Description of Grain Evolution Behaviors in Mesoscale during Electrical-Thermal-Mechanical Coupling Compression Processes for Ni80A Superalloy

Engine components, particularly exhaust valves, are manufactured by a specific forming process known as electric upsetting, which contributes to microstructures with finer grains which enhance the performance of these components. To this end, it is necessarily required to describe the grain evolution behaviors of heat-resistant alloys during the electrical-thermal-mechanical coupling forming process. The grain evolution behaviors of Ni80A superalloy including dynamic recrystallization (DRX) kinetics models and mesoscale cellular automaton (CA) model are solved from the acquired stress–strain curves in resistance heating isothermal compression tests. Following which, a multi-field and multi-scale coupling FEM model is established by embedding the multi-scale grain evolution models into the electrical-thermal-mechanical multi-field coupling compression model. Then the grain evolution behaviors in isothermal compressions with processing conditions are reproduced by simulations. The results reveal that during the isothermal compressions, recrystallized grains intend to bulge and generate around the original grain boundaries, representing as ‘necklace’ microstructures inhomogeneously distributed in the matrix, and then such grain morphology is gradually replaced by refined and equiaxed DRX grains. For a fixed strain, grain size decreases with decreasing temperature and increasing strain rate. Finally, the EBSD characterization results show that the developed FEM model can well describe the grain evolution behaviors of Ni80A superalloy in electrical-thermal-mechanical coupling compression process.