A morphological control strategy of γ′ precipitates in nickel-based single-crystal superalloys: an aging design, fundamental principle, and evolutionary simulation

Due to the excellent thermo-mechanical properties, nickel-based single-crystal superalloys (Ni-SXs) are widely used as a turbine blade material in aero-engine and gas turbine. Ni-SXs consist of regularly arranged γ′ precipitates, which exhibit an ordered L12 structure. As the main source of precipitation strengthening, the morphology of γ′ precipitates, including the size, shape, volume fraction, and spatial arrangement, plays a critical role in mechanical properties. Aging treatment is one of the most effective heat treatment processes on regulating the microstructure of Ni-SXs to bring the strengthening potential into full play, which usually consists of two or more steps. This article presents a review on the effects of multiple-stage aging processes on the morphology of γ′ precipitates including the temperature and time of the primary aging and secondary aging, also dissects the essential principle of the morphological change during aging from the perspective of thermodynamics including the combined contribution of interfacial energy and elastic energy. The morphological evolution behavior of γ′ precipitates during the aging process is summarized subsequently. In addition, coarsening theoretical models of γ′ precipitates and its application are briefly described. This review aims to establish the link between the aging treatment process and the micro-morphological evolution. Thus, some perspectives are put forward in this article which can provide the guiding references for the design of the aging treatment process of Ni-SXs.