Designing Hot Working Processes of Nickel Base Superalloys Using FEM Simulation

Abstract

Knowledge of correct flow stress curves of Ni-based alloys at high temperatures is of essential importance for reliable plasto-mechanical simulations in materials processing and for an effective planning and designing of industrial hot forming schedules like hot rolling or forging. The experiments are performed on a computer controlled servo-hydraulic testing machine at IBF (Institute of Metal Forming). To avoid an inhomogeneous deformation due to the influence of friction and initial microstructure, a suitable specimen geometry and lubricant is used and a thermal treatment before testing has to provide a microstructure, similar to the structure of the material in the real process. The compression tests are performed within a furnace, which keeps sample, tools and surrounding atmosphere at the defined forming temperature. The uniaxial compressions were carried out in the range of strain rates between 0.001 and 50 s−1 and temperatures between 950 and 1280°C. Furthermore two-stage step tests are carried out to derive the work hardening and softening behaviour as well as the recrystallisation kinetics of the selected Ni-based alloys. At the end of this work a material model is adapted by the previously determined material data. This model is integrated into the Finite Element program LARSTRAN/SHAPE to calculate a forging process of the material Alloy 617.