High-temperature Characteristics Research Articles

Recent progress on corrosion mechanisms of graphene-reinforced metal matrix composites

Abstract For components serving in high temperature, humidity, and salinity marine corrosive environment, it is vital to analyze the causes of corrosion behavior and corrosion mechanisms. Metal matrix composites (MMCs) are commonly used materials for offshore equipment. In this work, the corrosion factors of MMCs in marine environments are analyzed from the characteristics of high temperature, humidity, and salinity service environment, and the corrosion mechanisms are summarized. Graphene (Gr) has excellent comprehensive properties and great potential for applications in metal protection materials. In recent years, research into Gr anti-corrosive applications encompasses two aspects: pure Gr coatings and Gr composite coatings. Gr applied in MMCs is yet to be extensively studied. Therefore, this study analyzes the corrosion resistance of Gr–metal composites and discusses the corrosion resistance mechanisms of Gr-reinforced MMCs, which provides a reference for the design of Gr-reinforced metal composites and the optimization of corrosion resistance performance. Finally, future development directions for Gr–metal composites are proposed, and the critical factors such as defects, dispersion, content, size, arrangement, interface, and conductivity of Gr in the composites affecting their anti-corrosion properties are discussed.

The performance evaluation of extracted asphalt binder from dry process produced rubber modified asphalt mixture

Limited research studied the influence of rubber on asphalt binder in the dry process rubberized asphalt mixture. By using the extraction procedure, the asphalt binder interacted with rubber could be obtained and assessed. The goal of the research is to evaluate the accurate characteristics of asphalt binder from dry process rubberized asphalt mixture and determine the interacted rubber percentage in dry process rubberized asphalt mixture. Four extracted and two laboratory prepared asphalt binders were compared. The rheological performance, creep and recovery, and low temperature characteristics of different were evaluated with the dynamic shear rheology, multiple stress creep and recovery, and asphalt binder cracking device tests, respectively. The rubber modification and aged binder from the RAP enhanced the high temperature characteristics of the asphalt binder. Rubber modification increased the elastic property and deformation resistance of the asphalt binder and decreased the stress sensitivity of the asphalt binder. The coupling effect of aged asphalt binder and rubber addition enhanced the permanent deformation resistance of the asphalt binder to sustain heavy stress load. The aged binder from RAP deteriorated the low temperature characteristics of the extracted asphalt binder. The base asphalt binder with rubber had a better ability to dissipate the stress in the asphalt binder due to the decrease in temperature. The interacted rubber percentage was estimated by comparing the rutting parameter and percent recovery, and the estimation results based on the DSR and MSCR test had a good correlation. The interacted rubber percentage in the two types of rubber modified mixtures are 61.9% and 57.4%, respectively.

Investigation of the mechanisms on the abnormal features observed in thermal-mechanical testing of AA6061 under extrusion conditions

Hot extrusion is the most common forming technology for aluminium alloy AA6061 due to its good extrudability, and thus it is important to study its high-temperature deformation characteristics. In this study, three abnormal features are observed in thermal-mechanical testing under extrusion conditions of AA6061 specimens from one billet: 1) Two types of specimens with grey-coloured surface or silver-coloured surface appear after solution heat treatment (SHT); 2) The silver-coloured specimens show orange peel surface after hot compression tests; 3) The silver-coloured specimens have lower flow stresses than the grey-coloured specimens. This paper investigates the mechanisms behind the above abnormal features. A laser scanning confocal microscope is employed to examine the surface roughening, and electron back scatter diffraction is used to characterise microstructural changes. It is found that the main causes of the above behaviour are due to different initial grain morphologies and the evolution of dislocation density after SHT. The silver-coloured specimens initially have smaller columnar grains which undergo recrystallisation and extensive growth during SHT, and the dislocation density decreases significantly, leading to orange peel defect and low flow stress during compression tests, respectively. The grey-coloured specimens have larger columnar grains. After SHT, some grains undergo recrystallisation, but others still maintain the shape of the large columnar grains, and the dislocation density does not change significantly, resulting in surface oxidation with smooth surface after thermal-mechanical testing and 10–25 MPa (30–50%) higher flow stress compared to the silver-coloured specimens in compression tests.

