Thermally Activated Acoustic Relaxation in Nanostructured and Ultrafine-Grained Titanium

In the range of 5-325 K, the temperature dependence of acoustic properties - absorption and dynamic Young’s modulus - was studied in nanocrystalline and fine-crystalline technical purity titanium VT1-0. Measurements were performed using resonance mechanical spectroscopy at 2.4-3.7 kHz. The influence of grain size on low-temperature acoustic behavior was examined.Samples with varying grain sizes were produced by severe plastic deformation through rolling at 100 K and 290 K to true strains of 120-190%, followed by annealing at 525 K, 720 K, and 940 K. Their structures were characterized by electron microscopy and X-ray diffraction.Intense plastic deformation was found to induce an acoustic anomaly, peak P1, at 150-230 K. Transition from fine- to nanocrystalline states introduced an additional absorption peak, P2, at 43-78 K. A microscopic dislocation model was proposed to explain these phenomena. The activation parameters of P1 correspond to thermally activated detachment of dislocation segments from local defects, consistent with the Koiwa-Hasiguti peak. In contrast, the activation parameters of P2 reflect dislocation motion across a Peierls barrier via thermally activated kink pair formation, analogous to Bordoni peaks observed in fcc crystals.This study demonstrates how grain refinement and deformation strongly affect the acoustic response of titanium, revealing distinct mechanisms of dislocation dynamics at different temperature ranges.