Titanium's high-temperature elastic constants through the hcp-bcc phase transformation

The five independent elastic constants of hexagonal monocrystal titanium were determined up to the phase-transformation temperature, and the two isotropic elastic constants of polycrystalline titanium were determined beyond, up to 1300 K. Anomalous temperature dependences were observed just below the phase-transformation temperature: C11 and C66 increase with increasing temperature whereas C33 and C44 remarkably decrease, for example. To determine the Cij, we used the free-vibration resonance frequencies obtained by electromagnetic acoustic resonance. After the phase transformation, the resonance frequencies changed little with the temperature increase, showing that the bcc-phase elastic constants change little with temperature. The polycrystalline elastic constants remained unchanged up to 1300 K after the phase transformation. The anomalous temperature dependence near the transformation is interpreted in terms of the small c/a ratio of the hcp phase and change of the atomic distances to meet the Burgers lattice relationship. Temperature-insensitive elastic constants in the bcc phase suggest the stabilizing of the bcc phase with increasing temperature. © 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved