Plastic strain-induced olivine-ringwoodite phase transformation at room temperature: main rules and the mechanism of the deep-focus earthquake

Deep-focus earthquakes that occur at 350-660 km are theorized to be caused by strain-induced olivine-spinel phase transformation (PT). We introduce and apply dynamic rotational diamond anvil cell with rough diamond anvils to deform San Carlos olivine. While olivine was never transformed to spinel at any pressure at room temperature, we obtained olivine-ringwoodite PT under severe plastic shear at 15-28 GPa within seconds. This is conceptual proof of the difference between pressure- and plastic strain-induced PTs and that plastic straining can accelerate this PT from million years to timescales relevant for the earthquake. The PT pressure linearly reduces with increasing plastic strain, corresponding increasing dislocation density and decreasing crystallite size. The main rules of the coupled severe plastic flow, PT, and microstructure evolution are found

Effect of particle size on the phase transformation behavior and equation of state of Si under hydrostatic loading

High-pressure synchrotron X-ray diffraction (XRD) studies have been conducted on three types of Si particles (micron, 100 nm, and 30 nm). The pressure for initiation of Si-I->Si-II phase transformation (PT) essentially increases with a reduction in particle size. For 30 nm Si particles, Si-I directly transforms to Si-XI by skipping the intermediate Si-II phase, which appears during the pressure release. The evolution of phase fractions of Si particles under hydrostatic compression is studied. The equation of state (EOS) of Si-I, Si-II, Si-V, and Si-XI for all three particle sizes is determined, and the results are compared with other studies. A simple iterative procedure is suggested to extract the EOS of Si-XI and Si-II from the data for a mixture of two and three phases with different pressures in each phase. Using previous atomistic simulations, EOS for Si-II is extended to ambient pressure, which is important for plastic strain-induced phase transformations. Surprisingly, the EOS of micron and 30 nm Si are identical, but different from 100 nm particles. In particular, the Si-I phase of 100 nm Si is less compressible than that of micron and 30 nm Si. The reverse Si-V->Si-I PT is observed for the first time after complete pressure release to the ambient for 100 nm particles.Comment: 19 pages, 10 figures, 2 table

In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure

Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. We introduce rough diamond anvils to reach maximum friction equal to yield strength in shear and perform the first in-situ study of the evolution of the pressure-dependent yield strength and nanostructural parameters for severely pre-deformed Zr. {\omega}-Zr behaves like perfectly plastic, isotropic, and strain-path-independent. This is related to reaching steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for {\alpha}-Zr obtained with smooth and rough anvils are different, which causes major challenge in plasticity theory.Comment: arXiv admin note: substantial text overlap with arXiv:2208.0802

Unusual plastic strain-induced phase transformation phenomena in silicon

Pressure-induced phase transformations (PTs) in Si, the most important electronic material, have been broadly studied, whereas strain-induced PTs have never been studied in situ. Here, we reveal in situ various important plastic strain-induced PT phenomena. A correlation between the direct and inverse Hall-Petch effect of particle size on yield strength and pressure for strain-induced PT is predicted theoretically and confirmed experimentally for Si-I→Si-II PT. For 100 nm particles, the strain-induced PT Si-I→Si-II initiates at 0.3 GPa under both compression and shear while it starts at 16.2 GPa under hydrostatic conditions. The Si-I→Si-III PT starts at 0.6 GPa but does not occur under hydrostatic pressure. Pressure in small Si-II and Si-III regions of micron and 100 nm particles is ∼5–7 GPa higher than in Si-I. For 100 nm Si, a sequence of Si-I → I + II → I + II + III PT is observed, and the coexistence of four phases, Si-I, II, III, and XI, is found under torsion. Retaining Si-II and single-phase Si-III at ambient pressure and obtaining reverse Si-II→Si-I PT demonstrates the possibilities of manipulating different synthetic paths. The obtained results corroborate the elaborated dislocation pileup-based mechanism and have numerous applications for developing economic defect-induced synthesis of nanostructured materials, surface treatment (polishing, turning, etc.), and friction.This article is published as Yesudhas, Sorb, Valery I. Levitas, Feng Lin, K_K Pandey, and Jesse S. Smith. "Unusual plastic strain-induced phase transformation phenomena in silicon." Nature Communications 15, no. 1 (2024): 7054. doi: https://doi.org/10.1038/s41467-024-51469-5. © The Author(s) 2024. This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Prolonged mixed phase induced by high pressure in MnRuP

