Optimum Heat Treatment Conditions Research Articles

Effect of heat treatment on microstructure and mechanical properties of 18Ni-350 maraging steel fabricated by Wire and Arc Additive Manufacturing

An 18Ni-350 maraging steel single wall structure was fabricated using Wire Arc Additive Manufacturing (WAAM). Due to the rapid cooling and cyclic heating, elements such as Ni, Ti, and Mo were segregated within the single wall, resulting in a microstructure characterized by coarse primary dendrites and secondary dendrites. Various heat treatment were devised for the samples, encompassing Solution Treatment (ST), Solution + Aging Treatment (SAT), and Direct Aging Treatment (DAT). The findings revealed that elemental segregation persisted when the ST temperature was below 1050 °C, but disappeared when it exceeded 1150 °C, withthe microstructure transitioning from dendritic to equiaxed grains. ST resulted in the decrease of microhardness and tensile strength, but an enhancement in elongation. The effect of DAT was unsatisfactory for the improvement of mechanical properties while SAT could significantly improve them. Transmission Electron Microscope (TEM) analysis showed that a uniform distribution of Ni3Ti and Ni3Mo strengthening phases was formed in the martensitic matrix after SAT. The ultimate tensile strength of the sample reached 2163 ± 42MPa under the optimal heat treatment condition (SAT 1150 °C-1 h + 480 °C-6 h).

Effects of heat treatment on microstructure and mechanical properties of 17-4PH/IN625 bimetallic parts fabricated through extrusion-based sintering-assisted additive manufacturing

The mechanical properties of bimetallic composites are significantly influenced by their interfacial morphologies. This study delves into the impact of various heat treatment conditions on the microstructure and mechanical attributes of steel/nickel bimetallic (17-4PH/IN625) components produced through extrusion-based sintering-assisted additive manufacturing (ES-AM). The bimetallic composites were annealed at 1150°C for 1, 4, and 8 h, followed by an aging treatment at 482°C for samples annealed for 8 h. After annealing, microstructural heterogeneities, including variations in grain size and elemental distribution within the transition zone close to the interface, were observed. It was found that in the diffusion transition zone between the two alloy layers, the diffusion of iron (Fe) and nickel (Ni) elements increased with longer holding times, as corroborated by microhardness tests and quantified through theoretical parabolic diffusion law. The transition zone exhibited two distinct areas: an Fe-predominant zone and a Ni-predominant zone, with the latter containing oxides and molybdenum (Mo)- and niobium (Nb)-rich precipitates. No new phases emerged post-heat treatment; however, shifts in peak due to stress relaxation and the emergence of precipitates were identified through X-ray diffraction (XRD) observations. Microhardness within the transition zone increased following heat treatment, peaking at 186 HV1.0 after a 4-h annealing. The optimal heat treatment condition was identified as 1150°C for 4 h, which facilitated the development of uniform microstructures and improved bonding strength. This study demonstrates an enhanced interfacial bonding strength in 17-4PH and IN625 bimetallic parts manufactured through ES-AM, suggesting their wide-ranging potential applications in industry.

Effect of Pre-Weld Heat Treatment on the Microstructure and Properties of Coarse-Grained Heat-Affected Zone of a Wind Power Steel after Simulated Welding

