Phase Transformation Phenomena Research Articles

A secondary high-temperature precursor of the θ′-phase in Al-Cu-(Sc) alloys

The Al-Cu alloy is a historical model alloy system in the physical metallurgy of engineering aluminum alloys. Nevertheless, a few fundamental phenomena of phase transformation occurring in this simple alloy are still not adequately understood. Among all, for instance, the formation mechanisms of its key hardening θ′-phase remain mysterious. There is strong evidence that θ′-precipitates can form from a different high-temperature precipitation pathway, while their formation mechanism via the conventional pathway well-known since 1938 remains to be clarified. Using state-of-the-art electron microscopy, here we report a secondary high-temperature precipitation pathway of θ′-precipitates. It is demonstrated that led by a secondary high-temperature precursor, named θ′S-HTP, very fine θ′-precipitates can form in the undeformed bulk Al-Cu alloys at elevated temperatures (≥ 250 °C). Interestingly is that with Sc-microalloying the surviving rate of meta-stable θ′S-HTP precipitates increases drastically and the formed θ′-precipitates become much finer, significantly enhancing the alloys’ strength and thermal stability. It is also revealed that a θ′S-HTP precipitate can genetically evolve into a θ′-precipitate without having to change its morphology and orientation. Our study provides new insights into understanding the industry bulk alloys’ microstructures and properties.

Role of the microstructure and the residual strains on the mechanical properties of cast tungsten carbide produced by different methods

Cast tungsten carbide (CTC) is a biphasic, pearlitic-like structure composed of WC lamellae in a matrix of W2C. Besides excellent flowability, spherical CTC powders exhibit superior hardness and wear resistance. Nevertheless, the available literature generally fails to explain the physical mechanisms behind such a phenomenon. In the present work, the microstructure and the mechanical properties of the novel centrifugally-atomized spherical CTC have been extensively investigated. This material exhibited an extremely fine microstructure, with WC lamellae of 27–29 nm in thickness and bulk lattice strains of 1.0–1.4 %, resulting in a microindentation hardness of 31.4 ± 1.6 GPa. The results of this study clearly show that centrifugally-atomized CTC is mechanically superior to both spheroidized CTC and conventional cast-and-crushed CTC. In addition, the effect of a series of heat treatments on the bulk fracture toughness and the fatigue life of entire CTC particles was also investigated. The reduction of residual stresses in the bulk of particles upon annealing dramatically increased the indentation fracture toughness, whereas the bulk microindentation hardness remained essentially unaffected. Regarding the fatigue life of entire particles under uniaxial cyclic compressive loading, local phase transformation phenomena at the surface of the particles upon heat treatment were concluded to play the most critical role. Indeed, the cumulative fatigue damage was minimized in surface-carburized CTC powders, where compressive stresses were induced at the outermost surface.

A Crystal Plasticity Finite Element—Machine Learning Combined Approach for Phase Transformation Prediction in High Entropy Alloy

The mechanical properties of an alloy depend on its microstructure. The strength-ductility trade-off is a paradigm that existed for a long time. Advanced alloys, such as high entropy alloys (HEAs), utilize a dual-phase strengthening mechanism, which originates from the microstructural phenomena consisting of twinning and phase transformation, to significantly improve their mechanical properties. To understand the impact of phase transformation mechanism on stress–strain response, developments of crystal plasticity finite element models (CPFEM) and machine learning (ML) together with experimental methods have potential to capture the relationships between descriptive features and targeted phenomena. Here, ML models on local crystallography, local stresses, and energy-based driving forces are leveraged for phase transformation prediction in a HEA. The ML model (XGBoost classification model) uses a hybrid training data combining electron backscatter diffraction (EBSD) experimental data and CPFEM simulation results. This approach enhances prediction performance at optimum data sizes. This predictive model is implemented in multiple experimental measurements to validate our models and evaluates importance of different physical quantities on phase transformation phenomenon. The prediction accuracy reached over 95% compared to experimental data. The CPFEM-ML framework used in this study is expected to be applicable to other HEA systems to facilitate the understanding and prediction of the phase transformation.

