Prestrain and annealing effects on superalloy deformation: experiment and modelling

Accurate understanding of coupled deformation and annealing behavior is crucial for design and optimization of multi-pass forming. The two-stage uniaxial tensile tests with intermediate annealing were performed to explore the deformation behavior and microstructure evolution of the GH5188 superalloy. Experimental results reveal that increasing prestrain enhances yield strength but reduces the elongation and hardening exponent due to dislocation accumulation. A significant improvement in ductility and work-hardening is observed only under conditions of large prestrain and high annealing temperature. The enhancement is primarily attributed to the dislocation density reduction and the formation of abundant annealing twins during annealing. Furthermore, a new dislocation density-based constitutive model was developed, in which the parameters are characterized as the function of prestrain and annealing temperature. The model can accurately predict stress-strain relationships under varying prestrain and annealing processes, with an accuracy exceeding 93 %. Finite element simulations of a multi-pass forming process for a thin-walled superalloy part were carried out. Compared with the non-annealed condition, the predicted results based on the developed model align more accurately with the experimental observations, demonstrating the ability to capture the effects of deformation and annealing and its effectiveness in the actual forming application. This work provides a physically grounded modeling approach and theoretical support for optimizing multi-pass forming of alloys.