The effect of pre-weld heat treatment on the microstructure and low-temperature impact toughness of the coarse-grained heat-affected zone (CGHAZ) after simulated welding was systematically investigated through the utilization of scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). The Charpy impact test validated the presence of an optimal pre-weld heat treatment condition, resulting in the highest impact toughness observed in the CGHAZ. Three temperatures for pre-weld heat treatment (690, 720 and 750 °C) were used to obtain three different matrices (Steel 1, Steel 2, Steel 3) for simulated welding. The optimal pre-weld heat treatment is 720 °C for 15 min followed by water quench. Microstructure characterization showed that there is an evident microstructure comprising bainite (B) in Steel 1 and Steel 2 after pre-weld heat treatment, while the addition of martensite (M) with the pre-weld heat treatment temperature exceeds Ac1 by almost 60 °C (Steel 3). These differences in microstructures obtained from pre-weld heat treatment influence the refinement of high-temperature austenite during subsequent simulated welding reheating processes, resulting in distinct microstructural characteristics in the CGHAZ. After the optimal pre-weld heat treatment, Steel 2 subjected to single-pass welding thermal simulation demonstrates a refined microstructure characterized by a high density of high-angle grain boundaries (HAGBs) within the CGHAZ, particularly evident in block boundaries. These boundaries effectively prevent the propagation of brittle cracks, thereby enhancing the impact toughness.

Synthesis and upconversion luminescence properties of Ho3+-Yb3+ co-doped glass ceramics containing LiGd(WO4)2

Ho3+-Yb3+ co-doped glass ceramics containing LiGd(WO4)2 were prepared by melt crystallization method. By using the methods of differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmittance, and scanning electron microscopy (SEM), the optimal heat treatment condition for the samples was identified to be 580 °C/140 min. In these conditions, the transmittance of glass ceramic is about 75 % in the 380–780 nm range. In the upconversion emission spectra, strong green emission (543 nm) and red emission (650 nm) due to 5F4/5S2, 5F5→5I8 transitions are observed at 980 nm excitation. Additionally, the optimum doping concentrations of Ho3+ and Yb3+ were 0.12 % and 0.4 %. The crystal field changes around dopant ions were analyzed using J-O theory and Eu3+ probe to explain the up-conversion luminescence enhancement of glass ceramics containing LiGd(WO4)2. The chrominance coordinates of 0.12 % Ho3+-0.4 % Yb3+ co-doped glass ceramics are located in the green light region, and the color purity is 95.6 %. In summary, Ho3+-Yb3+ co-doped transparent glass ceramics containing LiGd(WO4)2 have potential applications in infrared detection and green solid-state lasers.

Investigating the wear resistance of high-chromium cast irons A532-class III-type A against high-energy abrasive particles

Regarding the widespread use of high chromium cast irons in manufacturing various industrial and mineral-processing parts such as liners, slurry pumps, and grinding balls, increasing erosion resistance is the key factor to enhance their performance. This research investigated three different chemical compositions of high chromium irons (in the eutectic and hypoeutectic range). Austenite destabilization process was conducted at two temperatures of 1060°C and 970°C followed by air cooling and then tempering at the range of 250°C to 400°C for 4 h. Erosion and bending tests were carried out on samples with optimal heat treatment conditions. Results show that the hardness of specimens heat-treated at 970°C, and also the low-carbon hypoeutectic specimens destabilized at 1060°C, increased by increasing tempering temperature over 300°C, which can be related to the formation of a higher volume fraction of M23C6 carbides. The best erosion resistance was observed in the low-carbon hypoeutectic specimen destabilized at 1060°C and tempered at 300°C. In addition, samples with higher erosion resistance exhibit lower bending strength. Finally, it was found that the principal wear mechanism was the occurrence of plastic deformation, and detachment of carbides from the surface before having an effective role in reducing wear.

Luminescence properties and thermal stability of Dy2O3/Sm2O3 doped glass ceramics containing NaBi(WO4)2

Dy2O3–Sm2O3 co-doped transparent glass ceramics (GCs) containing NaBi(WO4)2 crystalline phase were prepared by melt-curing-crystallization method. The optimal heat treatment condition is 580 °C/2 h. The optimum incorporation concentration of Dy2O3 is 0.4%, exceeding which a quenching phenomenon dominated by quadrupole-quadrupole interactions emerges. Meanwhile, when the concentration of Dy2O3 was fixed, the chromaticity coordinate of the sample moved the cool white light region to the warm white light region as the concentration of Sm2O3 increased. The temperature-dependent emission spectra of the 0.4% Dy2O3-0.7% Sm2O3 co-doped GC samples show that emission intensity at 575 nm at 185 °C still reaches 80% of the room temperature. The thermal quenching activation energy was 0.1537 eV and the activation energy after the addition of Mo6+ was 0.1957 eV. This study indicates that Dy2O3–Sm2O3 co-doped GCs containing NaBi(WO4)2 crystalline phase can achieve light-color tunable emission, which is potentially valuable for solid-state color rendering and illumination applications.

