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[Laser Institute of America ICALEO? 2015: 34th International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - Atlanta, Georgia, USA (October 18–22, 2015)] International Congress on Applications of Lasers & Electro-Optics - Hot wire laser cladding for repairing martensite precipitation hardening stainless steel
摘要： Martensite precipitation hardening stainless steel (M-PHSS) is widely used as load-bearing parts because of its excellent overall properties. It is economical and flexible to repair the failure parts instead of changing new ones. However, it is difficult to keep the properties of repaired layer as good as the substrate. Multi-pass layers were cladded on the surface of FV520B by hot wire laser cladding. Response surface methodology (RSM) was used to optimize processing parameters and predict formation quality of multi-pass cladding. Microstructure of the as-cladded layer was non-uniform and divided into quenched and tempered region. For the as-cladded layer, tensile strength was almost equivalent to that of the substrate, while ductility and impact toughness deteriorated much. With using laser scanning, microstructure of the clad layers was tempered to fine martensite uniformly. The ductility and toughness of clad layer were improved to be equivalent to those of the substrate, while the tensile strength was a little lower than that of the substrate. By adding TiC nanoparticles as well as laser scanning, the precipitation strengthening effect was improved and the structure was refined in the clad layer. As a result, the strength, ductility and toughness were all improved further. Finally, high quality clad layers were obtained with equivalent or even superior mechanical properties to the substrate, offering a valuable technique to repair M-PHSS.
关键词： Mechanical properties,Microstructure,Hot wire laser cladding,Martensite precipitation hardening stainless steel,Repair
更新于2025-09-16 10:30:52
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Numerical modeling of carbon distribution and precipitation during directional solidification of photovoltaic silicon
摘要： Numerical modeling is used to investigate carbon distribution and precipitation in directional solidification of multicrystalline silicon. Computations are performed for samples of 6 cm in diameter grown in a Vertical Bridgman Freezing (VGF) system starting from silicon feedstock with different grades of contamination in carbon. The value of the unknown reaction rate coefficient governing the carbon precipitation in the silicon melt was estimated in the present work by comparing the numerically computed concentration profiles to the experimental results taken from the literature. Numerical results show that the growth rate has a significant influence on the interface deflection, melt convection and carbon precipitation. It is found that the silicon samples grown from the melts of low carbon contamination (< 1018 at/cm3) exhibit low content in SiC precipitates, even if they are solidified at high growth rates (1–2 cm/h). The samples with high initial carbon contamination (5 × 1018 at/cm3) should be solidified at much lower rates (0.2 cm/h) in order to avoid the formation of SiC precipitates.
关键词： Carbon transport and precipitation,Directional solidification,Impurities,Semiconducting silicon,Computer simulation
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Light Shaping for Reconfigurable Microscale Temperature Control
摘要： Recycling rare-earth elements (REEs) from Nd-Fe-B magnet waste is an important step towards building a sustainable REE supply chain. In this study, two different processes were systematically investigated and compared. In the leaching stage, the effect of increasing H2SO4 or HCl concentrations were studied and it was determined that, although both can successfully promote REEs, B, Fe and Co leaching, HCl solutions extracted a wider range of metals. After leaching, the oxalate and double-sulfate precipitation methods were utilized to separate REEs from either HCl or H2SO4 leachates. Results suggest that, although > 99% REEs precipitation rates could be achieved with oxalate, the purity of REE-containing products is significantly affected by impurities like Fe and Co. In contrast, REE double-sulfate precipitation resulted in a product purity of > 99%; however, high levels of Na2SO4 (8 times the stoichiometric amount) were needed to achieve > 98% of REE precipitation.
关键词： rare-earth elements,precipitation,leaching,Nd-Fe-B magnets,recycling
更新于2025-09-12 10:27:22
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Synthesis of copper oxide quantum dots: effect of surface modifiers
摘要： Copper oxide quantum dots were synthesized via precipitation process. Different surface modifiers (SMs) such as polyvinylpyrrolidone (PVP), Polyethylene glycol sorbitan monooleate (Tween 80) and Cetyltrimethylammonium bromide (CTAB) were used for modification of the size and shape of CuO nanoparticles. The effects of some parameters such as the type of surface modifiers on the band gap, structure and microstructure of samples were investigated. All samples showed quantum confinement behaviors such as band gap widening, the size less than the Bohr radius and the blue-shift of adsorption edge. The change of morphology from rod-like in the presence of Tween-80 to spindle shapes in CTAB one confirmed the strategic role of covering the surface of CuO particles by SMs. Moreover, CuO quantum dots with mean crystallite size of 2.3 nm and band gap of 2-2.5 eV were synthesized successfully. Furthermore, high degree of dispersion belonged to CuO nanoparticle synthesized by CTAB SM due to the maximum zeta potential value (28.1 mV at pH=7.5).
关键词： Surface modifiers,Quantum dots,CuO,Precipitation
更新于2025-09-12 10:27:22
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Effect of Oxygen Precipitation in Silicon Wafer on Electrical Characteristics of Fully Ion-Implanted n-Type PERT Solar Cells
摘要： Fully ion-implanted n-type PERT solar cells with boron-implanted emitter and phosphorus-implanted back surface field were fabricated on the n-type silicon wafers obtained from the top part of the magnetic field-applied Czochralski ingot. It was observed that the electrical parameters are widely dispersed; among 11 solar cells, the best performing achieved 20.4% front side conversion efficiency, whereas the worst achieved 19.0%. Although the silicon wafers had low oxygen concentrations of 3–4 × 1017 atoms/cm3, the density of oxygen precipitates in the silicon wafers was on the order of 109 /cm3 as a consequence of the fully ion-implanted n-type PERT silicon solar cell processes. In addition, it was observed that the front side conversion efficiencies of the solar cells depended on the density of oxygen precipitates. Furthermore, the behavior of the oxygen precipitation during the fabrication processes of the solar cell is discussed.
