Hot deformation behavior of a re-containing nickel-based superalloy with a fine-grained structure

In the present work, compression tests were used to evaluate the deformability of the Russian nickel-based superalloy SDZhS-15 (Ni-28(Cr,Co)-12.5(Al,Ti,Nb,Ta)-9(Mo,W,Re)-0.17(C,La,Y,Ce,B), wt.%) in a fine-grained condition obtained by hot forging and annealing at subsolvus temperatures. The initial microstructure consisted mainly of γ grains with a size of 5-10 µm, coarse grain boundary precipitates of the primary γ′ phase with a size of 5-8 µm, intragranular dispersed precipitates of the γ′ phase with a size of 0.1-0.3 µm, and a small volume fraction of carbides. The volume fraction of the γ′ phase in the superalloy is about 68%, the γ′ solvus temperature is Ts=1220 °C. The compression tests were performed in the temperature range of Т=950-1175 °C with an initial strain rate of έ =5ξ10−4 s−1 (ε=65%). The tests showed that the fine-grained superalloy could be successfully deformed at T=950-1175 °C and έ∼10−4-10−3 s−1 without a formation of surface cracks. It was established that the deformation at T=1100-1175 °C corresponded to superplastic conditions (σ<100 MPa and m>0.3). Microstructure examination of the deformed samples revealed that dynamic recrystallization developed at T=950-1100 °C and the dynamic γ grain growth was observed at T=1125-1175°C. It was shown that the deformation at 1125 °C led to the formation of the most homogeneous and fine-grained structure.