Increasing Heat Treatment Temperature Research Articles

Effects of cooking methods and temperatures on quality and safety of dried red peppers (Capsicum annuum L.)

Dried red peppers (Capsicum annuum L.) are widely used in various cuisines. This study investigated the effects of different cooking methods, including pan-grilling and stir-frying, on the formation of quality-related compounds (volatile components and capsaicinoids) and safety-related compounds [furan, polycyclic aromatic hydrocarbons (PAHs), and acrylamide] in dried peppers. In addition, the changes in quality and safety indicators for each cooking temperature (180 °C and 220 °C) were also investigated. The increase of heating temperature resulted in higher contents of ketones, furans, and furanones, but also led to a more significant decomposition of capsaicinoids. In particular, the content of furan significantly increased during stir-frying at higher temperatures, while those of PAHs showed no significant difference regardless of heating conditions. In the case of acrylamide, its contents in the pan-grilling and stir-frying samples cooked at 220 °C (2840 and 2800 μg/kg) were significantly higher than those in the samples heated at 180 °C (1180 and 1010 μg/kg). Our results showed that both safety and quality aspects should be considered when dried red peppers are used for pan-grilling and stir-frying of foods.

Rotational effect of a cylinder on hydro-thermal characteristics in a partially heated square enclosure using CNT-water nanofluid

Rotating cylinder movement in a cavity flow is an exciting field of study in heat transfer. Considerable research has been carried out on rotating cylinders under MHD mixed convection in various types of enclosures. However, considering partially heated square enclosure and magnetic field using CNT-water nanofluid is very limited. This study's goal is to assess the hydrothermal phenomena in a square enclosure with a rotating cylinder. Simulation has been conducted for different rotational speeds (Ω) and dimensionless times (τ) to observe the thermal and fluid flow behaviour. The Galerkin Residual based finite element method has been used to conduct numerical calculations. The results are shown as isotherms, streamlines, and average Nusselt number at the cylinder wall. Moreover, the drag force at the moving wall, and the fluid properties such as the root mean square (rms) of velocity, the temperature, the vorticity functions, and the average fluid temperature are also presented. The heat transfer rate, drag force, rms velocity, and temperature increase with the rise of rotational speed and dimensionless time rise. Maximum vorticity occurs at Ω = 8 and τ = 1. The maximum vorticity function increases 12 times with the increasing rotational speed. Higher rotational speed leads to increased average fluid temperature. The case of Ω = 8, τ = 1 shows the most temperature variance, while Ω = 1, τ = 0.1 has the least. Increasing rotational speed results in higher drag force on the cylinder's surface. At Ω = 4, the drag force is 2.8 times greater than at Ω = 2. Overall, the fluid flow and thermal performance boost up while the rotating speed of the cylinder is higher.

Structure Dependent Electrochemical Behaviors of Hard Carbon Anode Materials Derived from Natural Polymer for Next-Generation Sodium Ion Battery.

Hard carbons are one of the most promising anode materials for next-generation sodium-ion batteries due to their high reversible capacity, long cycle life, and low cost. The advantage in terms of price of hard carbons can be further improved by using cheaper resources such as biomass waste as precursors. Lignin is one of the richest natural bio-polymer in the earth which can be obtained from woods. As the lignin has three-dimensional amorphous polymeric structure, it is considered as good precursor for producing carbonaceous materials under proper carbonization processes for energy storage devices. In this study, structural properties of lignin-derived hard carbons such as interlayer spacing, degree of disorder and surface defects are controlled. Specifically, lignin-derived hard carbons were synthesized at 1000 °C, 1250 °C, and 1500 °C, and it was confirmed that the structure gradually changed from a disordered structure to ordered structure through X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Hard carbons exhibit sloping regions at high voltage and plateau region at low voltage during the electrochemical processes for sodium ions. As the heat treatment temperature increases, the contribution to the overall reversible capacity of the sloping region decreases and the contribution of the plateau region increases. This trend confirms that it affects reversible capacity, rate-capability, and cycling stability, meaning that an understanding of structural properties and related electrochemical properties is necessary when developing hard carbon as a negative electrode material for sodium ion batteries.

