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Microstructure modelling of laser metal powder directed energy deposition of Alloy 718
摘要： A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
关键词： Modelling,Heat Treatment,Phase-field,Thermal Cycle,DED
更新于2025-11-21 11:18:25
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Fabrication and up-conversion fluorescence property of Er<sup>3+</sup>/Yb<sup>3+</sup> co-doped Ca-Si-Ti biomaterials
摘要： This work demonstrates bulk-type up-conversion biomaterials which could be used as a bone repair material with the ability to monitor bone mineralization. Er3+/Yb3+ co-doped Ca-Si-Ti (CST3: TiO2 content is 30 mol%) bulk biomaterials were prepared via containerless processing technique in an aerodynamic levitation furnace and with subsequently heat treatment. The up-conversion fluorescence property was influenced by Yb3+ doping concentration, heat-treatment and mineralization in simulated body fluid (SBF). Optimum emission intensities were obtained for the sample with 20 mol% of Yb3+ doping concentration and heat treatment at 937 °C for 2 h. Hydroxyapatite (HAP) deposition was observed on the surface of the samples after soaking in SBF for 14 days, and the up-conversion fluorescence intensity of the samples decreased with the increase of soaking time. This indicates that Er3+/Yb3+ co-doped CST3 materials are bioactive, in which the HAP mineralization in bone repair could be monitored by measuring the intensity change of up-conversion fluorescence.
关键词： Heat treatment,Up-conversion fluorescence,Containerless processing,Mineralization,Er3+/Yb3+ co-doped Ca-Si-Ti biomaterial
更新于2025-09-23 15:23:52
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Effects of Heat-Treatment on Photoluminescence Spectra and Photocatalytic Properties of Solution-Combusted ZnO Nanopowders
摘要： ZnO nanopowders were prepared by a solution combustion method (SCM). The SCM ZnO nanopowders were heat-treated at 200, 400, 500, or 700 °C for 30 min in air and the photoluminescence (PL) of the nanopowders was evaluated. Two strong PL emission peaks are generally recognized as the unique PL signature of ZnO, one is from the band-edge emission and the other corresponds to green emission. The green emission is derived from crystalline defects, and is a critical obstacle for the electrooptical applications of ZnO. Surprisingly, the PL spectra of the SCM ZnO powders showed a single sharp peak near 390 nm. Furthermore, the intensity of this blue emission doubled when the synthesized ZnO powder was heat-treated at 400 °C. The green emission appeared for the sample treated at 500 °C, and was the highest for that treated at 700 °C. To confirm the photocatalytic activity of the ZnO powder heat-treated at 400 °C, the removal of Ag ions from a used photofilm developer was evaluated, with complete removal within 10 min. The removal of the Ag ions by the ZnO powder heat-treated at 400 °C was more than two orders of magnitude faster than that achieved with the SCM ZnO powder. The relation between PL and photocatalytic activity was explained in terms of recombination of the photogenerated electrons. These results might be very useful for highly efficient photocatalyst applications.
关键词： Heat-Treatment,ZnO Nanopowder,PL Spectra,Solution Combustion Method
更新于2025-09-23 15:22:29
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A micro-structural corrosion mechanism on the thermal degradation of BaMgAl10O17: Eu2+ phosphor
摘要： The thermal degradation is a vital issue that restricting luminous efficiency and service life of BaMgAl10O17: Eu2+phosphor for chromogenic and illuminating fields. The effects of heat-treatment temperature on the luminescence properties and micro-structure of BAM were researched to accurately elucidate the thermal degradation mechanism. Some pieces of evidence for micro-structural corrosion were detected according to the results of PL, TL, XPS and IR. With the heat-treatment temperature increasing, a decrease of blue-emitting intensity and new red-emitting peaks revealed thermal degradation and activator oxidation. The XPS results showed the surface chemical composition changes and the micro-structure adjustment. The defects elimination detected by TL could be responsible for this micro-structural corrosion. IR results further confirmed the changes on bond forms. These were direct evidence and specific forms for the micro-structural corrosion due to the thermal degradation. Based on the relationship between micro-structural corrosion and luminescence properties, a micro-structural corrosion mechanism was given for the thermal degradation of BAM phosphor. The thermal degradation was caused in parallel by the micro-structure corrosion and the activated ion (Eu2+) oxidation.
