Tensile anisotropy associated microstructural and microtextural evolution in a metastable beta titanium alloy

Tensile anisotropy behaviour of metastable beta titanium alloy beta-21s (Ti-15Mo-2.7Nb-3Al-0.2Si) sheet in solution treated condition is evaluated at room temperature along three different orientation (rolling direction, 45 degrees to rolling direction and transverse direction). In addition to fractographic studies, the microstructural and microtextural evolution is investigated in the post-tensile deformed condition through optical metallography, scanning electron microscopy (SEM) and Electron Backscattered Diffraction (EBSD). Quantification of mechanical anisotropy by evaluating the % In-Plane Anisotropy (%IPA), Anisotropic Index (delta), yield loci and plastic strain ratio indicated considerable anisotropy in strengths and ductility. Irrespective of testing orientation, the deformed microstructure is characterized by fine to coarse planar slip bands, however the slip bands observed along 45 degrees is relatively widely spaced. The evolution of dislocation density obtained from kernel average mis-orientation (KAM) maps is unaffected by the tensile testing direction. Although EBSD derived Taylor factor maps revealed slip mediated deformation behaviour dominated by {110} < 111 > slip systems along all testing directions, the Taylor factor distribution divulged complex dependence on test orientation. Despite weak to moderate microtextural changes are noticed in a-fiber and n-fiber texture components, the textural evolution is strongly influenced by the testing orientation.