Adsorption and safe immobilization of Sr ions in modified zeolite matrices

In the present study, an Iranian natural zeolite (Sabzevar region) was evaluated as a natural adsorbent for the elimination and immobilization of strontium ions from an aqueous solution. For improving the adsorption efficiency of strontium ion, the zeolite surface was modified by the Schiff base ligand of bis (2-hydroxybenzaldehyde)1,2-diaminoethane (H2L). The natural zeolite and zeolite/H2L were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray fluorescence (XRF), BET and scanning electron microscope (SEM). Analysis of the natural zeolite showed that the zeolite is from the type of clinoptilolite and has a crystalline structure with the specific surface area 29.74 m2/g. The results showed that strontium adsorption onto modified zeolite increases compared to unmodified zeolite from 64.5% to 97.2% (at pH = 6). The effective parameters pH, adsorbent dosage, initial concentration of strontium ions, contact time, temperature, and interfering ions, were studied and optimized. The maximum adsorption efficiency was confirmed by modified zeolite and found to be 97.5% after 60 min of equilibrium time at pH 6, 0.05g as adsorbent dosage, and at 25 °C. Adsorption of strontium was confirmed by Langmuir model with maximum adsorption capacity of 10.31 mg/g. Kinetic studies showed that the adsorption of strontium ions on the adsorbent follows pseudo-second-order (PSO) model. Also, the thermodynamics of the adsorption process indicated that the adsorption of strontium on zeolite/H2L is an endothermic and spontaneous process, and the adsorption mechanism is a combination of physical and chemical adsorption. Finally, to manage the secondary waste generated from the adsorption process, strontium ions were immobilized in a zeolite structure. The results showed that the stabilization is well done with the thermal preparation process. After thermal treatment at 25–900 °C, modified zeolite satisfactorily retains strontium during back-exchange tests with NaCl solution. According to the results, the amount of strontium released from the adsorbent phase decreases from 52.6 to 1.6% with increasing heat treatment temperature.

Microstructure, residual stress and magnetic properties of Tb0.27Dy0.73Fe1.95 alloy heat treated in high magnetic field

The directionally solidified Tb0.27Dy0.73Fe1.95 alloys were heat-treated without and with a 12 T high magnetic field. The changes of the Widmanstatten precipitates (WSPs), magnetic domain structure, residual stress, and magnetic properties during the heat treatment were investigated. The high magnetic field reduced the WSPs content and residual stress in the alloys. The effect of the high magnetic field becomes more obvious with increasing heat treatment temperature. The high magnetic field also changed the magnetic domain structure by promoting the alignment of the magnetic moments along the easy magnetization axis and increasing the width of the magnetic domains. The magnetization rate and magnetostrictive property of the alloys were improved by the decrease of the WSPs content and residual stress, as well as the change of the magnetic domain structure.

Experimental Investigation on the Influence of Wave Impedance on Dynamic Mechanical Response of Granites undergone High Temperature.

Wave impedance is an important physical quantity to characterize the dynamic properties of materials. To explore the influence of wave impedance on the dynamic mechanical response of rock, the granite samples with a wave impedance gradient change are obtained by changing the heating temperature, and the impact compression test is carried out by using a split Hopkinson pressure bar (SHPB) device. The stress wave propagation law, dynamic stress-strain relationship, and fracture characteristics of rocks with different wave impedances are studied comparatively, and the influence mechanism of wave impedance on the dynamic mechanical response of rocks is comprehensively analyzed from two aspects of material properties and dynamics. The results show the following: (1) Under the action of the same incident wave, the reflected wave amplitude, transmission wave takeoff time, peak stress, peak strain, and equivalent average size of fragments of granite samples with different wave impedances are significantly different. (2) As the heating temperature increases, the wave impedance of granite continuously decreases and the degree of damage intensifies. Within the high-temperature treatment range of 400 to 600 °C, there is a damage wave impedance threshold between 7854 and 3081 g·cm-3·m·s-1. Below this wave impedance, granite will appear to have significant damage deterioration. (3) Under the same incident wave, the strain rate and loading rate of granite samples show negative correlation and positive correlation with wave impedance, respectively. There is a progressive relationship between rock wave impedance, stress wave propagation, strain rate history/stress history, and dynamic mechanical response.

