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Epitaxy and new stray grain formation mechanism during epitaxial laser melting deposition of Inconel 718 on directionally solidified nickel-based superalloys
摘要： The epitaxy behavior and stray grains (SGs) formation in the deposit during epitaxial laser melting deposition (E-LMD) of directionally solidified (DS) superalloys were investigated. Columnar dendritic structures were obtained by epitaxial solidification on the DS substrate. The deposit also remained the orientation of the substrate. The SGs at the fusion interface, which were hardly eliminated, were attributed to different SGs formation mechanisms. The SGs were divided into GB-SGs and MC-SGs by the distribution characteristics. The GB-SGs at the low-angle and high-angle grain boundaries with a new mechanism of dynamic recrystallization induced by accumulation of thermal strain and stress under repeated spatially variable heating and cooling. The MC-SGs around the carbides were related to the misoriented cellular crystal formation caused by the varied shape of the solid-liquid interface. The columnar to equiaxed transition (CET) was another mechanism of MC-SGs formation.
关键词： Stray grain,Nickel superalloys,Laser metal deposition,Recrystallization,Dynamic,Epitaxy,Microstructure
更新于2025-11-28 14:24:20
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Growth, optical, mechanical and thermal behavior of unidirectionally grown L-Glutaminium p-Toluenesulfonate crystal
摘要： Organic crystal of L-Glutaminium p-Toluenesulfonate (LGPT) was grown unidirectional by Sankaranarayanan and Ramasamy (SR) method. The grown crystal belongs to monoclinic crystal system with noncentrosymmetric space group P21. High resolution XRD confirms crystalline perfection of the grown crystal. Optical transmission shows that unidirectional grown crystal has higher transmittance and the lower cut-off wavelength is 290 nm. The emission wavelength of grown crystal is 410 nm and emission region is confirmed by luminescence spectra. The laser damage threshold value of unidirectional crystal has increased by 0.3 GW/cm2. The grown LGPT crystals belong to hard material category and it confirms the normal indentation size effect. The grown LGPT crystal is thermally stable upto 165 oC and decomposition of the molecules were elucidated by using TGA and DSC. Powder second harmonic generation measurement confirms the efficiency of the grown LGPT crystal is 0.8 times that of KDP.
关键词： Nonlinear optical materials,Crystal growth,Recrystallization,Optical properties
更新于2025-09-23 15:23:52
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Effects of laser surface melting on crystallographic texture, microstructure, elastic modulus and hardness of Tia??30Nba??4Sn alloy
摘要： The biocompatibility of orthopedic implants is closely related to their elastic modulus and surface properties. The objective of this study was to determine the effects of cold rolling, recrystallization and laser surface melting (LSM) on the microstructure and mechanical properties of a biphase (α″+β) Ti?30Nb?4Sn alloy. X-ray diffraction (XRD) texture analysis of the cold-rolled substrate revealed the [302]α″//ND texture component, while analysis of the recrystallized substrate showed the [302]α″//ND and [110]α″//ND components. The β-phase texture could not be directly measured by XRD, but the presence of the [111]β//ND texture component was successfully predicted by considering the orientation relationship between the α″ and β phases. Nanoindentation measurements showed that the elastic modulus of the cold-rolled substrate (63 GPa) was lower than that of the recrystallized substrate (74 GPa). Based on the available literature and the results presented here, it is suggested that this difference is caused by the introduction of crystal defects during cold deformation. The combined nanoindentation/EBSD analysis showed that the nanoindentation results are not affected by crystal orientation. LSM of the deformed alloy produced changes in hardness, elastic modulus and crystallographic texture similar to those produced by recrystallization heat treatment, creating a stiffness gradient between surface and substrate.
关键词： laser surface melting,stiffness-graded material,crystallographic texture,cold rolling,titanium alloy,recrystallization
更新于2025-09-23 15:21:01
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Study on laser annealing of niobium films deposited on copper for RF superconducting cavities
摘要： Niobium sputtered copper cavities were proposed as a kind of promising next generation superconducting cavities, but were still challenged by the Q-slope effect under high acceleration gradients. Current solutions focus on improving the film quality to make it more bulk-like, for which a higher substrate temperature is required. However, due to the limitation of the melting point of the copper substrate, both the deposition process and the post-annealing process cannot be performed at a high temperature. The laser annealing mentioned in this paper uses nanosecond pulsed laser as the heat source, and the local temperature field generated within the thickness scale of the niobium film can anneal the film without affecting copper substrate. Laser annealing system has been set up in Peking University, and experiments with niobium thin film on copper (Nb/Cu) samples have been carried out. Superconducting performance, surface topography and other properties of Nb/Cu samples before and after annealing are compared. Recrystallization of niobium films happened and various factors that may cause Q-slope have been suppressed according to the results. All these indicate the effectiveness of laser annealing and the possibility of being used in niobium sputtered copper cavities in the future.
关键词： Surface topography,Surface roughness,Recrystallization,Niobium thin film,Superconducting cavity,Laser annealing
更新于2025-09-23 15:19:57
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An effective strategy to boost 3D perovskite light-emitting diode performance via solvent mixing strategy
摘要： In this study, we demonstrate a simple method to achieve highly efficient perovskite light-emitting diode (PeLED) via casting the neat methylammonium bromide (MABr) in mixed solvents with different solubility on top of the perovskite layer for bulk recrystallization and interfacial passivation. The perovskite crystals reacting with MABr can be reformed orderly and stereoscopically with a reduced domain size on surface and reduced grain boundaries in bulk, which is advantageous to obtain strong fluorescence intensity and long exciton lifetime. The remaining MABr molecule that does not react with perovskite can attach on the recrystallized perovskite surface to develop a passivation layer, which can effectively eliminate exciton interface recombination in PeLEDs. The optimized PeLED exhibits a maximum luminance of 27692.2 cd m-2, which is more than 11 times and 2 times higher than the control device without MABr treatment and the control device with high MABr molar ratio and thin perovskite film thickness, respectively. This work provides an effective strategy to boost PeLED performance by optimizing mixed solvent ratios and concentrations of organic ligand MABr without changing the thickness of the emitting layer.