Preparation, luminescence and thermal stability of Tb3+/Eu3+ doped glass ceramics containing KAlSiO4 crystalline phase

The melt-crystallisation process was used to successfully synthesised Tb3+/Eu3+ doped glass ceramics with KAlSiO4 crystalline phase. The optimum heat treatment condition was determined to be 560 °C/90 min by DSC, XRD, SEM and optical transmittance curves, under which the optical transmittance of the glass ceramic in the visible region can reach 80%. Fluorescence spectroscopy was used to determine the energy transfer between Tb3+ and Eu3+, and it was discovered that the energy transfer mechanism was brought on by dipole-dipole interactions. The chromaticity coordinates of the 0.9%Eu3+-0.9%Tb3+ doped sample are (0.3627, 0.3389), it is close to the color of white light. According to variable temperature spectroscopy analysis, emission intensity of Eu3+/Tb3+ co-doped glass ceramics at 458 K can be maintained at 97% and 70% of room temperature at 543 and 614 nm, respectively, demonstrating that the sample has good thermal stability. The results of this study demonstrate the potential of Eu3+/Tb3+ co-doped glass ceramics with KAlSiO4 crystalline phase for use in white light emitting diodes, solid state colour development and other fields.

Preparation and luminescence properties of Tb3+-Sm3+ co-doped K3Gd(PO4)2 crystalline glass ceramics

In this paper, Tb3+-Sm3+ co-doped glass ceramics with K3Gd(PO4)2 crystal phase were successfully prepared by methods of melting curing crystallization. The optimal heat treatment conditions for the samples were determined to be held for 1.5 h at 750 °C by combining differential scanning calorimeter (DSC), x-ray diffraction (XRD) and scanning electron microscope (SEM). Under this condition, glass ceramics still have a high transmittance in the range of 400∼700 nm, up to 80 %. It was calculated that the optical band gap value of glass ceramic is smaller than that of glass, indicating that the sample structure was changed by heat treatment. Fluorescence lifetime and Dexter's theory demonstrate that Tb3+ transfers energy to Sm3+. By fixing the concentration of Tb3+ and changing the doping concentration of Sm3+, the luminous color of glass ceramics can be adjusted. At 458 K, the fluorescence intensity of Tb3+ and Sm3+ decreased to 89 % and 85 % of that at 298 K. Study shows that the prepared glass ceramics have potential applications in white light emitting diodes (WLEDs).

Influence of multilayer nanoarchitecture on phase transformations in the Ti-Cr-Zr system

