Reverse Transformation Research Articles

Thermomechanics of phase transformation induced localization in NiTi tubes. Part I experiments

This two-Part study aims to illustrate and elucidate the effects of thermomechanical interactions in pseudoelastic NiTi structures that arise in the course of the reversible transformations between the austenitic and martensitic phases. Transformation leads to inhomogeneous deformation with the two phases coexisting and to latent heat-induced local heating/cooling. Part I first presents the results of displacement-controlled isothermal tension and compression experiments on NiTi tubes covering the pseudoelastic temperature regime. The experiments are conducted in a constant temperature circulating bath which suppresses thermomechanical interactions so the transformation front velocity is governed strictly by the applied displacement rate. The load/unload hystereses traced, quantify the transformation stresses and strains and will be used to calibrate the constitutive model of Part II. A set of isobaric experiments in which NiTi tubes are taken through a cool/heat cycle under constant stresses of different levels follow. The experiments are conducted in a custom small-scale environmental chamber with a circulating air stream run by a feedback temperature controller, coupled to load-controlled mechanical loading. The evolution of helical bands of the alternate phase is captured using digital image correlation. The results demonstrate that under such loading histories a strong interaction develops between the evolving inhomogeneous deformation, the latent heat and the surrounding environment. The speed of propagation of the helical fronts slows down or accelerates so as to match the rate at which heat is removed/added to the specimen by the airflow. Thus, here the evolution of localized deformation is strongly coupled to the interaction between the latent heats and heat transfer from the environment. The effect of the stress level on these events is examined through eight isobaric experiments, which provide a rich data set for evaluating constitutive models and structural analyses of these experiments such as those in Part II.

Heterostructure catalyst coupled wood-derived carbon and cobalt-iron alloy/oxide for reversible oxygen conversion

As promising energy-storage devices, zinc–air batteries (ZABs) exhibit slow reaction kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurring at their electrodes. High-performance bifunctional catalysts must thus be synthesized to accelerate the reversible conversion of oxygen and improve the rate and overall performance of ZABs. Herein, we reported the promising prospects of self-supported composite electrodes composed of wood-derived carbon (WDC) and bimetallic cobalt-iron alloys/oxides (CoFe-CoFe2O4@WDC) as efficient electrocatalysts for alkaline ORR/OER. WDC provided a favorable three-phase interface for heterogeneous reactions owing to its layered porous structure and genetic stability, thereby enabling mass diffusion and improving reaction kinetics. The CoFe2O4 spinel surface was reduced to bimetallic CoFe alloy to form abundant heterostructure interfaces that promote electron transfer. Under alkaline conditions, the optimized composite electrode exhibited a remarkable high half-wave potential of 0.85 V and an exceptionally low overpotential of 1.49 V. It also exhibited stable performance over an impressive 2340 cycles in a ZAB. Theoretical calculations also confirmed that the heterointerface addresses the issue of proton scarcity throughout the reaction and actively facilitates the creation of O–O bonds during the reversible transformation of oxygen. This study introduces a new concept for developing bifunctional and efficient electrocatalysts based on charcoal and encourages the sustainable and high-value use of forest biomass resources.Graphical

Metastable microporous lanthanide silicates – Light emitters capable of 3D-2D-3D transformations

The synthesis of zeolites and porous heteropolyhedral silicates is usually accompanied by crystal phase transformations. Typically, this process is irreversible and characterized by a conversion from a metastable phase to a stable one. Here we demonstrate a reversible transformation between porous (K3LnSi3O9·nH2O) and layered (K3LnSi3O8(OH)2) structures exemplified by a dual synthesis (hydrothermal and solid-state transformation). We discuss structural and photoluminescent properties of the obtained microporous lanthanide silicates MS-4 (Minho-Sofia, solid number 4; K3LnSi3O9·nH2O, Ln = Y, Dy; orthorhombic, Pmc21). These materials are metastable, transforming from 3D porous to a 2D layered structure after prolonged crystallization time at hydrothermal conditions and returning to the same but distorted (≈ 2 % smaller lattice volume) porous 3D framework by calcination of 2D structure. The mechanism of 3D-2D structure transformation is driven by interzeolite-like transformation, while the rearrangement of common structural fragments controls 2D-to-3D conversion. We also show how the avoidance of Dy and preference for Y ions during MS-4 hydrothermal synthesis may be overcome by a 2D-3D conversion, allowing the production of white light emitters with controllable photoluminescence.

