Phase Transformations In Materials Research Articles

A Comparison of Sigma Phase Formation in Solubilized Hyper Duplex Stainless Steel and Super Duplex Stainless Steel Filler Metals

This study focuses on the kinetic analysis of sigma phase formation in filler metal wires on Super Duplex Stainless Steel (SDSS) and Hyper Duplex Stainless Steel (HDSS). Precipitation data reveal that in the solubilized microstructure, sigma phase kinetics are more prominent in SDSS. This increased susceptibility is attributed to the greater number of nucleation sites, which is facilitated by the larger interface area/volume and the higher chromium content in the ferrite. The difference in interface area/volume is significantly more influential in determining kinetics than the composition difference, with nucleation sites playing a central role. The sigma phase transformation in both materials was modeled using the JMAK kinetic law. The JMAK plots exhibit a transition in kinetic mechanisms, evolving from discontinuous precipitation to diffusion-controlled growth. In SDSS, the JMAK values indicate “grain boundary nucleation after saturation,” followed by “thickening of large plates.” In contrast, HDSS values point to “grain edge nucleation after saturation,” followed by “thickening of large needles.” The higher kinetics in SDSS are characterized by a smaller nucleation activation energy of 56.4 kJ/mol, in contrast to HDSS's 490.0 kJ/mol. CALPHAD-based data support the JMAK results, aligning with the maximum kinetics temperature of SDSS (875 °C to 925 °C) and HDSS (900 °C to 925 °C). Therefore, the JMAK sigma phase kinetics effectively describe the experimental data and its dual kinetics behavior, even though CALPHAD-based TTT calculations often overestimate sigma formation.

Constructing partially spinel phase in Mn-rich cathode material

As a cathode with earth-abundant element, Mn-rich oxide has been explored to enable the scaling of the Li-ion battery. However, the irreversible transition metals migration and phase transformations in Mn-rich materials have been proven to be detrimental, which trigger capacity degradation, voltage decay, and poor kinetics. In this work, using Li2MnO3 as model, spinel-layered biphase was constructed via Ti doping and de-lithiation modification, which exhibits higher available capacity of 236.9 mAh/g (55.6 mAh/g for pristine material) and improved rate performance. Compared with pristine Mn-based cathodes, the new phase delivers neglectable voltage degradation during electrochemical cycling. Based on systematic characterization, the new phase exhibits higher oxygen redox reversibility and accelerated kinetics of lithium ions transformation. This work provides a new strategy for designing high-energy density Mn-rich cathodes.

Effect of milling atmosphere on stability and surface properties of ZnO/vermiculite hybrid nanocomposite powders

The zinc acetate dihydrate and anhydrous zinc chloride were used as precursors for the sonochemical preparation of the zinc oxide/vermiculite and organically modified zinc oxide/vermiculite_chlorhexidine nanocomposite materials. The nanocomposites were mechanically processed via a high-energy ball milling for 30 min at 300 rpm using two types of atmospheres an air or a nitrogen. Changes in temperature and pressure inside the grinding vessels were measured during mechanical processing in an air atmosphere. The ZnO(Cl)/V_30/300 sample reached the highest pressure (1161 mbar) and temperature (30.3 °C) in the milling vessels and for the ZnO(ac)/V_CH_30/300 sample the highest temperature difference was measured at the beginning and at the end of the milling (7 °C). The phase transformation, chemical composition and particle size of the hybrid nanocomposite materials were investigated using X-ray diffraction method, Fourier-transform infrared spectroscopy, X-ray fluorescence spectroscopy, carbon phase analysis and particle size distribution analysis. Changes in morphology and particle arrangement were characterised using scanning electron microscopy. The effect of mechanical processing in a protective atmosphere on surface properties such as specific surface area, surface conductivity and ζ-potential were demonstrated in relation to the type of precursor used for the preparation of ZnO nanoparticles in the structure of hybrid nanocomposite materials.

Nanocalorimeter and Raman microscope combination technique to study polymorphic transition processes in pharmacy materials

This article describes an experimental setup for combining ultrafast on-chip calorimetry (nanocalorimetry) and Raman spectroscopy (Raman spectroscopy) to study phase transformations in polymer materials. A new method for calibration of a nanocalorimetric sensor under a laser beam of a Raman microscope for in situ measurements at various temperatures is developed.

