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Interaction between powder particle and gas-liquid interface of the melt pool during laser solid forming process
摘要： The three-dimensional (3-D) simulation of powder particle entering melt pool during laser solid forming (LSF) was carried out in our quest to establish a general representative model of this phenomenon. The effect of the gas-liquid interface on the motion state of the powder was analyzed, and the accuracy and universality of the model were verified using a high-speed photographic experimental approach. Further, the simulation process of the Ti-6Al-4V powder particle entering the high-temperature Ti-6Al-4V melt pool was carried out. The effects of the gas-liquid interface of the melt pool on the motion state of the powder particle and the disturbing of the powder particle on the melt pool were studied. It was found that the running speed of the particle experienced a rapid decrease and then a slower decrease in the process of entering the pool. Also, the particle serves as a transport medium of gases and carries the gases into the pool, which could form pores in the deposited layer. When the particles enter the melt pool at varied speeds, the ratio of the instantaneous speed of the particle entering the pool to the initial incident speed differs, which increases with increasing initial speed.
关键词： Melt pool,Laser solid forming,Powder particle,Gas-liquid interface,Interaction
更新于2025-09-23 15:19:57
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A Real-Time Method to Detect the Deformation Behavior during Laser Solid Forming of Thin-Wall Structure
摘要： Laser solid forming (LSF) is a promising additive manufacturing technology. In the LSF process, deformation behaviors dictate the accuracy of the produced parts. In this study, by using a laser displacement detector based on laser triangulation principle, an accurate and effective real-time detection method was established to monitor the real-time deformation behavior of the key position during the LSF of a thin-wall structure. The results confirmed that increasing thin-wall length results in increasing final deformation of the edge. The displacement fluctuation range and value in the middle of thin wall are both smaller than that of the positions near the end, while the entire displacement changing direction in the middle is opposite to that of the end positions. When the deposition process is paused, the deformation of the thin wall during the cooling stage will deviate the position of the deposited thin wall, resulting in the dislocation between the subsequent deposited part and that before the pause, which affect the dimensional accuracy of the thin wall structure. This non-contact real-time detection method also confirmed the ability to monitor the initiation of cracking during the LSF process, and a potential to be used for the on-line feedback control of deformation of detected key position of deposited structure.
关键词： laser solid forming,real-time detection,accuracy,crack,additive manufacturing,deformation behaviors
更新于2025-09-23 15:19:57
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Solidification Effect on the Microstructure and Mechanism of Laser Solid Forming Produced Flame-Resistant Ti-35V-15Cr Alloy
摘要： The block and thin-wall Ti-35V-15Cr samples were built by laser solid forming (LSF). The extremely sensitive thermal behavior condition in LSF results in significantly different microstructure. The microstructure of LSF-produced block sample mainly consists of epitaxial columnar dendritic grains, while that of the thin-wall sample is mainly composed of near-equiaxed grains together with sub-grains formed in the near-equiaxed grains.
关键词： sub-grains,Laser solid forming,temperature gradient,Ti-35V-15Cr,thermal cycling
更新于2025-09-23 15:19:57
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The New Technologies Developed from Laser Shock Processing
摘要： Laser shock processing (LSP) is an advanced material surface hardening technology that can significantly improve mechanical properties and extend service life by using the stress effect generated by laser-induced plasma shock waves, which has been increasingly applied in the processing fields of metallic materials and alloys. With the rapidly development of modern industry, many new technologies developed from LSP have emerged, which broadens the application of LSP and enriches its technical theory. In this work, the technical theory of LSP was summarized, which consists of the fundamental principle of LSP and the laser-induced plasma shock wave. The new technologies, developed from LSP, are introduced in detail from the aspect of laser shock forming (LSF), warm laser shock processing (WLSP), laser shock marking (LSM) and laser shock imprinting (LSI). The common feature of LSP and these new technologies developed from LSP is the utilization of the laser-generated stress effects rather than the laser thermal effect. LSF is utilized to modify the curvature of metal sheet through the laser-induced high dynamic loading. The material strength and the stability of residual stress and micro-structures by WLSP treatment are higher than that by LSP treatment, due to WLSP combining the advantages of LSP, dynamic strain aging (DSA) and dynamic precipitation (DP). LSM is an effective method to obtain the visualized marks on the surface of metallic materials or alloys, and its critical aspect is the preparation of the absorbing layer with a designed shape and suitable thickness. At the high strain rates induced by LSP, LSI has the ability to complete the direct imprinting over the large-scale ultrasmooth complex 3D nanostructures arrays on the surface of crystalline metals. This work has important reference value and guiding significance for researchers to further understand the LSP theory and the new technologies developed from LSP.
