Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations

Masakazu Tane (Corresponding Author), Hiroki Nishiyama, Akihiro Umeda, Norihiko L. Okamoto, Koji Inoue, Martin Luckabauer, Yasuyoshi Nagai, Tohru Sekino, Takayoshi Nakano, Tetsu Ichitsubo

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Abstract

In titanium alloys, theω(hexagonal)-phase transformation has been categorized as either a diffusion-mediatedisothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mecha-nism. Here we report a diffusionless isothermalωtransformation that can occur even above theωtransformationtemperature. In body-centered cubic β-titanium alloyed withβ-stabilizing elements, there are locally unstableregions having fewerβ-stabilizing elements owing to quenched-in compositional fluctuations that are inevitablypresent in thermal equilibrium. In these locally unstable regions, diffusionless isothermalωtransformationoccurs even when the entireβregion is stable on average so that athermalωtransformation cannot occur.This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization ofβphase on average. In the diffusionlessisothermal and athermalωtransformations, the transformation rate is dominated by two activation processes: adynamical collapse of{111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionlessisothermal transformation, theω-phase nucleation, resulting from the localized phonon softening, requiresrelatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slowerrates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, thenucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.
Original languageEnglish
Article number043604
JournalPhysical Review Materials
Volume3
Issue number4
DOIs
Publication statusPublished - 16 Apr 2019
Externally publishedYes

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titanium alloys
Titanium alloys
Nucleation
Titanium
softening
Stabilization
Activation energy
Phase transitions
Chemical activation
nucleation
phase transformations
titanium
stabilization
activation
activation energy
Hot Temperature

Cite this

Tane, Masakazu ; Nishiyama, Hiroki ; Umeda, Akihiro ; Okamoto, Norihiko L. ; Inoue, Koji ; Luckabauer, Martin ; Nagai, Yasuyoshi ; Sekino, Tohru ; Nakano, Takayoshi ; Ichitsubo, Tetsu. / Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations. In: Physical Review Materials . 2019 ; Vol. 3, No. 4.
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title = "Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations",
abstract = "In titanium alloys, theω(hexagonal)-phase transformation has been categorized as either a diffusion-mediatedisothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mecha-nism. Here we report a diffusionless isothermalωtransformation that can occur even above theωtransformationtemperature. In body-centered cubic β-titanium alloyed withβ-stabilizing elements, there are locally unstableregions having fewerβ-stabilizing elements owing to quenched-in compositional fluctuations that are inevitablypresent in thermal equilibrium. In these locally unstable regions, diffusionless isothermalωtransformationoccurs even when the entireβregion is stable on average so that athermalωtransformation cannot occur.This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization ofβphase on average. In the diffusionlessisothermal and athermalωtransformations, the transformation rate is dominated by two activation processes: adynamical collapse of{111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionlessisothermal transformation, theω-phase nucleation, resulting from the localized phonon softening, requiresrelatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slowerrates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, thenucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.",
author = "Masakazu Tane and Hiroki Nishiyama and Akihiro Umeda and Okamoto, {Norihiko L.} and Koji Inoue and Martin Luckabauer and Yasuyoshi Nagai and Tohru Sekino and Takayoshi Nakano and Tetsu Ichitsubo",
year = "2019",
month = "4",
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doi = "10.1103/PhysRevMaterials.3.043604",
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Tane, M, Nishiyama, H, Umeda, A, Okamoto, NL, Inoue, K, Luckabauer, M, Nagai, Y, Sekino, T, Nakano, T & Ichitsubo, T 2019, 'Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations', Physical Review Materials , vol. 3, no. 4, 043604 . https://doi.org/10.1103/PhysRevMaterials.3.043604

Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations. / Tane, Masakazu (Corresponding Author); Nishiyama, Hiroki ; Umeda, Akihiro ; Okamoto, Norihiko L. ; Inoue, Koji ; Luckabauer, Martin ; Nagai, Yasuyoshi ; Sekino, Tohru ; Nakano, Takayoshi; Ichitsubo, Tetsu.

In: Physical Review Materials , Vol. 3, No. 4, 043604 , 16.04.2019.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations

AU - Tane, Masakazu

AU - Nishiyama, Hiroki

AU - Umeda, Akihiro

AU - Okamoto, Norihiko L.

AU - Inoue, Koji

AU - Luckabauer, Martin

AU - Nagai, Yasuyoshi

AU - Sekino, Tohru

AU - Nakano, Takayoshi

AU - Ichitsubo, Tetsu

PY - 2019/4/16

Y1 - 2019/4/16

N2 - In titanium alloys, theω(hexagonal)-phase transformation has been categorized as either a diffusion-mediatedisothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mecha-nism. Here we report a diffusionless isothermalωtransformation that can occur even above theωtransformationtemperature. In body-centered cubic β-titanium alloyed withβ-stabilizing elements, there are locally unstableregions having fewerβ-stabilizing elements owing to quenched-in compositional fluctuations that are inevitablypresent in thermal equilibrium. In these locally unstable regions, diffusionless isothermalωtransformationoccurs even when the entireβregion is stable on average so that athermalωtransformation cannot occur.This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization ofβphase on average. In the diffusionlessisothermal and athermalωtransformations, the transformation rate is dominated by two activation processes: adynamical collapse of{111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionlessisothermal transformation, theω-phase nucleation, resulting from the localized phonon softening, requiresrelatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slowerrates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, thenucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.

AB - In titanium alloys, theω(hexagonal)-phase transformation has been categorized as either a diffusion-mediatedisothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mecha-nism. Here we report a diffusionless isothermalωtransformation that can occur even above theωtransformationtemperature. In body-centered cubic β-titanium alloyed withβ-stabilizing elements, there are locally unstableregions having fewerβ-stabilizing elements owing to quenched-in compositional fluctuations that are inevitablypresent in thermal equilibrium. In these locally unstable regions, diffusionless isothermalωtransformationoccurs even when the entireβregion is stable on average so that athermalωtransformation cannot occur.This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization ofβphase on average. In the diffusionlessisothermal and athermalωtransformations, the transformation rate is dominated by two activation processes: adynamical collapse of{111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionlessisothermal transformation, theω-phase nucleation, resulting from the localized phonon softening, requiresrelatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slowerrates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, thenucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.

U2 - 10.1103/PhysRevMaterials.3.043604

DO - 10.1103/PhysRevMaterials.3.043604

M3 - Article

VL - 3

JO - Physical Review Materials

JF - Physical Review Materials

SN - 2475-9953

IS - 4

M1 - 043604

ER -