Phase Transformation Process Research Articles

In-situ observation of nanoscale transformations in dehydrating lizardite

Dehydration of serpentine is an important prograde metamorphic reaction within the lithosphere and subduction zones, potentially causing profound changes in rock properties. Imaging these transitions in real time provides direct insight into the process. We have used in-situ transmission electron microscopy (TEM) to continuously monitor nanoscale transformations in lizardite from 20 to 600 °C. Phase transformation processes during dehydration are recorded and analyzed in real time, including the amorphization of lizardite, and the recrystallization of nanocrystalline forsterite and talc within amorphous dehydroxylate phases. These observations delimitate the role of dehydration temperature in controlling reaction kinetics and the nucleation of reaction products. Specifically, the higher the temperature, the faster the rate of lizardite dehydration, accompanied by faster and more extensive nucleation of nanocrystalline forsterite and talc. Furthermore, the lizardite crystal is observed to gradually shrink with dehydration while maintaining its structural integrity, leading to the expansion of nanoscale intergranular pores and the formation of interconnected pore networks.

Phase transformation at low temperature during low cycle fatigue and its Reversion in SS316L: An experimental and MD simulation study

The present study investigates the phase transformation processes in SS316L during Low Cycle Fatigue (LCF) and reversion heat treatment. The LCF tests were carried out at different strain amplitudes (0.6%, 0.8%, 1%, and 1.2%) at −80°C and 10−3 s−1 strain rate, which transforms γ-austenite phase to deformation induced martensite (DIM). Subsequently, all the deformed samples were annealed at 700°C for an hour to retransform DIM to the γ-austenite phase. Extensive microstructure analysis was performed using Electron Backscatter Diffraction (EBSD) and X-ray Diffraction (XRD) techniques to understand the phase transformation and reversion processes. Molecular dynamics simulated the DIM formation during LCF, revealing fcc to hcp (ε-martensite) and bcc (α’-martensite) phases in compression but no phase transformation during the tensile cycle.

Modelling diffusive phase transformations in multiphase systems using the Voronoi implicit interface method

Abstract This paper presents a general level set framework for modelling diffusive solid-state phase transformation processes in binary systems comprising several grains and phases. Notably, it is demonstrated how the Voronoi implicit interface method (VIIM) can be used to simulate microstructure evolution in polycrystals driven by diffusion. The key advantage of VIIM is that a single level set function can be utilized to describe the evolution of the microstructure. Thus, the computational cost is significantly reduced compared to more traditional approaches, in which each grain in the microstructure is assigned a separate level set function. Moreover, VIIM facilitates the reconstruction of a fully compatible grain boundary network without the presence of any void regions or grain overlaps. The reconstruction procedure does not require any special handling of junctions and can be easily extended to higher dimensions. Moreover, the reconstruction step enables an adaptive remeshing technique to be employed such that the mesh nodes conform with the location of the grain boundaries. Hence, the diffusion problem can be solved in distinct phase domains, demarcated by sharp interfaces. The kinetics of the phase interfaces are described by the amount of flux towards the interface in accordance with the theory of diffusion-controlled phase transformations. To examine the capabilities of the proposed model, both single-phase and multiphase problems are examined. For the single-phase problem, it is shown that the model behaves in accordance with analytical solutions and maintains mass conservation. For the multiphase problems, two model cases of polycrystals that share the same initial geometry but exhibit different phase distributions are investigated, as well as a representative microstructure example. The evolution of the microstructures towards an equilibrium state is in agreement with the expected phase fractions and demonstrates that the model produces reliable results. The error in mass conservation of the considered multiphase examples is within a margin of ±5%.

Solution-Mediated Phase Transformation Processes of Amorphous Iohexol: Mechanisms and Its Applications

Solution-Mediated Phase Transformation Processes of Amorphous Iohexol: Mechanisms and Its Applications

Conduction band photonic trapping via band gap reversal of brookite quantum dots using controlled graphitization for tuning a multi-exciton photoswitchable high-performance semiconductor.