Breathing Behavior and Superprotonic Conductivity of Two-Dimensional Flexible Metal-Organic Frameworks Tuned with Alkoxy Groups.

Flexible metal-organic frameworks (FMOFs) exhibit reversible structural transitions ("breathing" behaviors), which can regulate the proton transport passageway effectively. This property offers remarkable advantages for improving the proton conductivity. Our objective of this work is to design a single-variable flexibility synergistic strategy for the fabrication of FMOFs with high conductivity. Herein, four two-dimensional FMOFs, {[Co(4-bpdb)(R-ip)]·xsolvents}n (x = rich, 1-4), have been successfully designed and assembled (4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene and R-ip = MeO/EtO/n-PrO/n-BuO-isophthalate). Upon the release and/or absorption of different solvent molecules, they display reversible breathing behaviors, thereby resulting in the formation of the partial and complete solvent-free compounds {[Co(4-bpdb)(R-ip)]·ysolvents}n (y = free or poor, 1A-4A). This breathing behavior involves the synergistic self-adaption of the dynamic torsion of alkoxy groups and reversible structural transformation, leading to remarkable changes in cell parameters and void space, as evidenced by single-crystal X-ray diffraction, powder X-ray diffraction, and N2 and CO2 adsorption analyses. At 363 K and 98% relative humidity, 2A exhibits the best proton conductivity among the FMOFs. Its conductivity reaches 4.08 × 10-2 S cm-1 and is one of the highest conductivities shown by reported unmodified MOF-based proton conductors.

Ultraslow calorimetric studies of the martensitic transformation of NiFeGa alloys: detection and analysis of avalanche phenomena

We study the thermal properties of a bulk Ni55Fe19Ga26\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Ni}_{55}\\hbox {Fe}_{19}\\hbox {Ga}_{26}$$\\end{document} Heusler alloy in a conduction calorimeter. At slow heating and cooling rates (∼1Kh-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim {1}\\,\\hbox {K h}^{-1}$$\\end{document}), we compare as-cast and annealed samples. We report a smaller thermal hysteresis after the thermal treatment due to the stabilization of the 14 M modulated structure in the martensite phase. In ultraslow experiments (40mKh-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${40}\\,\\hbox {mK h}^{-1}$$\\end{document}), we detect and analyze the calorimetric avalanches associated with the direct and reverse martensitic transformation from cubic to 14 M phase. This reveals a distribution of events characterized by a power law with exponential cutoff p(u)∝u-εexp(-u/ξ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p(u)\\propto u^{-\\varepsilon }\\exp (-u/\\xi )$$\\end{document} where ε∼2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon \\sim 2$$\\end{document} and damping energies ξ=370μJ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\xi ={370}{\\upmu {\\rm J}}$$\\end{document} (direct) and ξ=27μJ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\xi ={27}{\\upmu {\\rm J}}$$\\end{document} (reverse) that characterize the asymmetry of the transformation.

Post-dynamic transformation from α to β phase and reverse transformation in Ti-10V-2Fe-3Al alloy during interrupted hot deformation

Interrupted hot deformation tests were carried out to study the phase transformation behavior of Ti-10V-2Fe-3Al alloy during isothermal holding after deformation. The results show that post-dynamic transformation (post-DT) from α to β phase occurred first during isothermal holding and the meta-β phase retransformed to α phase after a long holding time. This phenomenon is quite different from α+β titanium alloys in which only reverse transformation (RT, βα) took place during isothermal holding. Microstructure evolution of β-matrix was also investigated and it was found that static recovery was the main softening mechanism. Furthermore, phase transformation has a great influence on the static softening and mechanical response of interrupted hot deformation. Due to the occurrence of post-DT, the yield strength of reloading pass reduced and became lower than the initial pass when the holding time exceeds 900 s. And significant static softening was achieved. The driving and opposing force for post-DT and RT were derived and compared based on thermodynamic analysis. Since the deformation and holding temperature is close to β-transus temperature, post-DT has a lower energy barrier which can be easily overcome by stored energy. This may explain why the phase transformation direction in Ti-10 V-2Fe-3Al alloy is opposite to that in α+β titanium alloys during isothermal holding.

