High-temperature Mechanism Research Articles

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

Unveiling the Mechanisms of High-Temperature 1/2[111] Screw Dislocation Glide in Iron–Carbon Alloys

We have developed a self-consistent model for predicting the velocity of 1/2[111] screw dislocation in binary iron–carbon alloys gliding by a high-temperature Peierls mechanism. The methodology of modelling includes: (i) Kinetic Monte-Carlo (kMC) simulation of carbon segregation in the dislocation core and determination the total carbon occupancy of the core binding sites; (ii) Determination of kink-pair formation enthalpy of a screw dislocation in iron—carbon alloy; (iii) KMC simulation of carbon drag and determination of maximal dislocation velocity at which the atmosphere of carbon atoms can follow a moving screw dislocation; (iv) Self consistent calculation of the average velocity of screw dislocation in binary iron–carbon alloys gliding by a high-temperature kink-pair mechanism under a constant strain rate. We conduct a quantitative analysis of the conditions of stress and temperature at which screw dislocation glide in iron–carbon alloy is accomplished by a high-temperature kink-pair mechanism. We estimate the dislocation velocity at which the screw dislocation breaks away from the carbon cloud and thermally-activated smooth dislocation propagation is interrupted by sporadic bursts of dislocation activity.

Wear and aging behavior of vulcanized natural rubber nanocomposites under high-speed and high-load sliding wear conditions

The wear damage and aging behavior of natural rubber (NR) nanocomposites are very complex under severe conditions (high load, high-speed wear, or ablation). Little is known about the influence of strong interfacial friction on the high-temperature aging mechanism in the internal of NR nanocomposites. In this study, a set of UMT-TriboLab wear tester was used to study the wear and aging of NR nanocomposites, and to reveal their influence on the internal aging of specimens under severe conditions. Sliding wear tests were carried out with rubber-metal tribopair using a Block-on-Ring configuration. Different from mild wear conditions, the wear mechanism of NR nanocomposites under severe conditions experienced a transition from abrasive wear to adhesive wear. The viscous film formed by the degradation products on the wear surface was found to strongly affect the subsequent wear and aging behavior (wear weight loss, friction coefficient, temperature rise, etc.) of specimens. Layer-by-layer analysis showed that the heat diffusion caused by surface wear resulted in noticeable post-crosslinking in the internal layer of specimens while the oxidation reaction was limited to occur only on the specimen surface.

Isotopic signatures of magmatic fluids and seawater within silicic submarine volcanic deposits

Addressing questions of magma ascent, volcanic eruption dynamics, and volatile fluxes requires accurate measurement of magmatic water concentrations in volcanic glass. Glass in volcanic rocks in the deep-sea environment can experience rehydration (addition of external water) across a range of temperatures, and from different sources (e.g., seawater and hydrothermal fluids), which can lead to overestimation of magmatic-H2O. This study used H and O isotopes (δD and δ18O) to identify sources of rehydration in pumice and lava from the deep-sea 2012 volcanic eruption of Havre volcano, Kermadec Arc, and from a variety of older (tens to thousands of years) silicic submarine deposits across the Izu-Bonin Arc and Lau Basin. We find that old seafloor pumices were rehydrated up to 6 wt.% H2O by the diffusion of cold seawater over 100s to 1000s of years, and thus, enriched in δD, bulk-δ18O, and water-in-glass (wig) δ18O up to −30‰, +9‰ and −5‰ respectively. By contrast, the young Havre deposits exhibit a much wider range of both isotopic enrichment and depletion with δD = −50 to −120‰, δ18Obulk = +5.7 to +6.2‰, and δ18Owig = −10 to +4‰, depending on the eruptive units. Using magmatic degassing and vapor δD-H2O modeling, a volatile-melt δ18O-geothermometer, and previous textural studies of Havre 2012 deposits, we identify multiple high-temperature rehydration sources, timescales, and mechanisms. δD-depleted pumices were likely rehydrated by vapor co-existing in bubbles and vesicles at temperatures around and below the glass transition (320–670 °C) over timescales of a few minutes during clast cooling above the eruptive vent. Conversely, δD-enriched Havre pumice and lava from different deposits were most likely rehydrated by heated, δD-enriched seawater at glass temperatures > 100 °C. These results provide a natural confirmation of recent experimental findings, which tackle the fundamentals of H and O diffusion and isotope exchange in silicate materials at temperatures of 100–400 °C. Addressing the effects of rehydration, and thus accuracy of H2O measurements, in volcanic glasses and crystals is important for improving our understanding of conduit processes during volcanic eruptions, and the kinetics of glass hydration and alteration.

