Phase transformations in Ti–35Nb–7Zr–5Ta–(0.06–0.68)O alloys

✍ Scribed by J.I. Qazi; B. Marquardt; L.F Allard; H.J. Rack

• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 955 KB
• Volume: 25
• Category: Article
• ISSN: 0928-4931
• DOI: 10.1016/j.msec.2005.01.022

✦ Synopsis

The phase transformations occurring in Ti -35Nb -7Zr -5Ta -(0.06 -0.68)O h solution treated and aged between 427 and 593 -C for 8 h have been investigated. Aging at 427 -C resulted, respectively, in N, N + a and a phase formation for 0.06, 0.46 and 0.68 wt.% O. A modification in N 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 N phase in 0.06 wt.% O. Lenticular a precipitation was observed at higher O content, the volume fraction of a 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 a precipitates and an increase in their aspect ratio. Finally aging of these alloys resulted in the formation of precipitate free zones (PFZs) along prior h grain boundaries, the width of these zones increasing with an increasing aging temperature. These observations are consistent with the ability of O to suppress N phase formation through interruption of the b111À lattice displacement required for this phase's formation, while promoting a phase formation at higher O content, presumably through local ordering within the h phase.