Atomic mechanism of topologically close-packed phases twinning transformation in Ni-based single crystal superalloys during creep

This study systematically investigated the twinning transformation mechanism of topologically close-packed phases (μ phases) in a Ni-based single crystal superalloy during creep deformation. Two distinct types of twins were identified in the μ phase: misaligned (TB₁-type) and symmetric (TB₂-type) twins. The formation of the TB₁-type twin occurred when shear stress acted along the [1¯101]_μ direction within the (011¯2)_μ crystal plane of the μ phase, initially generating stacking faults, which subsequently evolve into a TB₁-type twin structure through atomic rearrangement. Interestingly, the transformation of TB₂-type twins followed two separate pathways: (1) further shear deformation of TB₁-type twins along the [1¯101]_μ direction within the (011¯2)_μ plane under external stress; (2) structural retention of P phase configurations resembling TB₂-type twin boundaries during the P→μ phase transformation. These findings provide fundamental insights into the relationship between TCP phase transitions and creep behavior, offering valuable theoretical guidance for the design of advanced superalloys.