Homogeneous Process Research Articles

Molecular insight into the dual effect of salts: Promoting or inhibiting the nucleation and growth of carbon dioxide clathrate hydrates

Facing the huge gap between the growing CO2 emissions and net-zero emissions target to mitigate global warming, the long-term storage of excess CO2 becomes an intractable issue. Sequestering CO2 in the oceans as clathrate hydrates is a promising solution. Many unanswered questions still exist at the molecular level regarding how ions in seawater kinetically affect the formation of CO2 hydrates, particularly the dual effect: as the concentration rises, salt ions shift from being a promoter of hydrate formation to becoming an inhibitor. Herein, we report the homogeneous nucleation process of CO2 hydrates in saline solutions via molecular dynamics simulations. Consistent with experimental findings, our results show that nucleation is promoted within certain salt concentration ranges; however, the evidence suggests that ions do not act as nucleation sites. Multiple ion-induced variations in the aqueous phase are analyzed, including changes in the mobility, structure, and CO2 solubility. We find that the presence of ions strengthens the hydrophobic interactions among the dissolved CO2 molecules, which are associated with the salting-out phenomenon, accounting for the promoting effect of salts at low concentrations. However, as the salt concentration increases, this advantage is offset, leading to the inhibiting effect at high salt concentrations. We demonstrate that anions are inevitably involved in the construction of the solid hydrate phase. Their presence disrupts the native tetrahedral connectivity of water molecules and imparts negative charges to the solid phase, thereby attracting cations. In addition to advancing our understanding of the intricate interactions among water, guest, and additive molecules to germinate ordered solid structures, these findings can accelerate the development and utilization of sustainable hydrate-based applications.

Influence of inhomogeneities in chemical composition and porosity of sintered steel on development of martensitic transformation

The article is devoted to the study of martensitic transformation in porous sintered steels. When analyzing the process of development of marten­sitic transformation in porous sintered steel, the influence of two factors was assessed: depletion of carbon in the near-surface layers of pores and a change in the energy balance due to relaxation of transformation stresses on free surfaces of the pores. The martensitic transformation was studied in porous steel with a carbon content of 1.56 wt. % obtained after pressing and sintering of a mixture of PZhRV iron powders and GK-3 graphite in hydrogen atmosphere at 1200 °C. Gas carburizing at 1100 °C and homogenization helped to achieve the specified carbon content. The samples were quenched in a sodium chloride solution at a temperature of 27 °C. Pre-cooling was used from temperatures Ast to 800 °C at a rate of 62 °C/s. X-ray microanaly­sis of carbon distribution was carried out using the installation CAMECA Microsonde M.S. 46 with a probe diameter of two microns. The martensite plates predominantly formed on the pores’ surfaces and their cross section had shape close to rhomboidal. The data obtained on the morphology of α′-phase crystals growing from pores and the study by X-ray spectral microanalysis of carbon distribution along the largest martensite plates convince us of the absence of any significant changes in carbon content and, as a consequence, their influence on development of martensitic transformation in the area of pores is not the leader. For sintered porous steels, an irremovable factor in the increase in temperature is the presence of porosity, in contrast to a removable factor – inhomogeneity of the chemical composition, which is caused by incompleteness of the alloy homogenization processes, both during sintering and during the austenitization process that precedes quenching.

Melt blending of commercial linear polyethylene with low-entangled ultra-high molecular weight polyethylene: From dispersion compatibility to viscoelastic scaling laws