关键词： charge balance,morphological manipulation,passivation,perovskite light-emitting diode,recrystallization
更新于2025-09-23 15:19:57
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A high power laser facility to conduct annealing tests at high temperature
摘要： The knowledge of material properties and their behavior at high temperatures is of crucial importance in many fields. For instance, annealing phenomena occurring during the thermomechanical processing of materials, such as recrystallization, have long been recognized as being both of scientific interest and technological importance. Different methods are currently used to study annealing phenomena and submit metals to heat loads. In this work, we present the design and the development of a laser-based facility for annealing tests. This experimental setup enables studies at the laboratory scale with great flexibility to submit samples to various spatial and temporal heating profiles. Due to the possibility of having optical access to the sample, laser heating can be combined with several non-contact diagnostics such as infrared imaging to control and analyze the temperature gradients. As a case study, we present a set of experiments performed to study the recrystallization kinetics of tungsten. We demonstrate that samples can be heated linearly with heating rate up to ～2000 K/s, at temperatures above 2000 K, for seconds or hours, with typical errors in the temperature measurement of around 1% that depend mainly on the determination of sample emissivity. Such studies are of crucial interest in the framework of nuclear fusion since the international thermonuclear experimental reactor nuclear reactor will operate with a full-W divertor.
关键词： tungsten,laser annealing,nuclear fusion,high temperature,recrystallization
更新于2025-09-19 17:13:59
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Contribution of Mechanical Stresses to the Surface Relief Formation Under Laser Irradiation of Semiconductors
摘要： The paper considers the effect of elastic stresses arising under pulsed laser irradiation of epitaxial layers of CdxHg1–xTe solid solutions on the formation of a periodic surface relief as a result of recrystallization of material melted by radiation.
关键词： semiconductor solid solution,pulsed laser radiation,surface recrystallization,thermoelastic stresses
更新于2025-09-16 10:30:52
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Surface Refining by Laser Scanning on Silicon Wafers
摘要： A YAG continue-wave laser has been used to refine the surface of silicon wafers in this study. During laser scanning, the irradiated region of the surface of the wafer experienced melting and subsequent recrystallization, which results in a redistribution of metal impurities in the molten pool along the depth direction. Cross-sectional micrographs of irradiated wafers have a clear boundary, which confirms the process of recrystallization, and the depth of molten region depends on the scanning parameters and the size of wafer. Secondary ion mass spectrometry measurements have been carried out to characterize the concentration of metal impurities. After redistribution of metal impurities, a final relative purity region was formed close to the surface. SIMS measurements demonstrate that the metal impurity concentration of the purity region has significantly reduced. The mechanism of the redistribution process of metal impurities in the molten pool has been qualitatively analyzed. All of the experimental results support that the CW laser scanning technology can effectively refine the specific surfaces of silicon wafers, and this technology has a great potential in the field of solar cells.
关键词： Silicon wafer,Laser scanning,Refining,Metal impurities,Recrystallization
更新于2025-09-16 10:30:52
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Bulk recrystallization for efficient mixed-cation mixed-halide perovskite solar cells
摘要： Today, the use of mixed-cation lead mixed-halide perovskite with a slight excess of lead iodide (PbI2) demonstrates the highest device performances in the literature. However, the presence of excess PbI2 in the film poses long-term stability concerns. Here, we propose a facile bulk recrystallization process by applying formadinium chloride (FACl) on perovskite to remove excess PbI2 in the formed crystal. We are able to demonstrate bulk recrystallization, proved and observed by the Grazing incidence XRD to analyze the crystal structure as a function of depth profiling. The reconstructed crystal displays improved optoelectronic qualities with reduced interfacial recombination as well as enhanced device stability. When measured under AM 1.5G spectral conditions the optimized champion device reached a maximum power conversion efficiency (PCE) of 20.2%.
关键词： bulk recrystallization,optoelectronic qualities,FACl,perovskite solar cells,PbI2,device stability
更新于2025-09-16 10:30:52
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AIP Conference Proceedings [AIP Publishing PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2019 - Tomsk, Russia (1–5 October 2019)] PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2019 - Infrared thermography inspection of severe friction on UFG stainless steel, copper and aluminum alloy
摘要： Friction-generated heat is an important factor that determines the stability of sliding friction conditions and thus has to be taken into account especially when using ultrafine-grained materials for tribological applications. Thermal stability of these materials under friction sliding conditions must be studied and the first approach here is to determine the temperature distributions below the worn surfaces. For this purpose, we used an IR thermal imaging camera attached to a tribological setup and three materials with different heat conductivity values: AISI 321 stainless steel, 5052 aluminum alloy and C11000 copper as specimens. The results show that even if the measured temperatures were below the standard recrystallization start temperatures, the recrystallization still was feasible due to severe friction-induced subsurface deformation.
关键词： Infrared thermography,sliding friction,recrystallization,thermal stability,UFG materials
更新于2025-09-16 10:30:52