Deformation Kinetics Research Articles

Understanding thermal-mechanical variations and resulting joint integrity of pressure-controlled linear friction welding of thin-steel sheets

Linear friction welding is a solid-state joining technology that bonds materials via friction heating and plastic deformation. This process is being extensively researched for welding metallic sheets with different dimensions; however, it involves difficulties in joining thin cross-sections due to extensive misalignment and unsteady plastic extrusion of softened materials at interfaces. This study introduces novel efforts for joining thin cross-sections through pressure-controlled oscillations and displacements, facilitating localized plastic flow essential for high-strength solid-state bond formation. This method is rare, and the results reveal base metal fractures in tensile-tested welded joints of 2 mm thick S45C steel sheets. The interfacial yielding at specific temperatures is obtained by applying pressure corresponding to the temperature-dependent strength of the material. Accordingly, the welding is attempted using a hydraulic-based clamping system designed to accommodate large sheet lengths while allowing precise control of the interface pressure and temperature to facilitate controlled material plastic discharge. However, the requisite joint evolution tracking remains infeasible due to the intricate weld designs and is instead uncovered through novel numerical investigations. Modeling simultaneous oscillations and forging displacement while maintaining pressure depicted the kinetics of continual interfacial deformation. The transient fluctuations in plastic stress and temperature increments distinguish the stages of forging under different conditions. The computed temperature vs. plastic strain and the measured change in interfacial microstructures from martensite to dynamically recrystallized very fine ferrite with fragmented small cementite explain the lower temperature welding for an increase in applied pressure, enhancing the understanding of linear friction welding of thin steel sections for industrial applications.

Kinetics of Adsorption-Induced Deformation of Microporous Carbons.

Equilibrium and kinetic behavior of adsorption-induced deformation have attracted a lot of attention in the last few decades. The theoretical and experimental works cover activated carbons, coals, zeolites, glasses, etc. However, most of the theoretical works describe only the equilibrium part of the deformation process or focus on the time evolution of the adsorption process. The present paper aims to cover the existing gap using the thermodynamic framework combined with the diffusion-based description of adsorbate time evolution inside an adsorbent. We obtained self-consistent equations describing equilibrium and out-of-equilibrium adsorption, as well as deformation processes. Further, the obtained equations were verified on the experimental data of carbon dioxide and methane on activated carbons. The model is capable of describing both equilibrium and kinetic adsorption and adsorption-induced deformation data. Additionally, we studied the possible influence of slow relaxation processes in the adsorbent on the adsorption process. The current work helps to interpret experimental data for time-dependent adsorption-induced deformation.

Influence of High Strain Dynamic Loading on HEMA-DMAEMA Hydrogel Storage Modulus and Time Dependence.

Hydrogels have been extensively studied for biomedical applications such as drug delivery, tissue-engineered scaffolds, and biosensors. There is a gap in the literature pertaining to the mechanical properties of hydrogel materials subjected to high-strain dynamic-loading conditions even though empirical data of this type are needed to advance the design of innovative biomedical designs and inform numerical models. For this work, HEMA-DMAEMA hydrogels are fabricated using a photopolymerization approach. Hydrogels are subjected to high-compression oscillatory dynamic mechanical loading at strain rates equal to 50%, 60%, and 70%, and storage and loss moduli are observed over time, e.g., 72 h and 5, 10, and 15 days. As expected, the increased strains resulted in lower storage and loss moduli, which could be attributed to a breakdown in the hydrogel network attributed to several mechanisms, e.g., increased network disruption, chain scission or slippage, and partial plastic deformation. This study helps to advance our understanding of hydrogels subjected to high strain rates to understand their viscoelastic behavior, i.e., strain rate sensitivity, energy dissipation mechanisms, and deformation kinetics, which are needed for the accurate modeling and prediction of hydrogel behavior in real-world applications.

