Experimental Characterization and Constitutive Modeling of the Effect of Prior Inelastic Strain on the Viscoplastic Behavior of AD730 at 700 °C

The influence of prior plastic deformation on the viscoplastic behavior of Ni‐based superalloys at high temperature is a critical aspect in the design of turbine disk components, as plastic strains can be introduced during quenching operations or intentionally applied through controlled pre‐spinning processes. In this study, the stress relaxation behavior of a polycrystalline Ni‐based superalloy (AD730) at 700 °C is investigated following various prior deformation conditions, including plastic strain obtained during tensile tests at room temperature (RT) and at 700 °C. For both temperature conditions, a significant increase in the viscoplastic strain rate, by up to two orders of magnitude, was observed at 700 °C with increasing prior plastic strain. This effect appears to saturate, as demonstrated by multiple stress relaxation tests. Moreover, creep pre‐strain was applied followed by stress relaxation, resulting in a similar impact compared to tensile prior plastic strain. A phenomenological constitutive model is developed, based on a two viscoplastic potentials framework that accounts for both hardening and viscous mechanisms under isothermal conditions. The impact of processing‐induced plastic strain under anisothermal conditions on relaxation and creep at 700 °C is also discussed.