Heat treatment effects on microstructure and mechanical properties of CVI SiCf/PyC/SiC composites with Cansas-Ⅲ SiC fibers

The microstructure and mechanical properties of CVI-Cansas-III/PyC/SiC composites were systematically investigated after heat treatment under high temperature argon atmosphere, ranging from 1000 °C to 1500 °C, for different time durations. The results showed that the Cansas-III fibres degraded with increasing heat treatment temperature, resulting in degradation of the fibre properties due to pyrolysis of the SiOC phase inside the fibres. The bending strength of the composites remained nearly constant upon heat treatment at 1000 °C and 1250 °C, while a decline in bending strength was observed upon increasing the heat treatment temperature and time, specifically at 1350 °C and above. Moreover, the composites maintained their pseudo-plastic fracture behaviour below 1450 °C, while displaying brittle fracture of the ceramic after 100 h of heat treatment at 1500 °C, due to the complete crystallisation of the fibres.

Microstructure evolution of Ti64-TiBw composites via electron beam powder bed fusion using as-prepared composite powder as feedstock

A self-designed spherical Ti64 powder containing nanosized TiB whisker(TiBw) was developed by electrode induction melting gas atomization (EIGA), which was used as feedstock to prepare Ti64-TiBw composites by electron beam melting (EBM). Nano-scaled TiBw distributed along the grain boundaries, forming a discontinuous network structure in EBM-Ti64-TiBw composites. In order to elucidate the effect of nano-sized TiBw on microstructure and properties of EBM-Ti64-TiBw composites, heat treatment of as-fabricated EBM-Ti64-TiBw is performed from 800 to 1200 °C with interval of 100 °C, to regulate the size characteristics (diameter, aspect ratio) of TiBw, the revolution of microstructure and interface were studied in detail. The results indicate that Ti64/TiBw interface structure transforms from a semi-coherent interface to a coherent interface with increasing heat treatment temperature (HTT). Furthermore, TiBw begin to coarsen after the heat treatment above the β-transus temperature, leading to a weakening of its pinning effect on Ti64 matrix, and the discontinuous network structure disappears at 1000 °C. The growth and coarsening of TiBw are closely related to the diffusion rate of B atom in α-Ti and β-Ti phases. This work provides a theoretical foundation for size control of TiBw reinforcement and the elucidation of its evolution effect on microstructure in EBM-Ti64-TiBw composites.

Effect of Solution Heat Treatment on the Microstructure and Microhardness of 7050 Aluminum Alloy

Today, 7xxx aluminum alloys are widely used in aerospace and other fields due to their excellent properties such as low density, high specific strength, and good processing performance. The heat treatment process of 7xxx aluminum alloy is crucial in controlling the strengthening phases and grain size, which is a significant way to enhance the alloy’s performance. In this study, solution heat treatment tests of 7050 aluminum alloys were carried out at different temperatures, ranging from 440 °C to 470 °C, with a holding time ranging from 0.5 h to 8 h, using a DIL 805A thermomechanical test machine. The microstructural evolution during the solution heat treatment was characterized using an optical microscope (OM), a scanning electron microscope (SEM), and a transmission electron microscope (TEM). The effects of the solution parameters on the alloy’s microhardness were analyzed using a digital Vickers microhardness tester. According to the ASTM E112-13 standard, The Anelli grain growth models were established to illustrate the grain size evolution during solution heat treatment, and a modified Anelli grain growth model was established. The results indicated that the grain size significantly increases with the increase in the solution heat treatment time and temperature. The Anelli grain growth model can illustrate the phenomenon of grain growth more accurately in the solution heat treatment process of 7050 aluminum alloy. It was found that prolonging the time and elevating the temperature of the solution heat treatment reduced the microhardness of the aluminum alloy because of the dissolution of the precipitates.

