Anisotropic tensile and ratcheting behavior of commercially pure titanium processed via cross rolling and annealing

Abstract

Microstructures, crystallographic textures, and mechanical properties for two different orientations along the rolling direction (RD) and transverse direction (TD) have been investigated in grade 2 commercially pure titanium sheet processed via cross rolling and annealing. The stress-strain curve has been simulated based on Viscoplastic self consistent (VPSC) model and relative slip/twin activity has been calculated for tensile and ratcheting deformation. The predicted slip/twin activity has been complemented with electron backscatter diffraction (EBSD) based deformation microstructure so as to shed light on the underlying micro-mechanism of anisotropic deformation behavior of cross rolled and annealed commercially pure titanium. The as received (AR) sheet exhibits equiaxed alpha grains with typical TD-split basal texture. After cross rolling, cross rolled (CR) sheet developed distinctly different RD-split texture. Both AR and CR sheet exhibit lower yield strength, higher elongation and higher ratcheting life for RD compared to TD orientation. However, the anisotropy in tensile properties have been found to be lower in CR sample, whereas the anisotropy in ratcheting properties have been found to be higher in CR sample compared to AR sample. VPSC simulation of tensile stress-strain response in the plastic regime reveals prism slip system {101¯0}<112¯0>, which acts as the primary mode of deformation in titanium gets suppressed with increase in strain, while basal and pyramidal slip activity rises in RD orientation and the situation is exactly reverse in case of TD orientation of cross rolled samples. In addition, electron backscatter diffraction based characterization of deformation microstructure reveals suppression of twinning activity too in CR samples. The manifestation of basal slip activity under controlled cyclic stress applied during ratcheting has been attributed for the augmentation of higher anisotropy in ratcheting response in CR samples.