When a defect is a pathway to improve stability: a case study of the L1₂ Co₃TM superlattice intrinsic stacking fault

Effect of solutes of transition metals (TM = Cr, Fe, Hf, Mn, Mo, Nb, Ni, Pt, Rh, Ru, Re, Ta, Ti, V, W, Y and Zr) on the local phase transition between the L1₂ and D0₁₉ structures in superlattice intrinsic stacking fault (SISF) of Co₃TM has been investigated. All the models employed herein, i.e. (1) the SISF-containing supercell, (2) the axial nearest-neighbor Ising (ANNI) model, and (3) both the L1₂- and D0₁₉-containing (L1₂ + D0₁₉) supercell, yield the same result regarding the stability of SISF in L1₂-type Co₃TM. In the view of bonding charge density, the atomic and electronic basis of local D0₁₉ phase transition in the SISF fault layers of Co₃TM are revealed. Especially, the negative SISF energy predicted by the L1₂ + D0₁₉ model suggests that both the SISF fault layers (i.e. the local D0₁₉ structure) and the L12 phase of Co₃TM can be stabilized through a coupling interaction between the fault layers and the solutes, paving a pathway to stabilize Co-base superalloys via Co₃TM precipitate. Moreover, the consist results of E_SISF via the ANNI model with the classical SISF-supercell method utilized in first-principles calculations supports the approach to efficiently distinguish various planar faults and predict their corresponding energies, such as SISF, superlattice intrinsic stacking fault, anti-phase boundaries, and so on.