The role of crystallographic texture on load reversal and low cycle fatigue performance of commercially pure titanium

Abstract

Microstructural and textural design of hexagonal close packed titanium is of paramount importance for in-service applications comprising of monotonic and cyclic loading. The effect of initial texture on load reversal and low cycle fatigue behaviour of commercially pure titanium was investigated using servohydraulic testing, electron back scatter diffraction (EBSD) and in situ experiments. Uniaxial tensile test on sample A with prismatic texture along the tensile axis showed lower yield strength but higher ductility and twin activity with multiple variants compared to orientation B with basal texture along the tensile axis. Tension-compression load reversal tests show distinct Bauschinger co-efficient for samples A and B at different strain while displacement control cyclic tests yield higher fatigue life for sample B. Higher extent of detwinning in sample B during load reversal in cyclic test releases the backstress and contributes to higher cyclic ductility. In situ EBSD experiments provide evidence of partial reversibility of twinned microstructure in titanium, which explains the formation of thin, small twins during cyclic deformation and rationalizes the difference in monotonic and cyclic ductility. Thus multiple twin variants with intersecting twins contribute to higher strain hardening and ductility in monotonic tension but cyclic life depends on the extent of detwinning.