The Site Preferences of Transition Elements and Their Synergistic Effects on the Bonding Strengthening and Structural Stability of gamma '-Ni3Al Precipitates in Ni-Based Superalloys: A First-Principles Investigation

2021-04-01
Advanced mechanical properties of Ni-based superalloys strongly depend on the site preferences of alloying X elements in gamma '-Ni3Al-X precipitates, which are associated with the partial bonding characteristics between Ni, Al, and X atoms. Therefore, in the current work, the site occupancy tendencies of transition X metals were revealed via first-principles ab initio calculations at 0 K. Bonding features of Ni-Al, Ni-X, and Al-X pairs were simulated by using the charge density difference (CDD), electron localization function (ELF), and density of states (DOS) methods, respectively. According to simulations, higher atomic size X elements preferably occupy Al sites of gamma '-Ni3Al-X intermetallics and lead to strong covalent-like directional bondings between themselves and their nearest neighbor (NN) Ni atoms along < 110 & rang; directions. However, if these larger X metals substituted for Ni sites, the bonding properties would differ by plane due to the nature of the L1(2)-type crystal structure of gamma '-Ni3Al-X precipitates. Considering all transition elements, refractory metals (i.e., X = Re, W, Mo, Ta, or Nb) appear as the most effective strength inducers, improving the structural stability of gamma ' phase, even if Ni site substitution of X = Re atoms would start to increase structural instability. On the other hand, relatively small alloying X elements having electron configuration similarities with Ni (i.e., X = Co, Cu, Rh, Pd, Ag, Ir, Pt, or Au) are more likely to worsen bonding strengthening. Instead, these transition X metals creating metallic bondings with NN Ni atoms would contribute to ductility and malleability of Ni-based superalloys. Furthermore, depending on the relative atomic size of gamma '-former and refractory elements, the phase and site preferences of refractory atoms would alter in multicomponent systems. As a result of the attractive or weak repulsive forces between Re-Re, Re-Mo, and Re-W pairs, the structural stability of the constituent phases would deteriorate and harmful topologically close-packed (TCP) phases would precipitate.
Citation Formats
R. Eriş, M. V. Akdeniz, and A. Mehrabov, “The Site Preferences of Transition Elements and Their Synergistic Effects on the Bonding Strengthening and Structural Stability of gamma ’-Ni3Al Precipitates in Ni-Based Superalloys: A First-Principles Investigation,” pp. 0–0, 2021, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/90355.