Brookite exists as the metastable phase of titania and often mediates the transformation of anatase to rutile. The photocatalytic competence of brookite relative to polymorphs anatase and rutile has generally been considered structurally and energetically unfavourable for reasons that remain largely unknown and unchallenged. However, the process of phase transformation and performance related cooperativity among all three polymorphs has recently unlocked alternative directions for exploring brookite photovoltaics. Here, we demonstrate the programmable re-configuration of anatase to quantum confined reduced graphene (rGO)-brookite and show it is entirely modulated by surface-driven effects. Key components to this mechanism suggest that the self-assembly of rGO-brookite quantum dots is defect driven through pathways that favour a direct-to-indirect band gap reversal resulting from the graphitization of brookite. The accompaniment of new bandgap characteristics under quantum confinement introduce new hybridized energy states at the graphitic carbon-brookite juncture by modulation of the intrinsic sp2 character to extrinsic sp3 clusters intermediate to graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs). Evidenced by the intercalation of photochromic/fluorescent carbazole and anthracene moieties within the rGO framework by self-assembly, we show that the acquired fluorescence and luminescence properties of rGO-brookite are multi-emissive and reversibly quenchable under light excitation and from solvent polarity differences. Further, tuning the excitonic response of rGO-brookite by modulation of the photoluminescence (PL) signal intensity signifies coordinated interaction between localised carbazole and benz(a)anthracene moities which can undergo further structural refinement to adapt more optimally to both internal and external energy waves. Distinguishable by a large red-shift in the photoluminescent emission peak at λ479 nm in the NIR region, we infer that a photoelectron sink driven by the quantum confinement of a narrow band gap of 0.78 eV formed from the orbital overlap of unoccupied interfacial sites promotes strong e-h+ coupling in the hybridized defect structure imposing a high charge separation by hindering e-h+ recombination. Modulation of interlayer spacing between rGO sheets and the synergy of complexation between intercalated carbazole/benz(a)nthracene can be adapted to achieve rapid photodegradation characteristics for DSSC applications.

Solution-mediated phase transformation of cocrystals at the solid-liquid interface: Relationships between the supersaturation generation rate and transformation pathway.

Cocrystals easily undergo solution-mediated phase transformation at the surface of dissolving cocrystals during dissolution, which significantly deteriorates the solubility advantage of cocrystals. Here, a new scenario for the phase transformation of liquiritigenin (LQ) cocrystals in which the boundary of phase transformation diffuses along the surface to the bulk of the cocrystal was identified. Additionally, depending on the rate of supersaturation generation, phase transformation processes to the anhydrate and hydrate of LQ compete during cocrystal dissolution. The liquiritigenin-nicotinamide (LQ-NIC) cocrystal yielded a higher supersaturation rate, causing the nucleation kinetics to dominate the recrystallization process and the formation of a metastable form of LQ. However, in the liquiritigenin-isoniazid (LQ-INZ) cocrystal, the low supersaturation rate leading to recrystallization was controlled by thermodynamics and the subsequent formation of monohydrates of LQ (less soluble). As a result, in plain buffer, a multistep pathway for phase transformation of the LQ-NIC cocrystal was observed, in which the cocrystal was firstly converted into the anhydrate LQ (metastable form) and subsequently transformed into LQ·H2O. A one-step phase transformation was observed for the LQ-INZ cocrystal, where the cocrystal was directly converted to LQ·H2O. In a buffer containing the Eudragit E100 (E100) additive, for the LQ-NIC cocrystal, the dissolution performance was improved, which can presumably be attributed to the solubilization effect of E100 on the anhydrate and the inhibitory effect on the transformation of the anhydrate to the monohydrate. However, for the LQ-INZ cocrystal, a negligible improvement in drug concentration was observed in the presence of E100 because of the slight effects of E100 on the solubility of LQ·H2O. These findings provide valuable insights into the phase transformation pathways of cocrystals at the solid-liquid interface and the effects of additives on the dissolution behavior of cocrystals.