Centennial Variation and Mechanism of the Extreme High Temperatures in Summer over China during the Holocene Forced by Total Solar Irradiance

Under the background of global warming, the frequency and intensity of extreme climate have increased, especially extreme high temperatures. In order to correctly predict the changes in the extreme high temperatures in summer in China in this century, it is urgent to deepen the understanding of the characteristics and physical mechanisms of the extreme high temperatures in summer on the centennial timescale. Many researchers have explored the mechanism of the influences of the variability of the solar cycle on climate change, while the mechanism of the influences of the centennial variation of solar activity on climate change remains elusive. Here, we use the outputs from the Control (CTRL) experiment, Total solar irradiance and Orbital (TSI_ORB) experiment, and Orbital (ORB) experiment from Nanjing Normal University-Holocene (NNU-Hol) experiments to study the extreme high temperatures in summer in China during the Holocene. On the basis of verifying the consistency of the centennial period between the TSI (TSI_ORB minus ORB plus CTRL) experiment and the reconstructed data, we compared the centennial variation characteristics of the summer extreme high temperature in the CTRL experiment and the TSI experiment. It shows that under the modulation of total solar irradiance, the centennial spatial pattern of the summer extreme high temperatures changed from dipole mode to uniform mode, with 300-year and 500-year periodicity, compared to the influence of only internal variability. On the centennial time scale, the greatest difference is located in northeast China. The subsidence movement and the reduction of cloud cover caused by the anticyclone under the control of high-pressure lead to the increase of downward solar radiation, thus making a positive center is showed in northeast China on the impacts of total solar irradiance. Furthermore, the center of the Rossby wave train in the barotropic structure of the upper circulation related to the summer extreme high temperature significantly moves northward. This barotropic structure is composed of continuous pressure ridges from Eurasia to North America and the North Atlantic, which is conducive to the increase of the summer extreme high temperatures. Furthermore, we investigated the underlying physical mechanisms. Under the influence of total solar irradiance, the Pacific Decadal Oscillation (PDO) with the same centennial cycle as extreme high temperatures lead to obvious subsidence movement and increase of radiation flux, causing an increase in extreme high temperatures over northeast China.

Boosted high-temperature electrical characteristics of AlGaN/GaN HEMTs with rationally designed compositionally graded AlGaN back barriers

Boosted high-temperature electrical characteristics of AlGaN/GaN HEMTs with rationally designed compositionally graded AlGaN back barriers

Cadomian Iron ore bodies in the Bafq-Saghand metallogenic province, Iran: genetic constraints from field observations and laser ablation ICP-MS mineral studies

ABSTRACT The volcano-sedimentary unit in the Bafq-Saghand metallogenic province (BSMP) of Central Iran hosts various types of iron ore bodies including Fe-oxides with jaspilite beds, Mn-dominated iron lenses, magnetite-apatite lenses, and massive magnetite-apatite deposits. The Fe-oxides with jaspilite beds and Mn-dominated iron lenses have limited outcrops and show volcano-sedimentary features in the field. The main features are the presence of syngenetic submarine rhyolite-hosted magnetite, lamination and bedding of iron ore body, jaspilite and dropstone. Volcano-sedimentary origin is testified by magnetite composition showing affinity to BIF and positive Eu and negative Ce anomaly. Magnetite-apatite lenses and massive magnetite-apatite deposits that having spatio-temporal correlation form the main economically important deposits. They have magmatic to high-temperature hydrothermal field characteristics (lava flow-like ore bodies, the presence of degassing tubes in ore bodies, occurrence of brecciated texture and developed Na-Ca metasomatism). Mineral composition (enrichment of LREE, magnetite and apatite negative Eu anomaly and Co/Ni < 1 in pyrites) is in agreement with magmatic and high temperature hydrothermal origin. We propose a hydrous and oxidizing mantle derived iron-rich basic magma that formed in an extensional post-collisional setting for origin of Kiruna-type IOA ore bodies of the BSMP. Fe-oxides with jaspilite beds and Mn-dominated iron lenses resulted from degassing or eruption of iron-rich magma during Ediacaran in a submarine environment. However, magnetite-apatite lenses and massive magnetite-apatite deposits formed from an Early Cambrian magmatic-hydrothermal transition system from a magnetite-crystal mush zone.

