On adiabatic shear localization in nanostructured face-centered cubic alloys with different stacking fault energies

Abstract

We have investigated the dynamic (or high strain rate) response of nanostructured face-centered-cubic alloys with different stacking fault energies after severe plastic deformation under uniaxial compression. It is found that adiabatic shear bands were easier to appear in those alloys with lower stacking fault energy, even though under quasi-static loading more obvious hardening behavior was observed with decreasing stacking fault energy. To understand the formation mechanism of adiabatic shear bands, firstly thermal softening during dynamic loading was considered. Dynamic tests within a wide range of temperature and interrupted loading revealed that adiabatic temperature rise prior to plastic instability has only minor effect on the onset of shear localization. Unlike medium/high stacking fault energy materials, strong textures have always been reported after severe plastic deformation in the metals with low stacking fault energy. Hence, influence of texture on the propensity to adiabatic shear bands was taken into account. The dynamic anisotropic behaviors show that the pre-existing texture formed during severe plastic deformation is responsible for the initiation of localized deformation, and the adiabatic temperature rise in the localized region promotes the formation of adiabatic shear bands. To verify the effect of texture on the formation of adiabatic shear bands we have incorporated preferred orientation of grains into finite element modeling based on crystal plasticity. An elastic-viscoplastic continuum slip constitutive relation was adopted to describe the mechanical response of materials, in which the dependence of slip systems' resistance on the temperature evolution was also considered. The simulation results are in good accordance with the experimental results. As such a more comprehensive picture of the formation of adiabatic shear bands in such materials has been uncovered along with the underlying mechanism.