Investigation on latent heat energy storage using phase change material enhanced by gradient-porosity metal foam

Utilizing an optimized gradient porosity can help with the temperature uniformity and alleviate the temperature aggregation. In this paper, a solid–liquid lattice Boltzmann (LB) model at the representative elementary volume scale (REV-scale) is established to investigate the enhancement mechanism of gradient porosity on LTES units. Three gradient porosity including Chinese-fan-shape, vertical and concentric distribution has been investigated. The findings demonstrate that a well-designed gradient porosity can significantly decrease the melting time, with the best performance observed when using a fan-shape arrangement of a certain gradient. In comparison to a homogeneous porosity, the fan-shape arrangement of a specific gradient reduces the melting time by 36.1 % and ensures a more uniform temperature distribution. Increasing the number of layers from two to five has no remarkable improvement on melting, not exceeding 4.4 % in total melting time. Conversely, increasing the porosity gradient leads to an increase in melting time of no less than 36.1 %. Furthermore, an extended dimensionless number Ram in a range of 150 ∼ 600 is investigated. The results suggest that, with the increase of Ram the temperature aggregation is more significant, and the gains in melting rate are unable to offset the increased heating temperature's impact on the melting time.

The Effect of Temperature on Molecular Structure of Medium-Rank Coal via Fourier Transform Infrared Spectroscopy.

Fourier transform infrared spectroscopy (FTIR) was used to study the molecular structure of four medium- and low-temperature heat-treated medium-rank coals. The FTIR spectral parameters, which consist of CH2/CH3, aromaticity (fa), aromatic carbon rate (fC), aromatic hydrogen rate (fH), oxygen-containing (C-O) rate (IR), organic matter maturity (M), and the degree of aromatic condensation (Dc), indicate different characteristics, including changes in the aromatic hydrocarbon structure, fatty hydrocarbon structure, hydroxyl structure, and oxygen-containing functional groups of medium-rank coal. The results show that with the increase in heat treatment temperature, the sulfur content in coal gradually decreases, but the C/H ratio gradually increases. Meanwhile, the content of kaolinite and pyrite in coal gradually decreases, whereas the content of dolomite and hematite gradually increases. With the increase in heat treatment temperature, the relative content of ether oxygen hydroxyl groups in the hydroxyl structure significantly decreases, but the relative content of self-associated hydroxyl groups increases. The relative content of alkyl ether (C-O) in oxygen-containing functional groups gradually increases, whereas the relative content of aromatic nucleus C=C vibration presents a trend of first increasing and then decreasing. In addition, -CH2- is the majority in the structure of fatty hydrocarbons, and the absorption peak intensity of asymmetric -CH3 stretching vibration increases with the increase in heat-treated temperature. The structure of aromatic hydrocarbons mainly consists of four substituted benzene rings (except for R-303.15 K), in which the relative content of the trisubstituted benzene ring decreases with the increase in heat treatment temperature. With the increase in the heat-treated temperature of medium-rank coal, Dc, fH, fC, and fa show a trend of first increasing and then decreasing, M and IR reveal a trend of first decreasing and then increasing, and CH2/CH3 present a gradually decreasing trend. In conclusion, during the increase in the heat treatment temperature of medium-rank coal, the length of the fatty side chains in the fatty hydrocarbon structure becomes shorter, the number of branch chains continuously increases, and the maturity and condensation degree of organic matter first increases and then decreases. On this basis, further research on the effect of coal gasification suggests combining various technologies such as 13C NMR, XRD, and TG-MS to obtain semi-quantitative structural information of molecules in coal from different perspectives.

Effect of Heat Treatment Time and Temperature on the Microstructure and Shape Memory Properties of Nitinol Wires.