This study investigates the dispersion and compatibility of low-entangled “dis-entangled” UHMWPE (dis-UH) in a high-density polyethylene (HDPE) matrix using solvent-free melt-blending conditions and compares it with entangled UHMWPE (eUH) in the same matrix. The findings reveal that dis-UH/HDPE exhibits a significantly lower viscosity ratio than eUH/HDPE (1 and 4, respectively), indicating a lower critical capillary number (Cacritical), thus enhanced dispersion and compatibility. Blends with varying dis-UH content up to 20 wt% show homogeneity, evidenced by DSC and SEM analysis, and demonstrate improved mechanical properties by 36 % in the maximum stress (σmax) and 39 % in Young's modulus (E). Linear viscoelasticity assessments reveal that higher dis-UH content slow the dynamics and increase the apparent weight average molecular weight (Mw), consistent with previous reports for linear entangled PE. The zero-shear viscosity (η0) scaling with Mw (η0∝Mn) is adjusted for high polydispersity, yielding a transitional point in the scaling exponent (n) from 3.6 to 3 at a reptation number of entanglement segments (Mr/Me) of ∼287, in line with theoretical predictions. To rationalize the success of the homogenization process, we propose a qualitative molecular picture inspired from the constraint release Rouse mechanism involved in the disorientation process of bi-disperse linear polymers. In the case of dis-UH/HDPE blends, with initially lower density of long-long entanglements within dis-UH, and the highest density of short-short entanglements within HDPE matrix, the formation of long-short entanglements between dis-UH and HDPE is facilitated, which results in successful homogenization process. In the contrary, the establishment of long-short entanglements in eUH/HDPE blends will require unwinding of the long-long entanglements, which holds a higher kinetic barrier compared to dis-UH/HDPE blends, leading to unsuccessful homogenization.

Homogeneous removal of heterogeneous CFRP composite via aluminum/polyimide laminate assisted femtosecond laser processing

Carbon fiber reinforced polymer (CFRP) composed of carbon fiber and polymer matrix has been used in extensive applications due to its light weight and superior strength. However, the distinct difference in physicochemical properties between two constituents poses a significant challenge for laser homogeneous processing of heterogeneous CFRP. Herein, an aluminum/polyimide laminate is introduced onto CFRP as an assisting layer during femtosecond laser processing, which prevents CFRP from direct energy deposition of low-energy edge of the Gaussian laser. Moreover, a synergetic mechanism of horizontal heat conduction of aluminum foil and vertical heat insulation of polyimide film is proposed and confirmed through temperature measurements and simulation calculations. The heat is dissipated through the aluminum foil and obstructed by the polyimide film, alleviating the detrimental heat transfer and accumulation on CFRP. Therefore, it significantly inhibits thermal damage and entrance size expansion. Compared with traditional femtosecond laser direct processing, the maximum reduction ratio of HAZ and taper are up to 98% and 83%, respectively. High-quality CFRP homogeneous processing with an ultra-low HAZ (0.7 μm), minimal taper (0.07°) and intact smooth sidewalls can be achieved. The method shows great potential to dramatically improve processing quality and broaden applications of heterogeneous composites.

Recovery of fluoride from wastewater in the form of cryolite granules by fluidized-bed homogeneous crystallization process

Aquatic ecosystems are harmed by high fluoride levels, which can disturb the equilibrium of water, plants, and animals and reduce biodiversity. Fluoride contamination in water sources can pose health risks and it is crucial to remove fluoride to prevent adverse effects on the environment and public health. Green technology is employed to recover fluoride from simulated fluoride-rich wastewater. The fluidized bed homogeneous crystallization (FBHC) process is an advanced methodology that removes contaminants from wastewater through supersaturation to recover nontoxic granules that can be used for other purposes. This study compared the fluoride recovery between batch crystallization and the FBHC process in terms of the molar ratio (MR) of [F−]:[Al3+] between [1] and [3] and the pH influence on the recovery and crystallization. The concentration of [Al3+] was varied at 37, 74, and 111 mM, along with the influent flow rates of 4, 8, and 12 mL·min−1. FBHC systems offer improved control of pH levels, creating a stable environment for crystallization. Unlike batch systems, these continuous operating systems are more resilient to pH fluctuations due to efficient mixing, maintaining a consistent pH throughout the process. Using Box-Behnken Design (BBD) for the FBHC, optimal conditions were 74 mM initial [Al] concentration, MR of [F−]:[Al3+] of [2]:[1], and 8 mL·min−1 influent flow rate resulted in 93 % fluoride removal (FR) and 91 % crystallization ratio (CR). XRD and SEM-EDS data showed similarities between the peaks and compositions of cryolite (Na3AlF6). FBHC was able to produce granules based on the reaction mechanism in the synthesis of cryolite.