Nanocrystalline thin films find extensive applications due to their high mechanical strength and wear resistance. However, the challenge is to prevent unwanted grain growth during operation, especially at high temperatures, due to the increased grain boundary volume, which elevates the system's overall energy. Addressing this issue necessitates identifying optimal heat treatment conditions and selecting appropriate chemistry to stabilize grain boundaries. This study investigates the grain growth and phase evolution within Ti-Cr-Zr magnetron sputtered nano multilayers with 5 and 10 nm individual layer thickness, subjected to vacuum heat treatment at 1100 °C for 5 and 10 min. Characterization involved X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). During deposition, evidence of diffusion was observed as the multilayers formed Cr4TiZr, TiCr2, and Cr2Zr, phases. The Ti-Cr-Zr nanoscale system multilayers with 10 nm individual layer thickness also exhibited the emergence of Ti0.3Zr0.7 phase. During heat treatment grain growth occurred, after 10 min an average grain size of 173.7 nm and 119.1 nm was noted for the Ti-Cr-Zr nanoscale system multilayer with 5 nm and 10 nm individual layer thickness, respectively. The different growth rates are attributed to their distinct interfacial volumes, influencing the reaction velocity due to the variations in nano-layer thickness. No new phases were formed after heat treatment for the case of 10 nm individual layer thickness coating. However, 5 nm individual layer coatings showed the emergence of Ti0.3Zr0.7 phase, not present after deposition. In conclusion, this research achieved the desired nano grain stabilization of the Ti-Cr-Zr system nanoscale multilayers after heat treatment at 1100 °C for 10 min. This process led to the complete decomposition of the multilayer structure, resulting in the formation of grains smaller than 200 nm, marking a significant step toward the effective control of grain growth in nanocrystalline materials.

Interfacial Chemical Stability of Doped Li7-XLa3Zr2 -X(Nb/TaX)O12 with LiCoO2 Electrode Material

Garnet-type oxide solid state electrolytes (SEs) are promising candidates due to their potential high ionic conductivity and chemical stability with Li for the replacement of flammable liquid electrolytes used in the current Li-ion batteries. Intense research has been focused on optimising the interface of garnets with Li, with the positive side to be somehow neglected. A significant issue of oxide SEs, hurdling their industrial application, is their poor contact with positive materials due to their rigidity. Poor interfacial contact leads to the need of co-sintering at high temperatures (> 400 °C), which enables side reactions and unwanted processes like cation intermixing, diffusion of elements and formation of non-conductive secondary mixed phases.In this work the chemical stability of Ta and Nb doped LLZO garnet SE was tested in contact with LiCoO2, a common positive material used in the battery industry. Initially, mixed powders of SE and active material were heat treated and studied using Raman spectroscopy and scanning electron microscopy to observe side reactions. In order to improve contact between the two materials, instead of already synthesized crystalline powder, nitrate precursors were also used for in-situ synthesis of LiCoO2 material in contact with the garnet. Mixtures of the SE powder and nitrate precursors for LiCoO2 were also heat-treated at various temperatures for different time periods in different gas atmospheres. The heat-treated materials were then analysed extensively using scanning electron microscopy coupled with energy dispersive X-Ray element mapping and with Raman microscopy to prove the existence or absence of secondary mixed phases at given conditions. Additionally, the optimized heat-treatment conditions were adapted for layered garnet SE/LiCoO2 samples to study the actual electrolyte/electrode interface at the same conditions used for powder mixtures. Based on the results the symmetrical LiCoO2/garnet SE/LiCoO2 cells will be prepared and tested electrochemically.

Effects of heat treatment on microstructure and mechanical properties of squeeze casting AlSi9Mg alloy flywheel housings formed with local supplementary pressure

Targeted squeeze casting components of the thick-walled locations with local supplementary pressure (LSP) can effectively realize the local forced shrinkage, which is very significant for the elimination of shrinkage defects. In this paper, the effects of solid solution temperature, solid solution time, aging temperature and aging time on AlSi9Mg aluminum alloy flywheel housing with large wall thickness difference and complex structure formed with LSP were investigated. The results showed that the LSP effectively refined the microstructure and accelerated the spheroidization process of eutectic silicon, which reduced the heat treatment holding time significantly. The twinning growth of silicon particles effectively hindered the dislocation motion, relieved the stress concentration, and improved the strength. The fishbone-like AlSiMnFe phase were passivated after heat treatment. Heat treatment can enhance the plasticity by breaking and spheroidizing the coarse needle-like eutectic silicon, and enhance the strength by refining and homogenizing the β" phase precipitated in the alloy. The optimum heat treatment parameters are solid solution at 540 °C for 210 min and aging at 175 °C for 480 min. Under the optimum heat treatment condition, the ultimate tensile strength, yield strength and elongation for the position with LSP reached 306.1 MPa, 237.5 MPa, 13.29 %.

