High Temperature Deformation Behavior and Constitutive Modeling for Flow Behavior of Alloy 718

Abstract

In the present work, hot deformation behavior of Alloy 718 was investigated over a temperature range of 1223–1373 K and strain rate range of 10−2–10 s−1. The flow curves were corrected for adiabatic temperature rise, particularly at high strain rates. Arrhenius type constitutive equations were derived for Alloy 718 to model the peak flow stress from apparent and physically based approaches. A stress exponent of 5 was obtained from the power-law equation, indicating that the deformation is governed by the dislocation climb mechanism within the aforementioned processing domain. Further, to model the flow behavior, a generalized constitutive equation was derived in which the effect of strain on the flow stress was incorporated. In addition, artificial neural networks (ANN) method was also employed to model the flow behavior. Statistical parameters such as regression coefficient (R) and average absolute relative error (AARE) indicated that the ANN method was more accurate in predicting the flow behavior with R = 0.99 and AARE = 0.79% compared to the apparent-based constitutive equation with R = 0.99 and AARE = 4.5%. Accuracy of the derived constitutive equation as a material model in finite element (FE) simulation studies was also evaluated. Flow curve predictions obtained from the FE simulation were comparable to the experimental results. The microstructure and hardness at different locations in the deformed samples were consistent with the strain distribution map generated by the FE simulation.