Ageing Characteristics of Stir Cast Al-5GNPs-1SiC Novel Composite

Background: Currently, aluminium alloys are extensively employed in many sectors due to their desirable characteristics such as rigidity, low weight, appropriate heat conductivity, and malleability. The alloy's mechanical characteristics will enhance as the solidification rate increases. Given the potential of aluminium (Al) alloys and their composites for both light structural and biomedical applications, it is wise to explore the development of a new Al component. Additionally, it is necessary to monitor recent trends in the development of functional Al-alloy and composite materials through an extensive patent search. Examining current patents in the relevant field justifies the need to study this element. Method: The present paper reports the study on a novel aluminium composite cast developed through a clean liquid metallurgical route, to assess the metallurgical, chemical, and mechanical parameters using an optical microscope, EDX, EDS, and SEM analysis. The novel composite Al-5GNPs-1SiC were prepared by stir casting technique at 600 rpm for 15 minutes. The solidified ingots were subjected to heat treatment, such as ice water quenching, followed by ageing the quenched novel aluminium composite at 100°C, 200°C, 300°C, and 400°C for two hours. For evaluation of hardness, tensile strength and microstructure; the desired samples were prepared as per usual standards. Graphene and silicon carbide reinforced aluminium composite were made in this study, both reinforced particles are dispersed homogenously in the aluminium matrix, making them an efficient reinforcing filer to avoid deformation. Results: The Al matrix with (5 wt. %) graphene and (1 wt. %) silicon carbide had 136 MPa yield strength, 266 MPa ultimate strength, 15 (%) elongation, and 106 (VHN) at aged 200°C. Furthermore, the morphological changes in the surface caused by ageing were analysed using a scanning electron microscope, as is the fracture appearance of the shattered specimen exposed to tensile strain. The results show that the silicon carbide particles do not have a higher impact in the phase transformation process during composite solidification up to (1 wt. %) because they have no significant influence on the novel composite phase structure. According to the SEM images, the dimples and cleavages are increased with (5 wt %) of graphene particles added to the Al matrix. A combination of ductile and brittle modes of fracture was identified during the tensile test of the novel composite, according to fractography analysis performed on the samples using scanning electron microscopy (SEM) pictures. Conclusion: Stir casting and quench ageing produce remarkable mechanical characteristics and structural homogeneity in the Al-5GNPs-1SiC novel composite.

Atomic migration and phase transformation processes in dental amalgams over 27 years, monitored by X-ray spectroscopy and X-ray powder diffraction

Abstract The identification of those intermetallic phases which constitute the complex multi-phase system of dental amalgams is rather contradictory in literature. This is intriguing, as the production processes of dental amalgams are standardized since a long time. The reason for the divergence on reported amalgam phases may be due to changes within the microstructure of dental amalgams occurring over time. With a combination of X-ray powder diffraction, Rietveld refinements and X-ray spectroscopy, we were able to show the differences in chemical phases and morphologies between a freshly prepared and a 27-year old dental amalgam sample. Atomic diffusion processes within the amalgam lead to transformation of initially formed intermetallic phases and to dissolution of phases present in the prealloyed metals which react with Hg to the dental amalgam. The main amalgam phases, Ag1+x Hg1−x and Ag2Hg3, remain stable but change in their relative concentrations: the first increases over time, while the latter decreases. The content of Cu6Sn5 as the third important constituent phase decreases over the years and concentrates in hollow spherical particles. The fourth phase is an fcc Ag–Cu mixed crystal which is only present in the freshly prepared amalgam and dissolves over the years. The silver amalgams form a matrix in which spherical Ag–Cu particles are embedded. Cu atoms migrate from within these particles towards their surface, react to η′ bronze and are substituted by Hg atoms, whereas the Ag atoms show virtually no mobility.

Optimizing the Elastic Modulus Temperature Coefficient of Ti-45Nb Alloy by Aging-Induced Nano-Precipitation α Phase.