Statistical uncertainty principle in Markov kinetics

A reciprocality between the statistical variance of observables of a thermodynamic state and that of their conjugate variables, as entropic forces, originates from the thermodynamic conjugacy with respect to an entropy function. This thermodynamic uncertainty principle in equilibrium can be derived from the Maximum Entropy principle and is independent upon underlying mechanistic details. We present, based on the Maximum Caliber principle as the dynamic generalization of Maximum Entropy, the formalism of the uncertainty principle in kinetics in time homogeneous Markov processes between transitional observables and their conjugate path entropic forces. A stochastic biophysical model for molecular motors is used as an illustrating example. The present work generalizes the phenomenological thermodynamics of uncertainties/fluctuations and is applicable to data ad infinitum.

The effect of the flipped row strategy on a number of kinematic variables in the Performance art and achievement of some basic skills in volleyball

This research aims at revealing the impact of flipped classroom strategy on a number of kinematic variables in the art of performance and achievement of some basic skills in volleyball; recognizing the differences between pre-tests and post-tests for both experimental and control groups، detecting the differences between both experimental and control groups in post hoc tests of the researched variables. Furthermore، the researchers applied the experimental curriculum in order to adapt it to the nature of the research. The research community consists of (160) students (males and females) from the Faculty of Physical Education، and the research sample reached (40) students of the second stage. The sample was then divided into experimental and control groups، randomly putting 20 students in each group; and the tested sample consists of (12) students due to the lack of commitment of some of them to apply the curriculum and the absence of many others. The two researchers then conducted the processes of homogenization and parity of the two groups، all of which show a value greater than 0.05. In addition، the sample ratio reached15%، and the two researchers in this study arrived at the conclusion that there was a difference in measuring skillful performance between accurate measurements (tests) and the measurement of art of performance by the residents. Moreover، the strategy of flipped classroom has the effect of improving some of the kinematic variables (working angles) of some of the basic skills in volleyball. Besides، there are kinematic variables of the human body that have much to do with the stage of learning skills (handling، receiving transmissions)، compared to variables that have little to do with the learning process when emphasized by the instructor.

Molecular motion behaviors of starch affect starch-polyphenol inclusion complex and digestibility among different stilbenes polyphenol structures

Starch-polyphenol V-type inclusion complex has become a hot topic due to its anti-digestibility and nutritional function. This paper aimed to explore the molecular motion behavior of starch affects starch-polyphenol inclusion complex and digestibility among different stilbene polyphenol structures (resveratrol (RA), pterostilbene (PB) and polydatin (PD) via the high-pressure homogenization (HPH) and heat moisture treatment (HMT) processes), which represented the fully extended and limited molecular motion behavior of starch, respectively. These results revealed distinct trends in complex formation among different stilbenes polyphenol structures, highlighting RA as particularly conducive to increasing single helix and V-type crystalline structures with the highest resistant starch (RS) content of 28.11 % due to its smaller steric hindrance. Novelty, in HPH environments with extended molecular motion behavior, the steric hindrance and hydrophobicity/CH-π interactions of polyphenols influence complex formation in the order of RA > PB > PD. Conversely, in HMT systems with limited molecular motion behavior, the limited movement of molecules emphasized the importance of hydrogen bond interactions between polyphenols and starch. Thus, the glucoside in PD enhanced its interaction with starch compared to methoxy-modified PB, leading to increased formation of inclusion complex with RS content of 18.61 %. Overall, these findings deepen the understanding of starch-polyphenol interactions.

Determination of interdiffusion coefficients in single crystal superalloys based on solute distribution at the dendritic scale using the Gaussian solution model

Since the initial solute concentration distribution of the sinusoidal solution model shows a significant deviation from the actual concentration distribution of nickel-based single crystal (SX) superalloy dendrites, it is limited to calculate the diffusion coefficient of SX in the homogenization treatment. Therefore, this work proposes a new Gaussian solution model to calculate the diffusion coefficients and the diffusion activation energy of alloying elements in SX superalloy at high temperatures. The diffusion activation energies of W, Ta, and Ti elements in the studied alloy are consistent with the results from other works. This model could more accurately determine the diffusion coefficient of elements during the dendrite homogenization process of SX superalloys since it reflects actual physical processes. Moreover, it has the potential to use in various alloy systems and contributes to the formulation of effective homogenization treatments.

