Abstract <p>The results of a study of the effect of the gamma-prime γ' phase precipitate size in the polycrystalline high temperature nickel superalloy EP741NP obtained by PM HIP technology using rapidly quenched PREP powder on their composition and partition of alloying elements between the γ' precipitates and the gamma γ matrix are presented. The methods of metallography, track autoradiography on boron, activation autoradiography on carbon, SEM, EDX, and OIM were used for a multiscale study of the structural features, precipitates of the intermetallic γ' phase, and distribution of boron, carbon, boride, and carbide phases in the bulk of the material during thermal aging, as well as in the area of intense coarsening of γ' precipitates in the necking zone around the mesocrack near the fracture zone of the sample after a high-temperature tensile test. The significantly larger size and elongated shape of the γ' phase precipitates near the fracture zone compared to the γ' precipitates in the bulk of the material are obviously due to the influence of localized plastic deformation around the mesocrack, including the intense movement of dislocations, on the coarsening of the γ'&#xa0;phase precipitates. It has been established that the abridged version of the chemical formula for the composition of the γ' phase precipitates corresponds to the formula (Ni, Co)₃(Al, Ti). The results obtained on the change in the concentrations of alloying elements in γ' precipitates and their partition between the γ' and γ phases with an increase in the size of γ' precipitates indicate that spinodal decomposition is the main possible mechanism of the above-mentioned change in the concentrations of alloying elements and their partition and that it is also applicable to the coarsening of γ' precipitates and the formation of a meso-modulated structure during thermal aging of the EP741NP superalloy obtained by PM HIP technology using rapidly quenched PREP powder.</p>