Pr3+-Er3+ co-doped Ba3.75Gd0.833Nb10O30 glass-ceramics for tunable luminescence, optical anti-counterfeiting and temperature sensing

Pr3+-Er3+ co-activated glass-ceramics containing Ba3.75Gd0.833Nb10O30 crystalline phase were prepared as a multifunctional material. The optimum heat treatment condition was determined to be 750 °C/90 min, as this condition is most favorable for luminescence. As the Pr3+ concentration increases, the emissions of 3P0 and 1D2 energy levels show different trends, leading to a shift in luminescence from orange to yellow. With the introduction of Er3+, the co-doped sample achieves orange-yellow-green tunable luminescence. The 0.3%Pr3+-0.3%Er3+ co-doped sample exhibits alternating yellow-orange-green luminescence during continuous excitation in the range of 250–500 nm, which has potential applications in optical anti-counterfeiting. In the temperature interval of 298–458 K, the maximum temperature sensitivities based on the NTCLs of Pr3+ and Er3+ were 0.82 × 10−2 K−1 (Sa) and 1.40 % K−1 (Sr). Meanwhile, the thermal repeatability ratio is higher than 92.3 %, which proved that it is a potential temperature sensing material. In addition, the concentration quenching, energy transfer and luminescence phenomena involved were analyzed in depth and their mechanisms were explained.

Thermally stable Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal with tunable luminescence

By using the melt crystallization process, Dy2O3/Sm2O3 co-doped glass ceramics (GCs) containing La2Sn2O7(LSO) crystal were successfully prepared. By using X-ray diffraction (XRD), the sample's phase was determined, and scanning electron microscopy (SEM), the sample's morphology was examined. The optimal heat treatment condition of glass ceramics was determined to be 650 °C/1.5 h. Under 362 nm excitation, the energy transfer of Dy3+→Sm3+ was observed in Dy2O3/Sm2O3 co-doped glass ceramic samples from the emission spectrum. Electric dipole-electric dipole interaction is identified as the mechanism of energy transfer from Dy3+ to Sm3+ according to the Dexter formula for energy transfer. The emission spectra of 0.5%Dy2O3-0.4%Sm2O3 co-doped glass ceramic samples in a range from 298 K to 458 K show that the samples have high thermal stability, and the thermal quenching activation energy at 575 nm has been estimated to be 0.265 eV. According to chromaticity coordinates and correlated color temperature, warm white light emission may be achieved by co-doping Dy2O3/Sm2O3 glass ceramics. The findings demonstrate Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal have a potential application prospect in warm white light-emitting diodes (w-LEDs).

Thermal stability of microstructure and corresponding hardness variations in two high-carbon nanostructured bainitic steels

The autotempering phenomenon and carbon partitioning from bainitic subunits during the bainite transformation suggest that the tempering behavior of the nanostructured bainite may be different compared to that of martensite. This article aims to investigate the thermal stability of the microstructure in two low alloy nanostructured bainitic steels containing 0.89 wt% carbon content. Nanostructured bainite was obtained after austempering at 250 °C for optimum heat treatment time. Nanostructured bainitic steels were tempered at the temperature range of 300–700 °C for 30 min. Additionally, the effect of prolonged austempering beyond the optimum heat treatment condition at austempering temperature was studied. Microstructural characteristics were evaluated using optical and field emission gun scanning electron microscopes and X-ray diffraction methods. Hardness variations during tempering of nanostructured bainite compared with that of martensite microstructure obtained in the same primary steels after austenitizing and quenching. Results indicated that microstructural characteristics of nanostructure bainite didn’t change significantly at heat treatment times longer than that needed for bainite transformation completion at isothermal bainite heat treatment temperature. Moreover, results approved the higher tempering resistance of nanostructured bainite compared to that of martensite in the same steel. It has been shown that tempering the nanostructured bainite up to 400 °C didn’t change the microstructure and hardness, while the changes were pronounced at higher tempering temperatures. It has been suggested that cementite precipitation was more significant when a higher number of dislocations were present in nanostructured bainite before starting the tempering process.

