Site preferences of alloying transition metal elements in Ni-based superalloy: A first-principles study

Atomistic characterization of chemical element distribution is crucial to understanding the role of alloying elements for strengthening mechanism of superalloy. In the present work, the site preferences of two alloying elements X -Y in γ-Ni of Ni-based superalloy are systematically studied using first-principles calculations with and without spin-polarization. The doping elements X and Y are chosen from the 27 kinds of 3 d, 4 d, 5 d group transition metals(Sc, Ti, V, Cr, Mn, Fe, Co,Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au) and Al. We find that the spin-polarized calculations for Re-Re, Re-Ru, Re-Cr, Ru-Cr show a strong chemical binding affinity between the solute elements and are more consistent with the experimental results. The binding energies of pairs between the 28 elements have an obvious periodicity and are closely related the electronic configuration of the elements. When the d-electrons of the element are close to the half full-shell state, two alloying elements possess attractive binding energies, reflecting the effect of the Hund's rule. The combinations of early transition metals(Sc, Ti, V, Y, Zr, Nb, Hf, Ta) have a repulsive interaction in γ-Ni. These results offer insights into the role of alloying elements for strengthening mechanism of superalloy.     

The effects of combining alloying elements on the elastic properties of γ-Ni in Ni-based superalloy:High-throughput first-principles calculations

Using high-throughput first-principles calculations, we systematically studied the synergistic effect of alloying two elements(Al and 28 kinds of 3 d, 4 d, and 5 d transition metals) on the elastic constants and elastic moduli of γ-Ni. We used machine learning to theoretically predict the relationship between alloying concentration and mechanical properties, giving the binding energy between the two elements. We found that the ternary alloying elements strengthened the γ phase in the order of Re Ir W Ru Cr Mo Pt Ta Co. There is a quadratic parabolic relationship between the number of d shell electrons in the alloying element and the bulk modulus, and the maximum bulk modulus appears when the d shell is half full. We found a linear relationship between bulk modulus and alloying concentration over a certain alloying range. Using linear regression, we found the linear fit concentration coefficient of 29 elements. Using machine learning to theoretically predict the bulk modulus and lattice constants of Ni_(32)XY, we predicted values close to the calculated results,with a regression parameter of R~2= 0.99626. Compared with pure Ni, the alloyed Ni has higher bulk modulus B, G, E,C_(11), and C_(44), but equal C_(12). The alloying strengthening in some of these systems is closely tied to the binding of elements,indicating that the binding energy of the alloy is a way to assess its elastic properties.