Influence of γ’ precipitate on deformation and fracture during creep in PM nickel-based superalloy

FGH96 is a powder metallurgy nickel based superally used for turbine disk of aero-engines. In the present study FGH96 alloy with four different γ′ precipitate microstructures were produced via solution heat-treatment with different cooling rates, and the maximum cooling rate reached 400 ​°C/min which was a super cooling rate for Nickel-based superalloy. The creep tests were conducted for PM FGH96 alloy under the testing condition of 704 ​°C and 690 ​MPa. The relationship between the creep properties and the distribution of γ’ precipitate was established. The creep mechanism was analyzed by using TEM and ACTEM, and the dislocation movement was studied at the atomic scale. The creep strain rate was calculated through a physically based crystal slip model established based on crystal plasticity. The calculated results were consistent with the test ones, illustrating the validity of the model. The fracture mechanism was also investigated, and the results showed that the creep cracks generated on the surface due to the oxidation. It was observed that the cracks propagated in different ways depending on the different average diameters of ​γ′ ​precipitate. With the decrease of the average ​γ’ ​precipitate size, the critical shearing stress increased and the resistance of the dislocation slipping increased. The fracture mechanism for the primary stage transformed from intragranular to intergranular due to the change of dislocation slipping. [Display omitted] •The relationship between the cooling rate, morphology of γ′ precipitate and creep mechanism has been investigated.•Even the size of γ′ precipitates is smaller than 50 ​nm, the deformation mechanism is still microtwining.•The critical shearing stress increases with the decrease of γ′ size, leading to better creep property of FGH96 superalloy.•With the decrease of size of γ′ precipitates, the fracture mechanism transforms from intragranular to intergranular.