Abstract
The phase transformations occurring in Ti-35Nb-7Zr-5Ta-(0.06-0.68)O β solution treated and aged between 427 and 593 °C for 8 h have been investigated. Aging at 427 °C resulted, respectively, in ω, ω + α and α phase formation for 0.06, 0.46 and 0.68 wt.% O. A modification in ω phase morphology, from near circular to ellipsoidal, was also observed with increasing O from 0.06 to 0.46 wt.%. Aging at higher temperatures resulted in resolution of the ω phase in 0.06 wt.% O. Lenticular α precipitation was observed at higher O content, the volume fraction of α increasing with increasing O at a constant aging temperature and with increasing aging temperature at a constant O content. The latter also resulted in coarsening of the α precipitates and an increase in their aspect ratio. Finally aging of these alloys resulted in the formation of precipitate free zones (PFZs) along prior β grain boundaries, the width of these zones increasing with an increasing aging temperature. These observations are consistent with the ability of O to suppress ω phase formation through interruption of the 〈111〉 lattice displacement required for this phase's formation, while promoting α phase formation at higher O content, presumably through local ordering within the β phase.
Original language | English |
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Pages (from-to) | 389-397 |
Number of pages | 9 |
Journal | Materials Science and Engineering C |
Volume | 25 |
Issue number | 3 |
DOIs | |
State | Published - May 2005 |
Externally published | Yes |
Event | Selected Papers Presented at the Materials Science and Technology 2004 Meeting: Titanium for Biomedical, Dental, and Healthcare - Duration: Sep 26 2004 → Sep 29 2004 |
Funding
The authors wish to acknowledge the assistance of Dr. Violeta Tsakiris during the early stages of this study. This research sponsored in part by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Freedom CAR and Vehicle Technologies, as a part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the US Department of Energy under contract number DE-AC-00OR22725.
Keywords
- Aging
- Biomaterials
- Metastable β-titanium alloys
- Omega phase
- Oxygen
- Phase transformations