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.
Original language | English |
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Pages (from-to) | 6247-6256 |
Number of pages | 10 |
Journal | Acta Materialia |
Volume | 60 |
Issue number | 18 |
DOIs | |
State | Published - Oct 2012 |
Externally published | Yes |
Funding
The authors would like to acknowledge the US National Science Foundation (DMR Award # 1006487), with Dr Alan Ardell as Program Manager) and the US Air Force Research Laboratory (AFRL contract FA8650-08-C-5226) for providing financial support for this study. In addition, the authors also gratefully acknowledge the Center for the Accelerated Maturation of Materials (CAMM) at the Ohio State University and the Center for Advanced Research and Technology (CART) at the University of North Texas for access to the experimental facilities used for this study.
Funders | Funder number |
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US National Science Foundation | |
Division of Materials Research | 1006487 |
Air Force Research Laboratory | FA8650-08-C-5226 |
Keywords
- Atom probe tomography (APT)
- Nucleation of phase transformations
- Precipitation
- Thermodynamics
- Titanium alloys