关键词： oxygen precipitation,conversion efficiency,ion implantation,n-type PERT solar cells,silicon wafers
更新于2025-09-12 10:27:22
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Ethanol-Precipitation-Assisted Highly Efficient Synthesis of Nitrogen-Doped Carbon Quantum Dots from Chitosan
摘要： Nitrogen-doped carbon quantum dots (NCQDs) were prepared from chitosan through a hydrothermal reaction. When ethanol precipitation was used as the puri?cation method, a high product yield of 85.3% was obtained. A strong blue ?uorescence emission with a high quantum yield (QY) of 6.6% was observed from the NCQD aqueous solution. Physical and chemical characteristics of the NCQDs were carefully investigated by transmission electron microscopy (TEM), X-ray di?raction (XRD), Fourier transform infrared spectra (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and transient ?uorescence spectra. Experimental results showed that diameters of the NCQDs were in the range of 2?10 nm. The carbon quantum dots possess good water dispersibility and precipitation by ethanol. When used for metal ion detection, the detection limit of the NCQDs for Fe3+ was as low as 1.57 μM. This work proposed a facile method to synthesize NCQDs from chitosan with high yield and demonstrated that carbon quantum dots derived from chitosan were promising for ion detection.
关键词： ethanol precipitation,metal ion detection,chitosan,hydrothermal reaction,Nitrogen-doped carbon quantum dots
更新于2025-09-12 10:27:22
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Precisely Controlled Microsphere Design via Visible‐Light Cross‐Linking of Functional Prepolymers
摘要： A new strategy for particle synthesis is enabled by utilizing modern synthetic, polymer, and photochemical techniques to facilitate the synthesis of highly narrow–disperse multifunctional microspheres from visible-light induced crosslinking of prepolymers in both a single and dual polymer system. The approach requires no stabilizers, bases, or initiators, and proceeds at ambient temperature to yield microspheres with a tunable size range (0.25–5 μm) in less than 4 h, depending largely on solvent composition, but also polymer concentration (2–10 mg mL?1), ratio, and irradiation intensity (3–20 W). Critically, the visible-light induced dimerization reaction exploited herein enables simple functional particle syntheses via a single polymer system. Underpinned by an in-depth kinetic analysis of the particle formation as well as a detailed small molecule study, the mechanism for particle formation is also elucidated. Importantly, inherent advantages of the system are exploited for surface functionalization of residual acrylate and hydroxyl groups (generating inherently fluorescent particles).
关键词： polymer chemistry,photochemistry,materials chemistry,precipitation polymerization,particle synthesis
更新于2025-09-11 14:15:04
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In situ investigation of precipitation in aluminium alloys via thermal diffusivity from laser flash analysis
摘要： In this work, a commercially available laser flash analysis (LFA) device is used for in situ precipitation monitoring in aluminium alloys by following thermal diffusivity for the first time. The LFA measurement methods and data processing are adapted to allow continuous heating experiments over a wide range of heating rates (0.001–1 K s-1). Methods for LFA temperature calibration and thermal lag correction are suggested. Results of continuous heating of Al Mn0.5Mg0.5 aluminium alloy from the as-cast state are compared to in situ differential scanning calorimetry (DSC) and ex situ transmission electron microscopy. It is shown comparing in situ LFA, and DSC substantially improves the interpretation of superimposed reactions, in particular, the precipitation and dissolution of Mn-containing dispersoids and Mg–Si-containing secondary particles.
关键词： DSC,In situ LFA,Thermal diffusivity,Aluminium alloys,Precipitation,LFA thermal lag correction
更新于2025-09-11 14:15:04
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Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion
摘要： Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to densify the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is necessary, and development of new post processing regimes guaranteeing the best performance of the material is required.
关键词： Hot isostatic pressing (HIP),Atom probe tomography,Transmission electron microscopy,Maraging steel,Precipitation hardening,Laser powder bed fusion
更新于2025-09-11 14:15:04
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The δ Phase Precipitation of an Inconel 718 Superalloy Fabricated by Electromagnetic Stirring Assisted Laser Solid Forming
摘要： Fabricating an Inconel 718 superalloy using electromagnetic stirring assisted laser solid forming (EMS-LSF) is a novel method to modify its microstructure and mechanical properties by consuming the Nb element in the γ phase to alleviate interdendritic segregation. The precipitate C after EMS-LSF can help to achieve the uniform di?usion of Nb, and can also improve its mechanical properties. The precipitation behavior of the δ phase in an EMS-LSF Inconel 718 superalloy with di?erent heat treatment processes has been investigated. The results show that the morphology of the δ phase changes from rod-like to a long-needle shape and tends to grow from the inter dendrite to the core dendrite with electromagnetic ?eld intensity increasing, which is accompanied by the “cutting” and “dissolution” of the Laves phase. Through precipitation kinetics analysis, the precipitation rate of the δ phase is seen to increase with the electromagnetic ?eld intensity increasing. Under a combination of electromagnetic stirring and laser solid forming, the microhardness of the Inconel 718 samples increased slightly due to the fact that a higher content of Nb was distributed in the core dendrite resulting from the serious convection of liquid metal, which can strengthen the matrix.
关键词： electromagnetic stirring,laser solid forming,laves phase,δ phase,precipitation behavior
更新于2025-09-11 14:15:04