Investigate on material removal of 3C-SiC crystals in nano-polishing via molecular dynamics

While 3C-SiC crystals are widely employed in engineering applications such as aerospace, energy, chemistry, and electronics, the challenge of enhancing surface friction and wear mechanisms in 3C-SiC materials persists. This work focuses on the nano-polishing velocity effect on the material removal mechanism of 3C-SiC crystals in the course of nano-polishing, which is related to material removal, mechanical response, phase transformation, and stress distribution. By employing molecular dynamics (MD) simulations, nano-polishing velocity is modified within a specified range, and its influence on the atomic motion and structural transformation of the workpiece is examined. The simulation results reveal that higher nano-polishing velocities diminish the subsurface damage and the extent of phase transformation induced by nano-polishing. However, the higher velocities also result in reduced machined surface quality and increased residual stress in 3C-SiC crystals. Therefore, it is challenging to address both the surface quality and subsurface quality of the material solely based on nano-polishing velocity. A recommended range of nano-polishing velocity, ranging from 200 m/s to 400 m/s, is deemed appropriate. This work offers a comprehensive understanding of the material removal mechanism of 3C-SiC at the atomic level and holds significant guiding value for achieving ultra-precision machining of surfaces and subsurfaces.

Theoretical investigation on the solid-liquid phase transition of gallium through free energy analysis.

Gallium, renowned for its notably low melting point and unique property of becoming liquid at room temperature, is a valuable constituent in phase change materials. In this study, we investigate the solid-liquid phase transition of gallium using the modified embedded atom method (MEAM) potential. It addresses the technique to compute the free energy difference between the solid and liquid without using a reference state. We examine various thermodynamic and dynamic properties, including density, specific heat capacity, diffusivity, and radial distribution functions. We compute the coexistence temperature of the solid-liquid phase transitions of gallium from free energy analysis. This information is crucial for understanding the behavior of the material under different pressure conditions and can be valuable for various applications, such as materials processing and high-pressure studies. The analysis, findings, and insights of the present work will be of great significance to the broad scientific and engineering communities in the field of phase transformation of materials. A series of molecular dynamics(MD) simulations were conducted using the LAMMPS software packages. The gallium atoms are modeled using the modified embedded atom method (MEAM) potential. To accurately predict the solid-liquid phase transitions of gallium, we calculated free energy by employing the "constrained λ integration" method, coupled with multiple histogram reweighting (MHR). The solid-liquid coexistence line is determined through the Gibbs-Duhem integration technique.

In situ annealing optimization by anomalous Hall effect for a high-entropy alloy

An in situ methodology was devised to refine the annealing parameters for a soft magnetic high-entropy alloy, Al0.7NiCoFe1.5Cr1.5. Anomalous Hall measurements were employed to elucidate the magnetic characteristics in real time during annealing. This approach facilitates the determination of an optimal annealing temperature range, centered approximately at 500 °C, within a single annealing process. After annealing, a notable 51.5% enhancement in the saturation magnetization was observed, accompanied by a significant 80.5% reduction in coercivity. Moreover, the methodology enables the acquisition of intricate insights into phase transitions occurring throughout the annealing process. The findings affirm the efficacy of the in situ technique for refining the annealing parameters and underscore its potential applicability in the exploration of microstructural and phase transformations in materials.

Plasma and Gas‐based Semiconductor Technologies for 2D Materials with Computational Simulation & Electronic Applications

AbstractThe technique of plasma processing is beneficial for wafer cleaning and precision etching of integrated circuits and essential in manufacture of advanced semiconductor devices with unmatched perfection. Research on two‐dimensional (2D) materials, such as transition metal dichalcogenides(TMDs), offers a promising solution to the challenges in semiconductor miniaturization. TMDs, with their atomic layer thicknesses and silicon‐like bandgaps, can be integrated using existing plasma systems. Different 2D crystal structures, such as 1T and 2H configurations, exhibit distinctive properties. Computational approaches are also developed to provide guidelines for controlled synthesis and etching of large‐scale and high‐quality 2D materials. Plasma/gas‐surface interactions during the synthesis, etching, and phase transformation of 2D materials are explored using atomistic simulations such as density functional theory and molecular dynamics. The reaction energetics, chemical species, and associated kinetics are discovered in the simulation study. These results decipher various mechanisms of 2D materials processing at the microscopic scale and predict certain optimal process parameters. Plasma/gas‐based semiconductor technologies are crucial in electronics because they enable production of advanced semiconductors. Plasma/gas etching allows precise and selective removal of material and plasma‐enhanced chemical vapor deposition enhances chemical reactions for efficient film deposition; therefore, these processes are majorly important for harnessing 2D materials in electronic applications.

