Effects of rare-earth elements on the oxidation behavior of γ-Ni in Ni-based single crystal superalloys: A first-principles study from a perspective of surface adsorption

摘要

The mechanism of rare-earth element (RE) effects on the oxidation resistance of Ni-based single crystal (SC) superalloys are investigated by studying the adsorption behaviors of an oxygen atom (O) on clean and RE-alloyed (RE = Ce, Dy, La) gamma-Ni(100) and gamma-Ni(111) surfaces via first-principles method. The results show that substituting a RE atom on the top layer of gamma-Ni surface could stabilize the adsorption of O on gamma-Ni surfaces, regardless of surface orientation. Detailed electronic structure analyses indicate that the increased chemical bonding strength between O and RE atoms is considered to be the main reason for this result. Furthermore, the adsorption energies of O on Ni(100) surface are further increased when a single RE atom substitutes at a subsurface layer site. The combined effects of RE-O interaction and local lattice distortion are responsible for this phenomenon. These results help to understanding the underlying mechanism for the oxidation resistances of Ni-based SC superalloys improved by a small amount of RE additions.