With the ongoing development and increasing prevalence of nano-twinned metallic materials, a deep understanding of the nucleation and growth mechanisms of twins has become pivotal. Such knowledge is essential for effectively controlling the size, number density, and interface structure of these twins, thereby optimizing material performance. Nevertheless, while significant strides have been made in understanding deformation, growth, and annealing twins, the nucleation and growth mechanisms of phase transformation twins remain shrouded in mystery. The dynamics involved in the pure displacement-type phase transformation twinning process are exceedingly swift, rendering the observation of nucleation and growth at the atomic scale a formidable challenge. Conversely, diffusion-displacement (mixed) solid-state phase transformations exhibit slower kinetics. This slower pace facilitates the observation and analysis of the nucleation and growth processes of phase transformation twins, achieved by comparing microstructures and chemical characteristics across various stages.