Shock Induced α-ε Phase Change in Iron: Analysis of MD Simulations and Experiment

Hawreliak, J.; Rosolanková, K.; Belak, J.; Collins, Gilbert; Colvin, Jeff; Davies, Huw M. L.; Eggert, J. H.; Germann, Timothy C.; Holian, Brad Lee; Kalantar, D. H.; Kadau, Kai; Lomdahl, Peter S.; Lorenzana, H. E.; Sheppard, J.; Stölken, James S.; Wark, J. S.

doi:10.1063/1.2263303

Cited by 6 publications

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“…These techniques has already been proven to show insight into atomistic response of shock compressed materials. With the development of simulated x-ray diffraction [24] we can begin directly compare experimental results with molecular dynamics simulations, which suggests the possiblity for making measurements of the microstructure of the material [25,26]. Image Plate Azimuthal Position (cm) FIGURE 6.…”

Section: Discussionmentioning

confidence: 99%

In-Situ Probing of Lattice Response in Shock Compressed Materials Using X-Ray Diffraction

Hawreliak¹,

Butterfield²,

Davies³

et al. 2008

AIP Conference Proceedings

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Abstract. Lattice level measurements of material response under extreme conditions are required to build a phenomenological understanding of the shock response of solids. We have successfully used laser produced plasma x-ray sources coincident with laser driven shock waves to make in-situ measurements of the lattice response during shock compression for both single crystal and polycrystalline materials. Using a detailed analysis of shocked single crystal iron which has undergone the α − ε phase transition we can constrain the transition mechanism to be consistent with a compression and shuffle of alternate lattice planes.

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Section: Discussionmentioning

confidence: 99%

In-Situ Probing of Lattice Response in Shock Compressed Materials Using X-Ray Diffraction

Hawreliak¹,

Butterfield²,

Davies³

et al. 2008

AIP Conference Proceedings

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“…The EXAFS data can be used to compare results from multimillion atom non-equilibrium molecular dynamic simulations [36,37] of shock compression of iron above the phase transition. The bcc lattice is compressed and there is a rearrangement consistent with the shuffle of alternate (110) planes to form the hcp phase.…”

Section: Martensitic Phase Transitionmentioning

confidence: 99%

First-Order Polymorphic and Melting Phase Transitions Under Shock Loading

Forbes

2012

Shock Wave Compression of Condensed Matter

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Some materials at high pressure have structural arrangements of atoms and molecules that are at a lower energy state than that at (P ¼ 0, v o , T-293 K) conditions. When this occurs a thermodynamic force on the material exists to change the configuration to the new one. This process is called a first-order phase transition that is characterized by the coexistence of several thermodynamic phases. It is well established that condensed matter can also undergo thermodynamic second order phase transitions in electric and magnetic properties that are not treated in this book. Readers interested in second order phase transitions seen in dynamic experiments consult the literature especially the articles by Keeler and Royce [1].Static studies of phase transitions provide the baseline for understanding many phase transitions. They can show if the mixed phase region is in thermodynamic equilibrium or in a metastable state. Inferring phase transformations under dynamic loading from experimental static data is very useful. The first order guess of the phase seen in dynamic experiments will be the same as observed in static experiments but this needs to be verified in real-time dynamic experiments. One must keep in mind that under dynamic loading, phases other than that seen in static experiments are a possibility. This was seen in a recent study of shocked polycrystalline iron [2] where fcc phases occurred in certain oriented crystal grains. Note that this shock study using intense x-rays directly confirmed experimentally the majority of the iron transition was martensitic in nature, which agrees with static studies.The kinetics of the transformation determines whether a new configuration occurs under shock loading. If the transformation takes many microseconds to occur it will not be seen in standard shock wave experiments and the material will be put into a thermodynamic metastable state. Since dynamic loading is different than static compression some transitions that require cooperative lattice motion can be accelerated due to the shear in a shock wave. This is what happens in the body center cubic (bcc or a) to hexagonal closed packed (hcp or ɛ) lattice transition in iron [3] at 130 kbar. Keep in mind that due to creation of defects,

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“…Fragment of the sample initially free of defects upon completion of the bcc-hcp transition. Medium loading rate, MD step = 360000: P = 35.261 GPa, ρ = 9.02 g/cm 3 . ATA colors: Blue -hcp structure, green and red -boundaries between the hcp grains.…”

Section: -P3 Epj Web Of Conferencesmentioning

confidence: 99%

“…First MD simulations of polymorphous transition in iron under shock compression conditions were reported in [1][2][3]. The EAM potential by Voter & Chen [4] was used in these simulations.…”

Section: Introductionmentioning

confidence: 99%

MD modeling of screw dislocation influence upon initiation and mechanism of BCC-HCP polymorphous transition in iron

Dremov

Ionov

Sapozhnikov

et al. 2015

EPJ Web of Conferences

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Abstract. The present work is devoted to classical molecular dynamics investigation into microscopic mechanisms of the bcchcp transition in iron. The interatomic potential of EAM type used in the calculations was tested for the capability to reproduce ab initio data on energy evolution along the bcc-hcp transformation path (Burgers deformation + shuffle) and then used in the large-scale MD simulations. The large-scale simulations included constant volume deformation along the Burgers path to study the origin and nature of the plasticity, hydrostatic volume compression of defect free samples above the bcc to hcp transition threshold to observe the formation of new phase embryos, and the volume compression of samples containing screw dislocations to study the effect of the dislocations on the probability of the new phase critical embryo formation. The volume compression demonstrated high level of metastability. The transition starts at pressure much higher than the equilibrium one. Dislocations strongly affect the probability of the critical embryo formation and significantly reduce the onset pressure of transition. The dislocations affect also the resulting structure of the samples upon the transition. The formation of layered structure is typical for the samples containing the dislocations. The results of the simulations were compared with the in-situ experimental data on the mechanism of the bcc-hcp transition in iron.

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Shock Induced α-ε Phase Change in Iron: Analysis of MD Simulations and Experiment

Cited by 6 publications

References 0 publications

In-Situ Probing of Lattice Response in Shock Compressed Materials Using X-Ray Diffraction

In-Situ Probing of Lattice Response in Shock Compressed Materials Using X-Ray Diffraction

First-Order Polymorphic and Melting Phase Transitions Under Shock Loading

MD modeling of screw dislocation influence upon initiation and mechanism of BCC-HCP polymorphous transition in iron

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