Dynamic Electrostatic Interfacial Engineering for Block Copolymer Microparticles with Reversible Structures.

Responsive nanoparticle surfactants (NPSs) can dynamically and reversibly modulate the interfacial interactions between incompatible components, which are essential in the interfacial catalysis, corrosion, and self-assembly of block copolymers (BCPs). However, NPSs with stimuli-responsive behavior often involve tedious chemical synthesis and surface modifications. Herein, we propose a strategy to in situ construct a kind of dynamic and reversible NPSs by the interfacial electrostatic interaction between the negatively charged nanoparticles (NPs) and the positively charged homopolymers. The NPSs assembled at the oil/water interface reduce the interfacial tension and direct the confined assembly of BCP. Meanwhile, the dynamic NPSs can be disassembled by increasing the pH value or introducing competitive electrostatic attractions, which can dynamically and reversibly change the interfacial properties as well as the alignment of polymer chains, enabling BCP microparticles with reversibly switchable lamellar and cylindrical structures. Furthermore, by the introduction of aggregation-induced emission luminogens as tails to the NPSs, the reversible transformation of BCP microparticles can be visualized by fluorescence emission, which is dependent on the nanostructures of microparticles. This work establishes a concept for dynamically manipulating interfacial interactions and reversibly switching BCP microparticles without time-consuming NPS synthesis, showing promising applications in the fabrication of smart materials with switchable structures and properties.

Predominant P3-Type Solid-Solution Phase Transition Enables High-Stability O3-Type Na-Ion Cathodes.

Layered O3-type oxides are one of the most promising cathode materials for Na-ion batteries owing to their high capacity and straightforward synthesis. However, these materials often experience irreversible structure transitions at elevated cutoff voltages, resulting in compromised cycling stability and rate performance. To address such issues, understanding the interplay of the composition, structure, and properties is crucial. Here, we successfully introduced a P-type characteristic into the O3-type layered structure, achieving a P3-dominated solid-solution phase transition upon cycling. This modification facilitated a reversible transformation of the O3-P3-P3' structure with minimal and gradual volume changes. Consequently, the Na0.75Ni0.25Cu0.10Fe0.05Mn0.15Ti0.45O2 cathode exhibited a specific capacity of approximately 113 mAh/g, coupled with exceptional cycling performance (maintaining over 70% capacity retention after 900 cycles). These findings shed light on the composition-structure-property relationships of Na-ion layered oxides, offering valuable insights for the advancement of Na-ion batteries.

Frequency effect on low‐cycle fatigue behavior of pseudoelastic NiTi alloy

AbstractThis study presents experimental results on the effect of loading frequency during low‐cycle fatigue on the fracture mechanism and properties of pseudoelastic NiTi wire. The uniaxial tensile tests were performed in stress‐controlled mode over the 0.1–10 Hz frequency range. It was shown that the number of cycles before specimen failure decreased with increasing frequency from 0.1 Hz to 1 Hz but increased at frequencies above 1 Hz. It was fractographically shown that fatigue striations were observed on the fracture surfaces of specimens tested at all loading frequencies. A new type of fatigue striations was described on fracture specimens tested at frequencies up to 1 Hz. They are characterized by different spacing between successive striations with a change in the slope of the fracture at the transitions between them. This feature may be associated with forward and reverse phase transformations during half‐periods of loading and unloading of nitinol.

Intramolecular Charge Transfer and Stimuli-Responsive Emission in Cholesterol-Appended Phenothiazine-Cyanostyryl-Based Donor-Acceptor Systems.