An experimental and kinetic study of the ignition delay characteristics of cyclopropane in air

As the smallest cycloalkane, cyclopropane is a highly strained three-membered ring hydrocarbon that exhibits high reactivity. In this work, the autoignition characteristics of cyclopropane have been investigated behind reflected shock waves. Experiments were conducted at pressures of 2, 5, and 10 atm, equivalence ratios of 0.5, 1.0, and 2.0, and temperatures ranging from approximately 1100 to 1500 K. The effects of temperature, pressure and equivalence ratio on ignition delay time have been investigated. Quantitative relationships have been yielded by the regression analysis of the experimental data. A high-temperature combustion mechanism of cyclopropane based on NUIGMech1.1 has been developed, and the predicted results are in good agreement with the experimental results. Reaction pathway and sensitivity analyses have been carried to determine the significant reaction pathways in the ignition process and key reactions that affect the ignition delay time. Finally, comparisons between the ignition delay time of cyclopropane and that of propene, cyclopentane, and cyclohexane have been conducted, and kinetic analyses have been performed to interpret the ignition difference between cyclopropane and the above-mentioned fuels.

Microstructure characterization of high temperature mechanisms in a Nb–Ti–Si alloy

The deformation mechanisms of an Nb–20Si–25Ti–6Al–3Cr–3Mo alloy deformed in compression at 1000 °C and at a strain rate of 10−4 s−1 have been investigated, using focused ion beam and transmission electron microscopy techniques. The initial microstructure of the alloy was constituted of a solid solution bcc Nbss matrix and of Nb5Si3 phases of β (tetragonal) and γ (hexagonal) crystallographic structures, with also hcp-Ti precipitates. As expected, the only phase which exhibited plastic deformation at 1000 °C was the Nbss matrix. Glide of b→=1/2111 dislocations has been observed, in planes compatible with {112} and {123} planes, or with cross-slip in {110} planes, as classically reported in bcc structures. Conversely, climb contribution has not been evidenced, probably because of rearrangement of the climbing dislocations in sub-boundaries. Fine δ-Nb11Si4 precipitates have been detected in the samples compressed at 1000 °C. Interactions of the δ-Nb11Si4 precipitates with the dislocations have been observed, which can potentially lead to strengthening of the Nbss phase.

On the formation of nanocrystalline aluminides during high pressure torsion of Al/Ni alternating foils and post-processing multilayer reaction

High pressure torsion of alternating foils of elemental Al and Ni is used for the production of highly deformed and highly reactive nanostructured Al/Ni multilayers. A continuous grain refinement of the microstructure from the center to the edge of the as-processed disc from approximately 25 µm down to 20 nm is observed. Using a combination of laboratory and synchrotron techniques the formation of a few Al3Ni nanocrystallites inside Al layers is confirmed in the as-processed multilayered material at high shear strain. Thermodynamic calculations at room temperature of heats of mixing and enthalpy values of phase formation for Al3Ni agree with the experimental observations. Post-processing annealing was performed using in situ TEM and calorimetry. The first phase that forms during the solid state multilayer combustion is confirmed to be Al3Ni followed by Al3Ni2, NiAl and Al2Ni3. High-temperature chip-calorimetry revealed that the onset of reaction is characterized by an activation energy of 1.4 eV (135 kJ/mol-at) and a total heat of reaction of − 39.0 kJ/mol-at. The latter confirms the self-propagating high-temperature synthesis mechanism of reaction of the as-processed multilayered material.

The effects of die temperature and cooling condition on friction behavior of bare 22MnB5 boron steel in hot stamping

ABSTRACT Hot stamping is an effective method to improve both the elongation and plasticity of ultra-high strength steels, thus a higher specific strength could be achieved, making it possible for weight reduction in motor vehicles. However, due to the die temperature rise and the cooling liquid within hot stamping applications, the friction in its forming stage is always a non-isothermal mode. Therefore, a high-temperature sliding-on-sheet-strip (SOSS) tribo-tester to simulate sliding friction in hot stamping of 22MnB5 hot stamping steel sheet was designed and custom-made. Then, it was employed to exploit High-temperature friction behavior and mechanism of bare 22MnB5 hot-stamping boron steel sheet under different die temperature and extra cooling conditions. Results show that the friction coefficient obtained under the pure die cooling conditions is lower than that obtained under extra cooling conditions, which is attributed to the formation of thicker oxide layers on the surface of specimen during the cooling process. In addition, the friction coefficient is obviously decreased when the die temperature increased to 200 °C, which is ascribed to the co-action of the destruction of the oxide layers and the formation of bainite.

