Precisely regulating the size and morphology of γ′ strengthened a novel nickel-based superalloy via varied cooling rates

The cooling rate after solid solution heat treatment has a significant impact on the γ′ precipitation behavior of forged nickel-based powder superalloys. Precise control of the cooling rate holds promise for further improving the service performance of deformed alloys. This study investigated the effects of different cooling rates on the γ′ precipitation behavior and mechanical properties of forged novel nickel-based powder superalloys. An in-situ high-temperature observation system with precise and controllable cooling rates was used in this study to analyze the effects of cooling rate on the morphology, volume fraction, and size distribution of the γ′. Additionally, nanoindentation tests were conducted to evaluate the mechanical properties of the solution-treated alloys at different cooling rates. The T4 treatment process with a cooling rate of 100 °C/s resulted in excellent overall mechanical properties, with a nano-hardness of 581 HV and an elastic modulus of 260 GPa. As the cooling rate decreases, the increase in the misfit between γ and γ′, led to coarsening and irregular growth of the γ′. The morphology of the γ′ changed from spherical to cubic and eventually to dendritic. The changes in the size and morphology of the γ′ led to alterations in the deformation mechanism, from weakly coupled dislocations shearing the γ′ to strongly coupled dislocations shearing the γ′, followed by stacking fault dislocations shearing the γ′, and finally evolving into dislocation pile-up around the large γ′.