Strain rate effect on the tension and compression stress-state asymmetry for electron beam additive manufactured Ti6Al4V

The present experimental investigation lays the groundwork for coupling the plastic flow stresses of an Additive Manufactured (AM) Ti6Al4V with the corresponding strain hardening rate responses and fracture morphologies for this material at varying strain rates and stress states for the first time. The macroscopic response was obtained under different stress states (uniaxial tension and compression) and deformation rates (ranging from quasi-static at 0.001 s(-1) to the high rate domain at 1500 s(-1)) to elucidate the tension-compression asymmetry and strain rate dependence of the material. The results identified that, (a) compressive yield strengths are higher than their tensile counterparts and (b) the strength differential effect is more prominent under high strain rates. The mechanical behavior is explained in terms of deformation mechanisms reasoned from close inspection of strain hardening rate curves. Dislocation glide and mechanical twinning contribution as dominant plastic units were identified in stages and their relation with deformation mode and rate was established. Based on fractography analyses of the tensile samples, a rate dependence showed a shift from classic cup-cone fracture at quasi-static rates to fracture along the shear plane at high strain rates. The high strain rate compression samples also show an interesting fracture morphology with high speed video capturing adiabatic shear localization.