Effect of temperature and inorganic salts concentration on syneresis rate of AM/DAC hydrogel

Compared with ordinary polyacrylamide, acrylamide copolymer of acryloyloxyethyl trimethylammonium chloride (AM/DAC) hydrogel is easier to reside in large pores and fractures in sandstone formation through electrostatic adsorption. However, the syneresis mechanism of AM/DAC hydrogel caused by high temperature and inorganic salts has not been clear. In this paper, the type of water in gelling solutions and hydrogels was analyzed by the DSC method, the results showed that the bound water in the hydrogel was transformed into free water and then the free water was separated from the hydrogel during the syneresis of AM/DAC hydrogel. Experimental investigations, including dynamic light scattering (DLS), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), phase-analysis light-scattering (PALS), and scanning electron microscope (SEM), have been conducted to elucidate the mechanism of temperature and inorganic salts on syneresis rate of AM/DAC hydrogel. The result showed that with the increase of temperature, the polymer in the AM/DAC hydrogel degraded and the molecular chain broken, which destroyed the grid of hydrogel and reduced the water holding capacity. At the same time, the formation of the hydrophobic group in the molecular chain led to the decrease of the hydrophilicity so that the AM/DAC hydrogel was easy to syneresis. In addition, the increase of temperature will promote the formation of crosslinking intermediate (di/trimethylol), improve the crosslinking rate between crosslinking intermediate and polymer, which makes the AM/DAC hydrogel easy to over crosslink. Inorganic salts diffused the electric double layer by compressing the polymer and competed with the hydrophilic groups on the polymer to absorb water, which will reduce the elongation and hydrophilicity of the polymer molecular chain. This will lead to the decrease of the hydrodynamic radius of polymer molecules in AM/DAC hydrogel, which is the main reason why inorganic salts promote hydrogel dehydration. Besides, inorganic salts had little effect on the formation rate and crosslinking rate of di/trimethylol. Therefore, reducing the molecular hydrodynamic radius of AM/DAC is the main reason why inorganic salts promote the syneresis of AM/DAC hydrogel. The research demonstrated the mechanism of high temperature and inorganic salts on syneresis rate of AM/DAC hydrogel. This study also provides technical guidelines for inhibiting hydrogel syneresis.

Controllable morphology, structure and optical properties of W–Eu Co-doped VO2 with a tunable phase transition temperature and band gap

Uncontrollable morphology, high phase transition temperature and vague phase transition mechanism of vanadium dioxide (VO2) hinder its large-scale application in smart windows and optoelectronic switches. In this paper, controllable VO2(B) powders co-doped with W–Eu were synthesized via a hydrothermal method using CH3COOH·2H2O and H2O2 as the reductant and assistant reductant, where W and Eu were derived from H2WO4 and Eu(NO3)3·6H2O, respectively. Most VO2(B) crystals transformed into VO2(M) after annealing. Pristine VO2 had a regular rectangular shape, and it would change to be fabric-like, spongy and coralloid after doping with W and Eu. Furthermore, the surface of W–Eu co-doped samples presented an urchin-like structure and nanorods appeared after annealing. Importantly, doping and annealing also have significant effects on the performances of VO2 samples. Upon W–Eu co-doping, the phase transition temperature of VO2 (M) samples decreased by an average of approximately 15 °C, and the energy band gap decreased from 0.70 eV to 0.33 eV corresponding to the change of phase transition temperature. Not only the thermochromic performances of VO2 were optimized, but also the mechanisms were explained accordingly in this paper.

