Compressive responses of ultrafine-grained titanium within a broad range of strain rates and temperatures

Mechanical behavior of ultrafine-grained (UFG) materials is affected by many factors including “intrinsic” ones such as grain size, dislocation density and concentration of impurities, and “extrinsic” ones such as temperature, strain rate and strain. To evaluate those contributions to the yield and flow stress of commercial-purity titanium, compressive mechanical tests were conducted at strain rates from 10⁻⁴ to 3 × 10³ s⁻¹ and temperature from 77 to 473 K. Microstructure characterization was also carried out to pin-down the underlying mechanisms responsible for the observed mechanical behavior. Results show that the primary strengthening sources for coarse-grained (CG) titanium comes from interstitials, which contribute ∼64% of the yield stress. Grain boundary strengthening, dislocation interaction and interstitials contribute ∼38%, ∼32% and ∼30% of the yield stress of UFG-Ti, respectively. The flow stresses of both CG and UFG titanium depends positively on strain rate and negatively on temperature, but neither strain rate sensitivity (SRS) nor temperature sensitivity (TS) is constant over a wide range. The SRS of titanium is found to increase with increase in grain size and temperature.