Elastic properties of single-crystalline ω phase in titanium

The elastic properties of single-crystalline omega (hexagonal) phase of titanium are studied. Understanding the elastic properties is important for the development of biomedical titanium alloys with a low Young's modulus. However, the elastic properties of the omega phase have remained unclear because of the difficulty in preparing a large single crystal consisting of a single phase of the omega phase, even though the omega phase has been believed to exhibit a higher elastic modulus than the beta (body-centered cubic) phase. In this work, pure titanium was severely deformed by high-pressure torsion processing, to obtain polycrystalline specimens consisting exclusively of the omega phase, which is metastable at room temperature. For the omega-phase polycrystal, the complete set of elastic stiffness components was measured by RUS combined with laser Doppler interferometery. By analyzing the elastic stiffness of the omega-phase polycrystal on the basis of an inverse Voigt-Reuss-Hill approximation, the elastic stiffness components of the single-crystalline omega phase were determined. The Young's modulus of the omega phase along < 0001 > was found to be clearly higher than that along < 11 (2) over bar0 >, and the shear modulus also exhibited anisotropy. Importantly, the Young's modulus and shear modulus of the metastable omega phase were higher than those of the beta phase and also higher than those of the alpha (hexagonal close-packed) phase, which is stable at room temperature. Furthermore, analysis by a micromechanics model using the determined elastic stiffness deduced the effect of omega phase formation on the elastic properties of beta-phase titanium alloys. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.