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1. Phase-field description of fracture in NiTi single crystals

   https://doi.org/10.1016/j.cma.2023.116677  

   Kavvadias, D.; Baxevanis, Th. (February 2024, Computer Methods in Applied Mechanics and Engineering)

   A phase-field model for thermomechanically-induced fracture in NiTi at the single crystal level, i.e., fracture under loading paths that may take advantage of either of the functional properties of NiTi–superelasticity or shape memory effect–, is presented, formulated within the kinematically linear regime. The model accounts for reversible phase transformation from austenite to martensite habit plane variants and plastic deformation in the austenite phase. Transformation-induced plastic deformation is viewed as a mechanism for accommodation of the local deformation incompatibility at the austenite–martensite interfaces and is accounted for by introducing an interaction term in the free energy derived based on the Mori–Tanaka and Kröner micromechanical assumptions and the hypothesis of martensite instantaneous growth within austenite. Based on experimental observations suggesting that NiTi fractures in a stress-controlled manner, damage is assumed to be driven by the elastic energy, i.e., phase transformation and plastic deformation are assumed to contribute in crack formation and growth indirectly through stress redistribution. The model is restricted to quasistatic mechanical loading (no latent heat effects), thermal loading sufficiently slow with respect to the time rate of heat transfer by conduction (no thermal gradients), and a temperature range below 𝑀𝑑, which is the temperature above which the austenite phase is stable, i.e., stress-induced martensitic transformation is suppressed. The numerical implementation of the model is based on an efficient scheme of viscous regularization in both phase transformation and plastic deformation, an explicit numerical integration via a tangent modulus method, and a staggered scheme for the coupling of the unknown fields. The model is shown able to capture transformation-induced toughening, i.e., stable crack advance attributed to the shielding effect of inelastic deformation left in the wake of the growing crack under nominal isothermal loading, actuation-induced fracture under a constant bias load, and crystallographic dependence on crack pattern. 

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2. Severe Plastic Deformation of Ceramics by High-Pressure Torsion: Review of Principles and Applications

   https://doi.org/10.1146/annurev-matsci-080423-122701  

   Edalati, Kaveh; Hidalgo-Jiménez, Jacqueline; Nguyen, Thanh Tam; Sena, Hadi; Enikeev, Nariman; Rogl, Gerda; Levitas, Valery I; Horita, Zenji; Zehetbauer, Michael J; Valiev, Ruslan Z; et al (July 2025, Annual Review of Materials Research)

   Ceramics are typically brittle at ambient conditions due to their covalent or ionic bonding and limited dislocation activities. While plasticity, and occasionally superplasticity, can be achieved in ceramics at high temperatures through thermally activated phenomena, creep, and grain boundary sliding, their deformation at ambient temperature and pressure remains challenging. Processing under high pressure via the high-pressure torsion (HPT) method offers new pathways for severe plastic deformation (SPD) of ceramics. This article reviews recent advances in HPT processing of ceramics, focusing primarily on traditional ceramics (e.g., oxides, carbides, nitrides, oxynitrides) and to a lesser extent advanced ceramics (e.g., silicon, carbon, perovskites, clathrates). Key structural and microstructural features of SPD-processed ceramics are discussed, including phase transformations and the generation of nanograins and defects such as vacancies and dislocations. The properties and applications of these deformed ceramics are summarized, including powder consolidation, photoluminescence, bandgap narrowing, photovoltaics, photocatalysis (dye degradation, plastic waste degradation, antibiotic degradation, hydrogen production, CO2 conversion), electrocatalysis, thermoelectric performance, dielectric performance, and ion conductivity for Li-ion batteries. Additionally, the article highlights the role of HPT in synthesizing novel materials, such as high-entropy ceramics (particularly high-entropy oxides), black oxides, and high-pressure polymorphs, which hold promise for energy and environmental applications. 