Effect of cooling rate and Nb addition on the strengthening in eutectic CoCr1.3FeMnNi0.7Nbx (0 ≤ x ≤ 0.45) high entropy alloys comprising of low stacking fault energy FCC phase

The CoCr1.3FeNi0.7MnNbx (0.3 ≤ x ≤ 0.45) eutectic high entropy alloy (EHEA) comprising of ultrafine lamellae of low stacking fault energy (SFE = 11 mJ/m2) face centered cubic (FCC) and Laves phase are synthesized at cooling rates of 2.5–10 K/s (arc melted ingots, AMIs) and 4.2 × 102 K/s (suction cast bars, SCBs). The microstructural investigation suggests that secondary dendritic arm spacing (SDAS) and interlamellar spacing are refined in SCBs due to a higher cooling rate than the AMIs. Whereas, deformation twins evolve in FCC phase due to its low SFE. The EHEAs exhibit a high yield strength of 1327 MPa for x = 0.367 SCB and a large fracture strain of 20% for x = 0.3 AMI under compression. Systematic investigation on the influence of Nb addition, microstructure refinement, and evolution of deformation twins during straining on the strengthening mechanisms reveals that the phase interface strengthening, solid solution strengthening, and twin boundary strengthening play critical roles in providing the high flow stress. The post-deformation analysis and the presence of multiple positive slopes in work hardening curves confirms that the concurrent effect of the evolution of dislocations, deformation twins, and their mutual interactions are solely responsible for the severe strain hardening at multiple stages during plastic deformation. The low values of strain rate sensitivity (0.0106–0.0111) and the activation volume (28b3-41b3) suggest that the deformation kinetics is governed by the dislocation interactions with the ultrafine lamellae interface and twin boundaries.

Lüders and Portevin–Le Chatelier processes in austenitic-martensitic TRIP steel

The authors studied the nature of mobile fronts of localized deformation that generate and propagate during deformation of metastable austenitic-martensitic TRIP steel VNS9-Sh along the entire length of the loading curve from the yield point to fracture. A joint research of the nature of the deformation fronts movement and kinetics of the magnetic phase accumulation made it possible to establish that the fronts under consideration are the fronts of the thermoelastic phase transformation of metastable austenite into martensite. This transformation is realized firstly by formation of the Chernov–Lüders bands and then the Portevin–Le Chatelier bands. Both processes are consistent with staging of the deformation curve, which contains a pseudo-plateau, a section with an increasing hardening coefficient, and a section with a decreasing hardening coefficient. It is shown that the deformation-induced phase transformation corresponds to the fronts propagating on the pseudo-plateau and on the section of loading curve with an increasing hardening coefficient. The Portevin–Le Chatelier bands, which are formed in the section of the loading diagram with a decreasing hardening coefficient, are not associated with “austenite-martensite” transformation and have a twin nature. The kinetics of thermoelastic transformation fronts, as well as deformation fronts in materials with a shear mechanism of shaping, can be described in terms of the autowave concept. On the yield plateaus, the phase transformation occurs through generation and propagation of localized plasticity switching autowaves. In the section with an increasing hardening coefficient, it continues through generation and movement of excitation autowaves. The propagation regions of excitation autowaves are limited in the sample space. They are set by the zones of origin and annihilation of primary switching autowaves which were formed on the yield plateau.

A mesoscale crystal plasticity model to predict room-temperature deformation and martensitic transformation of high-strength Quenching and Partitioning (Q&P) Steels and validation with synchrotron X-ray diffraction

Renowned for the superior mechanical properties and adeptness at cold-forming, Quenching and Partitioning (QP) steels have gained prominence as a promising candidate material in fabricating safety-critical components in various industries. The pertinent research on QP steels focus on the martensitic transformation of the Retained Austenite (RA) phase during cold-forming, a crucial mechanism that substantially influences the overall strength and ductility of QP steels. The austenite stability and transformation rate heavily rely on the local strain path and the initial microstructure, which is challenging for analytical prediction. In this paper, a mesoscale model is developed to capture the deformation and transformation kinetics of QP steels inside the microstructure. The model integrates the detailed explicit microstructure, acquired from characterization experiments, into a high-resolution finite element (FE) mesh. It distinctly model the deformation and interaction between the various phases and the effect on the transformation of RA. The model is validated with high energy X-ray diffraction (HEXRD) data, and shows excellent capability in predicting the asymmetric stress-strain behavior under uniaxial tension and compression, as well as the martensitic transformation rate. The model is used to investigate the strain and load partitioning effect of surrounding matrix to the transformation of RA, offering insights into the complex behavior of QP980 and facilitates further material development.

