Nucleation of Y-X-O (X=Al, Ti, or Zr) NCs in nano-structured ferritic alloys: A first principles comparative study

Nucleation of Y-Al-O, Y-Ti-O, and Y-Zr-O enriched nano-clusters (NCs) in nano-structured ferric alloys were comparatively investigated using first-principles calculations. Formation of various possible cluster configurations was energetically evaluated with respect to individually dissolved solute atoms, to explore the preferential precipitation and growth sequence of the NCs. Key results include the following observations. During the earliest nucleation stages, Y-Zr-O NCs are always the most energy favored to form in the supersaturated bcc-Fe based matrix, followed by Y-Ti-O and Y-Al-O NCs. All the three type NCs follow the same nucleation path that begins from the O-O pairs. Y has the strongest thermodynamic driving force to precipitate with the O-O pairs. The most stable six-atomic cluster configuration is predicted as –[2Y-3O-X]–. The (O-Y)-cores may constitute the stable nuclei of larger NCs which grow consistently by attracting extra solutes available nearby.