关键词： laser shock processing,stress effect,warm laser shock processing,laser shock marking,laser shock imprinting,laser shock forming
更新于2025-09-23 15:19:57
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Effects of TiO <sub/>2</sub> crystallinity and oxygen composition on forming characteristics in Pt/TiO <sub/>2</sub> /Pt resistive switching cells
摘要： “Forming” is a stage in resistive switching (RS) devices that occurs before switching and represents an important physical phenomenon in the universal operating mechanism of such devices. Forming in a resistance change material appears to be a kind of dielectric breakdown. In this study, we performed time-dependent forming (TDF) characterization of Pt/TiO2/Pt resistive switching cells with TiO2 layers of different crystallinities and oxygen compositions. We prepared two samples in which the grain boundary density and the density of oxygen vacancies differ, while both the TiO2 layers exhibited the similar crystal structures. Our results reveal that the Weibull slope and variation of time to forming are determined by the deposition method of the Pt bottom electrode (BE) ?lms. Moreover, the initial cell resistance and distribution of the TDF characteristics depend not only on the crystallinity but also on the oxygen composition of the TiO2 layers. The variation of time to forming increases as the distribution of initial resistance is reduced in Pt/NiO/Pt resistive switching cells with different NiO crystallinities. Conversely, the variation of time to forming decreases as the distribution of the initial resistance is reduced in the case of the Pt/TiO2/Pt cells. These results re?ect differences in both the grain boundary density (crystallinity) and the density of oxygen vacancies (oxygen composition) of resistance change materials used in the resistive switching cells. The clear difference of crystallinities and oxygen compositions might originate from differences in the oxide deposition mode during reactive sputtering.
关键词： oxygen composition,TiO2,forming,resistive switching,crystallinity
更新于2025-09-23 15:19:57
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Using Flickering Light to Enhance Nonimage-Forming Visual Stimulation in Humans
摘要： PURPOSE. Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate nonimage-forming visual functions such as pupillary constriction and circadian photoentrainment. Optimizing daytime nonimage-forming photostimulation has health benefits. We aimed to enhance ipRGC excitation using flickering instead of steady light. METHODS. Human subjects were tested with a three-dimensional matrix of flickering 463-nm stimuli: three photon counts (13.7, 14.7 and 15.7 log photons cm?2), three duty cycles (12%, 47%, and 93%) and seven flicker frequencies (0.1, 0.25, 0.5, 1, 2, 4, and 7 Hz). Steady-state pupil constrictions were measured. RESULTS. Among stimuli containing 13.7 log photons cm?2, the one flickering at 2 Hz with a 12% duty cycle evoked the greatest pupil constriction of 48% ± 4%, 71% greater than that evoked by an equal-intensity (12.3 log photons cm?2 s?1) continuous light. This frequency and duty cycle were also best for 14.7 log photons cm?2 stimuli, inducing a 58% ± 4% constriction which was 38% more than that caused by an equal-intensity (13.3 log photons cm?2 s?1) constant light. For 15.7 log photons cm?2 stimuli, the 1-Hz, 47% duty cycle flicker was optimal although it evoked the same constriction as the best 14.7 log photons cm?2 flicker. CONCLUSIONS. Pupillary constriction depends on flicker frequency and duty cycle besides intensity. Among the stimuli tested, the one with the lowest photon count inducing a maximal response is 13.3 log photons cm?2 s?1 flickering at 2 Hz with 12% duty cycle. Our data could guide the design of healthier architectural lighting and better phototherapy devices for treating seasonal affective disorder and jet lag.
关键词： pupillary light reflex,melanopsin,phototherapy,nonimage-forming vision
更新于2025-09-19 17:15:36
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DEFORMATION ANALYSIS OF H62 Cu ALLOY FOIL SUBJECTED TO MULTI-PULSED LASER DYNAMIC FORMING: SIMULATIONS
摘要： By utilizing the ABAQUS software, this paper simulates and analyzes the forming of the H62 foil subjected to multi-pulse laser dynamic forming (LDF). The Johnson–Cook failure mode is adopted to predict the fracture threshold value of the H62 foil. Compared with the single-pulsed LDF, the multi-pulsed LDF improves the limit depth and forming quality of the foil e?ectively. With the increase of impact number, the uniformity of foil is e?ectively improved. Appropriate peak pressure and impact number are important to increase limit forming depth and improve forming quality.