A novel fast fabrication of crystal-oriented hydroxyapatite ceramics via gel-casting in high magnetic field

Hydroxyapatite ceramics with oriented crystal structures are successfully fabricated via a novel and fast gel-casting process in high magnetic field for the first time. Experimental conditions as direction and duration of gel-casting in magnetic field were altered for selective crystal orientation of a,b-/c-plane of hydroxyapatites. The effect of slurry preparation process as ball-milling and freeze-drying on orientation degree and grain growth behavior of hydroxyapatite particles is elucidated with detailed analysis of the size distribution of particles, viscosity of slurry, microstructure and crystal structure of sintered bodies with assistance of SEM, XRD and advanced mapping observation of EBSD patterns. In addition, the influence of sintering temperature on the crystal phase transformation of the oriented outermost surface is also clarified through Raman spectroscopy in depth. It was found that the freeze-drying processed slurry shows potential in enhancing the crystal orientation degree than the ball-milling case, during where a suppressed grain growth phenomenon and inhibition of crystal phase transformation on highly oriented hydroxyapatite was also observed.

Computational Insight of Phase Transformation and Drug Release Behaviour of Doxycycline-Loaded Ibuprofen-Based In-Situ Forming Gel.

This research investigates the gel formation behaviour and drug-controlling performance of doxycycline-loaded ibuprofen-based in-situ forming gels (DH-loaded IBU-based ISGs) for potential applications in periodontal treatment. The investigation begins by exploring the physical properties and gel formation behaviour of the ISGs, with a particular focus on determining their sustained release capabilities. To gain a deeper understanding of the molecular interactions and dynamics within the ISGs, molecular dynamic (MD) simulations are employed. The effects of adding IBU and DH on reducing surface tension and water tolerance properties, thus affecting molecular properties. The phase transformation phenomenon is observed around the interface, where droplets of ISGs move out to the water phase, leading to the precipitation of IBU around the interface. The optimization of drug release profiles ensures sustained local drug release over seven days, with a burst release observed on the first day. Interestingly, different organic solvents show varying abilities to control DH release, with dimethyl sulfoxide (DMSO) demonstrating superior control compared to N-Methyl-2-pyrrolidone (NMP). MD simulations using AMBER20 software provide valuable insights into the movement of individual molecules, as evidenced by root-mean-square deviation (RMSD) values. The addition of IBU to the system results in the retardation of IBU molecule movement, particularly evident in the DMSO series, with the diffusion constant value of DH reducing from 1.2452 to 0.3372 and in the NMP series from 0.3703 to 0.2245 after adding IBU. The RMSD values indicate a reduction in molecule fluctuation of DH, especially in the DMSO system, where it decreases from over 140 to 40 Å. Moreover, their radius of gyration is influenced by IBU, with the DMSO system showing lower values, suggesting an increase in molecular compactness. Notably, the DH-IBU configuration exhibits stable pairing through H-bonding, with a higher amount of H-bonding observed in the DMSO system, which is correlated with the drug retardation efficacy. These significant findings pave the way for the development of phase transformation mechanistic studies and offer new avenues for future design and optimization formulation in the ISG drug delivery systems field.

Effect of precipitate shape and distribution on mechanical behavior of shape memory metallic glass composites by molecular dynamics method

The deformation behaviors of metallic glass composites enhanced with brick and cylindrical shape B2-CuZr precipitates were investigated by molecular dynamics method. Both specimens experience a two-stage phase transformation and triple-yielding phenomenon. The brick-shaped precipitate enhanced bulk metallic glass composite (BMGC) exhibits significantly improved strength and mildly enhanced plasticity compared to cylindrical shape inclusion reinforced BMGC. The larger aspect ratio of brick-shaped precipitate enhanced BMGC strengthens the composite by improving elastic lattice deformation along loading direction, while the enhanced plasticity is ascribed to smaller free path for mature shear bands formation. The deformation mechanism for brick-shaped BMGCs is shear band cutting through precipitates, while that for cylindrical shape precipitate reinforced BMGCs is shear band wrapping around crystalline particles. Both specimens display high strain at crystalline/amorphous interface (CAI) region and might experience interfacial stability issue.

