Hot deformation behavior and processing map of a typical Ni-based superalloy
The hot compressive deformation behaviors of a typical Ni-based superalloy are investigated over wide ranges of forming temperature and strain rate. Based on the experimental data, the efficiencies of power dissipation and instability parameters are evaluated and processing maps are developed to optimize the hot working processing. The microstructures of the studied Ni-based superalloy are analyzed to correlate with the processing maps. It can be found that the flow stress is sensitive to the forming temperature and strain rate. With the increase of forming temperature or the decrease of strain rate, the flow stress significantly decreases. The changes of instability domains may be related to the adiabatic shear bands and the evolution of δ phase during the hot formation. Three optimum hot deformation domains for different forming processes (ingot cogging, conventional die forging and isothermal die forging) are identified, which are validated by the microstructural features and adiabatic shear bands. The optimum window for the ingot cogging processing is identified as the temperature range of 1010-1040 oC and strain rate range of 0.1-1 1/s. The temperature range of 980-1040 and strain rate range of 0.01-0.1 1/s can be selected for the conventional die forging. Additionally, the optimum hot working domain for the isothermal die forging is 1010-1040 oC and near/below 0.001 1/s.