Anisotropic behavior and constitutive equations of superplastic deformation of a Ti-6Al-4V alloy

Anisotropic superplastic deformation, e.g., the development of elliptical cross-sections in initially round test pieces, has been reported in a number of materials. Such behavior has been usually attributed to texture (slip as the dominant deformation mode) and/or mechanical fibering. For superplastic titanium alloys, it is believed that contiguous α-phase grains, which is aligned parallel to the rolling/extrusion direction, act as barriers to grain boundary sliding and give rise to superplastic anisotropy. However, there are insufficient studies on the stress-strain rate behavior, i.e., constitutive equations, of anisotropic superplastic deformation. The present paper describes the results on anisotropic mechanical-properties (e.g., principal strains, flow stresses) in uniaxial tension and compression tests of Ti alloy specimens with various orientations. New constitutive equations are proposed to describe the anisotropic superplastic deformation behavior of materials with an elongated grain structure