Investigation on the Thermal Deformation Behavior of the Nickel-Based Superalloy Strengthened by γ′ Phase

The isothermal compression tests of the nickel-based superalloy Waspaloy were carried out under various temperatures from 1040 to 1120 degrees C and strain rates from 0.01 to 10 s(-1) with the height reduction of 60% and the flow stress curves were obtained. The curves show that the flow stress is greatly affected by the temperature and strain rates. Regression analysis of the experimental results was carried out to learn about the deformation behavior through the Arrhenius equation and came to the conclusion that the activation energy of Waspaloy is 669.7 kJ/mol. The constitutive equation of the Waspaloy was constructed. Meanwhile, the processing maps of the Waspaloy for the power dissipation and the flow instability were constructed. The processing map of the power dissipation and the flow instability depicts that the strain plays a major role in the processing maps. The instability zone is prone to appear at higher strain rates with the increasing strains. According to the instability processing map, there are three unsafe regimes around 1040-1120 degrees C/1.5-10 s(-1), 1040-1080 degrees C/0.02-0.1 s(-1) and 1110-1120 degrees C/0.02-0.3 s(-1) that should be avoided during deformation process. The power dissipation maps show that the maximum dissipation is prone to appear at low strain rates (0.01 s(-1)) when the strain is about 0.1 similar to 0.6 while at middle strain rates (0.1-1 s(-1)) when the strain is over 0.6, and when the true strain is 0.9, the optimum processing condition is around 1060-1120 degrees C/0.1-1 s(-1). The dynamic microstructures under different temperatures and strain rates were also obtained. We concluded that lower strain rates and higher temperatures are more applicable to obtain fully-recrystallized microstructures. Based on the instability maps and the power dissipation maps and the dynamic microstructures, the optimum deformation conditions are determined to be around 1080-1100 degrees C/0.1-1 s(-1) and 1040-1120 degrees C/0.01 s(-1).