Abstract
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 (ΘD) analysis.
Highlights
Ni-based single-crystal superalloys are one the most important high- temperature materials
The ΔH of L12-type γ-Ni3X (X=Al, Ti, V, Nb) phases at 0 GPa are -48.15, -53.05, -20.49, -21.82 kJ/mol, respectively. It indicates that L12-type γ-Ni3X phase is thermodynamically stable, the stability of the γ-Ni3X has following sequence: Ti> Al> Nb>V, and the ΔH of Ni3Ti, Ni3V are relatively close to -45.14 KJ/mol and -16.27 KJ/mol with previous research findings [15], indicating that the feasibility of the calculation method and the simulative results are accurate
4 Conclusion In this paper, the structural stability(ΔH), elastic constants(Cij ), bulk modulus (B), Yong’s modulus (E), shear modulus (G), Debye temperature (ΘD),and electronic structures of L12-type Ni3X (X=Al, Ti, V, Nb) phases under external pressure condition were systematically studied by first principles calculations
Summary
Ni-based single-crystal superalloys are one the most important high- temperature materials. The excellent mechanical properties of nickel-based single-crystal superalloys at high temperatures are depend mainly on the effect of the γ-Ni3Al strengthening phase in the alloy [10]. The large number of investigations on the γ-Ni3Al strengthening phase were found that the strengthening effect cannot meet the requirements for the performance of nickel-based single crystal alloys under high temperature conditions any more [11,12,13]. Li et al [14] investigated the mechanical properties of γ′′-Ni3Ta under variable pressure by means of theoretical simulations, and explored the internal mechanisms affecting its stability and mechanical strength. Gong et al [17] analyzed the effect of alloying elements on the occupation preference, structural stability and mechanical performance of γ′′-Ni3Nb based on density functional theory
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