Study of the stability of model emulsions mimicking petroleum with different types of non-ionic surfactants

This study conducted experiments to mimic petroleum emulsions for application in laboratory flow circuits. The science of emulsion formulation is still quite restricted when it comes to parameters that stabilize emulsions. The challenge is even greater when formulating emulsions of low dynamic viscosity. In this work, model emulsions were prepared with different oil phases, with 0.1 and 1.0 % v/v of the surfactants Span 60, Span 80, Triton X-100, and Triton X-114, with 10 and 30 % v/v of aqueous phase. The kinetic stability of the emulsions evaluated in terms of aqueous phase separation, droplet size distribution, dynamic viscosity, and interfacial tension. The homogenization process assessed to identify the emulsification regime of the emulsions, inertial or viscous, through the calculation of the smallest vortices formed. A study of the maximum superficial flow velocity conducted to provide users with a better understanding of the emulsions produced here. The results indicate that seven emulsions can used in laboratory flow circuits. Span 80 provided better stabilization of the emulsions for over 72 hours with droplet sizes in the range of 0.2–100.0 µm. As a novelty in this work, increasing the concentration of surfactant Span 80 causes a decrease in average velocity in flow, a reduction in droplet size, and a regime of turbulent viscous emulsification in axial flow.

Probability Bracket Notation for Probability Modeling

Following Dirac’s notation in Quantum Mechanics (QM), we propose the Probability Bracket Notation (PBN), by defining a probability-bra (P-bra), P-ket, P-bracket, P-identity, etc. Using the PBN, many formulae, such as normalizations and expectations in systems of one or more random variables, can now be written in abstract basis-independent expressions, which are easy to expand by inserting a proper P-identity. The time evolution of homogeneous Markov processes can also be formatted in such a way. Our system P-kets are identified with probability vectors and our P-bra system is comparable with Doi’s state function or Peliti’s standard bra. In the Heisenberg picture of the PBN, a random variable becomes a stochastic process, and the Chapman–Kolmogorov equations are obtained by inserting a time-dependent P-identity. Also, some QM expressions in Dirac notation are naturally transformed to probability expressions in PBN by a special Wick rotation. Potential applications show the usefulness of the PBN beyond the constrained domain and range of Hermitian operators on Hilbert Spaces in QM all the way to IT.

Enhanced mechanical properties and anti-wear performance of Cu45Mn8Ni40Sn7 medium entropy bronze alloy by multi-stage heat treatment

High/ medium entropy brass and bronze alloys exhibit considerable potential for application as structural materials. This study focuses on a Cu45Mn8Ni40Sn7 medium entropy bronze alloy that demonstrates excellent hardness, compressive strength, ductility, and wear resistance through a multi-stage heat treatment technique. The effects of heat treatment on the phase composition, microstructural evolution, mechanical properties, and tribological performance of the alloy were systematically investigated. The alloy, treated by homogenization (820 ℃/4 h)-solution (900 ℃/1 h)-aging (450 ℃/5 h), exhibits a hardness of 362 HV, yield strength of 626 MPa, ultimate strength of 1229 MPa, compressive strain of 47.2 %, fracture toughness of 20.7 MPa·m1/2, and maintains a low wear rate of 1.72×10−5 mm3·N−1·m−1. The processes of homogenization and solution treatment reduce dendrite segregation of elements and eliminate the detrimental lamellar structure at the grain boundaries. During the aging treatment of the alloy, sub-micron scale needle-like precipitates are formed, which play a significant role in enhancing its mechanical properties.

