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Influence of processing parameters on the microstructure and tensile property of 85 W-15Ni produced by laser direct deposition
摘要： The plate-like shape 85W-15Ni parts were produced by laser direct deposition technology with different processing parameters (laser power and scanning speed). The influence of processing parameters and their corresponding laser energy density on the microstructural characterization, phase composition and tensile property of 85W-15Ni samples was investigated. The results show that the relative density of samples increased with the laser energy density and the densification trend started to slow as the laser energy density reached 380-400 J/mm3, though the highest density value was obtained with laser energy of 425 J/mm3. With the increase of laser energy density, more disorder and fine W dendrites existed at the bonding region between deposition layers and more W-W grain boundaries formed at the central region of the layer. The 85W-15Ni samples produced with different processing parameters consisted of W and γ-Ni phase. To improve the tensile property, it is necessary to increase the laser energy density to obtain denser structure and reduce the residual pores or gaps. However, the excessive laser energy density resulted in the formation of more W-W grain boundaries that were detrimental to the tensile property. The best tensile properties were obtained at the laser energy density of 395 J/mm3.
关键词： 85W-15Ni,Laser direct deposition,Tensile property,Laser energy density,microstructural characterization
更新于2025-11-28 14:24:20
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Propulsion effects after laser ablation in water, confined by different geometries
摘要： A Nd:YAG laser with 7-ns pulses and pulse energies up to 10 mJ is used to induce an optical breakdown in the front surface of an aluminum rod, covered by a water layer. The rod is part of a ballistic pendulum. In this way, we study the propulsion effects by means of coupling coefficient and energy-conversion efficiency with respect to different confining geometries, volumes of water applied to the front surface of the rod, and the distance of this surface from the laser-beam focus. Holes with different dimensions are drilled on the target surface and filled with different volumes of water to examine the influence of the confinement by the liquid (a free boundary) and a solid-surface geometry on laser ablation effects. The rod movement and the water ejection after laser ablation are acquired by a high-speed camera with 10k frames per second. The results show that the confinement by cavity substantially increases the propulsion effects by shaping the ejected flow of the liquid; while the cavitation bubble, induced inside the water layer, plays a significant role in propulsion efficiency. From the presented results, it follows that the laser-propelled rod carries below 0.5% of the total mechanical energy after propulsion, while the rest of this energy represents the kinetic energy of the ablated water. As expected, moving the target surface away from the focal position decreases the ablative-propulsion efficiency. When the focus is moved inside the solid target, the decrease occurs due to lower conversion of the pulse energy into the energy of the cavitation bubble. If the focus is moved from the surface outward, the bubble moves towards the liquid–gas interface and it is not able to efficiently eject all the liquid from the target.
关键词： Cavitation bubble,Coupling coefficient,Laser propulsion,Nanosecond laser,Energy-conversion efficiency,Laser ablation
更新于2025-09-23 15:21:01
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Molecular dynamics simulation of coalescence kinetics and neck growth in laser additive manufacturing of aluminum alloy nanoparticles
摘要： Laser additive manufacturing emerged as an advanced manufacturing process to fabricate components in a layered fashion by fusing the powder particles. This process is multifaceted and pivotal to understand the underlying physics of the coalescence of powder particles during the process, which impacts the structural and mechanical properties of the build component. In this study, a classical molecular dynamics (MD) model is developed for the coalescence of pre-alloyed aluminum alloy (AlSi10Mg) particles during the laser additive manufacturing process. The model is employed to investigate the neck growth and coalescence kinetics of different pairs of particle size with changing the laser energy density from 7 to 17 J/mm2. The simulation results reveal that the unevenly sized particles undergo complete coalescence as compared with even-sized particles, and the neck growth rate of AlSi10Mg particles increases with an increase in laser energy density. Based on the present investigation, it is established that the coalescence kinetics of the AlSi10Mg nanoparticles are governed by the surface and volume diffusion and the surface energy reduction during the joining of particles. This analysis will act as a guideline to design process parameters and quality control for the printing of new components.
关键词： Molecular dynamics,Laser additive manufacturing,Coalescence,Laser energy density,Powder bed fusion
更新于2025-09-23 15:21:01
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Influence of Laser Energy Density on Acquisition and Wear Resistance of Bionic Semisolid Unit of 40Cr Steel
摘要： 40Cr steel is one of the most common materials for manufacturing brake camshaft of trailer. The brake camshaft is subjected to extreme wear during its service life. In order to enhance wear resistance, medium frequency induction hardening (MFIH) treatment is usually conducted on the surface of brake camshaft. However, conventional MFIH technique requires heating of the entire surface, which has the drawbacks of more power consumption, high production cost and easy deformation. Therefore, inspired by the bionic theory, a process named as ‘‘laser bionic semisolid treatment’’ method accompanied by favorable surface roughness and minimum distortion has been proposed herein as an alternative to MFIH method. By this means, bionic units with different surface roughness, sizes microstructure and hardness were manufactured on the surface of 40Cr steel. Then, the wear resistance of 40Cr steel with various laser energy densities was experimentally investigated. The results demonstrated that when the laser energy density was 18:00t3 (cid:2)3 J/ mm2, the bionic semisolid unit was obtained with the arithmetic mean surface roughness Ra of 1046.81 nm. Moreover, in the wear resistance of 40Cr steel due to the microstructure and higher hardness compared with the untreated sample, and its weight loss ratio was decreased by 71.90%. The mechanism of wear resistance enhancement was also discussed.
