Step Heating Research Articles

A cost-effective way of sintering Ce3+:YAG based ceramic phosphors for high power/high brightness phosphor-converted solid state light sources

Transparent or translucent Ce3+:YAG single-phase ceramics and Ce3+:YAG/Al2O3 ceramic composite were prepared by simple sintering in flowing oxygen at atmospheric pressure. The sintered samples presented similar optical transmittance spectra as those sintered in vacuum except the oxygen vacancies related absorption band peaked at 320 nm. SEM morphology of the ceramic plates showed dense microstructures when sintered at about 1700 °C, and the mechanism of densification in oxygen atmosphere was analyzed. In addition, the chromaticity and luminescence spectra of the light source prototypes combining blue LD and the as-prepared ceramics were measured, the effect of the optical transmittance, Ce3+ doping concentration and the secondary phase alumina on the color coordinates and luminous efficacy were also discussed. This process obviates the need for expensive sintering equipment and extra heat treatment steps, which may pave the way for obtaining Ce3+:YAG based ceramic phosphors for practical applications through a cost-effective method.

Novel use of selectivity of resonance Raman spectroscopy to study polytypism and mixed to pure phase conversion in individual InAs NWs on laser irradiation

Conversion of Wurtzite to Zincblende phase of InAs NWs at high simulated temperature (>1300 K) is investigated using resonance Raman spectroscopy with specially designed two step heating–cooling experiment. For smaller nanowires (diameter < 700 nm), the certainty of determining the polytypism using polarized Raman spectroscopy, reduces significantly. Low signal to noise ratio for smaller diameter NWs is improved by employing the wavelength dependent unpolarized and polarized Raman spectroscopy to examine the sensitivity of resonance Raman spectroscopy as an alternate for probing polytypism. Innovative use of resonance Raman spectroscopy to probe phase purity of the III-V individual nanostructures, where, conventional methods may not be applicable is realized in this work.This work paves the way for online monitoring of the conversion of mixed phase to phase pure III-–V nanowires using laser irradiation for their fast electronic device applications. Further, this kind of surface modification study provides basis for the futuristic crystal structure engineering, which can facilitate the controlled tailoring of material properties in order to enhance their functionality.

Influence of three dimensionality effects on thermal hydraulic performance for stepped micro pin fin heat sink

Influence of three dimensionality effects on thermal hydraulic performance for stepped micro pin fin heat sink

Numerical estimation of temperature response with step heating of a multi-layer skin under the generalized boundary condition

In this article, we discussed a one-dimensional bioheat transfer mathematical model that describes the process of temperature distribution in tissue for the multi-layer skin under the step heating generalized boundary condition. The finite difference scheme is used to estimate the temperature profile along with time and distance. We discussed the stability of the numerical scheme and also validated the accuracy of the numerical code by comparing the present results with the previous reference results. To remove heat from the skin is considered by the surface temperature, heat flux, and ambient temperature to be zero with the help of the unit step like function. Then, we observed that the skin temperature in the second kind boundary condition was slowly decreasing over time as compared to the first and third kind boundary conditions. The temperature or heat flux at the skin surface is assumed to be high then there is negligible effect of the blood perfusion rate on the temperature response over a short time period and the effect of blood perfusion rate is visible when the time duration is long. Effect of blood perfusion rate, heating and after removal of heating, water diffusion, and generalized boundary condition for the analysis of the behavior of temperature response in multi-layer skin are discussed in detail and the results obtained are presented graphically.

Utilization of Bayesian Optimization and KWN Modeling for Increased Efficiency of Al-Sc Precipitation Strengthening

The Kampmann and Wagner numerical model was adapted in MATLAB to predict the precipitation and growth of Al3Sc precipitates as a function of starting concentration and heat-treatment steps. This model was then expanded to predict the strengthening in alloys using calculated average precipitate number density, radius, etc. The calibration of this model was achieved with Bayesian optimization, and the model was verified against experimentally gathered hardness data. An analysis of the outputs from this code allowed the development of optimal heat treatments, which were validated experimentally and proven to result in higher final strengths than were previously observed. Bayesian optimization was also used to predict the optimal heat-treatment temperatures in the case of limited heat-treatment times.