Organic fluorescent molecules have received considerable attention owing to their various optoelectronic applications. Herein, we report the design and synthesis of two cholesterol-functionalized cyanostyrene-phenothiazine-based D-π-A systems that are emissive in both the solution and solid states. The newly synthesized cholesterol-appended phenothiazine-cyanostyrene diads PTCS-1 and PTCS-2 vary in the N-alkylation of phenothiazine, respectively, with─octyl and─hexyl chains. Both molecules are highly fluorescent and show reasonably good quantum yields in nonpolar solvents because of twisted intramolecular charge transfer (TICT). The molecules exhibit aggregation-induced emission in the solid state. Due to the presence of flexible alkyl chains in the phenothiazine and cholesterol moieties, PTCS-1 and PTCS-2 show mechanochromic luminescence switching in response to external shear stress and emission recovery under methanol vapor. Powder X-ray diffraction studies prove that the emission switching on the applied stimuli in both PTCS-1 and PTCS-2 is attributed to the reversible transformation between the crystalline and amorphous states. Time-dependent density functional theory (TD-DFT) studies are carried out to gain insight into the ICT interactions. TD-DFT analysis at the TD-M06-2X/def2-TZVP level further revealed that in both molecules, the lowest unoccupied molecular orbital (LUMO) + 2, LUMO, highest occupied molecular orbital (HOMO), and HOMO - 1 orbitals are responsible for the charge transfer interactions. These ICT interactions are identified as π-π* type interactions.

Temperature effects on the structure of lead metasilicate glass, supercooled liquid, crystal, and liquid: Vibrational anharmonicity and configurational transformations analyzed by molecular dynamics and Raman scattering

Raman spectroscopy and Molecular Dynamics (MD) simulations were employed to explore in detail the effects of temperature on the four stages of the PbO∙SiO2 system: glass, supercooled liquid, crystalline phases, and liquid. The Qn distribution up to 1153 K and the wavenumber temperature coefficients derived from vibrational anharmonicity were determined from the Raman data, whereas the structural transformation reflected in changes in the Qn population distribution up to 2400 K was inferred from MD simulations. The results indicate that reversible configurational transformations occur only in the higher temperature ranges of the supercooled liquid and more notably in the liquid state. During these transformations, the increase in the Q0 and Q1 populations occurs at the expense of the Q3 and Q4 populations. On the other hand, only vibrational anharmonicity was observed in the glass and crystalline states.

Tuning the Thermochemistry and Reactivity of a Series of Cu-Based 4H+/4e- Electron-Coupled-Proton Buffers.

Electron-coupled-proton buffers (ECPBs) store and deliver protons and electrons in a reversible fashion. We have recently reported an ECPB based on Cu and a redox-active ligand that promoted 4H+/4e- reversible transformations (J. Am. Chem. Soc. 2022, 144, 16905). Herein, we report a series of Cu-based ECPBs in which the ability of these to accept and/or donate H• equivalents can be tuned via ligand modification. The thermochemistry of the 4H+/4e- ECPB equilibrium was determined using open-circuit potential measurements. The reactivity of the ECPBs against proton-coupled electron transfer (PCET) reagents was also analyzed, and the results obtained were rationalized based on the thermochemical parameters. Experimental and computational analysis of the thermochemistry of the H+/e- transfers involved in the 4H+/4e- ECPB transformations found substantial differences between the stepwise (namely, BDFE1, BDFE2, BDFE3, and BDFE4) and average bond dissociation free energy values (BDFEavg.). Our analysis suggests that this "redox unleveling" is critical to promoting the disproportionation and ligand-exchange reactions involved in the 4H+/4e- ECPB equilibria. The difference in BDFEavg. within the series of Cu-based ECPBs was found to arise from a substantial change in the redox potential (E1/2) upon modification of the ligand scaffold, which is not fully compensated for by a change in the acidity/basicity (pKa), suggesting "thermochemical decompensation".

