Accelerating design of novel Cobalt‐based superalloys based on first-principles calculations

Abstract

The discovery of ordered γ' phase in Co-Al-W based superalloys opens up a pathway for the development of novel Cobalt-based superalloys. γ' phase from binary compounds was calculated by first-principles methods, and the third alloying elements were also considered to stabilize and strengthen γ' phase, the ordered γ' phase with higher stability and more excellent mechanical properties was confirmed herein in novel Cobalt-based superalloys. The formation energies and lattice parameters of Co-X (X = Al, Mo, Nb, Ta, Ti, V, W) and Co-Ti-Z (Z = Al, V, Cr, Mo, Ta, W) were calculated, the results show that X = Ti and Z = Mo are better choices. The doping of Mo can stabilize the ordered L12-γ' phase and improve the mechanical properties of the γ' phase when Mo occupies Ti sites. The occupying preference of alloying elements in Co3Ti lattice is analyzed, Al and Cr prefer to occupy Co sites in L12-Co3Ti lattice, while V, Mo, Ta and W prefer to occupy Ti sites. The as-cast microstructure of the five superalloys is typical dendrite with γ/γ' two-phase region in the inter-dendrite. Besides, segregation phenomenon can be observed in the as-cast microstructure of the superalloys, and Ti prefers to enriched in the inter-dendrite, while other elements tend to be distributed in the dendritic arms.