Machine Learning-Based Surrogate Model for Press Hardening Process of 22MnB5 Sheet Steel Simulation in Industry 4.0.

The digitalization of manufacturing processes offers great potential in quality control, traceability, and the planning and setup of production. In this regard, process simulation is a well-known technology and a key step in the design of manufacturing processes. However, process simulations are computationally and time-expensive, typically beyond the manufacturing-cycle time, severely limiting their usefulness in real-time process control. Machine Learning-based surrogate models can overcome these drawbacks, and offer the possibility to achieve a soft real-time response, which can be potentially developed into full close-loop manufacturing systems, at a computational cost that can be realistically implemented in an industrial setting. This paper explores the novel concept of using a surrogate model to analyze the case of the press hardening of a steel sheet of 22MnB5. This hot sheet metal forming process involves a crucial heat treatment step, directly related to the final part quality. Given its common use in high-responsibility automobile parts, this process is an interesting candidate for digitalization in order to ensure production quality and traceability. A comparison of different data and model training strategies is presented. Finite element simulations for a transient heat transfer analysis are performed with ABAQUS software and they are used for the training data generation to effectively implement a ML-based surrogate model capable of predicting key process outputs for entire batch productions. The resulting final surrogate predicts the behavior and evolution of the most important temperature variables of the process in a wide range of scenarios, with a mean absolute error around 3 °C, but reducing the time four orders of magnitude with respect to the simulations. Moreover, the methodology presented is not only relevant for manufacturing purposes, but can be a technology enabler for advanced systems, such as digital twins and autonomous process control.

Design of high strength Fe–C–Cu alloys for laser powder bed fusion

Two Co- and Ni-free high strength steel alloys from the Fe–C–Cu system, Fe-0.2C–6Cu wt.% (FeCu) and Fe-0.2C-3.5Cu-0.2Si–1Mo–1Cr-0.2 V wt. % (FeCu+), were designed and evaluated for use in laser powder bed fusion (LPBF) printing for non-stainless automotive applications. A computational materials design approach combined with melt-spinning was employed to design Co- and Ni-free printable compositions. Custom gas atomized powders were acquired and characterized for chemistry, contaminants, defects, and particle size distribution. Parameter development was performed on a Renishaw AM250 to obtain specimens with consolidation greater than 99.8% density. Single step heat treatment studies determined peak hardnesses of 426 VHN for the FeCu alloy and 435 VHN for the FeCu+ alloy. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) revealed the heat-treated microstructure to be lath martensite with 2.6–2.8 nm diameter Cu precipitates, within the same diameter range as previously reported for BCC Cu strengthening in other steels. Tensile tests demonstrated yield strengths of 1208 MPa for the FeCu alloy and 1274 MPa for the FeCu+ alloy. Process-induced porosity and lack-of-fusion defects were observed on the fracture surfaces of the printed tensile specimens. With further parameter optimization, these alloys have the potential to be a low-cost, high-strength steel option for use in metal 3D printing for automotive applications.

Effect of Dimple Arrangement on The Thermal Performance of Dimpled Stepped Plate Heat Sink

Thermal management of electronic devices is the biggest problem in the electronic industry today. Heat sinks are one such devices that are used to cater this need and addition of dimples to these devices are proved to improve the thermal performance further. In the present study, computational analysis is carried out for comparing the stepped fin heat sinks with inline and staggered dimple arrangements having same number of dimples on each fin plate at velocities in the range of 0.5m/s to 4.5 m/s for 9 cases. The results of the computational study are validated by comparing it with the experimental results of previous literature. The outcomes reveal that there is negligible difference in thermal performance of the two heat sinks at lower velocities and this gap widens with increase in velocity. Out of the two-heat sink model, heat sink with inline arranged dimples proved to have better thermal performance at all the velocities considered.

