Aging process design based on the morphological evolution of γ′ precipitates in a 4th generation nickel-based single crystal superalloy

In order to meet the design requirements of the aging treatment process of a 4th generation nickel-based single crystal superalloy (Ni-SX) developed independently, the effects of aging temperatures and aging times on the precipitation and morphological evolution of γ′ precipitates are studied. The morphological evolution behavior of γ′ precipitates during the aging process is summarized subsequently and the coarsening behavior of γ′ precipitates is discussed by comparing with the Lifshitz-Slyozov-Wagner model (LSW) and the trans-interface diffusion-controlled model (TIDC). It is demonstrated that primary aging temperature and secondary aging time dominate the size and squareness of γ′ precipitates respectively, a narrow primary aging temperature range and a suitable secondary aging time are allowed to obtain the optimized morphology of γ′ precipitates. The optimal aging process of the Ni-SX investigated in the present work is obtained for 1100-1120 °C/4 h and 870 °C/16 h, confirmed by the corresponding creep tests. The coarsening growth of γ′ precipitates in short-term aging also conforms to the LSW model well. Besides, the aging process design rules of various Ni-SXs of different generations are also summarized.