关键词： Micro-structural corrosion,Thermal degradation mechanism,BaMgAl10O17:Eu2+,Heat-treatment
更新于2025-09-23 15:22:29
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Optical, structural and luminescence properties of oxyfluoride phosphate glasses and glass-ceramics doped with Yb3+
摘要： The impact of Al2O3 and Y2O3 addition on the structure, Yb3+ luminescence and crystallization is investigated for glasses in the P2O5-SrO-Na2O system. Although the addition of Al2O3 and Y2O3 leads to a more connected phosphate network as evidenced using IR and Raman spectroscopies and increases the glass transition temperature, it does not affect strongly the site of the Yb3+. The addition of Al2O3 and Y2O slightly decreases the rate of the glass crystallization. Surface crystallization occurs upon heat treatment. Crystallization was confirmed by the presence of sharp peaks in the XRD patterns of the glasses. Independently of the glass composition, multiple different crystalline phases precipitate in the glasses upon heat treatment. The precipitation of the Na1O7P2Yb1 crystal phase leads to an increase of the excited state 2F5/2 lifetime of Yb3+ and also of the bandwidth of the Yb3+ emission band centered at 1μm.
关键词： nucleation and growth,Yb3+ doped phosphate glasses,Raman & Infrared spectroscopies,Yb3+ luminescence properties,heat treatment
更新于2025-09-23 15:22:29
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Structural transformations and spectroscopic properties of Ni-doped magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2 for broadband near-IR light emission
摘要： Ni:MgAl2O4 spinel shows a reversible random Ni2t site redistribution with increasing temperature. With the aim of determining the influence of the structure evolution induced by heat-treatment on the nature of luminescence centers in NiO-doped spinel-based magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2, the detailed spectroscopic study of the initial glass during its heat-treatments at increasing and decreasing temperatures has been performed and accompanied by an XRD analysis and Raman spectroscopy. The initial glass was X-ray amorphous. Its optical spectrum is mainly formed by absorption of [5]Ni2t sites with a small amount of [4]Ni2t ones. Crystals of the nucleating catalyst, ZrTiO4, about 4 nm in size, appear during heat-treatment at 800 °C, while the absorption spectrum of Ni2t ions remains near unchanged. At 850 °C, spinel crystals with size of about 6 nm precipitate, which is accompanied by a broadband luminescence in the near-IR centered at 1330 nm with a bandwidth of 380 nm. At 950 °C, there is a slight reduction in intensity of absorption bands attributed to [6]Ni2t site redistribution with increasing temperature. A decrease in the amount of the [6]Ni2t luminescent centers is not accompanied by a decrease in the luminescence intensity because of the increased size of spinel crystals. Additional low-temperature heat-treatment does not lead to a redistribution between [6]Ni2t sites in spinel crystals in favor of [6]Ni2t ones. An increase of the luminescence intensity after low-temperature heat-treatment is associated with additional spinel crystallization.
关键词： Glass-ceramics,Luminescence,Spinel,Heat-treatment,Nickel,Absorption
更新于2025-09-23 15:21:21
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Study on ?′-ferrite evolution and properties of laser fusion zone during post-weld heat treatment on Al-Si coated press-hardened steel
摘要： Laser welding of Al-Si coated press-hardened steel (PHS) was still a challenging due to the formation of ?-ferrite in the fusion zone. However, it was ambiguous on the ?-ferrite evolution during post-weld heat treatment (PWHT). In this study, Al-Si coated PHS was welded by laser ?ber and then heat-treated at various temperatures (650 ?C, 950 ?C and 1050 ?C), and the microstructure evolution was investigated by in situ-observation. Mechanical properties and formability of welded joints was analyzed. The results showed that ?-ferrite did not go through phase transformation during PWHT regardless of any temperature, but with a grain boundary ?atted and movement. The presence of coarse ?-ferrite after PWHT was the responsible for the decreasing of tensile strength and formability of welded joints. The initiation crack was easy to generate in the phase interface between ?-ferrite and martensite to form a local brittle fracture zone ?nally. This study results provides a new theoretical criterion for the properties improvement on the laser welding of PHS without removing Al-Si coating.
关键词： Laser welding,Post-weld heat treatment,Al-Si coating,Press hardened steel ?-ferrite
更新于2025-09-23 15:21:01
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Analysis of the Mechanical Behavior of AISI 4340 Steel Cylindrical Specimens Heat Treated with Fiber Laser
摘要： This paper describes a method for analyzing and improving mechanical behavior of a cylindrical workpiece made of AISI 4340 steel, by its heat treatment with a 3kW fiber laser source. Research and expertise acquired in recent years have shown that improving the mechanical properties of AISI 4340 steel by heat treatment significantly reduces the design dimensions and thus optimizes the final weight of the product. Understanding the impact that a laser heat treatment can have on mechanical properties and the fatigue life can lead to significantly optimizing the design dimensions. This research investigates the effect and control of laser heat treatment parameters to optimize the mechanical behavior of an AISI 4340 steel cylindrical standard-specimen, which has a diameter of the calibrated part of 9.00-mm. The control of the case depth and its uniformization were guided by experimental and numerical modeling. Tensile tests, fatigue tests (hysteresis loops), microhardness, optical microscopy, and scanning electron microscopy measurements were used to evaluate each condition of the experimental design. Results indicate that laser heat treatment increases fatigue endurance by more than 20% compared to non-hardened samples. Moreover, it is shown with a model of neural prediction, and a rigorous analysis of variance, that the numerical values of the mechanical properties are in direct agreement with the laser hardening input parameters.
