Characterization of Microstructure and Flow Behavior of a Hot-Deformed Ni-Based Superalloy: Effect of Primary Heat Treatment
摘要
The effect of homogenization heat treatment at 1200 °C for 2 hours on the hot deformation behavior and the corresponding microstructural evolutions of cast GTD-111 Ni-based superalloy has been studied. Hot compression tests were carried out at temperatures and strain rates of 950–1100 °C and 0.001–1 s−1, respectively. Optical and field emission scanning electron microscopes and electron backscatter diffraction were employed to study the microstructural evolutions due to hot deformation. The results showed that the homogenization heat treatment leads to the partial breaking of dendrite arms, partial dissolution of interdendritic phase, increase in the size of γ′ precipitates, formation of MC carbides (M is mainly Ta, Ti and W), dissolution of γ + γ′ eutectic phase, and increase in the flow stress of the alloy, depending on the deformation condition. It was found that the decrease in flow stress rises as the strain rate increases or the temperature decreases. A synergy between the dynamic recrystallization, breaking of dendritic structure, and coarsening of precipitates was found as the underlying microstructural mechanism of observed flow softening. Using the hyperbolic-sine constitutive equation, the apparent activation energy values for the cast and homogenized samples were determined as 860 and 986 kJ/mol, respectively.