Titanium-Niobium alloys have garnered extensive interest in various fields, such as aerospace, medical equipment, and scientific research instruments, due to their superior properties. Particularly, their anti-magnetic characteristics render them high potential in the watchmaking industry. The temperature coefficient of the elastic modulus of balance spring materials is a crucial parameter for assessing the impact of temperature on the properties of TiNb alloys. This study aims to explore the influence of heat treatment on the microstructural and elastic modulus temperature coefficient of the Ti-45Nb alloy. The results indicate that after short-term aging treatment, ω particles are enriched at grain boundaries and defects and are distributed in a necklace shape after erosion. After long-term aging treatment, the α phase appears in the material. The phase transformation process of low-temperature aging is β → β + β' → β + ω → β + ω + α. The grain size of the material does not change significantly after different treatments. Additionally, the effect of heat treatment on material properties was studied by a low-temperature dynamic elastic modulus tester. The results showed that the temperature coefficient of the elastic modulus of the material in its original state was relatively high, ranging from 50~220 × 10-6·°C-1. After long-time aging treatment, the temperature coefficient of the elastic modulus of the material decreased significantly due to the appearance of the α phase. The temperature coefficient of the elastic modulus of the material after 48 h of heat preservation treatment fluctuated at 0 ± 30 × 10-6·°C-1. The internal control standard of excellent products in the industry is -11~35 × 10-6/°C. This study provides significant practical implications for the application of Ti-45Nb alloy in the watchmaking industry by adjusting the heat treatment temperature and time to study the effects on organizational evolution and the temperature coefficient of the elastic modulus.

Pressure waves induced by the bcc-hcp phase transition in dynamically loaded single crystal iron

Pressure waves induced by the bcc-hcp phase transition in dynamically loaded single crystal iron

Optimizing Reversible Phase-Transformation of FeS2 Anode via Atomic-Interface Engineering Toward Fast-Charging Sodium Storage: Theoretical Predication and Experimental Validation.

Sodium-storage performance of pyrite FeS2 is greatly improved by constructing various FeS2-based nanostructures to optimize its ion-transport kinetics and structural stability. However, less attention has been paid to rapid capacity degradation and electrode failure caused by the irreversible phase-transition of intermediate NaxFeS2 to FeS2 and polysulfides dissolution upon cycling. Under the guidance of theoretical calculations, coupling FeS2 nanoparticles with honeycomb-like nitrogen-doped carbon (NC) nanosheet supported single-atom manganese (SAs Mn) catalyst (FeS2/SAs Mn@NC) via atomic-interface engineering is proposed to address above challenge. Systematic electrochemical analyses and theoretical results unveil that the functional integration of such two type components can significantly enhance ionic conductivity, accelerate charge transfer efficiency, and improve Na+-adsorption capability. Particularly, SAs Mn@NC with Mn-Nx coordination center can reduce the decomposition barrier of Na2S and NaxFeS2 to further accelerate reversible phase transformation of Fe/Na2S→NaFeS2→FeS2 and polysulfides decomposition. As predicted, such FeS2/SAs Mn@NC showcases outstanding rate capability and fascinating cyclic durability. A sequence of kinetic studies and ex situ characterizations provide the comprehensive understanding for ion-transport kinetics and phase-transformation process. Its practical use is further demonstrated in sodium-ion full cell and capacitor with impressive electrochemical capability and excellent energy-density output.

Effect of Deformed Prior Austenite Characteristics on Reverse Phase Transformation and Deformation Behavior of High-Strength Medium-Mn Steel.

In this study, microstructure evolution during prior austenite decomposition and reverse phase transformation processes was revealed in a high-strength medium-Mn steel. Furthermore, the relationship between deformed prior austenite characteristics and deformation behavior was studied. The results indicated that the recovery and recrystallization of the deformed prior austenite were significantly inhibited during hot rolling in the non-recrystallized zone, the grain size was obviously refined along the normal direction (ND), and that the strain hardening of prior austenite via hot deformation could increase the resistance of shear transformation, resulting in the preservation of high-density lattice defects in the quenched martensite matrix. Before the nucleation of intercritical austenite, the dislocation and grain boundary can provide fast diffusion paths for C and Mn, and the enrichment of C and Mn before intercritical austenite formation can reduce the critical temperature of ferrite/austenite transformation. The nucleated sites and driving force for intercritical austenite were strongly increased by rolling in the non-recrystallization region. The resistance of crack propagation was found to be enhanced by the sustained transformation-induced plasticity (TRIP) effect (via retained austenite with different stability) and for the laminated microstructure, the optimum properties were obtained as being a combination of yield strength of 748 MPa, tensile strength of 952 MPa, and total elongation of 26.2%.