Preparation and Properties of Graphene/Novel Degradable Plastics Hybrid Low Enthalpy of Phase Transition Materials

Graphene (GNs) were chosen to modify hybrid and novel degradable plastics PTLA/polymethyl methacrylate (PMMA). The low enthalpy of melting phase transformation (MEPT) materials (PTLA/PMMA)/GNs were prepared by adding the GNs at different mass fraction(1%, 2%, 3%, 4%) into PTLA/PMMA, and the properties of the hybrid phase change materials were characterized. The results indicated that the MEPT of PTLA/PMMA materials can be significantly reduced with the addition of GNs. The addition of 3% (mass) GNs made the MEPT of PTLA/PMMA material decreased by more than 50%. With the increase of GNs mass fraction, the MEPT hardly changed; Fourier transformed infrared (FT-IR) spectra showed that the interaction between GNs and PTLA/PMMA was physical; Scanning electron microscope (SEM) images showed that the components of GNs and PTLA/PMMA were mixed evenly without phase separation; The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) cycle performance tests showed that the decomposition temperature of the (PTLA/PMMA)/GNs material was up to 280 °C, and the properties could remain stable during the circulation process. The addition of GNs could effectively reduce the MEPT of the (PTLA/PMMA)/GNs material, increase the heat transfer efficiency, and have good thermal reliability.

Особенности фазовых и структурных превращений в композиционных материалах на основе систем несмешивающихся компонентов при воздействии концентрированных потоков энергии

The features of phase and structural transformations in composite materials based on systems of immiscible components Al – Be, Al – Be – Mg, Fe – Cu, Fe – Cu – Pb under the influence of concentrated heat sources — electric arc, electron and laser beams — are considered. It is shown that when materials of the Al – Be, Al – Be – Mg systems are exposed to an electric arc plasma and an electron flow, they are melted and subsequently cooled by grain grinding, formation of a zone of thermal influence and crystallization of the resulting new structures and phases. In zone of thermal influence, the enrichment of the aluminum matrix with Be particles is observed due to the thermal diffusion processes of their movement. When plasma is exposed to an arc discharge, pulsed and continuous laser radiation, as well as the flow of electrons on the composition Fe – Cu, Fe – Cu – Pb, a change in the morphology of the near-surface layer is observed: the irradiated material in the melt zone is exfoliated and in the process of crystallization the stratified phases are fixed in a solid state. The mechanism of stratification formation is associated with the limited solubility of the elements that make up the composition in the liquid and solid states.

Grain size and lattice compatibility enhanced figure-of-merit in Ba0.95Ca0.05Ce0.005ZrxTi0.995−xO3 material for pyroelectric energy conversion

Phase-transforming ferroelectric materials have attracted significant attention due to their potential for energy conversion from waste heat. Here, we explore the impact of grain size and lattice compatibility on the energy conversion figure-of-merit (FOM) of a phase-transforming ferroelectric system Ba0.95Ca0.05Ce0.005ZrxTi0.995−xO3 with Zr content ranging from 0.004 to 0.03. The results demonstrate that tuning grain size and lattice compatibility can significantly increase the FOM. The optimal composition Zr0.006 exhibits the highest FOM among its neighboring compositions, with a corresponding peak pyroelectric current density of 5.6 μA/cm2 generated from a temperature fluctuation of 30 °C at a temperature rate of 5 °C/s. This work provides a rational understanding of the effect of grain morphology and crystal structure on the pyroelectric properties for energy conversion.

