Conjugated precipitation of twin-related α and Ti2Cu phases in a Ti-25V-3Cu alloy

H.P. Ng, P. Nandwana, A. Devaraj, M. Semblanet, S. Nag, P. N. H. Nakashima, S. Meher, C. J. Bettles, M. A. Gibson, H. L. Fraser, B. C. Muddle, R. Banerjee

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Abstract

The formation of conjugated precipitates in a ternary Ti–25V–3Cu (wt.%) (Ti–24.4V–2.3Cu (at.%)) alloy subjected to isothermal aging at 500 C was investigated in this study. X-ray diffraction confirms that the equilibrium precipitates in the alloy are hexagonal α phase and bodycentered-tetragonal (bct) Ti2Cu intermetallic compound. These precipitates are composed of two geometrically symmetrical components, which are verified by transmission electron microscopy (TEM) to be twin-related variants of α and Ti2Cu phases. Atomic-level characterizations incorporating high-resolution TEM and atom probe tomography were used to investigate the early-stage nucleation process of the precipitates. The results reveal that precipitation occurs heterogeneously on plate-like (or disc-like) metastable Cu-enriched GP zones that preferentially inhabit {110}β planes. Crystallographic orientation analyses suggest that the Ti2Cu phase is related to the matrix via a definite orientation relationship of (013)Ti2Cu||(011)β and [100]Ti2Cu||[100]β, while the growth of the α phase is governed by the Potter’s OR such that (1101)α||(011)β and [1120]α||[111]β. (013)Ti2Cu and (1101)α are the twin planes of the respective phases. In spite of highly distinct crystal structures, the conjugated α and Ti2Cu phases attain a nearly perfect lattice correspondence along certain crystallographic planes, which results in a low interfacial energy configuration and favours the co-development of these phases.
Original languageEnglish
Pages (from-to)457 - 471
Number of pages15
JournalActa Materialia
Volume84
DOIs
Publication statusPublished - 2015

Keywords

  • b-Titanium alloy
  • Precipitation
  • Ti2Cu phase
  • Transmission electron microscopy
  • Atom probe tomography

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