Fused-Deposition Modeling 3D Printing of Short-Cut Carbon-Fiber-Reinforced PA6 Composites for Strengthening, Toughening, and Light Weighting.

Additive manufacturing of carbon-fiber-reinforced polymer (CFRP) has been widely used in many fields. However, issues such as inconsistent fiber orientation distribution and void formation during the layer stacking process have hindered the further optimization of the composite material's performance. This study aimed to address these challenges by conducting a comprehensive investigation into the influence of carbon fiber content and printing parameters on the micro-morphology, thermal properties, and mechanical properties of PA6-CF composites. Additionally, a heat treatment process was proposed to enhance the interlayer bonding and tensile properties of the printed composites in the printing direction. The experimental results demonstrate that the PA6-CF25 composite achieved the highest tensile strength of 163 MPa under optimal heat treatment conditions: 120 °C for 7.5 h. This corresponds to a significant tensile strength enhancement of 406% compared to the unreinforced composites, which represents the highest reported improvement in the current field of CFRP-fused deposition 3D printing. Additionally, we have innovatively developed a single-layer monofilament CF-OD model to quantitatively analyze the influence of fiber orientation distribution on the properties of the composite material. Under specific heat treatment conditions, the sample exhibits an average orientation angle μ of 0.43 and an orientation angle variance of 8.02. The peak frequency of fiber orientation closely aligns with 0°, which corresponds to the printing direction. Finally, the study explored the lightweight applications of the composite material, showcasing the impressive specific energy absorption (SEA) value of 17,800 J/kg when implementing 3D-printed PA6-CF composites as fillers in automobile crash boxes.

Dilatometric study of high silicon bainitic steels: Solid-state transformations

High silicon bainitic steels have gained significant recognition in various applications due to their exceptional properties, such as high strength, favourable corrosion resistance, and excellent high-temperature stability. This study investigates an alloy capable of generating a finer bainitic structure through a transformation at 260 °C, leading to the desired microstructure. Interestingly, other phenomena were discovered while pursuing optimal heat treatment conditions. At temperatures exceeding 850 °C, the alloy exhibits a tendency for graphite formation, which has intriguing implications for its mechanical properties. The high silicon concentration in the alloy significantly retards cementite growth, resulting in a microstructure composed solely of bainitic ferrite and residual austenite through the transformation of austenite below the bainite start temperature. Furthermore, it is observed that pearlite formed during rapid transformation at 650 °C does not exhibit the predicted equilibrium chemical composition. This discrepancy challenges the existing models of pearlite growth, which assume local equilibrium at the shared interface with austenite. This research aims to investigate the influence of silicon content on solid-state transformations in high-silicon steels using dilatometry, optical microscopy, scanning electron microscopy, and X–ray diffraction techniques. These analytical methods will provide insights into the intricate processes occurring during isothermal transformation temperatures, contributing to a deeper understanding of the material's behaviour and its potential applications.

Up-conversion color tunable and red luminescence of Ho3+/Yb3+ co-doped glass ceramics containing NaLaSiO4 crystals

By using the melt-annealing method, silicate precursor glasses were prepared. Optimal heat treatment conditions for glass ceramics at 610 °C for 90 min were established through a series of tests. Glass ceramics containing NaLaSiO4 crystals with β-K2SO4 structure were successfully synthesized after heat treatment. XRD patterns of glass ceramics were successfully fitted using Rietveld refinement, with rare earth ions entering the lattice by replacing sites of La resulting in a reduction in cell volume. A tunable emission from green light to red light was achieved by varying the Yb3+ doping concentration. By varying the concentration of Ho3+, the intensity of the up-conversion emission was significantly increased while maintaining high color purity in red light. The optimal concentration of Ho3+ was 0.4%, when the red light color purity was 98.9%. These results indicate that glass ceramics containing NaLaSiO4 crystals co-doped with Ho3+-Yb3+ could be used for up-conversion color-tunable emission and red luminescence.