Can Martensitic Phase Transformation Measured by Magnetic Methods be an Indicator of Fatigue Damage in Austenitic Steel at Elevated Temperature and Thermo-Mechanical Loading?

The phenomenon of phase transformation from paramagnetic γ austenite to ferromagnetic α' martensite in metastable austenitic stainless steels under fatigue loading is well investigated, especially at ambient temperature. Generally, it can be said that at ambient temperature, the amount of martensite is proportional to the accumulated plastic strain and, therefore, can be an early indicator of fatigue damage. The problem arises at elevated temperatures when the thermal energy can severely or even completely inhibit the phase transformation. In this case, the amount of α'-martensite can no longer be a good indicator of fatigue damage. The question is, where is the limit the deformation-induced martensite can still be used as a fatigue damage indicator? To answer this question, several fatigue tests have been performed on AISI 347 (X6CrNiNb18-10), a metastable austenitic stainless steel often used in the piping of European nuclear powerplants. Tests included isothermal fatigue tests as well as thermo-mechanical fatigue (TMF) loading in the range of 25 to 320 °C. Deformation-induced martensite was measured in situ by means of a uniaxial magnetic balance, from which the rate of phase transformation was obtained. Fatigue specimens were then cut to investigate the distribution of martensite in the gauge length by means of magnetic force imaging. The results showed that isothermal fatigue loading results in a steady decrease in phase transformation rate with temperature. Initial martensite nucleation was observed to be different at elevated temperatures and occurred only at the surface, where sufficient shear deformation was present. TMF tests showed higher than isothermal rates of phase transformation. Peak temperatures above 300 °C were nevertheless enough to severely reduce the formation of α' martensite, even when cooled back to ambient temperature in the other half of the TMF cycle.

Load-induced local phase transformation and modulus of shape memory alloys under spherical indentation by finite element method

Shape memory alloys are a unique class of materials that are capable of large reversible deformations under external stimuli such as stress or temperature. The present study examines the phase transformations and mechanical responses of NiTi and NiTiHf shape memory alloys under the loading of a spherical indenter by using a finite element model. It is found that the indentation unloading curves exhibit distinct changes in slopes due to the reversible phase transformations in the SMAs. The normalized contact stiffness (F/S2) of the SMAs varies with the indentation load (depth) as opposed to being constant for conventional single-phase materials. The load-induced phase transformation that occurred under the spherical indenter was simulated numerically. It is observed that the phase transformation phenomenon in the SMA induced by an indentation load is distinctly different from that induced by a uniaxial load. A pointed indenter produces a localized deformation, resulting in a stress (load) gradient in the specimen. As a result, the transformation of phases in SMAs induced by an indenter can only be partially completed. The overall modulus of the SMAs varies continuously with the indentation load (depth) as the average volumetric fraction of the martensite phase varies. For NiTi (Ea > Em), the modulus decreases with the depth, while for NiTiHf (Ea < Em), the modulus increases with the depth. The predicted young modules during indentation modeling agree well with experimental results. Finally, the phase transformation of the SMAs under the indenter is not affected by the post-yield behavior of the materials.

