Non-classical homogeneous precipitation mediated by compositional fluctuations in titanium alloys

S. Nag; Y. Zheng; R. E.A. Williams; A. Devaraj; A. Boyne; Y. Wang; P. C. Collins; G. B. Viswanathan; J. S. Tiley; B. C. Muddle; R. Banerjee; H. L. Fraser

doi:10.1016/j.actamat.2012.07.033

Non-classical homogeneous precipitation mediated by compositional fluctuations in titanium alloys

S. Nag, Y. Zheng, R. E.A. Williams, A. Devaraj, A. Boyne, Y. Wang, P. C. Collins, G. B. Viswanathan, J. S. Tiley, B. C. Muddle, R. Banerjee, H. L. Fraser

Research output: Contribution to journal › Article › peer-review

129 Scopus citations

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
Pages (from-to)	6247-6256
Number of pages	10
Journal	Acta Materialia
Volume	60
Issue number	18
DOIs	https://doi.org/10.1016/j.actamat.2012.07.033
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
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

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10.1016/j.actamat.2012.07.033

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title = "Non-classical homogeneous precipitation mediated by compositional fluctuations in titanium alloys",

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 = "Atom probe tomography (APT), Nucleation of phase transformations, Precipitation, Thermodynamics, Titanium alloys",

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year = "2012",

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AU - Nag, S.

AU - Zheng, Y.

AU - Williams, R. E.A.

AU - Devaraj, A.

AU - Boyne, A.

AU - Wang, Y.

AU - Collins, P. C.

AU - Viswanathan, G. B.

AU - Tiley, J. S.

AU - Muddle, B. C.

AU - Banerjee, R.

AU - Fraser, H. L.

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N2 - 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.

AB - 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.

KW - Atom probe tomography (APT)

KW - Nucleation of phase transformations

KW - Precipitation

KW - Thermodynamics

KW - Titanium alloys

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Non-classical homogeneous precipitation mediated by compositional fluctuations in titanium alloys

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