Search

Overcoming the trade-off relationship between strength and ductility has always been a challenge. In this article, a neatly arranged ultrafine bainite that is composed of multi-scale retained austenite was obtained by introducing weak chemical heterogeneity in low-alloy steel. The optimized microstructure makes transformation-induced plasticity (TRIP) behavior and coordinating deformation behavior between each phase to be smoother. This results in better comprehensive properties, with 28.5% and 9% increases in uniform elongation and toughness, respectively, and a similar strength. This study provides a new way to improve the properties of low-alloy steels. A strategy of weak chemical heterogeneity has been proposed in low-alloy steel, which effectively optimizes the microstructure and enhances the plasticity and toughness of steel. [ABSTRACT FROM AUTHOR]

Overcoming the trade-off relationship between strength and ductility has always been a challenge. In this article, a neatly arranged ultrafine bainite that is composed of multi-scale retained austenite was obtained by introducing weak chemical heterogeneity in low-alloy steel. The optimized microstructure makes transformation-induced plasticity (TRIP) behavior and coordinating deformation behavior between each phase to be smoother. This results in better comprehensive properties, with 28.5% and 9% increases in uniform elongation and toughness, respectively, and a similar strength. This study provides a new way to improve the properties of low-alloy steels.

Rapid heating is a promising technique for achieving excellent mechanical properties. This study innovatively applies rapid heating to a novel Ti–Mo martensite steel through in-situ observation experiments. By comparing the microstructure evolutions at heating rates of 1 and 30 °C/s, the relationship between microstructure and property evolution was elucidated. The results indicate that the refined austenite grains resulting from rapid heating stem from enhanced grain nucleation, accumulated dislocations, and the increased formation of new carbides under the large superheat. Furthermore, carbide maturation predominates during the slow heating process, while rapid heating accelerates new carbide precipitation with limited carbide maturation. Moreover, during rapid heating, both coherent and non-coherent relationships were observed between the (Ti, Mo, Fe)C particles and the martensite matrix, demonstrating a remarkable pinning effect on grain boundary migration. Nevertheless, during slow heating, large-sized (Ti, Mo)C carbides were formed, presenting a non-coherent relationship with the martensite matrix. Additionally, the primary differences in strength caused by rapid heating compared to slow heating include grain refinement, dislocation, and precipitation strengthenings, with dislocation strengthening playing the dominant role.

Low-dimensional yttrium oxide (Y2O3) nanostructures have garnered significant research interest due to their intriguing properties arising from the dimensional effect and the modulation of the band structure. However, the simple preparation of Y2O3 nanosheets is rarely investigated due to the inherent limitations posed by the counterpart bulk cubic or monoclinic crystal structure. Herein, the low-dimensional layered Y2O3 nanosheets are prepared by a facile route of rapid heating followed by centrifugation, in which its corresponding hydrous-chloride compound is used as the sole reagent. The formation stages of layered Y2O3 nanosheets and corresponding mechanisms are elucidated in detail. The x-ray diffraction results confirm that the intermediate product after rapid heating is yttrium oxychloride (YOCl), which converts to the single-phase Y2O3 with a 2D layered phase after centrifugation. In addition, the obtained Y2O3 nanosheets possess a direct optical bandgap of 5.49 eV, and thus may hold promise for use in electronic applications. This research provides a facile and low-cost method for the preparation of other low-dimensional nanosheets with similar structures. [ABSTRACT FROM AUTHOR]

Polymer-derived SiBCN ceramics with good high-temperature stability and temperature-sensitive properties can be used in real-time temperature monitoring in the aeronautical industry. However, previous investigations mostly focus on the temperature sensitivity of SiBCN ceramics but neglect the fast temperature conversion of the real operating environment and its effect on the temperature sensitivity, which hinders their further practical application. In this study, the response to rapid temperature changes of polymer-derived SiBCN was studied. SiBCN ceramics maintain excellent high-temperature semiconductor performance under rapid heating, and its direct-current (DC) conductivity increases with increasing temperature. The conductive mechanism conforms to the amorphous semiconductor formula, following three different transition mechanisms in different temperature regions. The resistance of SiBCN increases with the number of cycles during 100 cycles of 500–1200 °C, presenting excellent temperature-sensitivity and relatively good sensing stability. This work demonstrates that SiBCN ceramics can maintain excellent temperature-resistance under extreme environments with rapid heating and cooling, and it is hoped that this work could guide the development of temperature sensors for extreme environments in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

The rapid heating treatment with different tempering temperatures of 160, 200 and 320 °C was innovatively applied in one developed martensitic wear-resistant steel. The elaborate characterization on the evolution of microstructure-mechanical properties including the wear performance in different tempering temperatures were compared. Results manifested that the rapid heating treatment yielded a peak performance in the martensitic wear-resistant steel when tempered at 200 °C, by which the tensile strength and elongation were 1762.46 MPa and 13.13%, respectively, accompanied by the highest product of strength and elongation of 23.14 GPa·%. The enhanced work hardening contribution caused by the refined martensitic laths and carbides, as well as the appropriate recovery leaded to the peak performance at 200 °C. However, the mechanical properties both deteriorated by tempering at 160 and 320 °C subjecting to either the stress concentration or the coarsen carbides. Besides, the Baker–Nutting relationship between carbides and the matrix was established and furtherly proved the coarsen carbides resulted in the worst elongation by tempering at 320 °C. In addition, the main strength differences caused by different tempering temperatures were the grain refinement strengthening, dislocation strengthening, and precipitation strengthening, in which the grain refinement and precipitation strengthening played the dominating role. The current findings provide foundation for the industrial application of rapid heating techniques on the high-performance martensitic wear-resistant steels.

