Effects of alloying elements and temperature on the elastic properties of dilute Ni-base superalloys from first-principles calculations

Abstract

Due to their high strength and advantageous high-temperature properties, tungsten-based alloys are being considered as plasma-facing candidate materials in fusion devices. Under neutron irradiation, rhenium, which is produced by nuclear transmutation, has been found to precipitate in elongated precipitates forming thermodynamic intermetallic phases at concentrations well below the solubili-ty limit. Recent measurements have shown that Re precipitation can lead to substantial hardening, which may have a detrimental effect on the fracture toughness of W alloys. This puzzle of sub-solubility precipitation points to the role played by irradiation induced defects, specifically mixed solute-W interstitials. Here, using first-principles calculations based on density functional theory, we study the energetics of mixed interstitial defects in W-Re, W-V, and W-Ti alloys, as well as the heat of mixing for each substitutional solute. We find that mixed interstitials in all systems are strongly attracted to each other with binding energies of À2.4 to À3:2 eV and form interstitial pairs that are aligned along parallel first-neighbor h111i strings. Low barriers for defect translation and rotation enable defect agglomeration and alignment even at moderate temperatures. We propose that these elongated agglomerates of mixed-interstitials may act as precursors for the formation of needle-shaped intermetallic precipitates. This interstitial-based mechanism is not limited to radiation induced segregation and precipitation in W-Re alloys but is also applicable to other body-centered cubic alloys. Published by AIP Publishing. [http://dx.

Effects of Alloying Elements on the Stacking Fault Energies of Ni58Cr32Fe10 Alloys: A First-Principle Study

“…The calculated equilibrium unit cell volume (V), bulk modulus (B), shear modulus (G), and SFE of Ni are 10.97 10 −10 m 3 , 198.4 GPa, 102.7 GPa, and 140.9 mJm −2 , respectively. These values coincide well with the previous experimental and simulation values [17,[38][39][40], as listed in Table 1.…”

A comprehensive first-principles study of pure elements: Vacancy formation and migration energies and self-diffusion coefficients

“…Figure 8 also shows that the values for hcp La, Ce, and Pr are close to zero, see the explanation in Figure 9. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 20 Similar to the cases of elasticity, ideal shear stress, and stacking fault energy [63][64][65][66][67][68], due to vacancy migration can be understood qualitatively from the redistribution of charge density because (a) the denser the charge density, the stronger the bonding between atoms based on density functional theory; and (b) the non-spherical distribution of charge density retards the redistribution of charge density during vacancy migration, resulting in a larger value. As an example, Figure 9 illustrates the variation of atomic positions for vacancy migration within the basal plane of the hcp lattice from CINEB calculations.…”

Diffusion behavior in Nickel–Aluminum and Aluminum–Uranium diluted alloys

“…In the next section we present the analytical expressions for the tracer diffusion coefficients D ⋆ A and D ⋆ S in terms of the jump frequencies ω i defined in the five-frequency model through the full set of L-coefficients expressions in (17)(18)(19)(20)(21)(22)(23)(24)(25) and (26).…”

“…Table 8 presents the calculated frequencies (38) for two different temperatures with the migration energies taken from Tables 4 and 5. Using a different approach based on the Wert and Zener model [45], Zacherl et al [18,46], have studied diffusion in N i based diluted alloys using a temperature dependent frequency prefactor.…”