Role of thermally-stable deformation twins on the high-temperature mechanical response of an austenitic stainless steel

In the present study, a two-step thermo-mechanical processing consisting of cold work and heat treatment steps was performed to increase the operating temperature of 316 austenitic stainless steels. A hierarchical microstructure of thermally-stable, nano twin bands was achieved forming into bundles in elongated grains. The mechanical response of the samples with this microstructure was evaluated through uniaxial tension tests at temperatures ranging from 20 °C to 500 °C and compared with those from the fully annealed samples. The results demonstrate that such hierarchical microstructure leads to a significant increase in the elevated temperature yield strengths due to the presence of nano-twin boundaries and resulting decrease in dislocation mean free path and increase in dislocation storage capacity. In fact, the yield strength ratio of the twinned and annealed samples increases with increasing temperature up to 500 °C, indicating the effectiveness of pre-existing thermally-stable twin boundaries as the strengthening source at temperatures as high as 0.46 homologous temperature. The hierarchical microstructure also led to irregular serrations through dynamic strain aging in the stress-strain response at 500 °C, which is attributed to the bi-modal microstructural length-scales present in the structure affecting the diffusion distances during dynamic strain aging. This structure also increases the tensile strength, and without a total loss in ductility, even though the flow stress of the twinned samples surpasses the tensile strength of the annealed samples, especially at elevated temperatures. Total hardening rate is consistently higher in the twinned samples as compared to the annealed samples, indicating the positive role of nano-twin boundaries in the dislocation storage capacity at elevated temperatures. Overall, the present study clearly demonstrate the positive role of thermally stable nano-twins on the elevated temperature mechanical response of austenitic stainless steels.

Characterizing Changes in Grain Growth, Mechanical Properties, and Transformation Properties in Differently Sintered and Annealed Binder-Jet 3D Printed 14M Ni–Mn–Ga Magnetic Shape Memory Alloys

Ni–Mn–Ga Heusler alloys are multifunctional materials that demonstrate macroscopic strain under an externally applied magnetic field through the motion of martensite twin boundaries within the microstructure. This study sought to comprehensively characterize the microstructural, mechanical, thermal, and magnetic properties near the solidus in binder-jet 3D printed 14M Ni50Mn30Ga20. Neutron diffraction data were analyzed to identify the martensite modulation and observe the grain size evolution in samples sintered at temperatures of 1080 °C and 1090 °C. Large clusters of high neutron-count pixels in samples sintered at 1090 °C were identified, suggesting Bragg diffraction of large grains (near doubling in size) compared to 1080 °C sintered samples. The grain size was confirmed through quantitative stereology of polished surfaces for differently sintered and heat-treated samples. Nanoindentation testing revealed a greater resistance to plasticity and a larger elastic modulus in 1090 °C sintered samples (relative density ~95%) compared to the samples sintered at 1080 °C (relative density ~80%). Martensitic transformation temperatures were lower for samples sintered at 1090 °C than 1080 °C, though a further heat treatment step could be added to tailor the transformation temperature. Microstructurally, twin variants ≤10 μm in width were observed and the presence of magnetic anisotropy was confirmed through magnetic force microscopy. This study indicates that a 10 °C sintering temperature difference can largely affect the microstructure and mechanical properties (including elastic modulus and hardness) while still allowing for the presence of magnetic twin variants in the resulting modulated martensite.