Effect of tempering temperature and subzero treatment on microstructures, retained austenite, and hardness of AISI D2 tool steel

The presence of retained austenite in the hardening process of tool steel often causes the lower hardness compared to the hardness requirements and poor dimensional stability in the tool steel. The purpose of the present research is to determine the relationships between the tempering process with and without cryogenic treatment to the hardness and retained austenite amount of as-hardened D2 tool steel. The austenitizing temperature was 1020 °C, the tempering temperatures have variations of 180 °C, 280 °C, 380 °C, 480 °C, and 580 °C, and the subzero treatment has a temperature of −172 °C, followed by tempering at 180 °C, 380 °C, and 580 °C. This study aims to determine the appropriate treatment to obtain a minimum retained austenite percentage to prevent and mitigate the failure of AISI D2 tool steel in the industrial application process. An optical microscope with image processing software (Image-J analysis), as well as Brinell and Vickers hardness testing, is the characterization method used in this work. In general, plate martensite, bainite, retained austenite, and primary and secondary carbides are the phases contained in the microstructure. Tempering temperatures have the effect of increasing the secondary carbide precipitation and decreasing the retained austenite content (γr 3,671%–2,769%). However, the cryogenic treatment can provide a more efficient martensitic phase transformation process and minimal retained austenite content (γr 2,257%–1,199%). The increase in tempering temperature causes a decrease in hardness at a temperature of 180 °C–380 °C. On the other hand, the secondary hardening and phase transformation phenomena cause an increase in the hardness of the as-tempered sample at a temperature of 480 °C, before the sample reexperiences a significant decrease in hardness at a temperature of 580 °C due to diffusion that decreases the carbon content.

Monitoring the Local Structure and Magnetic Properties of the Dinuclear Cu2-Paddle Wheel Nodes in the Mesoporous Metal–Organic Framework, DUT-49(Cu), upon Adsorption-Induced Breathing Transitions

DUT-49(Cu) is a well-studied representative of flexible mesoporous frameworks, in particular, famous for long-lived overloaded metastable states in the presence of a variety of gases at defined temperatures, leading to “negative gas adsorption” transitions. Important mechanistic insights into these transitions in DUT-49 were obtained via in situ powder X-ray diffraction (PXRD) studies conducted in parallel to gas physisorption. However, for strongly X-ray absorbing probe molecules, such as xenon, such studies are not feasible, even if synchrotron radiation is used. Here we employ in situ electron paramagnetic resonance spectroscopy (EPR), PXRD, and adsorption isotherm measurements to explore the phase transformations in DUT-49(Cu) in the presence of xenon and compare its properties with the corresponding adsorption/desorption behavior of ethylene for this material. The antiferromagnetically coupled CuII–CuII dimers in the paddle-wheel (PW) units of this pillared layer MOF serve as local magnetic probes in the in situ EPR measurement. These experiments allowed us to monitor the op ↔ cp phase transformations during the xenon physisorption through the structural changes at the PW units encoded in the zero-field splitting parameters of the S = 1 state of the CuII dimers. The EPR data indicates an expansion of the unit cell for the cp phase in the presence of xenon. This novel EPR-derived insight into the phase transformation phenomena of the xenon-loaded DUT-49(Cu) could be validated by combined in situ EPR, PRXD, and adsorption isotherm measurements for ethylene adsorption over the same MOF material in a comparable temperature range.

Mechanism of Residual Stress Generation in Quenched Fe-Ni Alloy Cylinders Using Simulated Strains-Based Approach*

Abstract To elucidate the mechanisms of residual stress generation in quenched steel parts has been a longstanding problem. Qualitative explanations for the changes in the stress distribution in quenched cylinders appeared in the 1930s when it became possible to measure residual stresses in specimens. The explanation at that time used the concept of thermal and transformation stresses, which is still included in current textbooks. This concept is referred to here as the estimated stresses-based approach. To simplify the explanation of stress generation due to the combined effects of temperature change and phase transformations, quenching experiments were devised using Fe-Ni alloys in which only martensitic transformation occurs. On the other hand, since heat treatment simulations provide strains resulting from thermal, phase transformation, plastic, transformation plastic, and creep phenomena, a method to elucidate the mechanism using these strains was devised in the early 2000s and named the simulated strains-based approach. This paper contrasts the estimated stresses-based and simulated strains-based approaches to the mechanism of residual stress generation in quenched Fe-Ni alloy cylinders and highlights the superiority of the latter.