Hierarchical Architecture Engineering of Branch-Leaf-Shaped Cobalt Phosphosulfide Quantum Dots: Enabling Multi-Dimensional Ion-Transport Channels for High-Efficiency Sodium Storage.

New-fashioned electrode hosts for sodium-ion batteries (SIBs) are elaborately engineered to involve multifunctional active components that can synergistically conquer the critical issues of severe volume deformation and sluggish reaction kinetics of electrodes toward immensely enhanced battery performance. Herein, it is first reported that single-phase CoPS, a new metal phosphosulfide for SIBs, in the form of quantum dots, is successfully introduced into a leaf-shaped conductive carbon nanosheet, which can be further in situ anchored on a 3D interconnected branch-like N-doped carbon nanofiber (N-CNF) to construct a hierarchical branch-leaf-shaped CoPS@C@N-CNF architecture. Both double carbon decorations and ultrafine crystal of the CoPS in-this exquisite architecture hold many significant superiorities, such as favorable train-relaxation, fast interfacial ion-migration, multi-directional migration pathways, and sufficiently exposed Na+ -storage sites. In consequence, the CoPS@C@N-CNF affords remarkable long-cycle durability over 10000 cycles at 20.0Ag-1 and superior rate capability. Meanwhile, the CoPS@C@N-CNF-based sodium-ion full cell renders the potential proof-of-feasibility for practical applications in consideration of its high durability over a long-term cyclic lifespan with remarkable reversible capacity. Moreover, the phase transformation mechanism of the CoPS@C@N-CNF and fundamental springhead of the enhanced performance are disclosed by in situ X-ray diffraction, ex situ high-resolution TEM, and theoretical calculations.

Deformation kinetics of single-fiber polypropylene composites: Adhesion improvement at the expense of toughness

Despite the maturity of the technology, processing of fiber-reinforced thermoplastic materials remains challenging, and difficulties in processability often result in material formulations with high modulus and strength, yet rather poor ductility compared to the pure polymer matrix. To gain fundamental insight into the deformation mechanisms present in such materials, the complexity of the system is step-wise increased; first, the effect of the most commonly applied adhesion enhancement, the addition of MAH-g-PP compatibilizer, on the bulk properties is assessed. The small-strain tensile properties, i.e., modulus and yield stress, appear to be only marginally affected by the addition of such compatibilization agent, however, the strain-at-break is strongly reduced, even before the addition of the fiber reinforcement. Subsequently, using in-situ X-ray characterization methods upon tensile deformation, the time evolution of crystal structure and lamellar morphology is determined, and at first glance the compatibilizer addition appears to better preserve the crystalline structure. The onset of local failure (cavitation) is quantified at the interface of a single glass fiber. By increasing the adhesive interaction between fiber and matrix the stress concentration at the interface is increased, leading to an acceleration in void formation followed by unstable growth, which in turn strongly embrittles the composite. By the addition of various selective nucleating agents, it is demonstrated that the role of local phase composition and morphology on the deformation kinetics and subsequent failure mechanisms is much more pronounced than the increased adhesion between fiber and matrix by compatibilization or sizing effects. These findings may specify a new route towards tougher fiber-reinforced composites with reduced complexity in the material formulation.

Mechanical behaviors of metallic alloys dominated by thermo-kinetic synergistic effects upon materials processing

For most metallic alloys, improving strength is usually accompanied by losing ductility (and via versa) even if the work hardening rate keeps unchanged, however, the behind reasons still remain elusive to date. In the present work, we explore the underlying physics for such mechanical performance paradox from the perspective of synergistic effects between thermodynamics and kinetics of phase transition and deformation involved in materials processing. With age-hardenable aluminum alloys as typical examples, the hardening and softening effects are analyzed in terms of system energy accumulation and dissipation during precipitation nucleation and growth along with dislocation multiplication and annihilation. The key thermo-kinetic parameters of driving force and energy barrier are determined by performing relevant atomistic calculations. Analytical models for bridging mechanical performances and thermo-kinetics in terms of microstructural characteristics, which derive from classical phase transition and deformation theories, endow connotation for directing precipitation design, as confirmed by a 6xxx series alloy at the pre-determined aging temperature with ideal strength and ductility. Our work offers an insightful perspective toward understanding the strength and ductility paradox, which can benefit to further establish quantitative connections among processing routes, microstructures and mechanical performances of metallic alloys.