Study of step annealing method and the effect on optical, structural, morphological and transport properties of CH3NH3PbI3

Thermal annealing is used as a post-deposition processing method for the formation of solid-state organic-inorganic perovskite film of required phase by removing the remnant solvent in as coated film. In the present work, we have studied temperature, time and the application of giving a temperature step for thermal-annealing process. To provide temperature step heating treatment was given to the spin coated film in two consecutive steps; initially heating at lower temperature followed by at 100 °C for 30 min. We show that initial lower temperature annealing step improves crystallite size by retarding crystalline growth due to slower solvent evaporation and obtain improved absorption, phase, surface coverage and mobility. However, if this lower temperature step is not sufficient to step up the formation of desired phase, the second step of higher temperature annealing is also not able to form perovskite phase. This study is supported by studies like UV–visible absorption spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, SCLC measurements etc.

Effects of Stepped Heating on the Initial Growth of Oxide Scales on NiCrAlHf Bond Coat Alloy under Air and Water Vapor Atmospheres.

Temperature and atmosphere have a significant effect on the oxidation of MCrAlY (M = Ni, Co) bond coating. The initial growth behavior of the NiCrAlHf bond coat alloy was investigated at 1100 °C under different atmospheric conditions and using heating methods. A thick Al2O3 oxide layer and large HfO2 particles were observed, perhaps due to metastable oxide growth at low temperatures when using stepped heating. However, in air and water vapor atmospheres, the oxide scale was thinner and the HfO2 precipitates were smaller in stepped heating than in constant heating. The size and distribution of the HfO2 particles might have induced different microstructures, particularly voids within the oxide scale.

A novel sulfonated aromatic polyimide synthesis and characterization: Energy calculations, QTAIM simulation study of the hydrated structure of one unit

AbstractA new type of sulfonated polyimide was synthesized from a one‐step polycondensation reaction with perylene‐3,4,9,10‐tetracarboxylic dianhydride and 4,4′‐diamino‐2,2′‐stilbenedisulfonic. Pure characterization of sulfonated polyimide (SPI) was performed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, thermogravimetric analysis, differential thermal gravimetric analysis, ultraviolet–visible spectroscopy, and solubility tests. Moreover, the SPI film was prepared by a thermal imidization step heating procedure. Furthermore, quantum chemical calculations of the synthesized SPI were investigated with density functional theory (DFT) and time‐dependent density functional theory. By calculating the frontiers molecular orbital energies of the obtained polyimide, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and the energy gap (Δ) values were found for the one structural unit and three structural units of SPI, respectively. Also, QTAIM was carried out based on the AIMAll program. With the increase in water molecules, the average electronic energy density (HBCP) value decreased according to the results of QTAIM. The SPI can be used as a potential membrane in fuel cells.

Effects of Magnetic Abrasive Finishing on Microstructure and Mechanical Properties of Inconel 718 Processed by Laser Powder Bed Fusion

Surface finishing is challenging in the context of additively manufactured components with complex geometries. Magnetic abrasive finishing (MAF) is a promising surface finishing technology that can refine the surface quality of components with complex shapes produced by additive manufacturing. However, there is insufficient study regarding the impact of MAF on microstructure–property relationships for additively manufactured builds, which is critical for evaluating mechanical performance. In this work, we studied the effects of different combinations of MAF and heat treatment steps on the microstructure–property relationships of Inconel 718 superalloys made by laser powder bed fusion (LPBF). The application of MAF was found to significantly reduce the surface roughness and refine the grain size of aged alloys. Moreover, MAF was able to increase the alloy elongation, which could be further influenced by the sequence of MAF and different heat treatment steps. The highest elongation could be achieved when MAF was performed between homogenization and aging processes. This work indicates that an effective combination of surface finishing and heat treatment is critical for the improvement of alloy performance. Furthermore, it demonstrates a promising solution for improving the performance of LPBF Inconel 718 by integrating MAF and heat treatment, which provides new perspectives on the post-processing optimization of additively manufactured alloys.