Rapid heat treatment is an important method to improve the properties of steel. Moreover, the study of the phase transformation process plays an important role in the formulation of rapid heat treatment. This paper investigates phase transformation behavior and microstructure evolution of ultrafine bainite at varying heating rates, and reveals the influence mechanism of retained austenite on austenitizing. Results showed that the decomposition of retained austenite was influenced by the diffusion of Si element. Therefore, the decomposition temperature of retained austenite is severely affected by the heating rate. Retained austenite completely transformed into cementite and ferrite when heating rate was below 5 °C/s. A small amount of retained austenite was kept when the heating rate was higher than 5 °C/s. The kept austenite effectively suppressed the hysteresis of Ac1 and resulted in a unique mechanism of austenite grain formation. When the heating rate range was 5–10 °C/s, some new austenite skipped the nucleation process and grew directly on the kept austenite, forming the large austenite grains. And other new austenite was obtained via nucleation and growth process. Thus, the grain size of bimodal distribution is formed. This leads to the phenomenon of austenite memory effect. When the heating rate was increased to 50 °C/s and higher, the austenite grain size was less than 14 μm. Therefore, rapid heating makes the phase transition lag. When the heating rate is high enough, part of the austenite is kept, which has an important influence on austenitizing process of the steel.

The present study aims to clarify the possibility of rapid heating in the preparation of low-carbon ultrafine (UFG) steel. The effects of heating rate on the phase transformation, microstructure and precipitation of a low-carbon microalloyed steel were elaborately investigated. The results manifest that rapid heating potentially provides a simple and innovative process for the preparation of UFG steels just by increasing the heating rate. The parent austenite grains were refined due to the more reserved (Nb, Ti, V)C precipitates and dislocations within a short heating process by rapid heating. However, an effective holding time was proposed in the rapid heating to ensure the refined austenite grains. Moreover, the synthetic influences of initial increased grain boundaries and redissolved (Nb, Ti, V)C carbides provoked the abnormal grains with weakened thermostability. Redissolution of (Nb, Ti, V)C carbides were apparent during austenite nucleation at a slow heating rate, and it was verified during the isothermal holding stage by rapid heating. In addition, the austenitic phase transition occurred at higher temperature with the increase of heating rate, by which the transformation rate was accelerated.

Thermal error always exists in a machine tool and accounts for a large part of the total error in the machine. Thermal displacement in X-axis on a CNC lathe is controlled based on a rapid heating system. Positive Temperature Coefficient (PTC) heating plates are installed on the X-axis of the machine. A control temperature system is constructed for rapid heating which further helps the thermal displacement to quickly reach stability. The system then continuously maintains stable compensation of the thermal error. The presented rapid heating technique is simpler than the compensation of machine thermal errors by interference in the numerical control system. Results show that the steady state of the thermal displacement in the X-axis can be acquired in a shorter time. In addition, almost all thermal errors in constant and varying working conditions could be significantly reduced, by above 80% and 60%, respectively, compared to those without using the rapid heating. Therefore, the proposed method has a high potential for application on the CNC lathe machine for improving its precision.

The objective of the present paper is to investigate the effects of rapid heating and cryogenic cooling on on the microstructure and tensile properties of Al-Cu-Mg. The specimens were subjected to three heat treatment cycles in which the Infrared heating (IR) were used as the heating medium at the ageing stage, and the liquid nitrogen and water were used as the quenching mediums. The ageing temperature and time were 190⁰C and from 2 hours to 10 hours, respectively.The results indicated that by using IR at the ageing stage, the hardening rate enhanced because the rapid heating via this method leads to faster diffusion of the alloying elements. Moreover, the high density of nano-sized precipitates formed during ageingleads to higher strength and suitable ductility. Cryogenic treatment showed a negligible effect on both microstructure and tensile properties; however, it improved ductility. Overall, the combination of a high heating rate and cryogenic treatment led to the highest mechanical properties. SEM micrograph of the fracture surface of alloy demonstrated that in Cryogenic treatment+Artificial Ageing (CAA) condition, the surface had been fully covered by deep dimples in contrast to the Cryogenic treatment+Infrared Heating (CIR) and Water-Quench+ Infrared Heating (QIR) conditions which their dimples were shallow and also some facets were observed.

The stability of rock mass after fire is a concern of many engineering projects. In this paper, the effects of open fire and different cooling methods on granites were investigated. The static Brazilian test, dynamic Brazilian test, and P-wave velocity test were carried out to evaluate the mechanical properties and damage evolution behavior. A high-speed camera is employed to monitor the failure process of rock. The microstructures of the treated granites were observed by scanning electron microscope (SEM). The results showed that the fire duration and cooling treatment have a significant effect on the P-wave velocity, static nominal tensile strength, and dynamic nominal tensile strength of granite. These characteristics decrease rapidly during 0 to 10 min, and slowly decrease after 20 min. Compared to the air-cooling treatment, the water-cooling treatment has greater damage to the heated granite. To better understand the results, the rapid heating process of open fire heating was simulated using Abaqus software. The results reveal that there is a thinner compressive stress zone at the bottom of the specimen, and there is a large zone in the middle of the sample with higher tensile stress. The crack extension would be expanded due to high tensile stress, leading to the reduction of the tensile strength of the rock. This paper aims to better predict the degree of damage of rock materials after actual fire, as well as preliminarily explore the effect of the fire exposure duration and fire extinguishing method on the tensile properties of rock. [ABSTRACT FROM AUTHOR]