关键词： Fiber laser,Fatigue endurance,AISI 4340 steel,Mechanical behavior,Heat treatment
更新于2025-09-23 15:21:01
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AIP Conference Proceedings [Author(s) 3RD INTERNATIONAL SCIENCES, TECHNOLOGY & ENGINEERING CONFERENCE (ISTEC) 2018 - MATERIAL CHEMISTRY - Penang, Malaysia (17–18 April 2018)] - Influence of calcination temperature on the characteristic and sonophotocatalytic activities of Fe-doped TiO2 particles
摘要： In this study, 3 wt% Fe-doped TiO2 particles were prepared by sol-gel method using tetrabutyl titanate and iron (III) nitrate nonahydrate as precursors. Calcination of the prepared samples was carried out at temperature of 200, 400, 600 and 800 °C for 2 h. The effect of calcination temperature on the composition, structure and morphology of Fe-doped TiO2 were characterized using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscope (EDX) and X-ray Diffractometer (XRD). The FESEM images revealed changes in particle size from 34 to 148 nm for samples calcined at 200 to 800 °C, respectively. Meanwhile, XRD results demonstrated the presence of rutile phase in catalysts which were calcined above 600 °C. Sonophotocatalytic degradation of paracetamol using ultraviolet (UV) light and ultrasonic irradiation was performed to investigate the influence of calcination temperature on the catalytic activity of Fe-doped TiO2. Among all the calcined catalysts, the Fe-doped TiO2-600 achieved the highest degradation efficiency (74%) due to the presence of mixed anatase and rutile phases. This proved that calcination temperature is a critical parameter which affects the characteristics and catalytic activity of Fe-doped TiO2 catalyst in the sonophoto-degradation process.
关键词： Paracetamol,Sonophotocatalytic,Heat treatment,Fe-doped TiO2,Characteristics
更新于2025-09-23 15:21:01
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Application of Atom Probe Tomography to Complex Microstructures of Laser Additively Manufactured Samples
摘要： Additive Manufacturing (AM) technologies have gained increasing interest across multiple industrial sectors ranging from biomedical to aerospace. AM is not only used for prototyping, but also for tooling as well as for final part production. The computer-controlled, layer-by-layer building up process allows for increased design freedom enabling to produce almost any shape. Additional benefits are potential resource efficiency, increased product customization and lightweight design. Two prominent metal-based laser AM (LAM) techniques are laser powder bed fusion (LPBF) and laser metal deposition (LMD). In LPBF, a focused laser beam is scanned over a bed filled with metal powder to locally melt and fuse the powder to produce fully dense metal parts. The next layer of powder is then distributed and the laser scans again. LMD is a nozzle-based AM process in which a focused laser beam creates a melt pool in the build’s surface. Metallic powder is then injected into the melt pool through a nozzle. The 3D part is built by moving the nozzle/laser assembly forward track by track and layer by layer. Material produced by LAM exhibits a unique thermal history: initially, the material is cooled rapidly from the liquid state in the meltpool. Subsequently, the material experiences a cyclic reheating, the so-called intrinsic heat treatment (IHT), as neighboring tracks and further layers are deposited during the LAM process. Consequences of this thermal history are very complex, sometimes hierarchical microstructures with inhomogeneities at scales ranging from nanometers up millimeters. Fully understanding and characterizing these microstructures is challenging and requires the combination of methods spanning a similar range: from light optical microscopy (LOM) to electron microscopy to atom probe tomography (APT). Here we present examples how APT can deliver valuable information on complex microstructures to better understand the IHT, rapid solidification as well as phase separation in different metallic alloys. Here I will discuss examples in steel, Al- and Ni-based superalloys, and high entropy alloys (HEA).
关键词： Laser Additive Manufacturing,Additive Manufacturing,Phase Separation,Microstructures,Atom Probe Tomography,Rapid Solidification,Intrinsic Heat Treatment
更新于2025-09-23 15:19:57