关键词： finite element analysis,Laser dynamic forming,H62 Cu alloy foil,limit forming depth,multi impacts
更新于2025-09-19 17:13:59
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Formation Mechanism of Dilute Region and Microstructure Evolution in Laser Solid Forming TA15/Ti2AlNb Dual Alloy
摘要： TA15/Ti2AlNb multiple-layer samples and a dual-alloy sample were fabricated by laser solid forming (LSF) in this study. The formation mechanism of the dilute region and microstructure evolution of the dual alloy were analyzed. The results con?rmed a “step” distribution of the composition among several initial layers in the multiple-layer samples, which can be explained by calculating the ratio of the remelted zone to the deposited Ti2AlNb zone in each deposited layer. However, the “step” compositional distribution disappears, and the compositional variation tends to be more continuous and smooth in the TA15/Ti2AlNb dual-alloy sample, which is attributed to alloy elements’ di?usion at the subsequent multiple re-melting and the longer thermal cycle. The macrostructure of the TA15/Ti2AlNb dual-alloy sample consists of epitaxially grown columnar prior β grains at the TA15 side and equiaxed grains at the Ti2AlNb side, while the microstructure shows a transition of α+β→α+α2 +B2+O with increasing amounts of Ti2AlNb, leading to the microhardness also changing signi?cantly.
关键词： dilute region,microstructure evolution,laser solid forming,TA15/Ti2AlNb dual alloy
更新于2025-09-19 17:13:59
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Ge/Si Partitioning in Igneous Systems: Constraints From Laser Ablation ICP‐MS Measurements on Natural Samples
摘要： Mineral/melt and intermineral Ge/Si exchange coef?cients for nine common rock‐forming silicate minerals were determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS). Ge/Si mineral/melt exchange coef?cients were found to vary by up to a factor of 10. In ma?c and ultrama?c systems, Ge/Si mineral/melt exchange coef?cients are less than 1 for plagioclase (0.48) and olivine (0.72), close to 1 for clinopyroxene (1.17) and orthopyroxene (1.07), and greater than 1 for garnet (2.69). In felsic and silicic systems, the Ge/Si mineral/melt exchange coef?cient is less than 1 for quartz (0.23), plagioclase (0.67), and potassium feldspar (0.67) but much greater than 1 for biotite (4.80) and hornblende (3.95). We show that early, olivine‐dominated fractionation of primitive basalts does not fractionate Ge/Si signi?cantly, but subsequent cotectic crystallization of plagioclase and pyroxene can increase the Ge/Si ratio from 6 × 10?6 to 7 × 10?6. We show that the only way to decrease Ge/Si during magmatic differentiation is by crystallization of hornblende or biotite (though biotite is typically a late crystallizing phase), consistent with hornblende being a major fractionating phase in hydrous intermediate magmas. The high compatibility of Ge in hornblende makes this element, in conjunction with Si, a potentially useful approach for distinguishing between hornblende and garnet in the source regions of intermediate magmas. The high compatibility of Ge in micas suggests that Ge/Si systematics may also be useful in understanding the origin of ultrapotassic magmas, which are often thought to derive from phlogopite‐rich sources.
关键词： igneous systems,magmatic differentiation,Ge/Si partitioning,rock‐forming silicate minerals,LA‐ICP‐MS
更新于2025-09-19 17:13:59
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Molecular Technology (Life Innovation) || Self-assembled Monolayers from Carbon-Based Ligands on Metal Surfaces
摘要： Rift Valley fever virus (RVFV) is an arthropod-borne, zoonotic disease endemic to sub-Saharan Africa and the Arabian Peninsula. Outbreaks of Rift Valley fever have had up to 100% mortality rates in fetal and neonatal sheep. Upon infection of ruminant and human hosts alike, RVFV infection causes an at times severe hepatitis and pathology in many other organs. The enveloped virion contains a tripartite, predominantly negative-sense, single-stranded RNA genome, which codes for the proteins the virus needs to replicate both in mammalian hosts and insect vectors. Endemic countries often use attenuated RVFV strains for vaccination of livestock but there are no commercially licensed vaccines for humans or livestock in non-endemic areas. In the laboratory, RVFV can be readily propagated and manipulated in vitro using cell culture systems. Presented in this article are techniques routinely used in RVFV research that have proven successful in our laboratories.
关键词： Rift Valley fever virus,plaque assay,TCID50,virology,bunyaviruses,focus-forming assay,virus quantification,propagation
更新于2025-09-19 17:13:59