© 2022 Elsevier B.V.In compositional design of Ni-based superalloys, atomic size of alloying elements appears as the primary factor affecting alloy strengthening. Depending on atomic size, the phase partitioning preferences of alloying elements not only control the coarsening and dissolution characteristics of γ' precipitates, but also govern their morphological development upon aging. The current study, therefore, investigates the influence of larger atomic radius X = Hf element addition and its co-additions with smaller atomic radii refractory X = Mo(W) elements on the microstructural and mechanical properties of model Ni80Al15Hf5 and Ni80Al15Hf2.5Mo(W)2.5 superalloys. Accordingly, it is concluded that the replacement of 2.5 at% X = Hf addition with the same amount of X = Mo(W) additions reduces and increases γ' participation tendency of X = Hf and X = Mo(W) elements, respectively. Agreeing with classical Lifshitz-Slyozov-Wagner (LSW) kinetics, γ'-Ni3Al-Hf-W precipitates coarsen at a slower rate compared to their γ'-Ni3Al-Hf-Mo counterparts, both begin to agglomerate at longer aging times, i.e., 256 h. On the other hand, readily coarsened, aligned, and agglomerated γ'-Ni3Al-Hf precipitates start to dissolve in γ matrix after 16 h, which hence disobey LSW theory. Most probably, higher γ'/γ interfacial energy contribution of faster-diffusivity X = Hf element leads to this three-step temporal evolution of γ'-Ni3Al-Hf precipitates, i.e., (i) coarsening, (ii) alignment/agglomeration, and (iii) dissolution, to occur much earlier and accelerates the strength degradation. Conversely, X = Hf-W co-addition, which causes better mechanical strength than both X = Hf and X = Hf-Mo additions, reduces the degree of strength worsening possibly due to the beneficial contributions of X = W element at γ'/γ interfaces.