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

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 (alpha + beta and beta 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 alpha + beta phase were 0.990 and 7.81%, respectively. And in beta 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 alpha + beta phase, while lower at single beta 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.