Antimicrobial Properties of AgNP/TEMPO-Oxidized Cellulose Nanofiber/Chitosan Composite Fibers

This study successfully synthesized functionalized silver nanoparticle/TEMPO-oxidized cellulose nanofiber/chitosan (AgNP/TOCN/CS) composite fibers. First, the TOCN/CS composite fibers were prepared through the wet-spinning technique, yielding Ag/TOCN/CS composite fibers after immersion in a 5 mM AgNO3 aqueous solution for 3 h, followed by washing with 100 mL of deionized water five times. Second, upon heat treatment without adding other reducing agents, TOCN reduced the Ag+ in the Ag/TOCN/CS composite fibers to AgNP/TOCN/CS composite fibers on the surface of the CS fibers. The fiber color changed from white to yellow-orange when the temperature changed from 100 to 170 °C. In addition, the results suggest that the heat treatment at 130 °C for 20 min was the optimal heat treatment condition. Meanwhile, soaking the fibers in 50 mM ascorbic acid for 1 min is the best condition for ascorbic acid reduction. The antibacterial test results showed that the AgNP/TOCN/CS composite fibers formed via ascorbic acid reduction exhibited better antibacterial activity against both Escherichia coli and Bacillus subtilis than those produced via heat treatment. In summary, AgNPs formed on the fiber surface of AgNP/TOCN/CS composite fibers and showed antibacterial activity, confirming the successful addition of antibacterial properties to TOCN/CS composite fibers.

Preparation, optical, and thermal stability of Tb3+‐doped glass ceramics containing Al4Ti2SiO12

AbstractThe Tb3+‐doped transparent glass ceramics containing Al4Ti2SiO12 crystal are synthesized by the melt‐solid‐crystallization method. The optimal heat treatment conditions for the glass ceramic samples are determined to be 750°C, 1.5 h based on differential scanning calorimeter, X‐ray diffractometer, scanning electron microscope, and light transmittance curve. The luminescence properties of the glass ceramics samples are characterized by a fluorescence spectrometer. The emission spectrum revealed that the dominant emission is green attributed to Tb3+, the optimal doping concentration is 0.3%. And the thermal quenching activation energy of 0.3% Tb3+‐doped glass ceramics is 0.2554 eV, while the relative sensitivity is 1.50% K−1 at 298 K and the absolute sensitivity is 2.27×10−2 K−1 at 418 K through variable temperature fluorescence spectroscopy test and a series of calculations. These findings demonstrate the excellent stability and temperature sensitivity of glass ceramics, thereby highlighting their potential for use in green lighting and temperature sensing applications.

A study on demagnetization heat treatment of waste neodymium iron boron (NdFeB) magnets by using computer simulation

In this study, demagnetization heat treatment at 100 ∼400 °C is studied by using computer simulation to secure the optimal demagnetization heat treatment conditions for waste neodymium iron boron (NdFeB) permanent magnets. From the computer simulation, the temperature of the magnet during heat treatment is higher than the set temperature by up to 6 °C. Delay time occurs when the furnace internal temperature and magnet temperature reached the set temperature. A delay time of 15 minutes in an air atmosphere and 10 minutes in a nitrogen atmosphere occurs. The Nd magnet was completely demagnetized at 300 °C as the magnetic flux decreased when the heat treatment temperature increased up to 250 °C. The fully demagnetized magnet could be magnetized to the level of a new magnet. It was confirmed that NdFeB magnets heat treated up to 350 °C in a nitrogen atmosphere can be reusable due to stable demagnetization being possible without surface change.