Versatile morphology transition of nano-assemblies via ultrasonics/microwave assisted aqueous polymerization-induced self-assembly based on host–guest interaction

Nano-assemblies have wide applications in biomedicine, functional coatings, Pickering emulsifiers, hydrogels, and so forth. The preparation of assemblies mainly utilizes the polymerization-induced self-assembly (PISA) method, which can produce high-concentration nanoscale assemblies in one step. However, the initiation processes of most reported PISA are limited to thermal initiation. Here, we reported two green and efficient methods for synthesizing nano-assemblies with various morphologies using ultrasound (20 kHz)/ microwave (500 W) assisted aqueous-phase RAFT-PISA in 3 h and 1 h. Cyclodextrin (CD) and styrene (St) nucleating monomer were complexed in a 1:1 ratio. Then, using Poly (ethylene glycol) methyl ether as the macromolecular reversible addition-fragmentation chain transfer (RAFT) agent (PEG-CTA) to control the CD/St complexes, the conversion rate of St monomer was respectively 27 %–60 %, 20 %–30 % within 3 h and 1 h under ultrasonics/microwave assisted PISA. Results showed that the morphologies of the assemblies are not only related to the length of PS block, but also to the assistance types and the remaining monomer concentration. The results showed that only PEG45-b-PS90 and PEG45-b-PS241 assemblies prepared by ultrasonics assisted PISA form evolved lamellaes and vesicles (100 nm), which break through the limitation of kinetic freezing. But the ultrasonic reaction on morphology of assemblies is not all favourable. For one thing, it can promote the movement of particles; for another, it makes reverse morphology transformation and sphere is preferred morphology. Therefore, the main reason of morphology evolution is the remaining monomer concentration of PEG45-b-PS90 and PEG45-b-PS241 assemblies reaches to 55 %–65 %, which promoting the segment movement. The results showed that the morphology of the assemblies prepared by microwave assisted PISA changed from spherical micelles to short rods, and finally to vesicles (120–140 nm) as the length of hydrophobic PS block increases. The kinetic freezing problem was solved in microwave-assisted PISA due to the action of microwaves and more remaining monomer concentration. Both them can boost particles movement.

Origins of functional fatigue and reversible transformation of precipitates in NiTi shape memory alloy

The work clarifies several key questions in shape memory research that have eluded previous studies. The findings show that dislocation slip emanates at austenite-martensite interfaces during unloading and aligns with the internal twin boundary interface of martensite. It was observed that the type II internal twins of the martensite become parallel dislocations in the austenite. During reloading, these dislocations act as nucleation sites for the martensitic twins, reducing the nucleation barrier and the transformation stress. The precipitates facilitate martensite nucleation but also act as an obstacle to martensite front motion, restrict detwinning, and pin the interfacial dislocations during unloading, thereby contributing to residual strains and martensite stabilization. Martensite nucleation is not suppressed by the size of the thin film, which is of the order of 85 to 105 nanometers thick, and repeated transformation occurred cycle after cycle. Single crystals deformed in the <101>LD exhibited the best recoverability of up to 5.5 % and tensile stresses of up to 1.4 GPa. It was demonstrated for the first time that, when favorably oriented, Ni4Ti3 precipitates undergo a reversible phase transformation to R-phase and can accommodate up to 4 % reversible strains.

Enhanced deformation-induced FCC-HCP transformation of a metastable high-entropy alloy induced by a smaller grain size