Influence of six-step heat treatment on microstructures and mechanical properties of 5160 alloy steel

AISI 5160 alloy steel grade with complete martensite structure to get the high-strength steel sheets quenched at 900 (Q1), 870 (Q2), 840 (Q3) and 810°C (Q4), respectively and temped at 780°C (Q5) and 680°C (Q6), respectively. The results show ferrite and pearlite microstructural appeared in as-sheet conditions. The strengthening rarely increased with increasing heat treatment steps, while the percentage elongation gradually decreased. The hardness change was secure with that of strengthening for the quenched martensite. In contrast, differences between the initial martensite hardness were no noticeable changes. The Q4 hardening involved the peak hardness and maximum ultimate tensile strength due to carbide distribution in the martensite matrix. The coarse ferrite grains have occurred after Q5 cause significantly reduced hardness and tensile strength. However, the percentage elongation increased with increasing quenching step to Q5 hardening. The excellent 5160 steel performed by Q6 hardening characteristic gained most hardness, ultimate tensile strength, and elongation approximately 60 HRC, 835 MPa, and 12.09%, respectively. Martensite structure transformed to among carbide distribution tempered martensite matrix.

Fatigue and corrosion resistance of low modulus Ti-35Nb-7Zr-5Ta-0.35O beta Ti alloy for orthopedic implant applications

This study has examined the influence of heat treatment on the fatigue response and electrochemical behavior of low modulus beta Ti alloy Ti-35Nb-7Zr-5Ta-0.35O. The heat treatment step comprised of a sub-transus solution treatment (750 °C-8h) followed by aging (300–500 °C). Fatigue studies have shown that low temperature aging at 300 °C-8h and 350 °C-16h exhibited a comparatively improved fatigue resistance. Highest cyclic fatigue strength was obtained after aging at 350 °C-16h, a fatigue strength of 460 MPa for a cyclic life of 1 × 106 cycles, this being attributed to the presence of fine nanoscale omega precipitates. Inferior fatigue performance was observed after high temperature aging (450 °C-32h and 500 °C-8h). Corrosion studies indicated improved electrochemical behavior after aging at 350 °C-16h, reduced corrosion resistance being observed after high temperature aging (500 °C-8h).

Valorization of rubberwood waste into porous carbon

Rubberwood is one of the main Thailand goods exports. In each year, about 45,000 hectares of rubber tree are cut down, only about 30% of them is appropriated for furniture production while most of the rest is used as woodfuel. This research work focuses on the valorization of rubberwood waste into porous carbon and the optimization of carbonization process for the production of hierarchical porous carbon. Rubberwood wastes obtained from a rubberwood processing industry (in Thailand’s southern region) were treated with H3PO4 and subjected to two different carbonization methods. In the first method, the rubberwood was carbonized at 500°C for 1 h (PC-1step). The second method consisted of two steps of heat treatment, the rubberwood was pre-carbonized at 200°C for 15 min and subsequently carbonized at 500°C for 45 min (PC-2step). The physical properties of the porous carbon were investigated using thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and N2 adsorption-desorption isotherm techniques. The porous carbons obtained from both carbonization methods have hierarchical porous structures comprising the naturally existing tubular macropores (diameter 4-20 μm) and the micropores (diameter 0.3-1 nm) generated during carbonization process. The PC-2step provides a specific surface area of 336.2 m2 g-1 and a pore volume of 0.093 cm3 g-1, which are almost twice those of the PC-1step. It is possible that the pre-carbonization at 200°C would allow a slow and gradual evaporation of moisture within the wood, thus preserving pore walls in the materials. The obtained hierarchical porous carbons can be used in many applications such as energy storage, waste water treatment, air purification and metal recovery.