Synthesis of superparamagnetic Fe3O4–graphene oxide-based material for the photodegradation of clonazepam

The global concern over water pollution caused by contaminants of emerging concern has been the subject of several studies due to the complexity of treatment. Here, the synthesis of a graphene oxide-based magnetic material (GO@Fe3O4) produced according to a modified Hummers’ method followed by a hydrothermal reaction was proposed; then, its application as a photocatalyst in clonazepam photo-Fenton degradation was investigated. Several characterization analyses were performed to analyze the structure, functionalization and magnetic properties of the composite. A 23 factorial design was used for the optimization procedure to investigate the effect of [H2O2], GO@Fe3O4 dose and pH on clonazepam degradation. Adsorption experiments demonstrated that GO@Fe3O4 could not adsorb clonazepam. Photo-Fenton kinetics showed that total degradation of clonazepam was achieved within 5 min, and the experimental data were better fitted to the PFO model. A comparative study of clonazepam degradation by different processes highlighted that the heterogeneous photo-Fenton process was more efficient than homogeneous processes. The radical scavenging test showed that O2·-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${O}_{2}^{\\cdot -}$$\\end{document} was the main active free radical in the degradation reaction, followed by hydroxyl radicals (•OH) and holes (h+) in the valence layer; accordingly, a mechanism of degradation was proposed to describe the process.

Exploring the synthesis methodology and abnormal thermomagnetic properties of water-quenched alloys with antiperovskite Mn4C phase

We have devised a highly efficient methodology for the synthesis of high-purity Mn4C, involving arc-melting, subsequent homogenization, and water-quenching steps. This approach overcomes previous constraints associated with limited batch sizes and low purity, enabling the fabrication of substantially larger quantities. In pursuit of achieving the high-purity Mn4C phase, we conducted optimization studies on the stoichiometry of Mn/C in the raw materials, as well as on the homogenization temperature and time. Through this optimization process, we successfully produced highly pure Mn4C ingots by subjecting Mn4.7C alloys to homogenization at temperatures ranging from 1050 to 1200 ℃ for 5 hours, followed by rapid water quenching. The utilization of water quenching served to stabilize the Mn4C phase formed at high temperatures during the homogenization process, thus preventing its transformation into undesired low-temperature phases. The magnetic and physical properties of the samples with highly pure Mn4C phase, quenched from various temperatures, were investigated, revealing subtly distinct characteristics. The pure Mn4C sample obtained by quenching from 1100 °C exhibited a Néel temperature of approximately 950 K, a saturation magnetization of 8.4 Am2/kg, and a positive temperature coefficient (α) of magnetization of 0.0113 Am2/kg·K, respectively. Notably, the abnormal augmentation of thermomagnetic properties over a wide temperature range, from 5 to approximately 650 K, underscores the potential of high-purity Mn4C as a promising candidate for devices where the thermal stability of magnetic properties is of paramount importance.

Homogeneous versus heterogeneous Mn(II) oxidation in peroxymonosulfate assisting chlorination: Synergistic role for enhanced Mn(II) oxidation in water treatment

