Dynamic Deformation Behavior of the Electron Beam Melted Ti-6al Alloy

Abstract

In this study, dynamic deformation behavior of electron beam melted Ti-6Al-4V alloy and effect of initial defects on deformation process of the alloy were investigated with high strain rate experimental and numerical studies. Dynamic compression tests at the strain rates of 350, 850, 1250, 1750, 1950, and 2500/s at room temperature and at higher temperatures of 150 and 240 degrees C were performed using a split-Hopkinson pressure bar. Compression simulations in three dimensions (3D) with LS-Dyna software were conducted using the determined Johnson-Cook parameters of the Ti-6Al-4V alloy specimens, to assess the strain, temperature distribution during deformation. In addition, simulation studies with initial defects in the model were performed to investigate the effect of these defects on strain formation during compression. The experimental results showed that strain rates over 1250/s caused failure at 45 degrees to the loading direction. Adiabatic shear bands were observed for the specimens compressed at the strain rates of 1250/s and higher. As strain rate increased from 1250 to 2500/s, the type of adiabatic shear band altered from deformed to transformed type. The simulation results showed that initial defects in the specimen led to formation of higher plastic strain in the direction of 45 degrees around initial defects. This high strain might be the cause of formation of adiabatic shear band. The simulation results also indicated that void morphology could affect strain distribution in the specimen.