Solid-Solid Phase Transformation via Virtual Melting Significantly Below the Melting Temperature

Levitas, Valery I.; Henson, B. F.; Smilowitz, Laura; Asay, B. W.

doi:10.1103/physrevlett.92.235702

Cited by 100 publications

(133 citation statements)

References 16 publications

(30 reference statements)

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“…The driving force for VM in phase transformations in refs. (17)(18)(19)(20) is due to the relaxation of the deviatoric stresses and also disappears upon melting, as in the case of VM here. This suggests that our results here indirectly support the plausibility of VM in phase transformation as well.…”

Section: Discussionmentioning

confidence: 85%

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Virtual melting as a new mechanism of stress relaxation under high strain rate loading

Levitas

Ravelo

2012

Proc. Natl. Acad. Sci. U.S.A.

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Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (10 9 -10 12 s −1 ) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the h110i and h111i directions and Al shocked/compressed along the h110i direction.high strain-rate plasticity | relaxation of non-hydrostatic stresses | thermodynamics under uniaxial straining G eneration and motion of dislocations, twinning, and crystalcrystal phase transformations are the main mechanisms of plastic deformation and relaxation of nonhydrostatic stresses that are reflected in the deformation-mechanism maps (1, 2). Recent large-scale nonequilibrium molecular dynamics (NEMD) simulations of shockwave propagation in fcc metallic single crystals have revealed that for wave propagation along the h110i and h111i directions, melting occurs at temperatures below the equilibrium melt temperature T m ðpÞ at the corresponding shock pressure p-e.g., for Cu by 20% in ref. 3 and by 7-8% (AE4%) in ref. 4. However, for shockwaves along the h001i direction, superheating is observed. A possible mechanism for the observed melting below T m ðpÞ has been attributed to solid-state disordering due to high defect densities. Indeed, a small reduction in the melt temperature due to defects has been reported (5). It has also been argued that anomalous plastic flow rather than bulk melt can explain the experimentally observed low melt temperatures of Ta under pressure (6). Here, we propose a new deformation mechanism, under which melting can occur at temperatures much below T m ðpÞ in materials subjected to high deviatoric stresses (such as those produced under shock loading and isentropic deformation) and compete with defect nucleation mechanisms, as will be shown here in the case of metals. We have developed a thermomechanical theory of melting under uniaxial deformation that predicts extremely large driving forces. The thermodynamic driving force for melting is due to the energy and work of nonhydrostatic stresses. The theory is quite general and not materialspecific, and it is most applicable at deformation rates sufficiently high, where melting may proceed at rates faster th...

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Section: Discussionmentioning

confidence: 85%

“…The concept of the VM was introduced in refs. (17)(18)(19)(20) as an intermediate step in crystal-crystal, crystal-amorphous, and crystal-gas transformations. Here, however, VM was for the first time directly observed in MD simulations of plastic straining.…”

Section: Discussionmentioning

confidence: 99%

Virtual melting as a new mechanism of stress relaxation under high strain rate loading

Levitas

Ravelo

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…All homogeneous phases are stable or metastable independent of the driving force (temperature); i.e., thermodynamic instability, which is the source of the PT criteria, is impossible. On the other hand, for different materials and conditions, the third phase is observed in experiments [12] and conditions when it is present or not are found within more advanced models [13]. Some drawbacks of imposing constraint with the help of Lagrangian multipliers are presented and overcame in [11].…”

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confidence: 99%

Multiphase phase field theory for temperature- and stress-induced phase transformations

2015

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Thermodynamic Ginzburg-Landau potential for temperature-and stress-induced phase transformations (PTs) between n phases is developed. It describes each of the PTs with a single order parameter without an explicit constraint equation, which allows one to use an analytical solution to calibrate each interface energy, width, and mobility; reproduces the desired PT criteria via instability conditions; introduces interface stresses, and allows for a controlling presence of the third phase at the interface between the two other phases. A finite-element approach is developed and utilized to solve the problem of nanostructure formation for multivariant martensitic PTs. Results are in a quantitative agreement with the experiment. The developed approach is applicable to various PTs between multiple solid and liquid phases and grain evolution and can be extended for diffusive, electric, and magnetic PTs.

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“…The concept of internal, stress-induced virtual melting for a HMX crystal embedded in a polymeric binder [9] is of particular interest. According to this concept, during nucleation, nano-sized clusters of β-HMX dissolve in a molten binder and transform diffusionally into δ phase clusters.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of Polymorphic Transitions in Energetic Compounds

Чуканов¹,

Захаров²,

Korsunskiy³

et al. 2016

Cent. Eur. J. Energ. Mater.

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Available data on the kinetics of polymorphic transitions (PTs) in energetic compounds under isothermal conditions are summarized and discussed. It is shown that the general kinetic regularities of these processes (stepwise and continuous regimes) depend on their topotactic mode (frontal or quasihomogeneous, respectively). In reverse PTs, a nucleation stage is not observed, which is explained by the presence of nuclei of the low-temperature polymorph in the preheated sample. The influence of mechanical effects on the kinetics of PTs in molecular crystals is discussed.

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Solid-Solid Phase Transformation via Virtual Melting Significantly Below the Melting Temperature

Cited by 100 publications

References 16 publications

Virtual melting as a new mechanism of stress relaxation under high strain rate loading

Virtual melting as a new mechanism of stress relaxation under high strain rate loading

Multiphase phase field theory for temperature- and stress-induced phase transformations

Kinetics of Polymorphic Transitions in Energetic Compounds

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