Removal of Mn(II) is an essential step for addressing water discoloration in water treatment utilities worldwide. However, conventional chlorination suffers from poor oxidation of Mn(II) due to its low homogeneous oxidation kinetics. This study explored the oxidation capability of a new chemical dosing strategy employing peroxymonosulfate (PMS) to assist the chlorination process (PMS@Cl2) for effective Mn(II) oxidation. The study comprehensively explored both oxidation kinetics and underlying mechanisms associated with homogeneous and heterogeneous oxidation within the PMS@Cl2 system. At an [Mn(II)]0 of 1 mg/L, chlorination demonstrated inability in oxidizing Mn(II), with <10 % oxidation even at an elevated [Cl2] of 150 μM (∼10 mg/L). By contrast, PMS completely oxidized 100 % Mn(II) within a 30-minute reaction at a much lower [PMS] of 60 μM (kobs = 0.07 min−1 and t1/2 = 9 min), demonstrating its superior Mn(II) oxidation kinetics (over one order of magnitude faster than conventional chlorine). PMS@Cl2 exhibited an interesting synergistic benefit when combining a lower dose PMS with a higher routine dose Cl2 (loPMS@hiCl2), e.g. [PMS]:[Cl2] at 15:30 or 30:30 μM. Both conditions achieved 100 % Mn(II) oxidation, with even better values of kobs and t1/2 (0.16–0.17 min−1 and ∼4 min) relative to PMS alone at 60 µM. The synergic benefit of PMS@Cl2 was attributed to distinct functions played by PMS and Cl2 in both homogeneous and heterogeneous oxidation processes. Reactive species identification excluded the possible involvement of SO4•−, OH•, or chlorine radicals in the homogeneous oxidation of the PMS@Cl2 system. Instead, the dominant species was O2•− radical generated during the reaction of Mn(II) and PMS. Furthermore, the heterogeneous oxidation emphasized the important role of combining Cl2 dosing, which demonstrated an increased reactivity and electron transfer with the Mn−O−Mn complex, surpassing PMS. Overall, heterogeneous oxidation accelerated the oxidation kinetics of the PMS@Cl2 system by 1.1–2 orders of magnitude relative to the homogeneous oxidation of Cl2 alone. We here demonstrated that PMS@Cl2 could offer a more efficient mean of soluble Mn(II) mitigation, achieved with a relatively low routine dose of oxidant in a short reaction period. The outcomes of this study would address the existing limitations of traditional chlorine oxidation, minimizing the trade-offs associated with high residual chlorine levels after treatments for soluble manganese-containing water.

A cumulative damage model for tubes in nuclear power plants subject to continuous degradation and multi-effect shocks under dynamic environments

Continuous degradation and shocks are two vital damage mechanisms for tubes under dynamic environments in nuclear power plants (NPPs). In this work, we presented a cumulative damage model to evaluate the reliability of tubes in NPPs, which accounts for continuous degradation and random shocks. The dynamic environments were assumed to obey a homogenous Markov process. Continuous degradation was described as a general stochastic process with independent increments. A multinomial distribution was used to depict the multiple effects of Poisson-distributed shocks on tubes. The influence of dynamic environments on the cumulative damage process of tubes was also explicitly modeled. Closed-form reliability measures were derived, such as reliability functions and mean time to failure (MTTF) of tubes. Drawing upon a case study from the existing literature, the analytical solution was validated through a comparative analysis with the outcomes of Monte Carlo simulation (MCS) and other methodologies referenced in the literature. As a practical engineering application, the reliability of steam generator tubes made of Alloy 690 within pressurized water reactors (PWRs), which are susceptible to primary side stress corrosion cracking (PWSCC) and the effects of water hammer, was calculated. The findings indicate that the probabilities of steam generator tube rupture (SGTR) as estimated by the model and those inferred from operational experience have the same order of magnitude.

Unravelling the complexities of biotic homogenization and heterogenization in the British avifauna.

Biotic homogenization is a process whereby species assemblages become more similar through time. The standard way of identifying the process of biotic homogenization is to look for decreases in spatial beta-diversity. However, using a single assemblage-level metric to assess homogenization can mask important changes in the occupancy patterns of individual species. Here, we analysed changes in the spatial beta-diversity patterns (i.e. biotic heterogenization or homogenization) of British bird assemblages within 30 km × 30 km regions between two periods (1988-1991 and 2008-2011). We partitioned the change in spatial beta-diversity into extirpation and colonization-resultant change (i.e. change in spatial beta-diversity within each region resulting from both extirpation and colonization). We used measures of abiotic change in combination with Bayesian modelling to disentangle the drivers of biotic heterogenization and homogenization. We detected both heterogenization and homogenization across the two time periods and three measures of diversity (taxonomic, phylogenetic, and functional). In addition, both extirpation and colonization contributed to the observed changes, with heterogenization mainly driven by extirpation and homogenization by colonization. These assemblage-level changes were primarily due to shifting occupancy patterns of generalist species. Compared to habitat generalists, habitat specialists had significantly (i) higher average contributions to colonization-resultant change (indicating heterogenization within a region due to colonization) and (ii) lower average contributions to extirpation-resultant change (indicating homogenization from extirpation). Generalists showed the opposite pattern. Increased extirpation-resultant homogenization within regions was associated with increased urban land cover and decreased habitat diversity, precipitation, and temperature. Changes in extirpation-resultant heterogenization and colonization-resultant heterogenization were associated with differences in elevation between regions and changes in temperature and land cover. Many of the 'winners' (i.e. species that increased in occupancy) were species that had benefitted from conservation action (e.g. buzzard (Buteo buteo)). The 'losers' (i.e. those that decreased in occupancy) consisted primarily of previously common species, such as cuckoo (Cuculus canorus). Our results show that focusing purely on changes in spatial beta-diversity over time may obscure important information about how changes in the occupancy patterns of individual species contribute to homogenization and heterogenization.