High-temperature water-vapor reaction mechanism of barium strontium aluminosilicate (BSAS)

Environmental barrier coatings (EBCs) are used in commercial turbine engine applications as protection for ceramic matrix composites, yet the high-temperature water vapor reaction mechanism for EBC materials is not fully understood. Here, the water vapor reaction mechanism for barium strontium alumino-silicate (BSAS), an early generation EBC candidate, was determined from the time and temperature dependences of material loss. BSAS water vapor exposures were performed at 1200 °C, 1300 °C, and 1400 °C for 24, 48, and 72 h, at maximum gas velocities of ~ 240 m/s. FactSage thermodynamic calculations were shown to support the experimental findings, where the steam reaction mechanism consisted of volatilization of all BSAS oxide constituents as gaseous metal hydroxide species, i.e. Ba(OH)2, Sr(OH)2, Al(OH)3, and Si(OH)4 (g).

High-temperature wear mechanism of diamond at the nanoscale: A reactive molecular dynamics study

Diamond is highly wear-resistant at room temperature, while it suffers from rapid wear under the high-temperature tribological conditions. In this paper, we present a reactive molecular dynamics study to unveil the nanoscale wear mechanism of diamond with the evolution of temperatures. We find a critical temperature over which the mechanical failure and wear of diamond will be significantly accelerated. The diamond structure fails when the total stress reaches 157–165 GPa, which is composed of thermal stress and friction-induced stress. The thermal stress due to the restriction of thermal expansion substantially increases with temperature and contributes a major part to the total stress. At the critical temperature, the interfacial chemical bonding and the frictional contact are strongly intensified, with substantially increased contact quality and contact area. On the other hand, the temperature elevated to the critical value induces a drastic increase of sp and dangling bonds in diamond, leading to the internal collapse of the mechanical strength. Ultimately, the synergy of the enhanced frictional contact and decreased mechanical strength leads to the failure and wear of diamond. This work provides a novel insight into the wear mechanism of diamond under elevated temperatures, and contributes to the wear theory in diamond materials.

SURFACE STRENGTHENING AND FRICTION WEAR OF THE INNER WALL OF LIQUID SODIUM HYDROSTATIC BEARING

Sodium hydrodynamic bearings are parts which are easy to wear in order to improve the wear resistance of the inner wall and prolong the service life. In this paper, high-temperature element W was used as a variable to prepare cobalt-based alloy coatings with different contents of W. By testing the hardness and anti-wear performance of the coatings at high temperature, the microstructure and wear mechanism of the coatings were further analyzed in combination with crystal phase diagram and microscopic morphology diagram. The results show that the coefficient of friction of cobalt-based alloy coating decreases with the increase of W content under high-temperature dry rubbing, while the wear quantity increases with the increase of W content. Under high-temperature oil lubrication, the coefficient of friction of cobalt-based alloy coating is the lowest when the W content is 12%. The wear amount of cobalt-based alloy coating decreases with the increase of W content, and the wear mechanism changes from adhesion wear to abrasive wear with the increase of W content.

Moderate drought alleviates the damage to grain quality at high temperatures by improving the starch synthesis of inferior grains in japonica rice

In agricultural production, temperature and moisture are important factors affecting grain yield and quality. Although moderate drought at the grain-filling stage can effectively alleviate the damage caused by high temperature, the specific regulatory mechanism driving the effect of moderate drought at the high temperature on starch synthesis is still unclear. To explore the effects and mechanisms of high temperature and moderate drought on rice starch synthesis at the grain-filling stage, the activities of enzymes and expression levels of the genes involved in starch synthesis under four different treatments involving high temperature and/or water stress (CK, HT, WS, and HT+WS) were investigated in this study. The starch synthesis of a japonica inbred rice was measured under the four treatments during the grain filling. The results show that the effects of high temperature and moderate drought on grain filling mainly occur in the inferior grains of rice. Through the regulation of enzymes involved in starch synthesis and the expression levels of their main genes, the synthesis of rice starch can be affected. Therefore, the high temperature and moderate drought were antagonistic, and moderate drought can alleviate the damage to grain quality at a high temperature by improving the starch synthesis of inferior grains in japonica rice. This study provides a basis for stress-resistance cultivation and breeding strategies of rice with high temperature tolerance.

High-Temperature Deterioration Mechanism of Textile-Reinforced Concrete with Different Cementitious Materials

AbstractTextile-reinforced concrete (TRC), a new composite material commonly used for repair and reinforcement of engineered structural surfaces, is easily affected by high temperatures in the even...