Hexagonally structured MnRuP was studied under high pressure up to 35 GPa from 5 to 300 K using synchrotron X-ray diffraction. We observed that a partial phase transition from hexagonal to orthorhombic symmetry started at 11 GPa. The new and denser orthorhombic phase coexisted with its parent phase for an unusually long pressure range, {\Delta}P ~ 50 GPa. We attribute this structural transformation to a magnetic origin, where a decisive criterion for the boundary of the mixed phase lays in the different distances between the Mn-Mn atoms. In addition, our theoretical study shows that the orthorhombic phase of MnRuP remains steady even at very high pressures up to ~ 250 GPa, when it should transform to a new tetragonal phase.Comment: 15 pages, 5 figures, supplementary materia

Plastic strain-induced olivine-ringwoodite phase transformation at room temperature: main rules and the mechanism of the deep-focus earthquake

Deep-focus earthquakes that occur at 350-660 km are theorized to be caused by strain-induced olivine-spinel phase transformation (PT). We introduce and apply dynamic rotational diamond anvil cell with rough diamond anvils to deform San Carlos olivine. While olivine was never transformed to spinel at any pressure at room temperature, we obtained olivine-ringwoodite PT under severe plastic shear at 15-28 GPa within seconds. This is conceptual proof of the difference between pressure- and plastic strain-induced PTs and that plastic straining can accelerate this PT from million years to timescales relevant for the earthquake. The PT pressure linearly reduces with increasing plastic strain, corresponding increasing dislocation density and decreasing crystallite size. The main rules of the coupled severe plastic flow, PT, and microstructure evolution are found.This is a preprint from Lin, Feng, Valery Levitas, Sorb Yesudhas, and Jesse Smith. "Plastic strain-induced olivine-ringwoodite phase transformation at room temperature: main rules and the mechanism of the deep-focus earthquake." arXiv preprint arXiv:2307.11215 (2023). doi: https://doi.org/10.48550/arXiv.2307.11215. Copyright The Authors. CC-By-NC-ND 4.0. http://creativecommons.org/licenses/by-nc-nd/4.0/

Rough diamond anvils: Steady microstructure, yield surface, and transformation kinetics in Zr

Study of the plastic flow and strain-induced phase transformations (PTs) under high pressure with diamond anvils is important for material and geophysics. We introduce rough diamond anvils and apply them to Zr, which drastically change the plastic flow, microstructure, and PTs. Multiple steady microstructures independent of pressure, plastic strain, and strain path are reached. Maximum friction equal to the yield strength in shear is achieved. This allows determination of the pressure-dependence of the yield strength and proves that omega-Zr behaves like perfectly plastic, isotropic, and strain path-independent immediately after PT. Record minimum pressure for alpha-omega PT was identified. Kinetics of strain-induced PT depends on plastic strain and time. Crystallite size and dislocation density in omega-Zr during PT depend solely on the volume fraction of omega-Zr.This is a pre-print of the article Lin, Feng, Valery Levitas, Krishan Pandey, Sorb Yesudhas, and Changyong Park. "Rough diamond anvils: Steady microstructure, yield surface, and transformation kinetics in Zr." arXiv preprint arXiv:2208.08022 (2022). DOI: 10.48550/arXiv.2208.08022. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Copyright 2022 The Authors. Posted with permission

In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure

Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. We introduce rough diamond anvils to reach maximum friction equal to yield strength in shear and perform the first in-situ study of the evolution of the pressure-dependent yield strength and nanostructural parameters for severely pre-deformed Zr. {\omega}-Zr behaves like perfectly plastic, isotropic, and strain-path-independent. This is related to reaching steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for {\alpha}-Zr obtained with smooth and rough anvils are different, which causes major challenge in plasticity theory.This is a pre-print of the article Lin, Feng, Valery I. Levitas, Krishan K. Pandey, Sorb Yesudhas, and Changyong Park. "In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure." arXiv preprint arXiv:2303.13007 (2023). DOI: 10.48550/arXiv.2303.13007. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Copyright 2023 The Authors. Posted with permission