Phase separation and gelation of chemically reactive macromolecules.

Phase transitions are ubiquitous in inanimate systems, and recent discoveries have shown that they also play a key role in living cells. Many membrane-less, liquid-like organelles (“biomolecular condensates”) have been shown to form via liquid-liquid phase separation (LLPS). Intriguingly, several such condensates display irreversible aging behavior akin to gelation. In this work, we first construct a theoretical framework to investigate the phase behavior of multi-component macromolecular systems in which chemical reactions, phase separation and gelation are present concurrently. We then formulate a thermodynamically consistent phase-field model to study coupled compositional and structural phase transformation phenomena in chemically reactive, multi-component biomolecular systems undergoing LLPS. The mesoscale nature of phase-field models enables the study of spatially extended systems over macroscopic timescales. Results such as phase diagrams that capture LLPS and gelation, size distribution of droplets and morphology of gel-state condensates will be presented.

Comprehensive shape memory alloys constitutive models for engineering application

The current shape memory alloys (SMA) constitutive models have the problems of complicated calculation, inaccurate results, measuring difficult parameters, and inconvenient application, which brings about challenges for designing, analyzing, and simulating SMA’s macroscopic behavior in engineering. This paper proposed practical SMA constitutive models for accurate engineering calculation, which apply to both the single loading-unloading process and the multiple loading-unloading cycles. The more accurate SMA theoretical tensile curve and temperature-stress phase transformation diagram is introduced to derive the constitutive model. The more accurate calculation method of elastic modulus, phase transformation modulus, and critical phase transformation stress is proposed in this paper. The proposed constitutive model considers the incomplete phase transformation phenomenon and the variation of critical phase transformation stress under multiple loading and unloading conditions. It can accurately evaluate the critical phase transformation stress and stress-strain relationships at various temperatures. Tensile tests under various working conditions were conducted. The results demonstrated that the proposed constitutive model could well simulate the SMA’s macroscopic mechanical behavior at various temperatures, loads, and multiple loading-unloading cycles with accuracy, practicality, and efficiency.

Physical metallurgy of medium-Mn advanced high-strength steels

ABSTRACT Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences from those of established steel grades, especially pertaining to the microstructural variety that can be tuned and the associated micromechanisms activated during deformation. The interplay and tuning opportunities between composition and the many microstructural features allow to trigger almost all known strengthening and strain-hardening mechanisms, enabling excellent strength-ductility synergy, at relatively lean alloy content. Previous investigations have revealed a high degree of microstructure and deformation complexity in such steels, but the underlying mechanisms are not adequately discussed and acknowledged. This encourages us to critically review and discuss these materials, focusing on the progress in fundamental research, with the aim to obtain better understanding and enable further progress in this field. The review addresses the main phase transformation phenomena in these steels and their mechanical behaviour, covering the whole inelastic deformation regime including yielding, strain hardening, plastic instability and damage. Based on these insights, the relationships between processing, microstructure and mechanical properties are critically assessed and rationalized. Open questions and challenges with respect to both, fundamental studies and industrial production are also identified and discussed to guide future research efforts.