Effect of Alkyl Chain Length on High-Temperature Corrosion Inhibition Behavior and Mechanism of Imidazole Ionic Liquids: An Experimental, Density Functional Theory and Molecular Dynamics Simulation Study

Effect of Alkyl Chain Length on High-Temperature Corrosion Inhibition Behavior and Mechanism of Imidazole Ionic Liquids: An Experimental, Density Functional Theory and Molecular Dynamics Simulation Study

Understanding biomanufacturing of soy-based scaffolds for cell-cultured meat by vat polymerization

Emerging cell-cultured meat uses advances in stem cell biology and tissue engineering to manufacture animal-derived food from culturing. To achieve complex textures in cell-cultured meat, bioprinted soy-based polymers are proposed as a photosensitive edible scaffold material. Understanding the properties of these scaffolds across critical product development stages (i.e., cooking and consumption) is important in design for manufacturing. The results demonstrated that the thermomechanical and -chemical properties were not affected by high-temperature exposure associated with cooking. This research provides a foundation for high-temperature edible mechanics in photolithographic manufacturing of cell-cultured meat and establishes a new design space for tunable food properties.

Effects of natural and Marangoni convections on melting of high-temperature encapsulated phase change material under the earth and the moon gravities

The understanding of melting characteristics and mechanism of high temperature encapsulated phase change material (EPCM) is important for its application in heat storage systems. In this study, a two-dimensional axisymmetric numerical model is established to simulate the melting of spherical EPCMs with air void on the top. Besides buoyancy driven natural convection, Marangoni convection due to the thermocapillary force at the air-molten PCM interface is considered for the first time in this topic. To estimate thermocapillary force more accurately, the air-PCM interface is tracked by the coupled level-set and VOF method. The numerical simulations are conducted for EPCMs with Al2O3 shell and NaNO3 core with the different EPCM diameters and under the different gravity levels. It is found that Marangoni convection mainly affects the early and middle stages of PCM melting process, and its importance relative to buoyancy driven natural convection increases as the diameter of EPCM and gravity level decreases. For the EPCMs with diameter greater than 24 mm under the earth gravity, Marangoni convection has negligible effect, while for 12 mm diameter EPCM under the moon gravity, the complete melting time could be 19% shorter under the additional role of Marangoni convection. The solid PCM profile, fluid flow structure, melting ratio and heat transfer rate during the melting of EPCM under the effects of natural convection and Marangoni convection are also analyzed in detail.

Vortex phase diagram in 1111-type CaFe0.89Co0.11AsF single crystal

Studying the vortex properties in high-T c superconductors is crucial for understanding the high-temperature superconducting mechanism. However, until now, only a few vortex studies have been performed in 1111-type iron-based superconductors due to their smaller-sized single crystals. In this study, we have synthesized millimeter-sized CaFe0.89Co0.11AsF single crystals by the self-flux method. A three-dimensional vortex nature was confirmed in the thermally activated flux flow region. Second, a magnetization peak was observed on the isothermal magnetization curves. Meanwhile, the dominant role of normal point pinning was also confirmed. Finally, the various phase boundaries of the vortex were determined based on an analysis of the resistivity and magnetization data, and a complete vortex phase diagram of CaFe0.89Co0.11AsF single crystals was established.

Effect of block length on the network connectivity and temperature resistance of model, soft thermoplastic elastomers

We discuss the connection between high-temperature mechanics, block structure, and composition of a model series of industrially relevant, soft, thermoplastic elastomers (TPEs) containing polydisperse hard blocks (HBs). The high-strain deformation behavior of these materials results from the combination of multiple dynamics in the system, i.e., the HB associations and the mobile and entangled amorphous phase. Many soft-TPEs show a reduction in toughness with increasing temperature. Molecular weight (Mw) has been shown to improve the temperature-dependent mechanics by increasing network connectivity. In this work, we investigate the possibility to increase the network connectivity by tuning block length at constant Mw and composition. The average number of HBs per chain can be used to quantify network connectivity; however, by using block statistics, we show how increasing this value is not enough to increase the high-temperature mechanics, especially in the case of polydisperse HBs. Since temperature affects the HB ability to associate with each other, only the number of associated HBs per chain determines network connectivity. The experimental results are consistent with modeling predictions, revealing how decreasing the average block length influences the crystal stability, which ultimately controls network connectivity, and how this relationship is affected by temperature.