Studies on the abnormal effect of tensile strain on the MC→M₂₃C₆ in-situ transformation in Ni-based superalloy

Experiment and first-principles calculations were utilized to study the effect of tensile strain on the MC→M₂₃C₆ in-situ transformation in MC-M₂₃C₆ complex carbide as well as its micro-mechanism. The experiment indicates that strain inhibits the transformation. According to the calculations, Cr atoms will occupy M sublattice sites and diffusion through the V_M-(V_C)₆ vacancy clusters in MC. Nevertheless, a single V_M mechanism works during the diffusion of Cr atoms across the MC/M₂₃C₆ interface. Tensile strain as well as its direction can seriously influence the diffusion behavior of atoms by expanding or compressing the lattice. Generally, tensile strain will facilitate the diffusion of Cr atoms in MC and the flipping of diagonals. However, tensile strain decreases the lattice mismatch at the MC/M₂₃C₆ interface. Thus, the activation energy of the diffusion of Cr across the interface increases and the diffusion coefficient decreases. Strain inhibits the transformation mainly by restraining the diffusion of Cr atoms across the MC/M₂₃C₆ interface. The demonstrated concept enables a deeper understanding of superalloys and shed light on the rational design of higher property superalloys for various potential applications.