Segmentation of tomography datasets using 3D convolutional neural networks

Dendritic microstructures are ubiquitous in nature and are the primary solidification morphologies in metallic materials. Techniques such as X-ray computed tomography (XCT) have provided new insights into dendritic phase transformation phenomena. However, manual identification of dendritic morphologies in microscopy data can be both labor intensive and potentially ambiguous. The analysis of 3D datasets is particularly challenging due to their large sizes (terabytes) and the presence of artifacts scattered within the imaged volumes. In this study, we trained 3D convolutional neural networks (CNNs) to segment 3D datasets. Three CNN architectures were investigated, including a new version of FCDenseNet which we extended to 3D. We show that using hyperparameter optimization (HPO) and fine-tuning techniques, both 2D and 3D CNN architectures outperform the previous state of the art. The 3D U-Net architecture trained in this study produced the best segmentations according to quantitative metrics (intersection-over-union of 95.56% and a boundary displacement error of 0.58 pixels), while 3D FCDense produced the smoothest boundaries and best segmentations according to visual inspection. The trained 3D CNNs are able to segment entire 852 × 852 × 250 voxel 3D volumes in only ∼60 s, thus hastening the progress towards a deeper understanding of phase transformation phenomena such as dendritic solidification.

A low-cost approach to develop silica doped Tricalcium Phosphate (TCP) scaffold by valorizing animal bone waste and rice husk for tissue engineering applications

In the present study Hydroxyapatite (HAp) derived Tricalcium Phosphate (TCP) and Silica (SiO2) based scaffold was successfully fabricated for the first time by effective utilizing various waste such as animal waste bone (AWB) and rice husk (RH) as a source of HAp and SiO2 respectively. Scaffold development involved simple steps comprising of segregation of waste materials followed by sample preparation through die compaction and sintering (1000 °C and 1300 °C). Advanced characterization techniques like XRD, SEM, TEM, and FTIR were employed to study the properties of the waste materials as well as the developed composite scaffold. The presence of silica from RH combines with the HAp during high temperature sintering and initiates the phenomenon of phase transformation of HAp to TCP along with the formation of a glassy phase. The extent of phase transformation increases as the wt% of RH increases. XRD analysis revealed the development of different phases. SEM microstructure shows that the addition of silica restricts the grain growth and supports the formation of crystalline glassy phase termed as Si-TCP. FTIR results confirmed the presence of phosphate, carbonate, and hydroxyl groups in the sintered samples. The porosity of the scaffold was in the range of 34–61% and the compressive strength was up to 4.1 MPa. The SEM images of scaffold dipped in simulated body fluid (SBF) shows formation of apatite layer throughout the surface. The bioactivity of the scaffold was highly influenced by the addition of silica in the HAp matrix. The apatite forming ability of the developed porous was much greater than that of pure HAp for the same incubation period. The obtained properties of the developed scaffold are comparable to that of natural bone. Thus the present work creates an opportunity to use AWB for the development of composite for tissue engineering applications.

(Fe,Mn)3AlCx κ-carbide formation and characterization in pack aluminization of Fe–29Mn–9Al–0.9C lightweight steel

The Fe–Mn–Al–C lightweight steel has been widely studied due to its higher strength-to-weight ratio and potential applications for automotive vehicles, energy, transportation and mining industries. In general, the strength and ductility of the Fe–Mn–Al–C lightweight steel can be improved by the formation of nano-sized (Fe,Mn)3AlCx κ-carbide precipitates by a proper heat treatment below 800 °C. In this work, a unique micrometer scale κ-carbide phase transformation phenomenon induced by the pack aluminization in the Fe–29Mn–9Al–0.9C lightweight steel was firstly reported.Extremely large columnar-like (Fe,Mn)3AlCx κ-carbide grains with average length of 18.1 μm embedded in the Fe3Al matrix were discovered in the interdiffusion zone of aluminization layer, which were totally different from these nanoscale κ-carbides precipitated in the austenitic steel matrix. The increased Al content in the pack aluminide coating/substrate interface reduced the chemical potential of carbon and became the driving force for carbon diffusion toward the coating/substrate interface. Therefore, due to the extremely low solubility of carbon in the Fe3Al phase and the inward diffusion of carbon atoms, very long columnar-like (Fe,Mn)3AlCx κ-carbide phases were thus produced in the interdiffusion zone. The average chemical concentration of the κ-carbide was 43.9Fe–27.3Mn–20.3Al–8.5 C (in at.%). The average hardness, elastic modulus and the lattice parameter of κ-carbide were 8.8 ± 0.3 GPa, 285 ± 10 GPa and 0.3764 nm, respectively. This study provided detailed chemical compositions, hardness and elastic modulus of (Fe,Mn)3AlCx κ-carbide phase for better understanding the carbide precipitation and strengthening mechanism of Fe–Mn–Al–C lightweight steel.

