Formation mechanism of basin-like depression defect in electric upsetting process of Ni80A superalloy

A kind of surface instability, basin-like depression defect companied by mixed grain structure at the bottom of large-scale valve during electric upsetting process, would significantly influence the microstructures and mechanical properties of components. In order to analyze the forming process of the basin-like depression defect, a finite element model for the electric upsetting process of Ni80A superalloy was developed using multi-field and multi-scale coupling analysis method. Subsequently, a series of parameters loading path schemes for force and current were designed by varying the initial value, peak value and value level, and their effects on basin-like depression and mixed grain structure were simulated and uncovered. It is concluded that the changes of heating speed and pressurization speed result in the different flow velocities between the inner and outer layers of billet, thus exerting the basin-like depression. Simulation results also indicate that these defects can be optimized through the parameter coordination between force and current. Finally, the validity and reliability of the finite element model were verified by physical experiments in electric upsetting process.