In Ni-based superalloys, annealing twin boundaries (ATBs) are vulnerable sites for strain localization, hydrogen embrittlement, and subsequent failure during mechanical testing [1-3]. Recently, Zhang et al. [4], reported the presence of Ni3Nb-based γ'' precipitates at ATBs in a Ni-based superalloy which appear to cause additional strain localization and cracking at ATBs [4]. However, similar strain localization events have been noted in many other superalloys, such as ME3 and Rene88DT, which only exhibit homogeneously distributed γ' L12 precipitates. In addition, because ATBs in superalloys are low energy structures, the mechanism and driving force behind preferential precipitation of an ordered γ'' phase remain unclear. Thus, the present work is an effort to investigate ATB microstructures and their effect on deformation mechanisms of various superalloys.