Polymer-derived ceramic thin-film thermocouples for high temperature measurements

Thin-film thermocouples are used as temperature detection components in aircraft engines. However, the preparation of traditional thin-film thermocouples is complex, and their high-temperature stability performance attributes are poor. In this study, polymer-derived ceramic (PDC) technology is introduced to prepare polymer-derived ceramic thin-film thermocouples. Due to the superior high-temperature and adhesion performance characteristics of polymer-derived ceramics and the protective effects of the products of polymer precursors on the thin films, the performance attributes of thin-film thermocouples are greatly improved. After simplifying the preparation process and outputting a large thermoelectric potential, the polymer-derived ceramic thin-film thermocouple exhibits good repeatability, stability, and thermoelectric potential output consistency. At 1200 °C, the peak output is 203 mV, and the average Seebeck coefficient is approximately 182 μV/°C. The temperature measurement error is 0.316%. In the 8-h drift test, the coefficient first increases at 1.26 °C/h and then steadily decreases at −0.63 °C/h. This polymer-derived ceramic thin-film thermocouple has excellent performance and can be applied to the in situ monitoring of thermal components in high-temperature and harsh environments, such as engines.

High-temperature graphitization characteristics of vitrinite and inertinite

In order to explore the graphitization characteristic differences between vitrinite and inertinite in coal, this study conducted high-temperature thermal simulation experiments (at five temperature points: 1800°C, 2100°C, 2400°C, 2700°C, and 3000°C) using inertinite-rich and vitrinite-rich samples as graphitization precursors. The quantitative comparison for the evolution characteristics of their graphite lattice was carried out using high-resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), and Raman spectroscopy (Raman) techniques. HRTEM revealed that an evident increase in carbon layer numbers and degree of extension was observed with increasing treatment temperature, XRD showed the variation of lattice parameters (d002/La/Lc) with temperature, Raman data revealed the variation of lattice defects (R2/R3) with temperature. It was discussed about the differences of graphite lattice construction processes between inertinite and vitrinite, throughout the entire temperature range of the experiment, the d002 spacing of inertinite was always smaller than that of vitrinite, indicating a higher degree of graphitization. vitrinite exhibited a uniform and smooth evolution state throughout the entire heating process, while inertinite exhibited an “inert” state between 1800°C and 2100°C (d002 values stagnated near at 0.3440 nm). With increasing simulated temperature, the defect level (R2 and R3) of vitrinite rapidly decreased below that of inertinite, throughout the entire temperature range, vitrinite demonstrated superior defect healing ability in terms of both rate and capability compared to inertinite. Under high-temperature thermal simulation, the three-dimensional lattice construction and defect elimination of vitrinite exhibited synchronous evolution characteristics. On the other hand, the formation of the graphite lattice in inertinite showed an evolutionary trend of “first three-dimensional lattice construction, followed by gradual defect elimination”.

Evaluation of high-temperature formability for Ti-xMo-4Fe metastable beta alloys based on Mo contents

High-temperature formation technology is widely used to fabricate components with metastable β titanium alloys, a material characterized by balanced mechanical properties, including superb formability, corrosion resistance, and high strength. In high-temperature formation, it is crucial to control the formation conditions by linking the changes in those conditions caused by processing variables with microstructures and identifying the optimal conditions for high-temperature formation. As such, in this study, a Ti–Mo–Fe alloy was designed that is different from conventional metastable β titanium by adding molybdenum (Mo) and iron (Fe), which are relatively economical β stabilization elements. The mechanical characteristics of the alloy at room temperature were also examined by varying the Mo content, and a high-temperature compression test was conducted to evaluate its high-temperature characteristics and formability. The high-temperature compression test was performed at five different temperatures (700 °C, 750 °C, 820 °C, 900 °C, and 950 °C) to avoid β-transus and with four different strain rates 1 × 10−3/sec, 1 × 10−2/sec, 1 × 10−1/sec, and 1 × 100/sec. Then, the test results were utilized to create a processing map, which evaluated formability by examining plastic instability and energy distribution efficiency at different temperatures, strain rates, and reduction rates, the processing variables for high-temperature formation. Afterward, their connections with the microstructures were analyzed to determine the optimal conditions for the temperature formation of the newly designed Ti–Mo–Fe metastable β titanium alloy.