The constant challenges associated with metal oxide semiconductor (MOS) gas sensors, such as high operating temperature, low gas-sensing response, and prolonged recovery time towards NO 2 restrain their practical application. Herein, we put forward a novel thought via utilizing the synergistic interplay between La doping modification and chip rapid heating treatment to solve these drawbacks. Wherein, the 3 at% La-doped SnO 2 nanospheres treated at 200℃ by rapid chip heating (referred to as 3LS-200 NSs) exhibited exceptional performance. At room temperature, these nanospheres demonstrated a highly sensitive response of 3008–20 ppm NO 2 within a rapid response time of 9 seconds. Furthermore, this sensor exhibited a low detection limit of 200 ppb and long-term stability. The oxygen vacancy content of 3LS-200 NSs increased by 10.8 % compared with that prepared by normal heating treatment (3LS-200NH NSs) with slow heating rate. The exceptional gas sensing properties of 3LS-200 NSs towards NO 2 can be primarily attributed to the increase of oxygen vacancies, resulting in a reduced bandgap and the Fermi level shift of 0.07 eV toward the conduction band edge, hence enhancing surface electron transfer capability. This work presents a simple and energy-efficient strategy for commercial NO 2 detection. [Display omitted] • The La-doped SnO 2 hollow nanospheres were synthesized via a facile one-step hydrothermal method and rapid chip heating. • The La doping and rapid chip heating pretreatment contributed to efficient NO 2 detection. • The enhanced NO 2 gas sensing performance was explained by oxygen vacancies modulation and band structure adjustment. [ABSTRACT FROM AUTHOR]

This paper aims to present a novel rapid hot embossing approach and to study filling capacity of optical glass in the hot embossing process. Firstly, a novel rapid hot embossing device is developed, which consists of a rapid heating module and a precision loading module. Particularly, the rapid heating module allows a maximum temperature of 800 °C and a heating rate of 300 °C/min, with decent temperature control accuracy and uniform temperature distribution. In hot embossing process, by incompletely filling the microhole of silicon carbide mold, a microlens would be formed on the surface of glass disc, and the filling capacity of glass is quantified by the maximum height of the microlens. The tailor-made hot embossing device was exploited to conduct a series of experiments for evaluating effects of process parameters on the filling capacity of N-BK7 glass. Experimental results indicate that the filling capacity of glass could be enhanced by increasing the embossing force, the embossing temperature, the soaking time but decreasing the annealing rate. Furthermore, compared to soaking time and annealing rate, embossing force and embossing temperature have more significant influence on the filling capacity of N-BK7 glass. Therefore, the novel rapid hot embossing is a practical and promising technology for fabricating microstructures on glass materials with high softening points. [ABSTRACT FROM AUTHOR]

In order to discuss the production of syngas CO and hydrocarbons (HCs) and the effect of water on coal gasification reactivity, the gasification and combustion characteristics of coal were tested in a CO2 enrichment environment (O2 concentration≤10%) using a self-made CO2 laser beam with a 200 °C/s rapid heating system by changing the heating rate, oxygen concentration and moisture content of coal samples. The experimental results show that with the increase of heating temperature in the process of coal gasification and combustion, the mass loss of coal sample and the output of syngas increases continuously, and the relationship between the mass loss of coal sample and the transformed gas environment is air atmosphere>CO2-rich atmosphere> N2-rich atmosphere. On the other hand, in a CO2-rich gas environment, with the increase of heating temperature, the production of CO gas and HCs gas at 5%O2 concentration is relatively large. In addition, it is found that the amount of CO gas generated is relatively reduced, while the amount of HCs generated is relatively increased. This result shows that during the gasification and combustion of coal in CO2 enriched gas environment, the generation of CO gas mainly depends on O2 concentration, while the generation of HCs mainly depends on H2O.

Flash sintering (FS) is an important technique in the field of ceramic sintering. Nevertheless, conventional FS is less attractive for practical applications because of the complex shapes and small sizes of the specimens. In this study, using the novel electric field‐assisted hot pressing (FAHP) technique, we successfully achieved FS during the net‐shape hot pressing (HP) process for the first time. It was found that the 3 mol% yttria‐stabilized zirconia (3YSZ) can be flash sintered at 909°C using a fairly low DC field of 33 V/cm under 30 MPa pressure. The grain sizes of the FAHP‐sintered samples were 20% smaller than that of the HP‐sintered sample. When the current density limit is ≥240 mA/mm2, 3YSZ can be fully densified during the flash events. Careful analysis of the sintering curves suggests that although the carrier type or concentration is changed during flash events, it cannot explain the ultrafast densification. Additionally, we devised a qualitative method to analyze the densification mechanism. The results indicated that the ultrafast densification observed during flash events resulted from the synergistic effects of the rapid heating rate and peak sample temperature. Finally, the atomic force microscopy confirmed the lower grain boundary energy for the FAHP‐sintered samples, which accounts for the smaller grain sizes than the HP‐sintered sample. We believe that the FAHP technique could create new possibilities for theoretical and applied research on field‐assisted sintering techniques. [ABSTRACT FROM AUTHOR]

The objective of this work was to investigate the effect of rapid heating and cryogenic cooling on the fracture and tensile properties of Al-Cu-Mg samples. The specimens were subjected to three different heat treatment cycles in which the Infrared heating (IR) were used as the heating medium at the ageing stage, and the liquid nitrogen and water were used as the quenching mediums. The ageing temperature and time were 190⁰C and from 2 - to 10h respectively. The results indicated that by using IR at the ageing stage, the hardening rate enhanced because the rapid heating via this method led to faster diffusion of the alloying elements. Moreover, the high density of nanosized precipitates formed during ageing was another reason for higher strength and ductility. Cryogenic treatment had a negligible effect on both the microstructure and tensile properties. However there was an improvemnet in the ductility to some extent. Overall, the combination of a high heating rate and cryogenic treatment led to the highest mechanical properties. SEM micrographs of the fracture surface demonstrated that in Cryogenic treatment plus Artificial Ageing (CAA) condition, the surface was fully covered by deep dimples in contrast to the Cryogenic treatment plus Infrared Heating (CIR) and Water-Quench plus Infrared Heating (QIR) conditions which contained shallwer dimples. Some facets were also observed in the latter samples. [ABSTRACT FROM AUTHOR]