(Invited) Some Perspectives on Thermodynamics, Kinetics, Mechanics and Phase Transformations of Ionic and Mixed Conducting Ceramics

A perhaps oversimplified description of Professor Virkar's research of the last 45 years is thermodynamics, kinetics, (fracture) mechanics--which is thermodynamics at 0 Kelvin, and phase transformations of ceramic materials. I will reflect on some of his significant contributions in these areas, and echo them with a few recent research notes of my own.

Coupling diffusion and finite deformation in phase transformation materials

We present a multiscale theoretical framework to investigate the interplay between diffusion and finite lattice deformation in phase transformation materials. In this framework, we use the Cauchy–Born Rule and the Principle of Virtual Power to derive a thermodynamically consistent theory coupling the diffusion of a guest species (Cahn–Hilliard type) with the finite deformation of host lattices (nonlinear gradient elasticity). We adapt this theory to intercalation materials – specifically Li1−2Mn2O4 – to investigate the delicate interplay between Li-diffusion and the cubic-to-tetragonal deformation of lattices. Our computations reveal fundamental insights into the microstructural evolution pathways under dynamic discharge conditions, and provide quantitative insights into the nucleation and growth of twinned microstructures during intercalation. Additionally, our results identify regions of stress concentrations (e.g., at phase boundaries, particle surfaces) that arise from lattice misfit and accumulate in the electrode with repeated cycling. These findings suggest a potential mechanism for structural decay in Li2Mn2O4. More generally, we establish a theoretical framework that can be used to investigate microstructural evolution pathways, across multiple length scales, in first-order phase transformation materials.

DEVELOPMENT AND DETERMINATION OF PARAMETERS OF SEASONAL COLD ACCUMULATORS WITH PHASE TRANSFORMATION

The purpose of this study is to develop and justify the parameters of new structures of seasonal batteries with phase transformation of the storage material, which allow to get rid of deformations and destruction of the contacting elements of the battery structure when the aggregate state changes. The design of a seasonal battery with a phase transformation of the storage material is based on a shell that allows to compensate for the expansion of the material when the aggregate state changes. Determination of the dependence of the energy parameters on the geometric parameters and thermophysical parameters of the constituent elements of the seasonal battery with phase transformation, which allow the battery capacity and power at different stages of discharge and charge. The study of phase transition processes made it possible to establish the characteristic stages of charging and discharging the battery: heating the material to the phase transformation temperature; heat transfer for phase transformation 0°C; heating the material after the phase transformation; cooling the material to the phase transformation temperature; heat removal for phase transformation 0°C (in some cases hypothermia up to 3-4°C is possible; cooling of the material after the phase transformation. The largest battery power values occur at the stage of cooling the material to the temperature of the phase transformation and heating the material after the phase transformation (25.62 kW ). The lowest power of the battery (13.56 kW) is observed heating of the material to the temperature of the phase transformation and cooling of the material after the phase transformation, which is explained by the low heat exchange of the accumulating substance in the solid state. Based on the conducted research, recommendations were made that the prospects for the development and optimization of the design of seasonal batteries with the phase transformation of the accumulating material.

The phase transformation behavior of Mn-Al rare-earth-free permanent magnets

Rare-earth-free permanent magnet materials based on Mn show great promise for applications in electric motors and devices. The metastable ferromagnetic τ phase of the Mn-Al system has magnetic properties between those of the high-performance Nd-Fe-B magnets and the lower-performance ferrite magnets. However, the hybrid displacive-diffusional pathway of τ formation, from the parent ε phase through the intermediary ε’ phase, is still not fully understood. This phase transformation progression was studied in-situ using diffractive, calorimetric, and magnetometric techniques to show that the progression from ε to τ in Mn54Al46 at <450 °C involves the ordering of ε into ε’. Density functional theory calculations were performed on each phase and confirmed the experimental observation that the ε to ε’ to τ pathway is energetically favorable. Isothermal annealing of quenched-in ε at 350 °C demonstrated that ε’ is ferromagnetic, also in agreement with theoretical results, with a moderate coercivity of at least 50 kA/m. The τ phase was observed to nucleate along the prior ε phase grain boundaries and grow into the ε’ phase regions. A boundary front of ε’ was observed between the τ and ε phases. Both Kissinger and Flynn-Wall-Ozawa methods were used to determine the activation energies for the ε’ and τ phase transformations with values of ∼140 kJ/mol obtained for both phases. Therefore, the ordering transformation to ε’ and the hybrid displacive-diffusional transformation to τ were shown to overcome the same magnitude energy barrier. Both activation energies were less than previous τ phase activation energies measured on Mn55Al45 in the absence of a significant ε’ ordering exotherm, providing a kinetic benefit to the ε to ε’ to τ pathway at 350 °C. The results of this study give insight into the phase transformation of L10 binary materials as well as materials that undergo a disorder–order transformation followed by displacive shear.

