The strain hardening effect and dynamic recovery behavior of a Ni-based superalloy are studied by isothermal compressive tests. A new unified dislocation-density based constitutive model is developed to characterize the strain hardening effect and dynamic recovery behavior of the studied superalloy. In the developed constitutive model, some material parameters (yield stress, strain hardening coefficient, and dynamic recovery coefficient) are assumed as functions of initial grain size, deformation temperature, and strain rate. An iterative algorithm is designed to predict the high-temperature deformation behaviors under time-variant hot working conditions. The hot deformation parameters and material parameters can be updated in each strain increment. Comparisons between the experimental and calculated flow stresses indicate that the developed constitutive model can accurately describe the high-temperature deformation behavior of the studied superalloy. Furthermore, the developed constitutive model is also successfully used for analyzing time-variant hot working processes.

A unified physically based constitutive model for describing strain hardening effect and dynamic recovery behavior of a Ni-based superalloy

A simple Zerilli–Armstrong constitutive equation for modeling and prediction of hot deformation flow stress of steels

Effect of pre-treatment on hot deformation behavior and processing map of an aged nickel-based superalloy

Plane strain hot compression tests of 5754 aluminum alloy were conducted on a Gleeble-3500 thermo-mechanical simulator under various conditions. These tests simulated flat rolling to investigate how hardening and softening behaviors respond to controlled parameters, such as the deformation temperature and strain rate. This data allowed the parameters for the hot rolling process to be optimized. The restoration mechanism primarily proceeds via dynamic recovery, as shown by the deformed microstructure analysis and strain-stress curves. The dislocation density was used as internal state variable to develop a physical constitutive model, which characterized the evolution of the dislocation density caused by strain-hardening and dynamic recovery behaviors. The relationship between the flow stress and the dislocation density could be quantified with this model. The strain-hardening and softening behavior was analyzed in detail by Kocks-Mecking type plots. Furthermore, the relevant material coefficients were expressed as functions related to the temperature and the strain rate. The experimental flow stress was found to be in close agreement with the calculated, which confirms that the model developed herein can represent the flow behaviors of the 5754 aluminum alloy effectively.

A physical-based constitutive model to describe the strain-hardening and dynamic recovery behaviors of 5754 aluminum alloy

An enhanced Johnson-Cook strength model for splitting strain rate and temperature effects on lower yield stress and plastic flow

A modified Johnson-Cook constitutive equation of Ti-6Al-4V alloy is proposed based on hot compression tests performed in the temperature range of 1073-1323 K and strain rate 0.001-1 s−1. The experimental stress-strain data were employed to develop the modified Johnson-Cook constitutive equation of different phase regimes (α + β and β phase). The predicted flow stresses using the developed equation were compared with experimental data. Correlation coefficient (R) and average absolute relative error (AARE) were introduced to verify the validity of the constitutive equation. The values of R and AARE for α + β phase were 0.990 and 7.81%, respectively. And in β phase region, the values of R and AARE were 0.985 and 10.36%, respectively. Meanwhile, the accuracy, the number of material constants involved, and the computational time required of the constitutive equation were evaluated by comparing with a strain-compensated Arrhenius-type constitutive equation. The results indicate that accuracy of modified Johnson-Cook constitutive equation is higher than that of compensated Arrhenius-type model at α + β phase, while lower at single β phase region. Meanwhile, the time required for evaluating the material constants of modified Johnson-Cook constitutive equation is much shorter than that of the strain-compensated Arrhenius type ones.

Peng Zhai

Papers

A Modified Johnson-Cook Constitutive Equation to Predict Hot Deformation Behavior of Ti-6Al-4V Alloy