Shift of dynamic recrystallization kinetics in thermal compression induced by prior cold deformation treatment at Ni80A superalloy

To achieve the uniform and fine-grained microstructures during thermal deformation of nickel-based superalloys, a novel two-stage deformation approach was employed, involving prior cold deformation treatment (PCDT) and subsequent thermal deformation. Experimental investigations concerning this two-stage deformation method were carried out on Ni80A superalloy, encompassing various combinations of cold and thermal compression parameters. The analysis of microstructures revealed that PCDT significantly enhances dynamic recrystallization (DRX) process, resulting in fine-grained microstructures during thermal compression and expanding the processing-parameter domains for grain refinement. To clarify the shift of DRX kinetics in thermal compression induced by PCDT, the DRX kinetics models considering this pre-treatment were derived. These models demonstrated a linear inverse correlation between the activation energy within DRX kinetics models and prior stored energy from PCDT. This suggested that PCDT promotes the DRX process by reducing the activation energy during thermal compression. Following, the kinetics curves depicting DRX volume fraction during thermal deformation were drawn. Results indicated that under an identical thermal compression condition, the kinetics curve shifts towards decreasing strain with increasing of prior cold deformation. Under various thermal compression conditions, these kinetics curves for Ni80A superalloy processed with PCDT get shifted to the direction of decreasing strain when compared to the alloy without PCDT. These shifts underscore a pronounced acceleration of DRX process induced by PCDT. Finally, a finite element model incorporating DRX kinetics models was developed to further illustrate the influence of PCDT on the shift of DRX in an upsetting process, which shows a promising potential for theoretical calculations.