• A unique experimental apparatus was built to study rapid phase transition. • • HFE-7100 ON data for at high heating rates, 106 K/s, are measured for the 1st time. • • Results are obtained in the intermediate heating rates regime (105 to 106. • K/s). • • Maximum superheating degree of 14 K was obtained for a heating rate of 2.2・106 K/s. • • For slower heating rates, superheating spans 12 K for water and 4 K for HFE-7100. Effective thermal management of electronics is crucial for maintaining their reliability, longevity, and optimal performance. As electronic devices become increasingly compact and powerful, the need to explore new and innovative methods for thermal management becomes ever more critical. Rapid transitions of power lead to temperature spikes (hotspots) of up to 100 K, and thus can dramatically increase the failure occurrence of chips. Power spikes imply that heterogeneous nucleation occurs due to rapid heating, which can vary between 104 – 106 K/s, and hence the coolant is in its metastable region under various degrees of superheating. Gaining ONB data with respect to the heating rate holds significance for diverse applications including nuclear installations, engines, inkjet printers, and laser-based systems. In the present paper, we have refined the definition to a heterogeneous nucleation event due to a rapid heating process, that occurs when the timescale for the wall heating is shorter than the critical bubble's significant growth time. Data pertaining to the dependence of the onset of nucleate boiling (ONB) on the heating rate is presented for the first time. Experiments are performed with HFE-7100 fluid that is rapidly heated using a uniquely designed micro-heater, 122 × 234 μm2 in size. The newly designed and constructed system facilitates precise measurements of fast heating processes. In this study, we conducted a series of experiments spanning heating rates from 104 to ∼106 K/s. This range of heating rates was identified in our previous studies as an intermediate regime for water. The region of intermediate heating rates was previously proved in our research to be challenging to attain, due to the varying stability of the metastable zone; it is primarily attributed to pre-existing nucleation sites. Consequently, this led to a notable gap in the experimental results for water, within this particular region, in the literature. Notably, in the current study, we were able to achieve a maximum superheating degree of 14 K at a heating rate of 2.2·106 K/s. Preheated liquids reach the same superheating degree with different heating rates, depending on the coexistence and spinodal curves. It was found that water and HFE-7100 differ significantly in their metastable zone, and that the first zone, for slower heating rates, spans approximately 12 K for water, but only 4 K for HFE-7100. [ABSTRACT FROM AUTHOR]

This paper aims to present a novel rapid hot embossing approach and to study filling capacity of optical glass in the hot embossing process. Firstly, a novel rapid hot embossing device is developed, which consists of a rapid heating module and a precision loading module. Particularly, the rapid heating module allows a maximum temperature of 800 °C and a heating rate of 300 °C/min, with decent temperature control accuracy and uniform temperature distribution. In hot embossing process, by incompletely filling the microhole of silicon carbide mold, a microlens would be formed on the surface of glass disc, and the filling capacity of glass is quantified by the maximum height of the microlens. The tailor-made hot embossing device was exploited to conduct a series of experiments for evaluating effects of process parameters on the filling capacity of N-BK7 glass. Experimental results indicate that the filling capacity of glass could be enhanced by increasing the embossing force, the embossing temperature, the soaking time but decreasing the annealing rate. Furthermore, compared to soaking time and annealing rate, embossing force and embossing temperature have more significant influence on the filling capacity of N-BK7 glass. Therefore, the novel rapid hot embossing is a practical and promising technology for fabricating microstructures on glass materials with high softening points.

This study reports a newly designed induction heating system for efficient, fast, and safe flow-through heating. The system has a very simple architecture, which is composed of a transmitting coil, an isolating plastic pipe, and an embedded metal shell. Wireless energy transfer from the external coil to the internal metal shell through the pipe is essential for decreasing losses. Also, a large contact surface between a fluid and the immersed shell enables rapid heat transfer. The proposed heating system was systematically investigated for different shell geometries and the results were compared with a commercially available conductive flow-through heating device. As a proof-of-concept demonstration, a prototype of the designed induction heating system was manufactured and the heating measurements were conducted with water. Power transfer efficiency of the prototyped induction heating system was measured to be 97%. The comparative study indicates that such high-efficiency induction flow-through heating system offers a great potential for replacing the conventional conductive heating device used in household applications in which the rapid and compact heating is desired. [ABSTRACT FROM AUTHOR]

Visualization of the heat transfer phenomena induced by the rapid heating of nickel sheets was carried out using a Mach–Zehnder interferometer (MZI) and a high-speed camera. This phenomenon may be an important factor in heat transfer phenomena when the working fluids reach the thermodynamic critical point. The effect of heat transfer on the heating conditions of a nickel sheet was quantified by finite fringe analysis. The results show that isotherms near the heating surface with rapid heating are generated, and the induced isotherms are moved upward with similar patterns for different heating conditions. In addition, it is confirmed that the local Nusselt number decreases to the relationship of a secondary function if the thickness of the metal specimen is very thin and the time to reach the highest temperature is very short. Moreover, it decreased according to the increase of heating energy because the heat transfer mainly occurred by conduction and radiation rather than by convection, because the expansive force and compressive force between the fluid layers on the wall increased due to an increase in the heating energy in the beginning. [ABSTRACT FROM AUTHOR]