Назначение рациональных режимов электроэрозионной обработки деталей из титанового сплава ВТ5 на основе решения тепловой задачи о перемещении границы фазового превращения материала

The paper presents results of theoretical studies of the VT5 titanium alloy machinability by the electrodischarge machining method based on solving the thermal problem of the material phase transformation boundary displacement (Stefan problem). It proposes a method for determining parameters of electrical pulses for the VT5 alloy electrodischarge machining in order to increase the process productivity; recommendations are provided for that purpose. Density of the heat flux and its duration were determined necessary for implementation of the VT5 alloy electrodischarge machining process. Dependences were established of the minimum value of the heat flux pulse duration, when the VT5 alloy electrodischarge machining process was possible, and of maximum value of the heat flux pulse duration ensuring maximum removal of the VT5 alloy from the workpiece in one pulse, on the heat flux density. It is shown that for the maximum productivity of the VT5 alloy electrodischarge machining at the heat flux density used, it is necessary to assign effective duration of such a flux. Dependences of the heat flux effective duration on its density were established. Besides, to assign rational modes of VT5 ally electrodischarge machining, relationships were established and provided between the VT5 alloy machinability curves (dependences of the material penetration depth on the pulse duration) and other materials, including those for which rational modes are currently defined

Degradation Behavior of Layered Structure Cathode in Sulfide Based All-Solid-State Batteries

With declaration of carbon zero in response to climate change, the importance is also being bandied about developing large-scale energy storage system, especially for electric vehicle (EV). Commercialized EV with a highest development lithium-ion batteries (LIB) could operate over 300 miles per single charging, but liquid electrolyte-based LIB gives rise to a huge risk concerning about ignition and explosion. All-solid-state batteries (ASSBs) is considered to alternative next-generation battery that have high safety advantageous with removal the risk of ignition by applying non-combustible inorganic solid-electrolytes (SEs). In case of sulfide-based ASSBs, there were progressed in performance itself at cell capacity increase and cycling characteristic due to advance in cell configuration, composite cathode, and cell fabrication technique compared to early works. Nevertheless, it is still demanded improvement related to the cathode-electrolyte interface stability, and its dominant causes are electrochemical- and chemo-mechanical problems. Therefore, most of researchers have tried to figure out the behavior of all-solid-state batteries by providing external pressure, and then resolve degradation issues including contact loss and resistive layer formation. However, in practical and commercialization aspects, the external pressured cell can be a stumbling block to scale-up from lab to large-scale ASSBs stage.In this study, we evaluated electrochemical performance using by general coin cell to investigate behavior of ASSBs, which is consisted with LiNi0.5Co0.2Mn0.3O2/Li6PS5Cl/VGCF|Li6PS5Cl|In-Li. The ASSB coin cell showed a significant capacity degradation having 59 % of capacity retention in 50th cycles, as expected. Herein, the main cause of the rapid capacity decrease is likely to be due to the accelerated physical contact loss. In addition to this, we have expanded the scope of analysis to investigate if there are other causes entire range including cell- and material level. The degradation in cell level is the inhomogeneous electrochemical reaction, that is within composite cathode, resulting from analysis of electrochemical impedance spectroscopy, cross-sectional scanning electron microscopy, x-ray diffraction, and X-ray photoelectron spectroscopy. This induces more severe degradation on close to SE separator, resulting in intensification of SE deterioration accompanied by damage implying a phase transformation of the active material. Furthermore, even though the contact loss problem has improved through re-pressing, the capacity was not recovered, which is because the material itself has deteriorated.Moving on to the material level, many cracks are observed inside of the active material, and sulfur infused into grain-boundary of active materials that confirmed by energy dispersive X-ray spectroscopy. In addition, through analyzing transmission electron microscopy, the phase transformation both mixed and rock-salt phase was confirmed the cathode surface of not only secondary particle but also primary particle of interior cathode. For more specifically affirmed this, various analysis including Raman spectroscopy and inductively coupled plasma optical emission spectroscopy were conducted, and we confirmed that the major cause is due to depletion of the Li source. Therefore, the loss of active Li by infused sulfur caused acceleration of deterioration cathode making poor capacity retention. This study is meaningful in providing another guideline that should be regarded for practical all-solid-state batteries through a new consideration in cathode degradation.