In this study, the effect of heat treatment parameters on the optimized performance of Ni-rich nickel-titanium wires (NiTi/Nitinol) were investigated that were intended for application as actuators across various industries. In this instance, the maximum recovery strain and actuation angle achievable by a nitinol wire were employed as indicators of optimal performance. Nitinol wires were heat treated at different temperatures, 400-500 °C, and times, 30-120 min, to study the effects of these heat treatment parameters on the actuation performance and properties of the nitinol wires. Assessment covered changes in density, hardness, phase transition temperatures, microstructure, and alloy composition resulting from these heat treatments. DSC analysis revealed a decrease in the austenite transformation temperature, which transitioned from 42.8 °C to 24.39 °C with an increase in heat treatment temperature from 400 °C to 500 °C and was attributed to the formation of Ni4Ti3 precipitates. Increasing the heat treatment time led to an increase in the austenite transformation temperature. A negative correlation between the hardness of the heat-treated samples and the heat treatment temperature was found. This trend can be attributed to the formation and growth of Ni4Ti3 precipitates, which in turn affect the matrix properties. A novel approach involving image analysis was utilized as a simple yet robust analysis method for measurement of recovery strain for the wires as they underwent actuation. It was found that increasing heat treatment temperature from 400 °C to 500 °C above 30 min raised recovery strain from 0.001 to 0.01, thereby maximizing the shape memory effect.

Physicochemical and Functional Properties of Thermal-Induced Polymerized Goat Milk Whey Protein.

Goat milk whey protein products are a hard-to-source commodity. Whey protein concentrate was directly prepared from fresh goat milk. The effects of the heating temperature (69-78 °C), time (15-30 min), and pH (7.5-7.9) on the physicochemical and functional properties of the goat milk whey protein were investigated. The results showed that the particle size of the samples significantly increased (p < 0.05) after heat treatment. The zeta potential of polymerized goat milk whey protein (PGWP) was lower than that of native goat milk whey protein. The content of the free sulfhydryl groups of PGWP decreased with increasing heating temperature and time, while an increase in surface hydrophobicity and apparent viscosity of PGWP were observed after heat treatment. Fourier Transform Infrared Spectroscopy analysis indicated that heat treatment and pH had considerable impacts on the secondary structure of goat milk whey protein. Transmission electron microscope images revealed that heat induced the formation of a large and uniform protein network. Additionally, the changes in the physicochemical and structural properties contributed to the improvement of the emulsifying and foaming properties of goat milk whey protein after heat treatment. The results may provide a theoretical basis for the applications of polymerized goat milk whey protein in related products.

Modelling of large biomass and coal particle based on a novel C-DAEM: A numerical study on heat transfer and pyrolysis behavior

Using two kinds of large-size fuel particles with thermal resistance, i.e., lignocellulosic biomass (Beech, BH) and Shenmu bituminous coal (SMBC), a comprehensive and systematic study on volatile evolution and temperature distribution history inside the particle was conducted in this work. The pyrolysis behaviors of BH and SMBC were characterized through a novel C-DAEM and traditional DAEM. Pyrolysis experiments of large biomass and coal particles were conducted in three different particle size ranges of two different heating temperatures. Results showed that C-DAEM was better than DAEM. Moreover, both particle size and heating temperature have an influence on overall temperature but through different ways. Thermal disturbance peak (TDP) existed in TDSC curves, while pyrolysis reaction peak (PRP) existed only in 773 K of BH. Particle size affected the overall temperature mainly by changing the thermal disturbance transfer time, e.g., TDP of BH-L1 happened in 27.3s, TDP of BH-L2 happened in 56.2s, and TDP of BH-L3 happened in 94.4s. Heating temperature affected the overall temperature mainly by directly changing the heat flux, e.g., time of TDP in BH-L3 and BH–H3 was nearly the same, while the corresponding peak value was consistent with the increase in heating temperature.

Heat-Treated Aramid Pulp/Silica Aerogel Composites with Improved Thermal Stability and Thermal Insulation.

In this work, we prepared heat-treated aramid pulp/silica aerogel composites (AP/aerogels) and investigated in detail the feasibility of improving thermal stability and thermal insulation via tailored heat treatment. The microstructure and FTIR spectra reveal that AP/aerogels are formed by a physical combination of the silica aerogel matrix and aramid pulps. When the heat treatment temperature increases, the density slightly decreases and then increases to the maximum due to the significant volume shrinkage. The pyrolysis of aramid pulp and the collapse of silica skeletons occur during heat treatment; nevertheless, the typical structures of AP/aerogels do not change significantly. It is also found that both the hydrophobicity and the thermal insulation decrease with the increasing heat treatment temperature. We note that when the heat treatment is at 600 °C, the AP/aerogel still maintains a low density of 0.19 g/cm3 and a contact angle of 138.5°. The thermal conductivity is as low as 26.11 mW/m/K, measured using the transient hot wire method. Furthermore, the heat-treated AP/aerogels can avoid heat shock and possible thermal hazards during practical thermal insulation applications. The onset temperatures of the thermal decomposition of AP/aerogels increase from 298.8 °C for an untreated one to 414.7 °C for one treated at 600 °C, indicating that the thermal stability of AP/aerogels is improved significantly. This work provides a practical engineering approach to expand the thermal insulation applications of silica aerogel composites.