A warm stamping process of 1 and 1.2 GPa ultra-high strength steel sheets at comparatively low temperatures using rapid resistance heating was investigated to produce high strength parts. The effects of the heating temperature and rate on mechanical and surface properties of warm-stamped parts were examined. For a rapid heat rate of 100 °C/s around a heating temperature of 300 °C, the hardness of the formed parts increased from that of the as-received sheets, and the hardness for the 1.2 GPa sheet approached that of conventional hot-stamped parts from 22MnB5 steel sheets. The increase in hardness appeared only for rapid heating, and not for slow heating using a furnace. The increase in hardness is due to the transformation of retained austenite into martensite at comparatively low temperatures using rapid resistance heating and cooling. For the comparative low heating temperature, the non-coated sheet hardly oxidised, and the galvannealed sheet having high corrosion resistance did not exhibit the exfoliation of the coating layer, whereas the springback did not improve. [ABSTRACT FROM AUTHOR]

The study is focused on using an image analysis to explain the effects of several cycles of rapid heat treatment on the microstructure of 0.213 wt. % carbon steel. The samples examined are subjected to a diffusional heat treatment followed by several cycles of a rapid heat treatment. The process of the diffusional heat treatment involves heating the samples from an ambient temperature to 850oC in an electric muffle furnace for 56 min and then quenching in running water. In order to improve further the mechanical properties of the heat treated samples, they are subjected to several cycles of rapid heating. Each cycle comprises preheating the furnace to 900oC prior to the samples charging. The treated samples are subjected to a microstructural examination using optical microscopy followed by an image analysis using Image J software. The mechanical properties of the heat treated samples are characterized through ultimate tensile, hardness and impact tests. The results reveal that the grain size decreases from 1.07 µm in the control sample to 0.79 µm in the three-cycle sample and increases to 0.86 µm in the four-cycle one. It is also observed that the two-cycle sample shows the highest ductility (15356.3 N/mm2) and the lowest ultimate strength (833.375 N/mm2). This implies that the two-cycle rapid heat treatment is required for grain refinement in mild carbon steel. [ABSTRACT FROM AUTHOR]

Effects of the fiber type, dosage and length on the explosive spalling of ultra-high-strength concrete under rapid heating and rapid cooling were experimentally investigated. The mechanism of spalling resistance was examined by comprehensive thermal analysis, X-ray diffraction analysis, scanning electron microscopy and mercury porosimetry. The burst time is extended but the spalling is unaffected by the addition of steel fiber. The spalling resistance is improved with the addition of polypropylene (PP) fiber or PP and steel fibers. Ultra-high-strength concrete with 0.20% (vol.) PP fiber has excellent spalling resistance. The resistance to explosive spalling is enhanced with 12- or 19-mm-long PP fibers. PP fiber improves the spalling resistance mainly through the formation of tubular channels.

Visualization of the heat transfer phenomena induced by the rapid heating of nickel sheets was carried out using a Mach–Zehnder interferometer (MZI) and a high-speed camera. This phenomenon may be an important factor in heat transfer phenomena when the working fluids reach the thermodynamic critical point. The effect of heat transfer on the heating conditions of a nickel sheet was quantified by finite fringe analysis. The results show that isotherms near the heating surface with rapid heating are generated, and the induced isotherms are moved upward with similar patterns for different heating conditions. In addition, it is confirmed that the local Nusselt number decreases to the relationship of a secondary function if the thickness of the metal specimen is very thin and the time to reach the highest temperature is very short. Moreover, it decreased according to the increase of heating energy because the heat transfer mainly occurred by conduction and radiation rather than by convection, because the expansive force and compressive force between the fluid layers on the wall increased due to an increase in the heating energy in the beginning.

Micro process engineering as a process synthesis and intensification tool enables an ultra-short thermal treatment of foods within milliseconds (ms) using very high surface-area-to-volume ratios. The innovative application of ultra-short pasteurization and sterilization at high temperatures, but with holding times within the range of ms would allow the preservation of liquid foods with higher qualities, thereby avoiding many unwanted reactions with different temperature–time characteristics. Process challenges, such as fouling, clogging, and potential temperature gradients during such conditions need to be assessed on a case by case basis and optimized accordingly. Owing to the modularity, flexibility, and continuous operation of micro process engineering, thermal processes from the lab to the pilot and industrial scales can be more effectively upscaled. A case study on thermal inactivation demonstrated the feasibility of transferring lab results to the pilot scale. It was shown that micro process engineering applications in thermal food treatment may be relevant to both research and industrial operations. Scaling of micro structured devices is made possible through the use of numbering-up approaches; however, reduced investment costs and a hygienic design must be assured.

Microstructure and mechanical properties after induction hardening have a significant effect on the wear resistance performance and lifetime of 55CrMo steel ball screw. In the paper, the dilatometric curves were recorded at the different heating rate by a Gleeble-1500D thermo-mechanical simulator to determine the effect of heating rate on the austenitizing temperature of 55CrMo steel. Heat treatment of some specimens was performed by the Gleeble-1500D thermal simulator at the different heating temperature, holding time and cooling rate to investigate the effect of induction hardening parameters on the phase transformation, microstructure and microhardness of 55CrMo steel. Microstructure of specimen was analyzed using an optical microscope and a scanning electron microscope. Volume fraction of retained austenite was measured using an x-ray diffractometer. The mechanical properties were evaluated by a microhardness tester. The results show that the austenitizing temperature of 55CrMo steel increases with the increasing heating rate. Increasing the heating temperature, holding time and cooling rate of specimen is helpful in obtaining a uniform cryptocrystalline martensite. Volume fraction of retained austenite is less as the heating temperature is in the range of 900-950 °C. In the induction hardening of 55CrMo steel, the heating temperature should be in the range of 900-1000 °C. [ABSTRACT FROM AUTHOR]

