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Article
Non-classical Homogeneous Precipitation Mediated by Compositional Fluctuations in Titanium Alloys
Acta Materialia (2012)
  • S. Nag, Ohio State University - Main Campus
  • Y. Zheng, Ohio State University - Main Campus
  • R.E.A. Williams, Ohio State University - Main Campus
  • A. Devaraj, University of North Texas
  • A. Boyne, Ohio State University - Main Campus
  • Y. Wang, Ohio State University - Main Campus
  • Peter C. Collins, Ohio State University - Main Campus
  • G.B. Viswanathan, Ohio State University - Main Campus
  • J.S. Tiley, Wright Patterson Air Force Base
  • B.C. Muddle, Monash University
  • R. Banerjee, University of North Texas
  • H.L. Fraser, Ohio State University - Main Campus
Abstract
This paper presents experimental evidence of homogeneous precipitation of the α-phase within the β matrix of a titanium alloy, and then accounts for this phase transformation by a new, non-classical mechanism involving compositional fluctuations, based on the pseudo-spinodal concept [1]. This mechanism involves local compositional fluctuations of small amplitude which, when of a certain magnitude, can favor thermodynamically certain regions of the β matrix to transform congruently to the α-phase but with compositions far from equilibrium. Subsequently, as measured experimentally using the tomographical atom probe, continuous diffusional partitioning between the parent β- and product α-phases during isothermal annealing drives their compositions towards equilibrium. For a given alloy composition, the decomposition mechanism is strongly temperature dependent, which would be expected for homogeneous precipitation via the compositional fluctuation-mediated mechanism but not necessarily for one based on classical nucleation theory. The applicability of this mechanism to phase transformations in general is noted.
Keywords
  • Nucleation of phase transformations,
  • Titanium alloys,
  • Atom probe tomography (APT),
  • Thermodynamics,
  • Precipitation
Publication Date
2012
DOI
10.1016/j.actamat.2012.07.033
Publisher Statement
Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.
Citation Information
S. Nag, Y. Zheng, R.E.A. Williams, A. Devaraj, et al.. "Non-classical Homogeneous Precipitation Mediated by Compositional Fluctuations in Titanium Alloys" Acta Materialia Vol. 60 Iss. 18 (2012) p. 6247 - 6256
Available at: http://works.bepress.com/peter-collins/5/