Discrepancy in ductility improvement in repeated stress relaxation of AA7075

The stress relaxation test is a commonly used transient test to determine the deformation kinetics during plastic deformation. This study reports the time-dependent deformation behavior of AA7075 alloy under different temper conditions. The deformation parameters, such as the apparent and true activation volume were estimated using single and repeated stress relaxation tests respectively. The results indicate that dislocation–dislocation interaction plays a critical role in the deformation behavior of the solution-treated condition, whereas dislocation–precipitate interaction dominates in the aged specimens. Additionally, the study found that single stress relaxation enhances the ductility of the deforming specimen, regardless of the temper condition. The ductility during repeated relaxation however had negative effects in aged samples. The possible mechanisms responsible for this discrepancy are discussed, providing a comprehensive overview of the time-dependent deformation behavior of AA7075 alloy.

Role of Mn content on processing maps, deformation kinetics, microstructure and texture of as-cast medium Mn (6–10 wt% Mn) steels

In the present work, the hot deformation behaviour of as-cast medium Mn steels with nominal Mn content of 6, 8, and 10 wt% were studied using the thermomechanical simulator in the temperature and strain rate range of 1173 to 1373 K and 10−3 - 10 s−1 respectively. The flow curves of the three steels revealed significant work hardening followed by a plateau at strain rates ≥1s−1 in the entire temperature range. At lower strain rates (<10−2s−1) noticeable softening is observed after a strain of 0.2 in all three steels. The extent of softening is lower in 10 wt% Mn steel in comparison to the 6 and 8 wt% Mn steels. Analysis of processing maps reveals that in steels with 6 and 8 wt% Mn, regions of ‘high’ strain rate sensitivity (m) (0.2 - 0.25) are found to occur in similar temperature and strain rate regimes of 1273–1323 K and 10−2s−1 respectively. These steels also showed similar apparent activation energies for hot deformation (380–390 kJmol−1), stress exponents (4.6) and dynamic recovery/recrystallization evolution with strain. The steel with 10 wt% Mn, has higher apparent activation energy for hot deformation (450 kJmol−1), higher stress exponent of 5.1, higher dynamic recovery and lower dynamic recrystallization. The observed activation energies correlate well with the activation energy for self-diffusion (QSD) of Fe in austenite containing Mn as an alloying element. In the ‘low’ m regimes, higher dynamic recovery (evaluated using kinetic analysis) was observed in the 10 % Mn steel as compared to the 6 and 8% Mn steels. In the ‘high’ m regimes, the dynamic recrystallization fraction (estimated from kinetic analysis and from parent grain reconstruction analysis) was lower in the 10 % Mn steel when compared to the 6 and 8 wt % Mn steels. This behaviour can be attributed to the higher dynamic recovery observed in the 10 % Mn steel. From the analysis of processing maps, kinetic analysis and microstructure, the optimum strain, strain rate and temperature for the thermomechanical processing of as-cast medium Mn steels with Mn in the range of 6 to 10 wt% are ≤ 0.6, ≤10−2s−1 and 1273 to 1373 K respectively.