Slightly graphitization might be incurred on CVD diamond films when suffering instantaneous high temperature thermal shock. In this paper, phase transitions of CVD free-standing diamond films have been studied experimentally at the temperature range of 1500–1800 °C through a plasma rapid heating process. Raman spectra and X-ray photoelectron spectra (XPS) are compared and discussed for the purpose of measuring the percentage of graphitic carbon component in CVD diamond films after heat treatment at different temperatures. An obvious optical degradation took place in both visible and infrared bands with the increased treating temperature. The result indicates that graphitization is dominated along grain boundaries rather than in internal grains. In addition, the nitrogen related absorption peaks were not covered by the enhanced optical absorption background, which was caused by the opaque graphitic carbon formed at high temperature. Nitrogen concentrations have also been evaluated for these graphitized diamond films and there is no evidence to show the movement or aggregation of nitrogen atoms. [ABSTRACT FROM AUTHOR]

Fast charging is a key enabler of mainstream adoption of electric vehicles (EVs). None of today's EVs can withstand fast charging in cold or even cool temperatures due to the risk of lithium plating. Efforts to enable fast charging are hampered by the trade-off nature of a lithium-ion battery: Improving low-temperature fast charging capability usually comes with sacrificing cell durability. Here, we present a controllable cell structure to break this tradeoff and enable lithium plating-free (LPF) fast charging. Further, the LPF cell gives rise to a unified charging practice independent of ambient temperature, offering a platform for the development of battery materials without temperature restrictions. We demonstrate a 9.5 Ah 170 Wh/kg LPF cell that can be charged to 80% state of charge in 15 min even at -50 °C (beyond cell operation limit). Further, the LPF cell sustains 4,500 cycles of 3.5-C charging in 0 °C with <20% capacity loss, which is a 90x boost of life compared with a baseline conventional cell, and equivalent to >12 y and >280,000 miles of EV lifetime under this extreme usage condition, i.e., 3.5-C or 15-min fast charging at freezing temperatures. [ABSTRACT FROM AUTHOR]

The invasive brown marmorated stink bug, Halyomorpha halys, is causing economic and ecological damage in invaded areas. Its overwintering behavior warrants mitigation practices in warehouses and shipping operations. The aim of this study was to characterize the mortality response curves of H. halys adults to short high-temperature exposure. Here we compared field-collected individuals entering (ENA) and exiting diapause (EXA). EXA adults displayed increased susceptibility to high temperatures compared to ENA individuals. Complete mortality of all tested individuals was obtained after 10 min exposure at 50.0 °C, and after 15 (EXA) or 20 min (ENA) at 47.5 °C. The nutritional status of these insects had no effect on high-temperature tolerance. The mortality curves obtained here may be used for the definition of cost-effective heat treatments aimed at the H. halys control.

Thermal nanoimprint lithography is playing a vital role in fabricating micro/nanostructures on polymer materials by the advantages of low cost, high throughput, and high resolution. However, a typical thermal nanoimprint process usually takes tens of minutes due to the relatively low heating and cooling rate in the thermal imprint cycle. In this study, we developed an induction heating apparatus for the thermal imprint with a mold made of ferromagnetic material, nickel. By applying an external high-frequency alternating magnetic field, heat was generated by the eddy currents and magnetic hysteresis losses of the ferromagnetic nickel mold at high speed. Once the external alternating magnetic field was cut off, the system would cool down fast owe to the small thermal capacity of the nickel mold; thus, providing a high heating and cooling rate for the thermal nanoimprint process. In this paper, nanostructures were successfully replicated onto polymer sheets with the scale of 4-inch diameter within 5 min.

Generally, the compression forming process is mainly used to fabricate the pre-form of CFRP product in resin transfer molding(RTM) process. The laminate is deformed under the low pressure because only fabrics and binders are used in pre-form process. However, the laminate consisted of prepreg is deformed under the high pressure and warm temperature to improve the surface quality and remove the voids in perperg compression forming(PCF) process. Therefore, the evaluations of tool-ply friction behaviors are required under the condition of high pressure and warm temperature. Several parameters have been investigated to determine their effect on the friction coefficient between the tool and laminate: normal pressure, laminate temperature, tool temperature, atmosphere temperature, and laminate orientation. In this study, the friction behaviors were evaluated for several important parameters of normal pressure, laminate orientation and atmosphere temperature. This paper describes two experimental method for measuring the friction behaviors of thermoplastic composites. The pull-through and rotational friction tests were performed to compare the friction behaviors according to the operating direction in the tests. In addition, the relationship of stribeck curve was evaluated under the conditions of high pressure and warm temperature. [ABSTRACT FROM AUTHOR]

Prepreg compression forming(PCF) is well known for the manufacturing process with high mechanical properties, low equipment cost and high surface quality. Generally, the temperature difference and rapid heat transfer between the tool and laminate can lead to some problems such as heat distortion, low formability and bad surface quality. Therefore, this paper attempts to solve these problems by using the rapid heating and cooling device, similarly to injection molding. It is possible to heat the tool above T g and cool it down under T g within few minutes. Also, the defect of distortion is prevented by rapid cooling system. In this study, the manufacturing process of CFRTP B-pillar reinforcement was designed based on structural analysis and thermal forming analysis. First, the thickness of laminate satisfying the energy absorption of conventional steel product was determined through structural analysis. Second, the thermal properties of the prepreg was evaluated for the thermal forming analysis. The thermal forming analysis of CFRTP laminate was carried out to determine the holding force. Finally, B-pillar reinforcements of CFRTP were fabricated and evaluated their dimensional accuracies and shear angle. [ABSTRACT FROM AUTHOR]

