The kinetics of the ω to α phase transformation in Zr, Ti: Analysis of data from shock-recovered samples and atomistic simulations

Zong, Hongxiang; Lookman, Turab; Ding, Xiangdong; Nisoli, Cristiano; Brown, Don W.; Niezgoda, Stephen R.; Sun, Jun

doi:10.1016/j.actamat.2014.05.049

Cited by 47 publications

(37 citation statements)

References 36 publications

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“…A dislocation mediated shear mechanism is consistent with very recent atomistic modeling by Zong et al, informed by preliminary analysis of the data presented here [41]. In that work the evolution of ω fraction is fit to a modified Kohlrausch-Williams-Watts equation [42]or stretched exponential of the form η(t) ∝ t −α · exp − t τ (T ) β , there η is the ω fraction, t −α is an pre-factor that accounts for non-thermally activated events, T is the ab-solute temperature, and τ is the relaxation time or time for ≈37% of the transformation to take place.…”

Section: Discussionsupporting

confidence: 70%

“…Knowing that growth in α volume fraction occurs at both these temperatures, albeit with differing rates (refer to Figure 3b), it can be inferred that there is a higher energy barrier associated with nucleation in comparison to that of growth from existing α. This is again counter to the predictions of Zong et al [41], demonstrating the need for further in-situ experimental studies to inform the theory and modeling. At sufficiently high temperatures, nucleation of α from ω parents dominates the reverse transformation, with the growth of the original α happening simultaneously.…”

Section: Discussioncontrasting

confidence: 52%

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Isothermal annealing of shocked zirconium: Stability of the two-phase α/ω microstructure

et al. 2015

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Under high pressure conditions, Zr undergoes a phase transformation from its ambient equilibrium hexagonal close packed α phase to hexagonal ω phase. Upon returning to ambient conditions, the material displays hysteretic behavior, retaining a significant amount of metastable ω phase. This study presents an in-situ synchrotron X-ray diffraction analysis of Zr samples shock-loaded to compressive peak stresses of 8 and 10.5 GPa and then annealed at temperatures of 443, 463, 483, and 503K. The evolution of the α phase volume fraction was tracked quantitatively, and the dislocation densities in both phases were tracked qualitatively during annealing. Upon heating, the reverse transformation of ω → α does not go to completion, but instead reaches a new metastable state. The initial rate of transformation is faster at higher temperatures. Samples shock-loaded to higher peak pressures experienced higher initial transformation rates and more extensive transformation. Dislocation content in both phases was observed to be high in the as-shocked samples. Annealing the samples reduces the dislocation content in both phases, with the reduction being lesser in the ω phase, leading to the postulation that * Corresponding Author

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Section: Discussionsupporting

confidence: 70%

Section: Discussioncontrasting

confidence: 52%

Isothermal annealing of shocked zirconium: Stability of the two-phase α/ω microstructure

et al. 2015

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“…In contrast, it has been previously reported that, based on reversion studies, 18 the activation energy for the x to a backtransformation increased with the maximal load applied to the material. Samples used in the reported experiments 18 were initially of high purity and shocked to either 8.5 or 10 GPa. The recovered samples were then heated while using x-ray diffraction to determine reversion time constants.…”

Section: Figmentioning

confidence: 60%

“…Initial work in this area focused on boundary and impurity effects, 5,15,16 followed by some initial kinetics, 17,18 and then orientation pathways via theoretical 19,20 approaches. Recent experimental investigation has focused on the orientation relationships between a and x.…”

Section: A Scientific Background On A-x Transition In Zirconiummentioning

confidence: 99%

Pressure-induced kinetics of the α to ω transition in zirconium

Jacobsen

Velisavljevic

Sinogeikin

2015

Journal of Applied Physics

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Diamond anvil cells (DAC) coupled with x-ray diffraction (XRD) measurements are one of the primary techniques for investigating structural stability of materials at high pressure-temperature (P-T) conditions. DAC-XRD has been predominantly used to resolve structural information at set P-T conditions and, consequently, provides P-T phase diagram information on a broad range of materials. With advances in large scale synchrotron x-ray facilities and corresponding x-ray diagnostic capabilities, it is now becoming possible to perform sub-second time resolved measurements on micron sized DAC samples. As a result, there is an opportunity to gain valuable information about the kinetics of structural phase transformations and extend our understanding of material behavior at high P-T conditions. Using DAC-XRD time resolved measurements, we have investigated the kinetics of the α to ω transformation in zirconium. We observe a clear time and pressure dependence in the martensitic α-ω transition as a function of pressure-jump, i.e., drive pressure. The resulting data are fit using available kinetics models, which can provide further insight into transformation mechanism that influence transformation kinetics. Our results help shed light on the discrepancies observed in previous measurements of the α-ω transition pressure in zirconium.

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“…Experimental works on Zr or Zr-2.5%Nb alloy by Perez-Prado et al 5,37 does see the b phase at lower pressure and it may well be that this observation is supported by the non-uniform (shear) stress applied to the sample. 38 More detailed works on pathway under shear stress and experiments at high hydrostatic pressure are needed to further clarify the phase metastability.…”

Section: -3mentioning

confidence: 99%

Metastable phase transformation and hcp- ω transformation pathways in Ti and Zr under high hydrostatic pressures

Gao

Ding

Lookman

et al. 2016

Applied Physics Letters

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The energy landscape of Zr at high hydrostatic pressure suggests that its transformation behavior is strongly pressure dependent. This is in contrast to the known transition mechanism in Ti, which is essentially independent of hydrostatic pressure. Generalized solid-state nudged elastic band calculations at constant pressure shows that α-Zr transforms like Ti only at the lowest pressure inside the stability field of ω-phase. Different pathways apply at higher pressures where the energy landscape contains several high barriers so that metastable states are expected, including the appearance of a transient bcc phase at ca. 23 GPa. The global driving force for the hcp-ω transition increases strongly with increasing pressure and reaches 23.7 meV/atom at 23 GPa. Much of this energy relates to the excess volume of the hcp phase compared with its ω phase.

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The kinetics of the ω to α phase transformation in Zr, Ti: Analysis of data from shock-recovered samples and atomistic simulations

Cited by 47 publications

References 36 publications

Isothermal annealing of shocked zirconium: Stability of the two-phase α/ω microstructure

Isothermal annealing of shocked zirconium: Stability of the two-phase α/ω microstructure

Pressure-induced kinetics of the α to ω transition in zirconium

Metastable phase transformation and hcp- ω transformation pathways in Ti and Zr under high hydrostatic pressures

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