Physics-based modelling and data-driven optimisation of a latent heat thermal energy storage system with corrugated fins

Solid-liquid phase transformation of a phase change material in a rectangular enclosure with corrugated fins is studied. Employing a physics-based model, the influence of fin length, thickness, and wave amplitude on the thermal and fluid flow fields is explored. Incorporating fins into thermal energy storage systems enhances the heat transfer surface area and thermal penetration depth, accelerating the melting process. Corrugated fins generate more flow perturbations than straight fins, improving the melting performance. Longer and thicker fins increase the melting rate, average temperature, and thermal energy storage capacity. However, the effect of fin thickness on the thermal characteristics seems insignificant. Larger fin wave amplitudes increase the heat transfer surface area but disrupt natural convection currents, slowing the melting front progress. A surrogate model based on an artificial neural network in conjunction with the particle swarm optimisation is developed to optimise the fin geometry. The optimised geometry demonstrates a 43% enhancement in thermal energy storage per unit mass compared to the case with planar fins. The data-driven model predicts the liquid fraction with less than 1% difference from the physics-based model. The proposed approach provides a comprehensive understanding of the system behaviour and facilitates the design of thermal energy storage systems.

Critical Issues of Vanadium-Based Cathodes Towards Practical Aqueous Zn-Ion Batteries.

Aqueous zinc-ion batteries (ZIBs) are gaining significant attention for their numerous advantages, including high safety, high energy density, affordability, and environmental friendliness. However, the development of ZIBs has been hampered by the lack of suitable cathode materials that can store Zn2+with high capacity and reversibility. Currently, vanadium-based materials with tunnel or layered structures are widely researched owing to their high theoretical capacity and diversified structures. However, their long-term cycling stability is unsatisfactory because of material dissolution, phase transformation, and restrictive kinetics in aqueous electrolytes, which limits their practical applications. Different from previous reviews on ZIBs, this review specifically addresses the critical issues faced by vanadium-based cathodes for practical aqueous ZIBs and proposes potential solutions. Focusing on vanadium-based cathodes, their ion storage mechanisms, the critical parameters affecting their performance, and the progress made in addressing the aforementioned problems are also summarized. Finally, future directions for the development of practical aqueous ZIB are suggested.

Experimental and Numerical Study on Dynamic Response of Foam-Nickel Sandwich Panels under Near-Field Blast Loading.

The explosion products, such as shock waves, fragments and heat energy formed by explosion, act on the plate structure, which may cause structural damage, material failure and even phase transformation of material. In this paper, the damage mechanism and protective effect of near-field blast load on sandwich structure based on foam-nickel core material were studied. Firstly, the near-field explosion test was conducted to investigate the blast response of the foam-nickel sandwich structure subjected to blast shock from 8701 explosive at near-field position. The deformation characteristics and stress history of the sandwich structure on the acting location of blast load were carefully investigated via experimental methods. A finite element model of near-field explosion was established for effective numerical modelling of the dynamic behaviour of the sandwich structure using the explicit dynamics software ANSYS/LS-DYNA for more comprehensive investigations of the blast shock response of the sandwich structure. The finite element model is reasonable and validated by mesh independence verification and comparing the simulated response behaviour to that from the experimental results for the sandwich structure subjected to near-field blast load. On this basis, the damage mechanism and protection effect of the near-field explosion impact on foam-nickel cores with different density and porosity are simulated more systematically. The investigated results from the experiments and a series of numerical simulations show the large deformation effect due to the extensive energy absorption, which suggests that the sandwich structure based on foam-nickel core material may be expected to become a new choice of protective structure under near-field blast load.