Numerical study on reaction and heat transfer of supercritical aviation kerosene with pyrolysis and steam reforming in a corrugated cooling channel

Coking and heat transfer deterioration of supercritical aviation kerosene pose grave challenges to regenerative cooling of scramjet engines. In the present study, reaction and heat transfer characteristics of supercritical China aviation kerosene No. 3, RP-3 undergoing simultaneous pyrolysis and steam reforming reactions in a corrugated channel are numerically studied. Compared with reacting flow of RP-3 in the smooth channel, temperature and coke deposition are much lower in majority part of the corrugated channel. The maximum temperature difference between the smooth and corrugated channels is up to 300K. The maximum heat transfer coefficient in the corrugated channel is almost three times of that in the smooth channel under the same condition. However, low-velocity and high-temperature zones are formed near the corrugated micro-structures and cause coke accumulation and heat transfer deterioration along the flow direction of the corrugated channel. With the increase of wall heat flux, both temperature and velocity increase significantly in the corrugated channel. The conversion of RP-3 and formation of coke are also enhanced with increasing wall heat flux. Moreover, the total heat transfer coefficient first increases and then decreases with wall heat flux. The maximum total heat transfer coefficient increases from 4000W/m2∙K to 18,000W/m2∙K with wall heat flux increasing from 0.3MW/m2 to 1.8MW/m2. Periodic wavy structures are found at the interface between the corrugated micro-structure and the bulk flow, which is pronounced when wall heat flux is 1.3MW/m2 or above. With the increase of flow time, local turbulent kinetic energy decreases due to the interaction between the corrugated micro-structures and the wavy structures. The interaction between the corrugated structures and complex reaction and heat transfer leads to intersection of the distributions of temperature and coke in the smooth and the corrugated channels. An empirical heat transfer correlation formula is obtained as Nu=0.1Re0.65Pr1.94 for RP-3 reacting flow in the corrugated channel. The study provides better insight into interaction mechanism between chemically reacting flow and micro corrugated structures.

Evolution of phase stability and structural properties in CrFeNiTiV high-entropy alloy under high-temperature heat treatment conditions

A novel equiatomic CrFeNiTiV high entropy alloy (HEA) was prepared by mechanical alloying (MA) and following spark plasma sintering (SPS). Further, the effects of heat treatment temperature on the phase, microstructure, and mechanical properties of HEAs were investigated. The results indicated the formation of a single body-centered cubic (BCC) phase after 30 h of MA. After SPS, it is found that the separation of a single phase into BCC, Ni3Ti, and TiC-rich phases, owing to the large atomic radius and mixing enthalpy of Ti with other elements. Compared with sintered HEA, the initial phases did not change after heat treatment at elevated temperatures, but the coarsening of phases was observed. The microscopic results confirmed that all phases are homogeneously distributed with good interfacial bonding after heat treatment at 1000 °C. The hardness and elastic modulus of HEA increased with increasing heat treatment temperature up to 1000 °C, due to increased precipitation of Ni3Ti and TiC-rich phases and then slightly reduced for the sample heat treated at 1100 °C HEA owing to the coarsening of existing phases. The creep displacement was reduced for the heat-treated HEAs compared to the SPS sample, suggesting improved creep resistance after heat treatment. In addition, an artificial neural network was used to predict the hardness behavior of heat-treated HEAs, and it exhibited an excellent accuracy of about 93.4%. Therefore, the present study provides valuable insights into the phase stability and mechanical properties of HEAs suitable for high-temperature applications.

