Effect of crystallographic texture on ratcheting response of commercially pure titanium

Abstract

The effect of crystallographic texture on ratcheting behavior of cold rolled and annealed plate of commercially pure titanium has been investigated. Flat fatigue test specimens of two different orientations along rolling and transverse direction have been machined to obtain distinct texture with crystallographic direction close to 〈101¯0〉–〈112¯0〉 and 〈0001〉 ║ loading direction for sample A and B respectively. The microstructure, texture and grain boundary characteristics of tested specimens have been analyzed using electron backscatter diffraction data. The significant anisotropy in strain hardening for monotonic loading is not manifested in anisotropy in ratcheting response and shows only 20% lower fatigue life in orientation B compared to A under same stress cycle condition. The anisotropy in ratcheting response has been attributed to the unique combination of dislocation activity and twin variant selection in orientation A and B. Orientation A with higher Schmid factor for prism slip efficiently partitions the accumulated backstress by activating prism slip and detwinning of thin multiple twin variants which causes slow accumulation of ratcheting strain for higher number of cycle. While in orientation B prism slip is restricted and detwinning is difficult due to formation of thick single variant extension twins that causes its early failure.