High-Temperature Partial Discharge Characteristics of Power Module Packaging Insulation Under Square Pulse With High Dv/Dt Based on Down-Mixing Method

Partial discharge (PD) in the high voltage packaging insulation under square pulse with a high slew rate (SR or dV&#x002F;dt) is one of the main causes of the power module failure, especially for wide bandgap (WBG) devices. But PD under fast square pulse at high temperatures is rarely studied and one of the critical reasons is the lack of an effective PD detection method under fast square pulses. In addition, the existing PD standard defines the PD criterion under sinusoidal alternating current (AC) situations, which is not the actual working condition of the power module. To address that, this paper proposes a down-mixing PD detection method and explores the influence of temperature on the PD characteristics of the power module packaging insulation. The results show that the partial discharge inception voltage (PDIV) decreases as the temperature increases. The PDIV under square pulse is always higher than that under AC voltage. The less the SR and the greater the pulse width (PW) of the square pulse, the lower the PDIV. Physical-based models for PDIV estimation concerning SR, PW, and temperature are proposed for industrial reference. Moreover, statistical analysis of PD magnitude, number, and occurrence phase under square pulse indicates that PD number decreases but PD magnitude increases with the increase in temperature. Higher temperature leads to PDs with large magnitudes, which may accelerate the degradation of packaging insulation.

Corrosion characteristics of Inconel 625 cladding layer and NiCrMoAl cladding layer in molten NaCl-KCl and NaCl-KCl-Na2SO4

The high-temperature corrosion characteristics of Inconel 625 and NiCrMoAl cladding layers were investigated in molten NaCl-KCl and NaCl-KCl-K2SO4. In NaCl-KCl, the corrosion was dominated by “electrochemical” mechanism, subsequently triggering “chlorine-active corrosion” mechanism. NiCrMoAl cladding layer provided significantly higher corrosion resistance than Inconel 625 cladding layer, due to the generated greatly Al2O3 enhanced the difficulty of inward diffusion of Cl-. In NaCl-KCl-K2SO4, protective Al2O3 and Cr2O3 faced “basic fluxing” mechanism, considerably aggravating the corrosion. Additionally, Al easily reacted with SO42-, which further consumed Al and generated free S, causing NiCrMoAl cladding layer to suffer serious corrosion than Inconel 625 cladding layer.

High-Temperature Crystallization Characteristics of CaF2-SiO2 Fluxes Geared Towards High Heat Input Submerged Arc Welding

High-Temperature Crystallization Characteristics of CaF2-SiO2 Fluxes Geared Towards High Heat Input Submerged Arc Welding

Experimental analysis of deformation-adapted binders and their mixture performance

In this study, three deformation-adapted binders (rubber asphalt [RA], modified asphalt [MA], and polyurethane [PU]) and their mixtures were selected as the research objects to determine their performances under the same evaluation indices. First, the high-temperature, low-temperature, compressive, and tensile properties of three deformation-adapted binders were examined by performing anti-flow, low-temperature flexibility, compression permanent deformation, and tensile tests, respectively. Second, the road and recovery performance of the deformation-adapted mixtures were investigated through rutting, Marshall stability, low-temperature trabecular bending, tensile and Overlay Tester tests. From the extracted outcomes, it was demonstrated that, among the three deformation-adapted binders, PU exhibited superior high-temperature, low-temperature, compression, and tensile characteristics, followed by MA and RA. Furthermore, the deformation-adapted mixture of PU displayed the best high-temperature, low-temperature, water stability, and fatigue crack resistance performance. The deformation-adapted mixtures of RA and MA also had excellent performance in terms of tensile, compression, and strength recovery characteristics. Notably, the deformation-adapted mixtures of PU only exhibited excellent tensile and compression recovery properties, while the strength recovery properties were not good.