Additive manufacturing Cr-Mo-Si-V steel: Systematic parameter assessments, precipitation behavior of in-situ VC-M23C6 and strengthening mechanisms

Additive manufacturing Cr-Mo-Si-V steel: Systematic parameter assessments, precipitation behavior of in-situ VC-M23C6 and strengthening mechanisms

Solid‐Solid Phase Transformation Behavior of ϵ‐CL‐20 Induced by Typical Organic Solvents: A Theoretical and Experimental Study

AbstractThe solid‐solid phase transformation of ϵ‐CL‐20 induced by external conditions is one of the bottlenecks limiting the widespread applications of CL‐20‐based energetic materials. Herein, we report the investigation on the influence of solvent polarity on ϵ‐CL‐20 solid‐solid phase transformation behavior both theoretically and experimentally. Density functional theory (DFT) calculation was performed to evaluate the possibility of ϵ‐CL‐20 phase transformation induced by organic solvent molecules from the perspective of ϵ‐CL‐20 electronic structure and molecular structure variations. Additionally, experimental study of ϵ‐CL‐20 phase transformation induced by 1,2‐dichloroethane, ethanol, and methanol gas environment was conducted. Solvent with higher polarity was confirmed to significantly vary molecular surface electrostatic potential and molecular conformation of ϵ‐CL‐20 molecule. Furthermore, ϵ‐CL‐20 critical phase transformation temperature decreased when using inducing solvent with higher polarity. And the observed maximum phase transformation rate was the one induced by the highest polarity solvent. A four‐parameter model was established to describe the phase transformation process as a function of time based on the experimental results. Possible ϵ‐CL‐20 solid‐solid phase transformation mechanism was proposed. Hopefully, these results will be beneficial for the rational preparation and utilization of CL‐20‐based energetic materials.

The change of phase composition and the morphology of particles of hydrothermal titanosilicate precipitates during their aging

During the study of phase formation under conditions of hydrothermal synthesis of alkaline titanosilicate systems (NH₄)₂TiO(SO₄)₂⋅H₂O или TiOSO₄⋅H₂O-Na₂SiO₃-NaOH-H₂O it was found that the formed titanosilicate solid phases differ both in composition and structure. The process of their aging under conditions of long-term exposure without forced heating is accompanied mainly by the loss of free water without noticeable structural and morphological changes. The exposure to the temperature of 70–100°С significantly accelerates the process of solid phase transformation. In these conditions, a porous system of particles is formed, which is confirmed by an increase in their specific surface area and total pore volume, as well as by an increase in the activity of the powders to absorb single- and double-charged cations. The effectiveness of hydrochloric acid treatment of fresh and especially aged precipitates on the ordering of the structure with the formation of crystals of a clear frame shape, inherent in the minerals zorite and ivanyukite, which contributes to increasing the sorption capacity of the final product is shown. The obtained results are used to adjust the technological regulations, which are used to test the technology of titanosilicate sorbent on the pilot plant.

Enhancing Mechanical Performance of Sinter-Based Additively Manufactured Ti-6Al-4V Parts Through Hydrogen Sintering and Phase Transformation (HSPT) Process

Enhancing Mechanical Performance of Sinter-Based Additively Manufactured Ti-6Al-4V Parts Through Hydrogen Sintering and Phase Transformation (HSPT) Process

A lightweight semi-active ankle exoskeleton utilized NiTiCu-based shape memory alloys for energy storage.

