Tensile Deformation Behaviors of Pure Ti with Different Grain Sizes under Wide-Range of Strain Rate.

In this study, pure titanium equivalent to Grade 1 was subjected to tensile tests at strain rates ranging from 10-6 to 100 s-1 to investigate the relationship between its mechanical properties and its twinning and slip. Deformation properties and microstructures of samples having average grain sizes of 210 µm (Ti-210), 30 µm (Ti-30), and 5 µm (Ti-5) were evaluated. With increasing strain rates, the 0.2% proof stress and ultimate tensile strength increased for all samples; the fracture strain increased for Ti-210, decreased for Ti-5, and changed negligibly for Ti-30. Comparing high (100 s-1) and low (10-6 s-1) strain rates, twinning occurred more frequently in Ti-30 and Ti-210 at high strain rates, but the frequency did not change in Ti-5. The frequency of 1st order pyramidal slip tended to be higher in Ti-30 and Ti-5 at low strain rates. The higher ductility exhibited by Ti-210 at high strain rates was attributed to the high frequency of twinning. In contrast, the higher ductility of Ti-5 at low strain rates was attributed to the activity of the 1st order pyramidal slip.

Evaluation of depth of dislocation visibility in SEM electron channeling contrast imaging in Ti-6Al-4V alloy using serial sectioning method.

In this study, we conducted a quantitative evaluation of dislocation density by scanning electron microscopy electron channeling contrast imaging for α grains of a Ti-6Al-4V alloy deformed at room temperature. The depth of visibility of dislocations is experimentally measured as 140 to 160 nm by a serial sectioning observation. This result is compared with the theoretical value and applied to evaluate dislocation density. These factors confirm that the theoretically calculated value of the depth of visibility, at 5 to 6 times the extinction distance, is valid for the hexagonal close-packed Ti alloy.