This study reports the grain-size-dependent deformation-induced face-centered cubic (FCC)–hexagonal close-packed (HCP) transformation behavior of Fe49.5Mn30Co10Cr10C0.2Ti0.1V0.1Mo0.1 (at. %) high-entropy alloy in the medium grain size range (10–20 μm), their mechanical properties, and deformation mechanisms. The materials annealed at 900 °C for 1 h (A900-1) and 10 h (A900-10) showed a fully FCC, recrystallized microstructure with a larger grain size in the latter owing to grain growth during annealing. The A900-1 sample exhibited a larger strength–ductility balance and a higher strain hardening rate than the A900-10 sample. The A900-1 sample, with a larger number of grain boundary nucleation sites of the deformation-induced HCP phase, exhibited a higher HCP transformation rate than the A900-10 sample in the early stage of deformation below 10 % strain, whereas both materials showed similar HCP transformation rates at strain levels higher than 30 %. The emission of deformation-induced HCP plates in both neighboring grains from the same grain boundary (A900-1) and the activation of the deformation-induced HCP phase in a single grain and only dislocations in the neighboring grains (A900-10) suggest the importance of grain boundary stress in the observed phenomena. The observed additional mechanisms other than dislocation slip and deformation-induced HCP phase, that is, reverse FCC-HCP transformation, HCP {101‾2} twinning, and kink banding, could contribute to deformation accommodation and stress relaxation, thereby leading to the excellent ductility of the investigated materials.

Ultrafast reversible phase engineering in MoTe2 thin film via polaron formation

The emergence of various polymorphs in two-dimensional transition metal dichalcogenides provides an opportunity for robust phase engineering by temperature, strain, laser irradiation, and external charge doping (Keum in Nat. Phys. 11:482, 2015; Song in Nano Lett. 16:188, 2016; Cho in Science 349:625, 2015; Kim in Nano Lett. 17:3363, 2017). This provides means to develop homojunction of metal–semiconductor, enhance mobility, reduce contact resistance, and observe novel quantum critical phenomena in mesoscopic systems. The rich physics paves the way for ultrafast light-induced switching/memory devices and optical data processing in optoelectronics. However, the fundamental temporal evolution of the laser-driven phase transformation, in particular regarding heat and charge carriers, remains elusive. We report an ultrafast reversible structural transformation in MoTe2 by coherent phonon dynamics through polaron formation at room temperature. At a high photon density, the generated coherent phonons are coupled with excitons to form polarons. The strong exciton–phonon coupling disturbs and dephases the coherent phonons of the semiconducting 2H phase in MoTe2, and generates lattice distortions to further stabilize new coherent phonons of the metallic 1T’-phase, manifested by the emergence of the corresponding phonons in each phase. This structural transformation is fully reversible within a few picoseconds by switching on/off the laser. The nonlinear response of the phonon intensity to the excited carrier density in the intermediate region indicates a gradual structural transformation through coexisting 2H and 1T’ phases.

Discovering the Order-Disorder Transition in Quinoline Intercalated Vanadium Oxide with Superior Calcium Storage via Polyhedral Distortion.

Calcium-ion batteries (CIBs) are considered as potential next-generation energy storage systems due to their abundant reserves and relatively low cost. However, irreversible structural changes and weak conductivity still hinder in current CIBs cathode materials. Herein, an organic molecular intercalation strategy is proposed, in which V2O5 regulated with quinoline, pyridine, and water molecules are studied as cathode material to provide fast ion diffusion channels, large storage host, and high conductivity for Ca ions. Among them, V2O5-quinoline (QVO) owns the largest interplanar spacing of 1.25 nm and the V-O chains are connected with organic molecular by hydrogen bond, which stabilizes the crystal structure. As a result, QVO exhibits a specific capacity of 168 mAh g-1 at 1 A g-1 and capacity retention of 80% after 500 cycles at 5 A g-1 than the other materials. Furthermore, X-Ray diffraction and X-ray absorption spectroscopy results reveal a reversible order-disorder transformation mechanism of Ca2+ for QVO, which can make full use of the abundant active sites for high capacity and simultaneously achieve fast reaction kinetics for excellent rate performance. These results demonstrate that QVO is a promising cathode material for CIBs, providing more choices for the development of high-performance CIBs.