Nowadays, exoskeletons have a place in many fields, such as industrial production, medical rehabilitation, and military. However, there are still many shortcomings in the existing exoskeleton, such as heavyweight and complex structures for active exoskeleton. The driving ability of passive exoskeletons is limited. To reduce the energy consumption of wearers, based on the characteristics of the semi-active ankle exoskeleton, this paper proposes to use NiTiCu-based shape memory alloys (SMA) as the energy storage source to improve the power density. Compared to NiTi-based SMA, the phase transformation process of NiTiCu-based SMA is more rapid, which can solve the response delay problem to a certain extent. The ankle exoskeleton uses SMA deformation to compress the bias spring. When the human ankle joint needs auxiliary torque, the SMA releases the energy stored by the bias spring and transfers the energy to the ankle exoskeleton to achieve the effect of assisting the human ankle joint. During the assistance process, a control system based on the SMA mathematical model is constructed. The above-mentioned ideas provide a new approach for further expanding power density and can be widely applied in the field of robotics. During characterization, this semi-active ankle exoskeleton can effectively complete the movement state of upstairs and walking, achieve an effective power of 180 N, and store maximum energy up to 5J for the human ankle.

Effect of Mo on the Phase Transformation, Microstructure, and Hardness of Q500qENH Weathering Steel of Bridge Construction during Continuous Cooling

This article investigates the precipitation behavior of Mo element in the continuous cooling phase transformation process of weathering steel of bridge construction and its influence on microstructure and hardness. The results demonstrate that the addition of Mo leads to the narrowing of the phase transformation interval of proeutectoid ferrite and pearlite, the expansion of the bainite transformation zone, a delayed bainite phase transformation process, and the refinement of bainite microstructure. Moreover, theoretical calculations of bainite phase transformation kinetics reveal that the average activation energy for bainite transformation in Mo‐free and Mo‐containing steels is 94.8 and 134.0 kJ mol−1, respectively. The new grains of Mo‐free steel mainly grow in a 2D mode, while Mo containing steel mainly grows in a 1D mode, which confirms the retarding effect of Mo on bainite grain growth. Additionally, Mo significantly increases the number density and refines the size of precipitated phases in weathering steel of bridge construction. Within the cooling rate range of 0.1–30 °C s−1, the hardness of weathering steel of bridge construction is enhanced by Mo, with the magnitude of hardness increment decreasing as the cooling rate increases. This behavior is primarily governed by the combined influence of phase transformation strengthening and precipitation strengthening.

Enhancing strength, ductility, and thermal fatigue resistance in Stellite 21 coatings via Mn alloying and Transformation-Induced Plasticity

Enhancing strength, ductility, and thermal fatigue resistance in Stellite 21 coatings via Mn alloying and Transformation-Induced Plasticity

Adsorption characteristics of As(III) by schwertmannite: new findings in mineral-phase transformation and microbial effects

The amount of As(III) adsorbed and the interfacial process are closely associated with the phase transformation of Schwertmannite (SCH). At present, studies on the adsorption characteristics of As(III) on SCH and the accompanying phase transformation process, especially the related mechanisms under the mediation of iron-reducing bacteria (FeRB) and sulfate-reducing bacteria (SRB), are limited in existing literature. With the help of continuous characterization, the adsorption behavior of As(III) on SCH was explored, as well as the transformation processes of SCH during these processes. The findings revealed that the SCH, synthesized by the KMnO4 oxidation and ethanol modification methods, exhibited excellent physical adsorption capacity for As(III) due to their increasing specific surface area and porosity. At room temperature (20°C), the saturation adsorption capacities of As(III) by M-SCH and Y-SCH reached 62.69 and 58.62 mg/g, respectively. Moreover, the generation and phase transformation of As(III)-bearing ferrihydrite were observed within a 60-min timeframe. It is the first time this phenomenon has been observed in such a short time, which is presumed to be an intermediate stage in the transformation of SCH into goethite. Furthermore, both FeRB and SRB could enhance the adsorption capacity of SCH for As(III). Comparatively, SRB has a more substantial impact on SCH’s phase transformation. These insights are valuable for the practical application of SCH in treating As(III) pollution.