The results of experimental study of heat transfer and crisis phenomena at pool boiling of liquid nitrogen with different heating conditions on the surface with capillary-porous coating are presented. Porous coatings with different thicknesses (400 and 1390 μm), morphology and high porosity (up to 80%) were obtained using the new plasma spraying technique. It was shown that at steady-state heat release the heat transfer at boiling essentially depends on the thickness and morphology of the coating. The maximum enhancement (∼300%) compared to the smooth heater was detected to coated heater with a thickness of 1390 μm at low heat fluxes. The mechanism of heat transfer enhancement at pool boiling by using the capillary-porous coatings was proposed. Heat transfer hysteresis was detected for the heater with the coating of 400 μm. For the smooth heaters and the heater with 1390 μm coating, the heat transfer coefficients almost coincide with an increase in the heat flux and with its decrease. Data on the effect of coatings with different thicknesses on the critical heat flux (CHF) at boiling under steady-state heat release are presented. It is shown that for the smooth heaters the value of critical heat flux at rapid heating decreases in comparison with steady-state heat release. Capillary-porous coatings have a significant influence on development of the transition process and crisis phenomena at stepwise heat release. There is degeneration of boiling crisis development at rapid heating on the coated surfaces at the heat fluxes below the value of the CHF at steady state heat release. Fast transition to film boiling at stepwise heat release on the coated heaters with different thicknesses is observed at the heat fluxes 2 times higher than the critical heat fluxes, obtained at steady state heating. [ABSTRACT FROM AUTHOR]

Polycrystalline CVD free-standing diamond films have been heat treated through a rapid heating process using a direct current (DC) arc plasma jet system within the temperature range of 1500–2000 °C. The optical transmission of the diamond film decreases when the treatment temperature exceeds 1500 °C. When the diamond film was annealed to 1800 °C for just 1 min, the infrared (IR) transmittance at λ = 10.6 μm of the film was significantly decreased from 60.5% to 4.0%, due to the transformation from diamond to graphite. Further increase of the temperature to 2000 °C leads to complete loss of optical transmittance in only 30 s, due to the detrimental occurrence of graphitization. XRD patterns indicate that graphite ultimately grows preferentially along the (0002) plane by forming disordered or turbostratic graphite as intermediate product. Raman spectra and SEM images verify that at 1500–1850 °C graphitic carbon transforms from the diamond surface in the form of protruding submicron crystallites, which were still containing a number of sp 3 C C bonds. In addition to graphitization on the external surface, the diamond-graphite phase transition also occurs along the grain boundaries and the calculated activation energy of the grain boundary graphitization process is 276 kJ·mol − 1 for the CVD diamond. [ABSTRACT FROM AUTHOR]

A finite element formulation based on a higher-order layerwise theory is presented for the first time to investigate thermally induced vibrations of functionally graded material (FGM) sandwich plates and shell panels. The properties of FGM sandwich are assumed to be position and temperature dependent. The upper and lower layers of the sandwich panel are considered to be made of pure ceramic and metal, respectively and the elastic properties of FGM core are varied according to a power-law function. The top surface is exposed to a thermal shock and the bottom surface of the panel is either kept at a reference temperature or thermally insulated. The one-dimensional transient heat conduction equation is solved using a central difference scheme in conjunction with the Crank-Nicolson method. A higher-order layerwise theory is used for FGM sandwich panels, in which a higher-order displacement field for the FGM core and a first-order displacement field for the facesheets are assumed. The governing equations are solved using Newmark average acceleration method. It is shown that the proposed layerwise finite element formulation is simple and can easily be applied to investigate FGM sandwich plates and shell panels subjected to rapid heating. [ABSTRACT FROM AUTHOR]

The structure and kinetics of the formation of austenite in medium-carbon steel during shortterm heating above the temperature Ac followed by accelerated cooling are analyzed. It has been shown that the abnormal formation of pearlite in steel results from the concentrational and structural inhomogeneity of austenite, as well as the presence of carbide particles in ferrite areas. [ABSTRACT FROM AUTHOR]

A novel method for ultrashort capillary column gas chromatography (GC) analysis is introduced, which employs on-column injection and detection and rapid temperature programming. Using 10-20 cm long capillary columns, results showed that the method provides efficient and very rapid separations for relatively simple mixtures. Moreover, the on-column aspect of the method used here is demonstrated to avoid the extra column analyte degradation that can occur in traditional approaches to such separations. As a result, the developed method allows for the first time the GC analysis of some very large and (or) highly thermally labile analytes, such as polypeptides and drug molecules that are normally prone to decomposition. As an application, this method is further used to monitor pharmaceutical degradant formation as a function of temperature and was found to provide similar results to those obtained from conventional high-performance liquid chromatography analysis. Overall, the findings indicate that this ultrashort GC column approach could be useful in these areas and potentially others, where relatively simple GC analysis and universal flame ionization detection is desirable. [ABSTRACT FROM AUTHOR]