Adhesion strength and pendulum hardness of some coatings in wood heat-treated by different methods

Beech (Fagus sylvatica L.) and pine (Pinus sylvestris L.) wood specimens were heat-treated separately at three different temperatures (170 °C, 190 °C, and 210 °C) with steam treatment method (STM), oil treatment method (OTM), and hot-air treatment method (HTM). Then, the specimen surfaces were coated with water-based, polyurethane-based, and oil-based varnishes according to industrial applications. The study results show that both hardness and adhesion strength values of STM and HTM treated specimens were similar for both wood species. In contrast, these values were generally lower in OTM-treated specimens. For all applied methods, heat treatment temperature had no significant effect on hardness values. Varnish adhesion strength decreased in all heat-treated wood specimens compared to untreated specimens. Adhesion strength also decreased in STM- and HTM-treated specimens with increasing heat treatment temperature. Hardness values increased in all specimens coated with polyurethane- and water-based varnish compared to the specimens without varnish. However, hardness decreased in the specimens coated with oil-based varnish. In contrast, the highest adhesion resistance was determined in the specimens coated with oil-based varnish under all heat treatment conditions. In addition, the heat treatment method is more effective relative to the hardness values and the treatment temperature is more effective relative to the adhesion strength of varnished pine and beech specimens.

Selective laser melting of AlCoCrFeMnNi high entropy alloy: Effect of heat treatment

The dilemma concerning the trade-off between the strength and ductility of alloys has persistently been a significant problem in engineering applications. Conventional techniques such as grain refinement, severe plastic deformation, and precipitation strengthening usually increase strength at the expense of ductility. High entropy alloys with dual-phase structures, on the other hand, generally display excellent strength-ductility synergy. In this study, we attempted to mix pre-alloyed powders of two distinct phases (body-centered cubic - bcc and face-centered cubic - fcc) to fabricate AlCoCrFeMnNi HEAs with a dual-phase structure by selective laser melting. Furthermore, we investigate the impact of varying heat treatment temperatures (900 °C, 1000 °C, and 1100 °C) on its phase composition, microstructure, and mechanical properties. The results show that with an increase in the heat treatment temperature, the volume of the fcc phase increases gradually and the volume of the bcc phase decreases. The columnar structure in the fcc phase transforms into a cellular structure, and a spinodal decomposition is observed with the bcc phase. As the heat treatment temperature increases, the yield strength decreases while the elongation substantially increases, with the samples heat-treated at 1100 °C showing the best comprehensive properties (yield strength ∼700 MPa, tensile strength ∼950 MPa, and ∼15% ductility).

Direct tensile mechanical properties and damage fracture mechanisms of thermally damaged coal measures sandstone under high strain rate loading

The direct tensile mechanical properties of highly thermally damaged rock under high strain rate loads are a key basic mechanical problem that must be solved for the stability and effective control of surrounding rock stability in the combustion control area of an underground coal gasification project. In this paper, a two-dimensional equivalent grain-based model (GBM) unit and Split Hopkinson Tension Bar (SHTB) numerical model for thermally damaged coal-measures sandstone were constructed using particle flow code (PFC). The comparison with the experimental results shows that the numerical method can accurately describe the dynamic direct tensile behavior of thermally damaged sandstone. The following conclusions are drawn: The dynamic tensile strength of thermally damaged sandstone shows a significant strain rate-strengthening effect. With the increase in thermal damage temperature, the dynamic tensile strength of sandstone increases first and then decreases. The generation and development of hot cracks in a high-temperature environment is the fundamental reason for the change in macroscopic mechanical properties. The dynamic tensile failure process of thermally damaged sandstone can be divided into four stages: the dynamic damage initiation, the dynamic damage development, the damage crack penetration, and the sample dynamic fracture. With the increase in impact velocity, the initial kinetic energy, elastic strain energy, dissipated energy, and elastic strain energy ratio in the failure process of thermally damaged sandstone gradually increase. In contrast, the dissipated energy ratio gradually decreases. As the heat treatment temperature increases, the elastic strain energy and the ratio of elastic strain energy increase first and then decrease.