High-temperature solid particle erosion characteristics and damage mechanism of AlxCoCrFeNiSi high-entropy alloy coatings prepared by laser cladding

The solid particle erosion effects on AlxCoCrFeNiSi high-entropy alloy coatings (HEAcs) prepared by laser cladding under different erosion conditions were investigated. Furthermore, the transformation of the microstructure and properties of the prepared HEAcs under high-temperature conditions and the effect of oxidation on erosion behavior were analyzed. The results show that the hardest Al1.0 HEAc (711 HV0.2) presents typical brittle erosion characteristics, as fracture toughness deteriorates with increasing Al content. When the erosion temperature reaches 700 °C, the erosion rate decreases due to precipitation enhancement and oxidation affecting the erosion behavior.

Enrichment characteristics of deep shale gas in tectonically complex regions of the southeastern sichuan basin, China

In recent years, breakthroughs have been made in deep shale gas exploration in the Wufeng-Longmaxi formations in the complex tectonic region of the Sichuan Basin and southeastern margin, indicating promising prospects for exploration and development. This study focuses on the Nanchuan area of the complex tectonic region of the southeastern Sichuan Basin margin, using data from drilling wells and experimental analysis tests to investigate deep shale gas enrichment characteristics, particularly the effects of changes in the formation environment such as formation temperature and pressure on deep shale gas enrichment. The study concludes that: (1) The dominant sedimentary phase zone is the basis for hydrocarbon formation in shale gas reservoirs, with the Wufeng Formation–the first member of Longmaxi Formation in the study area—formed in a deep-water shelf sedimentary environment with high-quality shale development, which provides favorable material conditions for the formation of shale gas reservoirs. (2) Organic carbon content controls the degree of development of nanoscale organic matter pores, and the high-pressure-ultra-high-pressure environment helps maintain pores and improve the physical properties of deep shale. (3) Deep shale gas exhibits typical geological characteristics of high temperature, high ground stress, and exceptionally low permeability. The study finds the influence of temperature on the adsorption capacity of shale is more significant than that of pressure, and deep shale gas is primarily free gas. High pressure can slow down or inhibit gas flow, which is beneficial to shale gas preservation. (4) Gas diffusion is complex, with high temperature increasing the diffusion of gas, aggravating the migration and escape of gas, while high pressure can slow down or inhibit gas flow, which is beneficial to shale gas preservation. (5) The burial depth and pressure coefficient show a positive correlation, and the burial depth has a more significant effect on the pressure coefficient of syncline shale gas, indicating that preservation conditions of deep syncline shale gas reservoirs are becoming better. Residual syncline core with larger depths, inner-sag uplift, and slopes with reverse faults can be favorable targets for shale gas exploration in complex tectonic zones.

In-service detection of high-temperature pressure pipeline welds based on DR technology

High-temperature pressure pipeline is an important medium conveying equipment in industrial production. Due to its high temperature and high-pressure characteristics, it is very important to implement effective in-service detection. This paper focuses on the successful application of X-ray digital imaging detection (DR) technology in the process of leak detection and disposal of petrochemical pipeline flange welds and analyzes the advantages of DR technology for in-service detection of the high-temperature pressure pipeline. Finally, the shortcomings of the current application and further research directions are put forward.

High Temperature Characteristics of Composite Materials Composed of Silicone Gel and Barium Titanate in High Voltage Power Modules

The blocking voltage of silicon carbide (SiC) device is greater than 10 kV. High voltage can cause high electric field inside SiC power module. Improving the insulation properties of the encapsulation material of power module becomes an urgent requirement. The electrical field-dependent permittivity (FDP) material composed of silicone gel and barium titanate (BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) can be used to reduce the high electric field. However, the related research on FDP materials is limited to the room temperature conditions. It is not enough since the operating temperature of power module is higher than the room temperature because of the power loss, and the temperature has a great influence on the performance of FDP material. This paper focuses on the high temperature performance of this composite material in reducing electric field. Firstly, the simulation results show that the triple point between metallization, ceramic and silicone gel is both stressed by high electric field and high temperature. Increasing the dielectric permittivity of the encapsulation material can reduce electric field stress. Secondly, the breakdown voltage and aging properties of silicone gel and the composite were analyzed. The Curie temperature of the FDP material was measured experimentally, which proved that the Curie point of the FDP material would not be changed by the silicone gel. Thirdly, the permittivity of FDP material at different temperatures and the mechanism of reducing the electric field stress are investigated.

