Enhancing turbomachinery efficiency requires increasing the turbine entry temperature (TET), pushing operating conditions beyond 1000°C. This extreme environment necessitates the development of advanced refractory materials, with nickel-based superalloys remaining the benchmark due to their exceptional mechanical properties. Over decades of industrial innovation, these biphasic alloys— comprising a disordered γ matrix reinforced by an ordered γ‘ phase—have raised fundamental metallurgical questions: – What is the primary driver of their high mechanical strength? – Is it dictated by alloy chemistry, the ordered γ‘ phase, the lattice misfit between γ and γ‘, or dislocation interactions at phase interfaces? To address these questions, the creep behavior of two single-crystal superalloys, MC2 and MCNG, is investigated at 1050°C. The objective is to establish a hierarchy of key strengthening mechanisms and contribute to the optimization of next-generation materials for aircraft engines. A multi-scale analysis (macro, meso, micro) reveals significant differences in the formation and evolution of rafting structures between these alloys (Figure 1). The addition of heavy elements such as rhenium alters both the intrinsic properties of each phase and their morphology.