Industrial gasifiers and combustors are assumed to reach particle heating rates of 10 5 –10 6 °C/s and understanding how particles behave in these extreme conditions can improve the utilization of solid fuels in these reactors and in downstream applications. By studying intermediate devolatilization processes during solid fuel pyrolysis, detailed models for solid fuel conversion can be formulated. Key objectives of this study included (1) investigate possible mechanisms that promote the formation of synthesis gas components and char, (2) compare the devolatilization behavior of pyrolysis by varying particle size, hold time, and temperature and (3) correlate char deactivation with hold time. The objectives of the study were accomplished using a wire-mesh reactor with a uniform heating rate of 500 °C/s in nitrogen under atmospheric pressure. A design of experiments approach was used to quantify the effects that hold time, temperature, and particle size had on char yield, evolved gas composition, and apparent activation energy of pine stem wood and wheat straw. Key results indicate that with increased temperature and hold time more volatiles evolve from the fuels and favor carbon monoxide and methane production at higher temperatures. Apparent activation energy of the volatile matter decreases with hold time. An abbreviated model for apparent activation energy correlates well with experimental data and assumes that along a devolatilization pathway, that not all volatiles are driven from the fuel. [ABSTRACT FROM AUTHOR]

In this study, a working coil coupled with magnetic flux concentrators for barrel induction heating in an injection molding machine was investigated. Induction heating process simulations were developed to evaluate the effects of magnetic flux concentrators to the temperature distribution at surface inside a barrel of an injection molding machine. Different pitches of magnetic flux concentrators were applied to study the uniform heating capability of induction heating system with heating coil coupled with magnetic flux concentrators via commercial software, ANSYS. Models of working coils coupled with magnetic flux concentrators were experimented to verify the simulation results. The results from simulation and experiment agreed well. Simulation results showed that, changing diameters of a barrel or varying operation frequency of induction power supply had no effect on uniform temperature distribution at the inside surface of the barrel. [ABSTRACT FROM AUTHOR]

The characteristics of homogeneous boiling in ethanol subjected to rapid heating with a linearly increasing boundary temperature condition have been studied by applying a theoretical model. A finite liquid control volume or cluster at the liquid boundary hasbeen considered in this model where energy is stored due to external heating while some energy is consumed due to bubble nucleation and subsequent growth. A particular state of liquid heating has been defined as the boiling explosion condition when massive scale vaporization causes the liquid sensible energy to decrease. As the size of liquid cluster, two different length scales have been adopted such as, size of a critical vapor embryo ( 2r c ) and thermal penetration depth . For ethanol heating with initial and boundary conditions identical to those reported in the literature, the model predicts the time of the homogeneous boiling explosion with reasonable agreement with the experiments with the liquid cluster size being assumed to be that of a critical vapor embryo ( 2r c ); while the consideration of the thermal penetration depth results in late prediction of the occurrence of boiling explosion. However, the temperature at the boiling explosion essentially corresponds to the same for both sizes of the liquid cluster. The obtained results have been presented and discussed in terms of the average liquid temperature rise inside the liquid cluster, maximum attainable cluster temperature and time to reach the boiling explosion condition for a wide range of boundary heating rates (10-10 9 K/s). [ABSTRACT FROM AUTHOR]

The formation of ZrB 2 through reaction of ZrO 2 with B 4 C without adding carbon has been studied at different temperatures between 1020 °C and 1600 °C. The ratio of ZrO 2 /B 4 C was optimized to produce a single phase ZrB 2 . By introducing Si species into reaction mixture, composite powders of ZrB 2 –SiC, ZrB 2 –SiC–B 4 C are produced. The SiC in composite powder was well distributed in ZrB 2 matrix and the powder was successfully air plasma coated on to CC composite. To scale up the process in a continuous furnace, the reactant mixture of (ZrO 2 +B 4 C+Si) was rapidly heated by suddenly introducing the reactant compact in to an air furnace held at different temperatures between 900 °C and 1700 °C. The extent of reaction after short duration of 3–5 min has been studied. The formation of ZrB 2 and SiC was confirmed through XRD and SEM analyses in samples reacted at and above a temperature of 1300 °C. Though coarsening due to agglomeration was observed with increase in reaction temperature from 1300 °C to 1700 °C, sub-micron sized particles were seen existing even after reaction at 1700 °C. A possible furnace design for continuous operation has been proposed. [ABSTRACT FROM AUTHOR]

Regularities of the formation of physicomechanical properties of the VT16 alloy (Ti-3.33Al-5.18Mo-4.57V, wt %) quenched after furnace and rapid heating have been established using optical microscopy, X-ray diffraction (XRD), and dynamic mechanical analysis. It has been shown that changes in the modulus of elasticity of the VT16 alloy correlate with a decrease in the volume fraction of the α phase in the structure, except for a slight increase in the modulus of elasticity (related to the presence of the ω phase) in the case when quenching temperatures of 800-825°C were used. It has been found that the use of rapid heating to the quenching temperature leads to an increase in the temperature of the alloy transition into the single-phase β state, hampers grain growth during heating for quenching at temperatures close to the polymorphic-transition temperature, and creates conditions for more efficient strengthening in the course of subsequent aging. [ABSTRACT FROM AUTHOR]

Abstract: In this study we investigate the role of gas phase oxygen on ignition of nanothermite reactions. By separately evaluating the temperature at which ten oxidizers release gas phase species, and the temperature of ignition in an aluminum based thermite, we found that ignition occurred prior to, after or simultaneous to the release of gas phase oxygen depending on the oxidizer. For some nanothermites formulations, we indeed saw a correlation of oxygen release and ignition temperatures. However, when combined with in situ high heating stage microscopy indicating reaction in the absence of O2, we conclude that the presence of free molecular oxygen cannot be a prerequisite to initiation for many other nanothermites. This implies that for some systems initiation likely results from direct interfacial contact between fuel and oxidizer, leading to condensed state mobility of reactive species. Initiation of these nanothermite reactions is postulated to occur via reactive sintering, where sintering of the particles can commence at the Tammann temperature which is half the melting temperature of the oxidizers. These results do not imply that gas phase oxygen is unimportant when full combustion commences. [Copyright &y& Elsevier]