Effects of Grain Size and Tensile Direction on Strain Rate Sensitivity of Tensile Properties in Pure Titanium Cold-Rolled Sheet

ASTM grade 1 titanium sheets with the strong TD-split type basal texture and grain sizes ranging from 9 to 152 µm were subjected to tensile tests at tensile speeds ranging from 0.1 to 100 mm/min to investigate the strain rate dependency, while considering anisotropy. The yield and flow stresses at each strain level increased proportionally with the logarithm of the strain rate. The slope of these proportionalities, namely, the strain rate sensitivity index of m decreased with increasing grain size and tensile angle to rolling direction, θ. However, in the high-strain region, the larger the grain size, the higher the index m. Meanwhile, uniform elongation decreased with an increase in strain rate except for a θ value of 90°, where uniform elongation was roughly constant. However, the highest uniform elongation was observed in relatively large grain-sized specimens when θ changed from 0° to 45°. There was an average reduction in local elongation with increasing strain rate and grain size; however, an inversed trend was observed with increasing grain size in specimens with a grain size of 9—36 μm when θ was 45°.