High-Temperature Dislocation Climb in the γ′ Rafts of Single-Crystal Superalloys: The Hypothesis of a Control by Dislocation Entry into the Rafts
Résumé
The good mechanical resistance to high-temperature creep of [001] oriented single-crystal superalloys is due to the properties of the rafts, i.e., platelets of the L12 γ′ phase embedded in a γ matrix. At temperatures higher than 900 °C, the plastic strain of the rafts results from the climb of dislocation pairs with a total a⋅⟨100⟩ Burgers vector and/or from the climb at the γ/γ′ interfaces of a/2⋅⟨110⟩ dislocation segments. This climb motion involves the exchange of vacancies between these dislocations and vacancy sinks such as pores and the specimens’ surfaces. In this paper, we suggest that the entry of a⋅⟨100⟩ dislocations into the rafts requires the overcoming of a threshold stress and show that this hypothesis gives a natural explanation to some of the most salient aspects of their mechanical behavior.