Impact of the solution cooling rate and of thermal aging on the creep properties of the new cast & wrought René 65 Ni-based superalloy

Aeroengines turbine disks can encounter temperature in excess of 700°C-750°C for hundreds to thousands of hours in the rim sections during service operations, exposures which may affect the viscoplastic properties of the alloys due to strengthening particles' growth. The present work aims at quantifying and analyzing the impact of γ′-size evolutions and of intermetallic grain-boundary precipitation during long-term thermal exposures at 700°C and 800°C on the creep properties at 700°C of the newly developed René 65 alloy. In an aim to separate both effects, various sub-solvus solution heat treatments with different cooling rates were used to achieve γ′ sizes comparable to a given thermal exposure in the 700-800°C range, without the precipitation of secondary intermetallic particles at grain boundaries. Using this methodology, it is shown unambiguously that the precipitation of TCP phases at grain boundaries is deleterious to the creep properties at 700°C/800 MPa.