2020 Volume 61 Issue 12 Pages 2320-2328
Strain rate dependencies of deformation behavior of commercial purity titanium specimens having different grain sizes were systematically investigated. Ultrafine-grained titanium with an average grain size of 0.07 µm (UFG-Ti) fabricated by multi-directional forging followed by conventional thermo-mechanical processing, and fine-grained (FG-Ti) and coarse-grained (CG-Ti) specimens with an average grain sizes of 0.8 and 12 µm attained by its, respectively, annealing at 773 and 973 K for 1.8 ks were prepared. The FG- and UFG-Ti specimens exhibited strong strain-rate dependence of 0.2% proof stress, while that of CG-Ti ones were almost constant regardless of applied strain-rate. In-situ X-ray diffraction measurements during tensile tests were also conducted at synchrotron radiation facility, SPring-8. Using the modified Williamson-Hall and the modified Warren-Averbach methods, the activated slip systems and change in dislocation density during deformation were estimated. As a result, it was found that 〈a〉 and 〈c + a〉 slips were activated in FG- and UFG-Ti specimens. On the other hand, the activation of 〈c + a〉 slip was never observed in the CG-Ti ones. It can be, thus, concluded that the different strain-rate dependency of deformation behaviors of specimens with different grain sizes were ascribed to the difference in the deformation mechanisms.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 465–473.