Dislocation Substructures Evolution and an Informer Constitutive Model for a Ti-55511 Alloy in Two-Stages High-Temperature Forming with Variant Strain Rates in β Region.

The high-temperature compression characteristics of a Ti-55511 alloy are explored through adopting two-stage high-temperature compressed experiments with step-like strain rates. The evolving features of dislocation substructures over hot, compressed parameters are revealed by transmission electron microscopy (TEM). The experiment results suggest that the dislocations annihilation through the rearrangement/interaction of dislocations is aggravated with the increase in forming temperature. Notwithstanding, the generation/interlacing of dislocations exhibit an enhanced trend with the increase in strain in the first stage of forming, or in strain rates at first/second stages of a high-temperature compressed process. According to the testing data, an Informer deep learning model is proposed for reconstructing the stress-strain behavior of the researched Ti-55511 alloy. The input series of the established Informer deep learning model are compression parameters (compressed temperature, strain, as well as strain rate), and the output series are true stresses. The optimal input batch size and sequence length are 64 and 2, respectively. Eventually, the predicted results of the proposed Informer deep learning model are more accordant with the tested true stresses compared to those of the previously established physical mechanism model, demonstrating that the Informer deep learning model enjoys an outstanding forecasted capability for precisely reconstructing the high-temperature compressed features of the Ti-55511 alloy.

An experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine

Amine compounds are an important class of nitro-containing fuels and represent as promising renewable fuels. However, the structural effect from the alkyl group on the combustion characteristics of amines remains an urgent problem to promote their usage in practical engines. To probe and replenish the combustion properties of amine fuels, this work reported an experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine over a wide range of conditions. Specifically, a high-pressure shock tube is used to measure the ignition delay times under the temperature range from 1100 K to 1700 K with pressure of 2 and 5 bar and the equivalence ratios of 0.5, 1.0 and 2.0. The pyrolysis characteristics is studied using a single-pulse shock tube at fuel concentration of 0.5% diluted by argon in the temperature range 950–1400 K at 5 and 10 bar with the residence time around 1.6 microsecond. A detailed kinetic mechanism is developed to simulate the experimental results. To improve the accuracy of the detailed mechanism, primary initial reactions of cyclohexylamine including the hydrogen abstraction reactions and the CN decomposition reaction are theoretically studied at G4//M06–2X/6–311++G(d, p) level of theory with transition state theory and RRKM/mater equation. The detailed kinetic mechanism shows good prediction accuracy of the ignition delay times and pyrolysis product distributions under different temperature, pressure and equivalence ratio conditions. Sensitivity analysis results indicate that the most sensitive reaction is O2 + H = O + OH with the most negative sensitivity coefficient and the abstraction reaction of vinylamine with OH radical, C2H3NH2 + OH = C2H3NH + H2O also exhibits large sensitivity coefficients. Reaction path analysis reveals that the abstraction reactions control the initial oxidation of cyclohexylamine and cyclohexen-1-amine, cyclohexen-2-amine, and cyclohexen-3-amine are also major intermediates during the oxidation of cyclohexylamine besides small pyrolysis products.

Study on high-temperature oxidation and hot corrosion characteristics of Cr60Ni40 laser cladding layer

In order to investigate the high-temperature characteristics of Cr-based alloy, Cr60Ni40 laser cladding layer (60 wt% Cr and 40 wt% Ni) were prepared and subjected to high-temperature oxidation test and hot corrosion test. The results prove that there are Cr segregation and large particles of Cr precipitated within the raw Cr60Ni40 cladding layer. During the high-temperature test, Cr2O3 protective film was generated on the surface of the cladding layer, protecting the substrate to different degrees. However, the particles precipitation of Cr caused uneven growth of Cr-rich oxide, and the Cr segregation brought about internal corrosion with Cr2O3 as the main products.