thermodynamics, and associated electronic structure of L1₂-type Ni₃X (X = Al, Ti, V, Nb) phases is investigated using a first-principles approach. It is shown that pressure leads to volume compression of the Ni₃X phase and reduction of the lattice parameters. The increase of pressure promotes the increase of elastic constants, bulk modulus, shear modulus, and Young's modulus. And there is an extremely strong linear correlation between the pressure and the elastic constants. The calculated elastic constants indicate that the pressure leads to strong mechanical stability and ductility of the Ni₃X phase. Mechanical anisotropy of the Ni₃X phase also increases with increasing pressure. The electronic analysis shows that the increase in pressure leads to enhanced Ni-d-orbitals and X-d-orbitals hybridization and increased electron transfer. The order in terms of electron accumulation intensity is Ni₃Ti > Ni₃Nb > Ni₃V > Ni₃Al. It is more directly reflected in the charge density difference diagram. This is in agreement with the results of the enthalpy of formation (ΔH) and Debye temperature (Θ_D) analysis.

Microstructural Characterization of Nb/Inconel 601 Interface Obtained in the Explosive Welding Process

This work presents the microstructure of the cross-section of a newly developed Nb/Inconel 601 weld with particular attention paid to the continuity, morphology of the interface, and the microstructural changes within its vicinity. Both scanning (SEM) and transmission (TEM) electron microscopy techniques are excellent tools to analyze the microstructure that affects both mechanical and corrosion resistance properties of the obtained product. Grain size examination and their orientation together with the character of grain boundaries by the electron backscattered diffraction (EBSD) technique were performed followed by chemical composition determination across the interface with energy-dispersive X-ray spectroscopy (EDS) in SEM. Then, the microstructure observations of the mixed region located at the Nb/Inconel 601 interface using the TEM technique allowed its chemical and phase composition to be revealed.

Charge optimized many-body (COMB) potential for dynamical simulation of Ni-Al phases

An interatomic potential for the Ni-Al system is presented within the third-generation charge optimized many-body (COMB3) formalism. The potential has been optimized for Ni3Al, or the γ' phase in Ni-based superalloys. The formation energies predicted for other Ni-Al phases are in reasonable agreement with first-principles results. The potential further predicts good mechanical properties for Ni3Al, which includes the values of the complex stacking fault (CSF) and the anti-phase boundary (APB) energies for the (1 1 1) and (1 0 0) planes. It is also used to investigate dislocation propagation across the Ni3Al (1 1 0)-Ni (1 1 0) interface, and the results are consistent with simulation results reported in the literature. The potential is further used in combination with a recent COMB3 potential for Al2O3 to investigate the Ni3Al (1 1 1)-Al2O3 (0 0 01) interface, which has not been modeled previously at the classical atomistic level due to the lack of a reactive potential to describe both Ni3Al and Al2O3 as well as interactions between them. The calculated work of adhesion for this interface is predicted to be 1.85 J m(-2), which is in agreement with available experimental data. The predicted interlayer distance is further consistent with the available first-principles results for Ni (1 1 1)-Al2O3 (0 0 0 1).