Deformation kinetics of coal–gas system during isothermal and dynamic non-isothermal processes

Gas-induced coal deformation plays a crucial role in fields like potential CO2 sequestration in coal and coalbed methane production. Since the gas sorption process in coal has an exothermic nature, temperature changes can inherently impact sorption and induced deformation behavior in coal. The current research aims to study the evolution of deformation behavior in terms of kinetics over time under isothermal (318 K) and non-isothermal (318→298 K) conditions for coal exposed to different gases (CO2, CH4, and He). The results indicate that sorption deformation kinetics are influenced by gas types, gas pressures, and coal composition inhomogeneity. Four linear strains measuring strain kinetics in various micro-regions on coal surfaces reveal heterogeneous behaviors linked to the distribution of macerals. Regarding the non-isothermal process, deformation kinetics display distinct patterns for the three gases. A temperature decrease causes sample shrinkage when exposed to CH4 and He, while swelling occurs with CO2 exposure, which may result from a combined effect of temperature change and differing sorption mechanisms of these gases in coal. Additionally, the temperature decrease leads to a phase state change in CO2, transitioning from supercritical to gas to liquid. The study shows continuous deformation kinetics, with no significant impact of the phase change on the deformation behavior observed.

Investigation of non-uniform oxidation based on a mechanochemical phase field model with nonlinear reaction kinetics and large inelastic deformation

A mechanochemical model is proposed to investigate the non-uniform oxidation of thermal barrier coatings (TBCs) that involves large inelastic deformation and nonlinear reaction kinetics. The large-deformation theory incorporates the higher-order term of geometric nonlinearity for a more precise description of the deformation and stress evolution in an oxide layer. The effect of stresses on the reaction kinetics is considered, which is expressed as the Eshelby stress tensor to account for the conformational volume change and deformation energy. A nonlinear reaction kinetics is adopted for a more accurate description of the nonequilibrium thermodynamic processes. The 2D simulations reveal a non-uniform oxide growth, three modes of oxide-metal interfacial morphology evolution, and tensile stress concentrations in the oxide scale. These simulation results agree with the experimental observations that cannot be described by the previous models. With the model, it is further demonstrated that a stable interfacial morphology and a significantly reduced tensile stress can be achieved by increasing the creep rate of the oxide and the flatness of the oxide-metal interface. This model thus provides an approach to extend the service time of TBCs.

Deformation-induced γ → αʹ-martensitic transformation in austenitic stainless steel obtained by electron beam additive manufacture

The relationship between strain hardening and kinetics of deformation γ → αʹ phase transformation in chromium-nickel steel Fe–19Cr–9Ni–0.7Ti–0.06C wt. % obtained by electron beam additive manufacture was studied under uniaxial static tension at room temperature and at liquid nitrogen temperature. Additively-produced steel had a two-phase (γ + δ) structure with an increased content of δ-ferrite (≈14 %). Post-production heat treatment at 1100 °С (for 1 h) allowed to reduce its volume content down to 6 %, that is, a predominantly austenitic structure in steel was close to those for analogues obtained by traditional metallurgical methods. Plastic deformation of additively-produced steel was accompanied by the formation of deformation αʹ-martensite, the volume fraction of which increased with an increase in the strain and with a decrease in the test temperature. Using the method of magnetophase analysis, it was shown that at room temperature, kinetics of the deformation γ → αʹ transformation was sluggish and it, as well as the stage and magnitude of the strain hardening, weakly depended on the content of δ-ferrite in the structure of steel obtained by the additive method. At the same time, increased content of the δ-phase under these deformation conditions contributed to an increase in the yield strength and reduced elongation to failure of the additively obtained samples. At low-temperature deformation, when the rapid kinetics of deformation γ → αʹ transformation was observed, the formation rate of αʹ-martensite under plastic deformation was slower and strain hardening was weaker in steel with a larger volume fraction of δ-ferrite than those in the samples with low content of δ-phase.

Microstructural and mechanical properties evolution of 690 nickel-based alloy subjected to severe hand disc grinding conditions