High-temperature oxidation behavior and subsurface phase transformation of high-Mn high-Al steel

High-Mn steels are widely used in engineering applications because of their high strength, high hardness, and excellent toughness. In the industrial production of high-Mn steel, the steel is easy to be oxidized during the homogenization process, which may affect the properties of high-Mn steel. In this work, high-Mn high-Al steel with composition of (25–32)wt-%Mn-(8–11)wt-%Al-1wt-%C-Fe was prepared, the oxidation behavior and subsurface phase transformation of steel at 800 °C–1200 °C were investigated by thermogravimetric analysis, scanning electron microscope and X-ray diffraction. The results show that the curve of oxidation weight gain with time is in good agreement with linear equations below 900 °C, which obey the parabolic rate law in the temperature range of 1000 °C–1200 °C. The steel matrix would be covered by the oxide scale earlier at higher temperatures, which decreases the oxidation reaction rate and makes the turning point of the oxidation reaction rate reach faster at higher temperatures. The Mn-depleted zone resulting from the selective oxidation of Mn is formed in the steel matrix epidermis, leading to the subsurface phase transformation, which may deteriorate the steel properties.

Evolution of liquid phase during homogenous non-equilibrium melting of Ta at superheating temperature.

Homogenous melting at superheating temperature is commonly described by classical nucleation theory (CNT), but the atomic mechanism of the formation and development of critical liquid nuclei is still unclear. Molecular dynamics simulations were conducted to analyze the melting process of Ta. It is found that the process of subcritical liquid clusters evolving into critical liquid nucleus occupies most of the melting time, and merging between neighboring liquid clusters is the main path for subcritical liquid clusters to grow in size. Total melting time is strongly affected by the distribution of formation sites of subcritical liquid clusters, which has been considered random in homogenous melting. This work depicts a clear picture of the formation and development of liquid phase during the homogeneous melting process at superheating temperature and suggests an internal factor of melting mechanism.

Study on precipitation in (CoCrFeMnNi)90Al6Ti4 high entropy alloy

(CoCrFeMnNi)90Al6Ti4 high entropy alloy (HEA) was prepared by adding Al and Ti elements into CoCrFeMnNi HEA. The alloy underwent processes including copper mold suction casting, 1473 K homogenization, 30 % cold rolling + 1273 K annealing + 1073 K aging, and water quenching and heating treatment. Microstructure and phase composition of both as-cast and heat-treated (CoCrFeMnNi)90Al6Ti4 HEA were studied using metallographic microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and transmission electron microscope (TEM). The effect of heat treatment processes on the precipitation of second phases in (CoCrFeMnNi)90Al6Ti4 HEA was investigated, and mechanical properties of as-cast and heat-treated (CoCrFeMnNi)90Al6Ti4 HEA were studied via hardness tests. The results show that in as-cast (CoCrFeMnNi)90Al6Ti4 HEA, the second phase precipitated is primarily L21 structured AlTiNi2 phase. After homogenization, cold rolling, annealing, and aging processes, both the quantity and size of the second phase increase, with a small amount of nanoscale L12 phase appearing after aging treatment. With the progression of heat treatment, the hardness of (CoCrFeMnNi)90Al6Ti4 HEA increases, and mechanical properties are improved.