Microstructural evolution of GH4742 superalloy during hot deformation and subsequent solvus treatment

Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 °C). When deformed near the γ′ solvus temperature (1110 °C), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 °C), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 °C), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 °C, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.