This present experimental research paper investigates the effects of severe hand disc grinding conditions on microstructure and mechanical properties evolution of a nickel-based alloy. Hand grinding is an abrasive process widely used in manufacturing industry. This manual process is used for different surface geometries, and it is often applied as the final operation that provides the effective physico-chemical properties of the surface and its sub-layers. To study the effects of manual disc grinding, a prerequisite consists in identifying the manufacturing parameters such as the feed, the normal force and the orientation of the tool with the manufactured surface. Which is neither easy to reproduce from one operator to another knowing the manual aspect of this manufacturing process nor rigorous to carry out a repeatable experimental plan. Therefore, a test bench with independent controlled parameters is required to reproduce the manual grinding process and achieve advanced studies. Mechanical properties and microstructural evolutions of a nickel-based alloy ground under very high thermomechanical loading due to abrasive material removal process were investigated through micro-hardness, XRD, SEM, EDS and EBSD analysis. The typical surface integrity characteristics are presented. Qualitative and quantitative EBSD measurements were performed to evaluate the local strain condition of the material after extreme thermomechanical processing on subsurface integrity of the nickel-based alloy. The microstructure of the material in the modified layer consists of a highly refined grain structure with an enhanced microhardness of up to 75% compared to the bulk material. It is assumed that the first 20 μm of the modified layer also called white layers in nickel-based alloy are formed by severe plastic deformation during material removal process. Keywords: surface integrity, nickel-based alloy, hand disc grinding, severe plastic deformation, grain refinement, SEM, EBSD. • Multi-scale and multi-physic surface characterization approaches to understand severe disc grinding-induced material modifications of nickel-based alloy. • A gradient of material mechanical properties occurred involving changes in its yield strength. • XRD and micro-indentation are complementary techniques to characterize the work-hardened layer induced by disc grinding. • Thermomechanical effects from disc grinding lead to severe plastic deformations of the metal workpieces yielding highly deformed grain structure, severe work hardening resulting in grain refinement under severe cutting conditions. • Presence of disc grinding-induced surface defects such as ductile tearing, material re-deposition (micro-welding) and debris are also concerns which can deteriorate functional performance of components. • SEM and EBSD analyses revealed the presence of a cold-worked layer consisting of a partially nanostructured region generated during grinding by the combination of a severe plastic deformation and high thermal kinetics.

Understanding the recrystallization kinetics in aluminium alloy billets with poorly developed cast structure

The paper describes the study of structure evolvement in A0 aluminum and 8011 and 8006 aluminum alloy billets with a low degree of the cast structure working when rolled at 300&ndash;500 &deg;C and 3&ndash;8 s&ndash;1 strain rate. The grain structure was studied by optical microscopy with Axiovert 40 MAT microscope, intermetallic particles analysis was made using JEOL 6390A scanning electron microscope. Grain structure analysis showed that a dendritic structure gradually stretching in the direction of strain is observed in the cast state. Review of the effect of deformation modes and subsequent annealing on the grain structure helped obtain analytic equation to describe recrystallization kinetics. The effect of the Zener-Hollomon parameter value on recrystallization kinetics during subsequent annealing was demonstrated. It was established that at this stage of thermomechanical processing recrystallization kinetics strongly depends both on the Zener-Hollomon parameter and on the amount of strain. The higher content of such impurity elements as silicon and iron gives larger amount of secondary metastable fine particles. This leads to an increase in recrystallization inhibiting force determining recrystallization progress in many respects. Moreover, the number of second phase particles will determine how much the amount of strain affects deformation kinetics. The highest recrystallization rate is observed in pure aluminum, the lowest &ndash; in alloy 8006. At low values of the Zener-Hollomon parameter, recrystallization process in this alloy can be fully blocked.This research was funded by the Russian Science Foundation; Project 18-79-10099-П, https://rscf.ru/project/21-79-03041/.

Study of Surfactant‐Induced Deformations at the Interface of Emulsion Droplets by Digital Image Analysis of Droplet Projections

AbstractEmulsion droplets do not always have smooth surfaces. Under certain conditions, the formation of surface‐active species at oil–water interfaces leads to interfacial instabilities that cause a spontaneous increase in the droplet surface area, which results in fascinating droplet morphologies. The specific system presented in this study consists of stearic acid encapsulated in an oil droplet and the quaternary ammonium surfactant cetyltrimethylammonium bromide in the aqueous phase. This system is studied by examining the deformation of single emulsion droplets hanging on a capillary tip. By using digital image analysis, the relative perimeters and fractal dimensions from the droplet outlines are calculated and the influences of several process parameters on their temporal development are studied. It is demonstrated that the surfactant concentration, pH value, salt addition, alcohol addition, and viscosity have a considerable impact on the droplet morphology and possible causes for this behavior are discussed. Through this study, important insights are gained into the deformation mechanism and kinetics that can potentially guide the future preparation of particles with special surface morphologies.

