Coupled Severe Plastic Deformations, Phase Transformations, and Microstructure Evolution under High Pressure: Four-scale Theory and In-situ Experiments

ORAL · Invited

Abstract

During compression in a diamond anvil cell (DAC), materials undergo large plastic deformations, which cause various phase transformations (PTs). We formulated new concept that these PTs should be treated as plastic strain-induced PTs under high pressure rather than pressure-induced PTs. Pressure- and stress-induced PTs occur by nucleation at the pre-existing defects below the yield. Strain-induced PTs occur by nucleation at new defects (e.g., dislocation pileups) permanently generated during plastic flow. Strain-induced PTs require completely different thermodynamic and kinetic treatments and experimental characterization. New in situ experimental results are obtained under compression of materials in a DAC and torsion in rotational DAC (RDAC). Drastic reductions of the PT pressure compared with hydrostatic loading and the appearance of new phases are demonstrated. Thus, graphite in RDAC was transformed to nanocrystalline hexagonal and cubic diamond at 0.4 and 0.7 GPa, respectively, which are 50 and 100 times lower than the PT pressures under hydrostatic loading! This could be a precursor of new technology of plastic strain (defect) induced diamond synthesis. New rules of coupled severe plastic deformations, PTs, and grain and dislocation structure evolution under high pressure are discovered for Zr. Numerous phenomena with potential technological applications are revealed for combined effect of plastic flow and particle size on PTs between 7 Si phases. A four-scale theory was developed. Molecular dynamics and first-principle simulations were used to determine PT criteria under six stress tensor components. At the nanoscale and microscale, nucleation at evolving dislocation pileups was studied with developed nanoscale and scale-free phase-field approaches. A strain-controlled kinetic equation was derived and utilized in the large-strain macroscopic theory for coupled PTs and plasticity. At the macroscale, the behavior of the sample in DAC/RDAC is studied using the finite element approach. Various experimental effects are reproduced. The obtained results offer new fundamental understanding of strain-induced PTs and methods of searching for new high-pressure phases and phenomena.

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Publication: [1] Levitas V.I. High Pressure Mechanochemistry: Conceptual Multiscale Theory and Interpretation of Experiments. Phys Rev. B, 70, 184118 (2004).
[2] Levitas V.I. High-Pressure Phase Transformations under Severe Plastic Deformation by Torsion in Rotational Anvils. Material Transactions, 2019, 60, 1294-1301, invited review.
[3] Levitas V.I. Phase transformations, fracture, and other structural changes in inelastic materials. International Journal of Plasticity, 2021, 140, 102914, 51 pp., invited review.
[4] C. Ji, V.I. Levitas, H. Zhu, J. Chaudhuri, A. Marathe, Y. Ma, Shear-Induced Phase Transition of Nanocrystalline Hexagonal Boron Nitride to Wurtzitic Structure at Room Temperature and Low Pressure. Proceedings of the National Academy of Sciences of the United States of America, 109, 191088 (2012).
[5] Gao Y., Ma Y., An Q., Levitas V. I., Zhang Y., Feng B., Chaudhuri J. and Goddard III W. A. Shear driven formation of nano-diamonds at sub-gigapascals and 300 K. Carbon, 2019, 146, 364-368.
[6] Pandey K. K. and Levitas V. I. In situ quantitative study of plastic strain-induced phase transformations under high pressure: Example for ultra-pure Zr. Acta Materialia, 2020, 196, 338-346.
[7] Lin F., Levitas V.I., Pandey K.K., Yesudhas S., Park C. Laws of high-pressure phase and nanostructure evolution and severe plastic flow. September 9, 2022, 29 pp. Research Square, DOI: https://doi.org/10.21203/rs.3.rs-1998605/v1.V.I.
[8] Levitas V.I., Chen H., Xiong L. Triaxial-stress-induced homogeneous hysteresis-free first-order phase transformations with stable intermediate phases. Phys. Rev. Lett., 118, 025701 (2017).
[9] Levitas V.I., Chen H., Xiong L. Lattice instability during phase transformations under multiaxial stress: modified transformation work criterion. Phys. Rev. B, 96, 054118 (2017).
[10] Zarkevich N. A., Chen H., Levitas V.I., and Johnson D. D. Lattice instability during solid-solid structural transformations under general applied stress tensor: example of Si I?Si II with metallization. Phys. Rev. Lett., 121, 165701 (2018).
[11] Chen H., Zarkevich N. A., Levitas V. I., Johnson D. D., and Zhang X. Fifth-degree elastic energy for predictive continuum stress-strain relations and elastic instabilities under large strain and complex loading in silicon. NPJ Computational Materials. (2020) 6, 115.
[12] Javanbakht M. and Levitas V.I. Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear. Physical Review B, 94, 214104 (2016).
[13] Levitas V.I., Esfahani S.E., and Ghamarian I. Scale-free modeling of coupled evolution of discrete dislocation bands and multivariant martensitic microstructure. Phys. Review Lett., 121, 20570 (2018).
[14] Esfahani S.E., Ghamarian I., Levitas V.I. Strain-induced multivariant martensitic transformations: A scale-independent simulation of interaction between localized shear bands and microstructure. Acta Materialia, 2020, 196, 430-443.
[15] Feng B., Levitas V.I., Li W. FEM modeling of plastic flow and strain-induced phase transformation in BN under high pressure and large shear in a rotational diamond anvil cell. Int J Plasticity, 2019, 113, 236-254.

Presenters

  • Valery I Levitas

    Iowa State University

Authors

  • Valery I Levitas

    Iowa State University