Thermodynamic re-modelling of the Cu–Nb–Sn system: Integrating the nausite phase

Currently available Cu–Nb–Sn phase diagrams lack the recently discovered nausite phase (Cu,Nb)Sn2, which is an important intermediate in the course of thermal processing of superconducting Nb3Sn wires. Processing decisively determines the resulting microstructure of Nb3Sn and, thus, its superconducting properties. Lack of suitable and complete phase diagrams, however, obstructs rational design of such thermal processing procedures. To close this gap and to obtain valid knowledge of homogeneity and stability range of nausite, various Cu–Nb–Sn samples, which are heat-treated between 300 °C and 500 °C, are investigated. By means of energy-dispersive X-ray spectroscopy (EDX), a temperature-dependent homogeneity range of nausite is observed, which covers average mole fractions of Cu between 0.09 and 0.15. This is correlated with a change in the mean atomic volume and can be seen in the lattice parameters determined by X-ray diffraction (XRD). Additionally performed first-principles calculations on different CuSn2 and NbSn2 model structures confirm this trend. Furthermore, the peritectic decomposition of nausite to NbSn2 and liquid at 586 °C is determined by means of in situ XRD and differential scanning calorimetry (DSC). By using the CALPHAD (CALculation of PHase Diagrams) approach, all these findings are used to extend a previous thermodynamic description of the Cu–Nb–Sn system by including the nausite as an additional phase. With this noteworthy integration, the updated modelling of the Cu–Nb–Sn system can be used for optimizing the multistage heat-treatment steps during processing superconducting Nb3Sn wires.

Dating of granite-related tin mineralisation at Quy Hop, Vietnam: Constraints from zircon and cassiterite U–Pb and muscovite 40Ar/39Ar geochronology

Quy Hop is an important tin mining district in the North Central Coast province of Vietnam. The exposed magmatic plutons include Late Oligocene – Early Miocene granitoid and Middle Triassic granitic gneiss. Tin mineralisation in the area is spatially associated with biotite granite of the Ban Chieng Complex. Quartz vein-type and greisen-type tin ores occur in quartz-sericite-graphite schist of the Ordovician-Silurian Song Ca Formation and the greisenised granite of the Late Oligocene Ban Chieng Complex, respectively. The lack of accurate geochronological dates for the tin deposits and spatially associated granitic rocks limits our understanding of the genetic relationship between tin mineralisation and granitoid intrusions. In this study, granitic zircon and cassiterite laser ablation and inductively coupled plasma mass spectrometry U–Pb and muscovite 40Ar/39Ar dating techniques were applied to address this lack of understanding. Granitic zircon U–Pb dating of two biotite granite samples obtained from Ban Chieng yielded intersection ages of 26.65 ± 0.33 and 23.89 ± 0.15 Ma, interpreted here as representative igneous emplacement ages. Cassiterite U–Pb analyses yielded 207Pb/206Pb–238U/206Pb intersection ages of 26.81 ± 1.92 Ma for the quartz vein ore from Suoi Bac and 23.23 ± 0.89 Ma for greisen ore from Ban Ngoc. Muscovite 40Ar/39Ar laser step heating of the greisen ore yielded a plateau age of 23.87 ± 0.14 Ma and a corresponding inverse isochron age of 23.85 ± 0.16 Ma. These geochronological results strongly suggest that tin mineralisation at Quy Hop occurred in the period between 26 and 23 Ma and, therefore, is closely genetically related to the Late Palaeogene granites of the Ban Chieng Complex. The exploration implication of the new age data is considerable, indicating that biotite granite intrusions may be favourable for tin mineralisation across the entire Phu Hoat Terrane.

Performance analysis on parallel condensing air-source heat pump water heater system

Based on the technology of heat pumps, a parallel condensing air-source heat pumps water heater systems providing domestic hot water is proposed to improve the energy efficiency of common ASHPWH system. Considering the climate in southern China, two operating modes of system are designed to adapt to the different water temperature conditions. the simulation model was built to analyzed the factors affecting system performance. Taking Changsha, China as an example, the COP and the energy consumption of system in each month are analyzed. We can find that the parallel condensing air-sources heat pumps water heater system can effectively disperse the total heating quantity by steps heating; the average COP in summer mode increases from 5.42 to 6.44, approaching 19.00%; the average COP in winter mode increases from 4.05 to 5.45, approaching 34.68%. The system has excellent energy-saving effect especially in winter.