Valery I. Levitas, Anson Marston Distinguished Professor in Engineering and holder of the Murray Harpole Chair in Engineering in the Departments of Aerospace and Mechanical Engineering at Iowa State University, and a frequent APS user, recently published a comprehensive review paper, “Strain-induced phase transformations, chemical reactions, microstructure evolution, and severe plastic deformations under high pressure,” in Progress in Materials Science, 2026, Vol. 158, 101625, 118 pages.

It is known that processes involving severe plastic deformation (SPD), phase transformations, and chemical reactions (PTs/CRs) under high pressure are widespread for obtaining new nanostructured high-pressure phases and their processing, mechanochemical synthesis, military applications, geology, and astrogeology. SPD drastically reduces the pressure required for PTs/CRs by one to two orders of magnitude and PT hysteresis; leads to hidden metastable phases, which cannot be obtained otherwise; and substitutes 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 with 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 economical defect-induced synthesis of high-pressure phases and nanostructures. Coupled analytical, computational, and 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 the low-pressure-temperature Earth crust, and the mechanochemical origin of life beyond Earth.

Figure 1. (a) Schematics of rotational diamond anvil cell (RDAC). (b) Left: Criterion for Si-I→Si-II PT for triaxial normal stresses predicted by phase-field approach (PFA) (plane) and confirmed by DFT calculations (dots). Right: rotated figure until plane is visible as a line. (c) Nucleation of high-pressure phases (red) at dislocation pileup against grain boundary under compression and shear obtained with nanoscale PFA (left) and MD (right). (d) Distributions of the high-pressure phases (red) and dislocations in the polycrystalline sample under compression and shear obtained with microscale (or scale-free) PFA. (e) Experimental particle-size dependence of the minimum pressure for Si-I→Si-II PT under hydrostatic loading and plastic straining, and a sketch of particle-size dependence of the yield strength for the direct and inverse Hall-Petch relation. The correlation between the particle size’s direct and inverse Hall-Petch relations on the yield strength and the minimum pressure for strain-induced PT is deduced, which supports the dislocation pileup-based nucleation mechanism. (f) XRD patterns for compression of Si with100 nm particle size. Numbers on the left side are pressures averaged over the phase mixture. Numbers in parentheses near the Si phases indicate the pressure within those phases. Much larger (by 5-7 GPa) pressure in HPPs Si-II and Si-III than in Si-I at the beginning of PTs is direct experimental confirmation of the strong stress concentrators, which could be due to dislocation pileups only. (g) Phase fraction of ω-Zr versus weighted plastic strain for α-ω PT in Zr: good correspondence between theoretical predictions and points from the RDAC experiments32. (h) Good correspondence between radial distributions of the experimental phase fraction of ω-Zr (symbols) and lines from the finite element simulations for various pressures at the sample center (shown near lines). (i) Evolution of the phase fraction of wurtzitic BN transformed from the hexagonal BN during torsion in RDAC in the quarter of a sample: finite element results. (j) and (k) Plots of the crystallite size and dislocation density in ω-Zr versus phase fraction of ω-Zr, which allows one to design the synthesis of α-ω nanocomposites with desired crystalline size (smaller than the steady crystalline size of 40-60 nm after SPD at 6-14 GPa) and dislocation density.