Reverse ε→γ transformations of temperature-induced and stress-induced martensites in Fe–Mn–Si alloys with shape memory effect

In this work we argue that the reverse martensitic transformation (MT) of the stress-induced martensite (SIM) of Fe–Mn–Si-based alloys for moderate prestrains occurs in essentially thermoelastic-like way, in contrast to non-thermoelastic MT of temperature-induced martensite (TIM). We compare, using a number of complementary experimental techniques, the temperatures and the kinetics of the reverse ε→γ martensitic transformation of SIM and TIM for commercial and model Fe–Mn–Si alloys after various thermomechanical treatments. We claim that two studied phenomena are generic in Fe–Mn–Si-based alloys of different compositions and microstructure: first, opposite to the conventional effect of stabilization of martensite by prestrain, the reverse MT during heating of alloys prestrained in bending and tension starts well below (up to 100 K) the start temperature of the reverse MT for the TIM of the same alloy. The difference between engineering temperatures of the start of the reverse transformation, As, for SIM and TIM reaches ca. 50 K, pointing to a need to consider different As for TIM and SIM, AsTIM and AsSIM. Second, the reverse transformations of TIM and SIM show very different kinetics. The reverse MT of SIM is diffuse over the temperature range exceeding 100 K. The reverse MT of TIM, on the contrary, is well localized within the temperature range of ca. 20 K. The experimental observations can be interpreted assuming that, due to the differences in the formation mechanisms of SIM and TIM, the latter shows non-thermoelastic behaviour, whereas the SIM shows similarities with the thermoelastic martensites stabilized by prestrain.

Microstructural mechanisms endowing high strength-ductility synergy in CoCrNi medium entropy alloy prepared by laser powder bed fusion

CoCrNi medium entropy alloy (MEA) exhibits significant potential as a structural component for engineering applications. However, the traditional processing methods for pursuing the superior mechanical properties of CoCrNi MEA are often time-consuming and inefficient. Laser powder bed fusion (LPBF) offers substantial processing flexibility without the need for complex secondary processing. In this study, we optimized the processing parameters for CoCrNi MEA through an orthogonal experimental design, achieving as-printed CoCrNi components with a relative density of up to 99.4 %. The microstructure of the as-printed CoCrNi revealed hierarchical features, including the molten pools, equiaxed and elongated columnar grains, sub-grain cellular microstructures, and high-density dislocation networks. The mechanical properties of as-printed CoCrNi were exceptional, demonstrating a synergistic combination of strength and ductility (yield strength: approximately 660.91 MPa, tensile strength: approximately 892.78 MPa, elongation: approximately 33.28 %, and a product of strength and elongation: 27.45 GPa %). Experimental characterization elucidated the activation and interplay of mechanisms such as dislocations, stacking faults, twinning-induced plasticity, and transformation-induced plasticity. These mechanisms collaboratively enhanced the refinement and heterogeneity of substructures, thereby endowing the as-printed CoCrNi with significant strength-ductility synergy. Molecular dynamics simulations indicated that, in the initial stages of plastic deformation, a significant activation of Shockley partial dislocations occurred, leading to the formation of stacking faults and the emergence of Hexagonal Close-Packed (HCP) phases. As plastic deformation progressed, a reverse phase transformation from HCP to Face-Centered Cubic (FCC) took place, resulting in the formation of nanotwins. This transformation generated a heterogeneous microstructure comprised of both nanotwins and HCP phases, suggesting a sequential twinning and phase transformation pathway in as-printed CoCrNi: from FCC to HCP, and subsequently to FCC nanotwins.

Superior combination of strength and ductility in Fe–10Mn-0.6C steel trigged by austenite reversion transformation

Austenite reversion transformation process was employed on Fe–10Mn-0.6C steel to adjust the content and stability of austenite and the transformation-induced plasticity effect was effectively improved. With increasing annealing temperatures from 550 °C to 590 °C and 620 °C, the content and proportion of lath-like austenite significantly increased. Austenite exhibited different stability after annealing at different temperatures, mainly related to the distribution of Mn and C. The higher the local Mn and C concentration, the more stable austenite, vice versa. After annealing at 620 °C for 6 h, the highest austenite content of 61 % was achieved, and half of that had a lath-like morphology. The steel had a superior combination of ultimate tensile strength of 1500 MPa and elongation of 59 %, resulting from the enhanced transformation-induced plasticity effect. The key reason was the alternating distributions of austenite and ferrite laths, accompanied with the formation of nanotwins in the austenite with high stability.