Effects of Interlayer Properties on Electrochemical Ion Intercalation and Electrosorption in Layered and 2D Electrode Materials

The kinetics of electrochemical intercalation and electrosorption processes are often limited by the solid-state diffusion of ions inside the lattice of the host material. While some of these limitations can be mitigated by nanostructuring of the electrode material, there is a large interest in the electrochemical energy storage community to find materials with structural motifs that allow for intrinsically fast ion diffusion, even in bulk-sized particles.In this presentation, it will be highlighted how interlayer properties, such as interlayer distance and interlayer chemistry, affect electrochemical ion intercalation and electrosorption processes in layered host materials. Using the examples of hydrogen titanates1 and Ti3C2Tx MXenes2, it is demonstrated that the presence of structural interlayer atoms or molecules can increase the accessibility of ions to the interlayer space. In the model layered host material TiS2, it is shown that increased interlayer spacing and reduced deformation during ion intercalation can lead to a change from diffusion-limited to non-diffusion limited (or pseudocapacitive) charge storage behavior,3 providing some of the most compelling experimental evidence of the intimate relationship between deformation, interlayer distance, and intercalation kinetics in layered host materials.This contribution will emphasize the importance of interlayer properties of layered and 2D materials for electrochemical ion intercalation and electrosorption processes and provide perspectives and design strategies for next generation ion insertion hosts with fast kinetics for high power energy storage. Fleischmann, S. et al. Interlayer separation in hydrogen titanates enables electrochemical proton intercalation. J. Mater. Chem. A 8, 412–421 (2020).Liang, K. et al. Engineering the Interlayer Spacing by Pre-Intercalation for High Performance Supercapacitor MXene Electrodes in Room Temperature Ionic Liquid. Adv. Funct. Mater. 31, 2104007 (2021).Fleischmann, S., Shao, H., Taberna, P.-L., Rozier, P. & Simon, P. Electrochemically Induced Deformation Determines the Rate of Lithium Intercalation in Bulk TiS2. ACS Energy Lett. 6, 4173–4178 (2021).

Electrochemically Induced Deformation Determines the Rate of Lithium Intercalation in Bulk TiS2

Understanding the kinetic limitations of intercalation reactions is essential to create high-power intercalation host materials. In this Letter, we show the existence of both diffusion-limited and non-diffusion-limited lithiation regimes in the model material bulk TiS2. The regions can be clearly identified by electrochemical impedance spectroscopy. A decreasing charge-transfer resistance is observed with increasing electrode polarization in the diffusion-limited region, whereas it remains constant when the electrochemical process is non-diffusion-limited. We highlight how TiS2 interlayer deformation is closely tied to the intercalation kinetics. While regions of TiS2 interlayer expansion/contraction are correlated with diffusion limitations, lithiation occurring under constant interlayer spacing is non-diffusion-limited: the material exhibits pseudocapacitive behavior. Larger TiS2 interlayer spacing results in faster ionic transport. The study sheds light on the close ties between deformation, interlayer distance, and intercalation kinetics in a model layered host material.

Deformation kinetics of a TRIP steel determined by in situ high-energy synchrotron X-ray diffraction

The microstructure design and the development of predictive approaches exploiting the transformation-induced plasticity (TRIP) effect require a keen understanding of the kinetics governing the strain-induced martensitic transformation. In this work, in situ high-energy synchrotron X-ray diffraction is applied to track the deformation kinetics of a commercial AISI 301LN metastable austenitic stainless steel in real-time. The kinetics obtained, providing the behaviour of the bulk material during room temperature tension up to a true strain of 0.3, unambiguously reveals the transformation sequence of ε and α′ martensite which is discussed with respect to the evolution of texture and slip. These results are enhanced with microstructure analysis including electron backscattered diffraction and transmission Kikuchi diffraction. The insights provided shed light on the role of ε during α′ transformation in metastable austenitic stainless steels and show that the latter is triggered by the general activation of slip.