Superior dynamic shear properties and deformation mechanisms in a high entropy alloy with dual heterogeneous structures

Both heterogeneous grain structure and dual nanoprecipitates were designed in a Al0.5 Cr0.9FeNi2.5V0.2 high entropy alloy (HEA), and the dynamic shear responses were investigated by hat-shaped specimens in split Hopkinson pressure bar tests. The present HEA with heterogeneous structure displays an unprecedented synergy of dynamic shear strength and ductility, as compared to the literature data for other metals and alloys. The excellent dynamic shear properties in the unaged samples could be due to the dynamical grain refinement, the dislocations hardening, and the precipitation hardening. The aged samples with a higher volume fraction of coherent L12 nanoprecipitates display even better dynamic shear properties, as compared to the unaged samples, which can be attributed to the triggered planar dislocation slip, the stored higher density of dislocations, the formation of dislocation substructure and the more pronounced precipitation hardening for postponing the occurrence of the adiabatic shear band (ASB). The high strain rate, high strain/stress magnitude, high adiabatic temperature rise, and fast-cooling process within ASB were observed to induce the dynamic recrystallization and the phase transformation from FCC phase to B2 phase, and this newly observed phase transformation phenomenon was not observed before under quasi-static deformation conditions.

A large deformation constitutive model for plastic strain-induced phase transformation of stainless steels at cryogenic temperatures

In this paper, a new constitutive model for plastic behavior of the metastable austenitic stainless steels at cryogenic temperatures is presented. The constitutive model is a phenomenological hyperelastic-based large deformation model developed in the framework of continuum damage mechanics considering the dissipative phenomena of strain-induced phase transformation and damage growth during plastic deformation. To solve the coupled nonlinear set of equations, incremental equations and the related implicit integration method have been developed. Numerical analysis is performed by implementing the constitutive model in a UMAT subroutine in ABAQUS/STANDARD. In addition, experiments have been conducted to identify the material model parameters for AISI304 steel at the 77K temperature. In addition to calibration, the constitutive model was validated via a tensile test of a notched sample. Also, the model has been compared with the experimental data at 4.2 K available in the literature. The results show that the model is well able to predict the hardening behavior, martensite evolution, and damage growth during the plastic deformation until the fracture with acceptable accuracy.

Unveiling the Electrocatalytic Activity of 1T'-MoSe2 on Lithium-Polysulfide Conversion Reactions.

The dissolution of intermediate lithium polysulfides (LiPS) into an electrolyte and their shuttling between the electrodes have been the primary bottlenecks for the commercialization of high-energy density lithium-sulfur (Li-S) batteries. While several two-dimensional (2D) materials have been deployed in recent years to mitigate these issues, their activity is strictly restricted to their edge-plane-based active sites. Herein, for the first time, we have explored a phase transformation phenomenon in a 2D material to enhance the number of active sites and electrocatalytic activity toward LiPS redox reactions. Detailed theoretical calculations demonstrate that phase transformation from the 2H to 1T' phase in a MoSe2 material activates the basal planes that allow for LiPS adsorption. The corresponding transformation mechanism and LiPS adsorption capabilities of the as-formed 1T'-MoSe2 were elucidated experimentally using microscopic and spectroscopic techniques. Further, the electrochemical evaluation of phase-transformed MoSe2 revealed its strong electrocatalytic activity toward LiPS reduction and their oxidation reactions. The 1T'-MoSe2-based cathode hosts for sulfur later provide a superior cycling performance of over 250 cycles with a capacity loss of only 0.15% per cycle along with an excellent Coulombic efficiency of 99.6%.