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3. Strain-induced phase transformations, chemical reactions, microstructure evolution, and severe plastic deformations under high pressure

   https://doi.org/10.1016/j.pmatsci.2025.101625  

   Levitas, Valery I (April 2026, Progress in Materials Science)

   Processes involving SPD and phase transformations and chemical reactions (PTs/CRs) under high pressures are widespread for obtaining new nanostructured high-pressure phases and their processing, mechanochemical synthesis, military applications, geology, and astrogeology. SPD drastically reduce the pressure required for PTs/CRs (by one-two orders of magnitude) and PT hysteresis; lead to hidden metastable phases, which cannot be obtained otherwise, and substitute reversible PTs/CRs with irreversible ones. This review includes breakthroughs in understanding multifaceted interactions between high-pressure PTs/CRs, SPD, and microstructure evolution from the viewpoint of advanced mechanics and thermodynamics of materials under stress and plastic strain tensors. A novel concept of plastic strain-induced PTs/CRs under high pressure is explored using four-scale theory and simulations (from atomistic to nano- and scale-free phase-field approaches to macroscale) coupled to in situ experiments in traditional and rotational diamond anvil cells, and their integration. Its development revealed various phenomena and misinterpretations, resolved numerous puzzles, found the first general rules in these fields, and suggested ways for economic defect-induced synthesis of high-pressure phases and nanostructures. Coupled analytical/computational/experimental approaches are developed for complete characterization of occurring processes and finding all heterogeneous scalar and tensorial fields. Various material classes (metals, ceramics, rocks, semiconductors, powders, etc.) are considered. Applications include high-pressure torsion, surface treatment (polishing, cutting, etc.), high-pressure mechanochemistry and tribology, PTs/CRs in shear bands leading to severe transformation/reaction-induced plasticity and self-blown-up processes, mechanisms of deep-focus earthquakes, the appearance of microdiamonds in low-pressure-temperature Earth crust, and the mechanochemical origin of life beyond Earth. Unresolved problems and future directions are outlined. 

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4. Plastic strain-induced phase transformations in silicon: drastic reduction of transformation pressures, change in transformation sequence, and particle size effect

   Yesudhas, Sorb; Levitas, Valery I.; Lin, Feng; Pandey, K. K.; Smith, Jesse (March 2023, arXivorg)

   Pressure-induced phase transformations (PTs) between numerous phases of Si, the most important electronic material, have been studied for decades. This is not the case for plastic strain-induced PTs. Here, we revealed in-situ various unexpected plastic strain-induced PT phenomena. Thus, for 100 nm Si, strain-induced PT Si-I to Si-II (and Si-I to Si-III) initiates at 0.4 GPa (0.6 GPa) versus 16.2 GPa (∞, since it does not occur) under hydrostatic conditions; for 30 nm Si, it is 6.1 GPa versus ∞. The predicted theoretical correlation between the direct and inverse Hall-Petch effect of the grain size on the yield strength and the minimum pressure for strain-induced PT is confirmed for the appearance of Si-II. Retaining Si-II at ambient pressure and obtaining reverse Si-II to Si-I PT are achieved, demonstrating the possibilities of manipulating different synthetic paths. 

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5. High-throughput prediction of oxygen vacancy defect migration near misfit dislocations in SrTiO ₃ /BaZrO ₃ heterostructures

   https://doi.org/10.1039/D3MA00850A  

   Ebmeyer, William; Dholabhai, Pratik P. (January 2024, Materials Advances)

   Among their numerous technological applications, semi-coherent oxide heterostructures have emerged as promising candidates for applications in intermediate temperature solid oxide fuel cell electrolytes, wherein interfaces influence ionic transport.Since misfit dislocations impact ionic transport in these materials, oxygen vacancy formation and migration at misfit dislocations in oxide heterostructures are central to their performance as an ionic conductor. Herein, we report high-throughput atomistic simulations to predict thousands of activation energy barriers for oxygen vacancy migration at misfit dislocations in SrTiO3/BaZrO3 heterostructures. Dopants display a noticeable effect as higher activation energies are uncovered in their vicinity. Interface layer chemistry has a fundamental influence on the magnitude of activation energy barriers since they are dissimilar at misfit dislocations as compared to coherent terraces. Lower activation energies are uncovered when oxygen vacancies migrate toward misfit dislocations, but higher energies when they hop away, revealing that oxygen vacancies would get trapped at misfit dislocations and impact ionic transport. The results herein offer atomic scale insights into ionic transport at misfit dislocations and fundamental factors governing the ionic conductivity of thin film oxide electrolytes. 

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