关键词： bionic semisolid unit,40Cr steel,wear resistance,laser energy density,surface roughness
更新于2025-09-23 15:21:01
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Development of low laser energy levels in small-incision lenticule extraction
摘要： Purpose: To evaluate the outcomes of 4 low laser energy levels after small-incision lenticule extraction (SMILE) surgery. Setting: Zhongshan Ophthalmic Center, Guangzhou, China. Design: Prospective randomized clinical trial. Methods: This study evaluated consecutive patients who had SMILE to correct myopia or myopia with astigmatism. Eyes were placed into groups based on the laser energy used during surgery (ie, 105 nJ, 110 nJ, 115 nJ, or 120 nJ). All patients had a thorough ophthalmic examination preoperative and at 4 timepoints over 3 months postoperatively. Black areas and surface regularity of the extracted lenticules were observed and evaluated qualitatively and quantitatively. Results: The study comprised 124 eyes of 62 patients (40 women, 22 men), with 31 eyes in each laser energy group. The incidence of black areas was 45.16% (14 of 31 eyes), 12.90% (4 of 31 eyes), 16.13% (5 of 31 eyes), and 12.90% (4 of 31 eyes) for 105 nJ, 110 nJ, 115 nJ, and 120 nJ, respectively. The mean time for lenticule creation was the longest in the 105 nJ group (P = .015). The greatest increase in corneal thickness postoperatively occurred with 105 nJ (P < .05). Regression was highest in the 105 nJ group at 3 months (P < .01). However, corneal horizontal coma (C8) was lowest in the 105 nJ group at 1 week (P = .032). The lenticular surface in the 110 nJ group was the smoothest (P = .011). All contrast sensitivity values varied with time and recovered to preoperative levels by 1 week or 1 month. In all eyes, the uncorrected distance visual acuity and corrected distance visual acuity were good, with no statistically significant differences between the 4 energy groups. Conclusions: The 105 nJ group, in which the lowest energy was used, had the highest risk for black areas, serious postoperative corneal edema, and a significant healing response.
关键词： small-incision lenticule extraction,laser energy levels,black areas,SMILE,corneal edema
更新于2025-09-23 15:19:57
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Spectral characteristic of laser-induced plasma in soil
摘要： The spectral characteristic of laser-induced plasma in soil was studied in this work, plasma under the condition of different time delays and irradiances. Moreover, the time evolution characteristics of plasma temperature and electron density were discussed. Within the time delay range of 0–5 μs, the spectral intensity of the characteristic lines of Si Ⅰ: 288.158 nm, Ti Ⅰ: 336.126 nm, Al Ⅰ: 394.400 nm and Fe Ⅰ: 438.354 nm of the four main elements in two kinds of national standard soil decayed exponentially with time. The average lifetime of the spectral lines was nearly 1.56 μs. Under the condition of different time delays, the spectral intensity of Pb Ⅰ: 405.78 nm in soil increased linearly with laser energy. However, the slope between the spectral intensity and laser energy decreased exponentially with the increase of time delay, from 4.91 to 0.99 during 0–5 μs. The plasma temperature was calculated by the Boltzmann plot method and the electron density was obtained by inversion of the full width at half maximum (FWHM) of the spectrum. The plasma temperature decreased from 8900 K to 7800 K and the electron density decreased from 1.5×1017 cm-3 to 7.8×1016 cm-3 in the range of 0–5 μs.
关键词： soil,time delay,electron density,laser energy,LIBS,plasma temperature
更新于2025-09-23 15:19:57
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Some analyses on optimal energy-extraction efficiency in a free-electron laser
摘要： In this paper, the energy-extraction efficiencies of the electron beam are studied for several cases of free-electron laser (FEL). For an initially cold electron beam, the optimal initial detuning for the maximum energy-extraction efficiency and the corresponding saturation length are given. A scheme of the ‘top up’ is proposed to enhance the efficiency: after the electron energy being modulated somewhat, a phase shift and a step-down of the phase bucket are introduced, so that all electrons are located near the upper separatrix of the bucket in the phase space. Finally, the energy-extraction efficiency can be increased by 30% compared with that of the normal undulator case. For a linear tapering undulator with an initially cold electron beam, the simple scaling laws for the maximum energy-extraction efficiency and the corresponding optical power gain are obtained. For a tapered undulator with the pre-bunched electron beam, our analysis gives that the energy-extraction efficiency reaches the maximum when the phase bucket height of the tapered undulator is equal to the amplitude of the detuning modulation. The numerical results validated this reasoning and show that the efficiency has a large increase compared with the case of the unbunched electron beam. The single stair-step undulator is investigated, the optimal step and the corresponding saturation power and saturation length are given by analysis, they agree well with the numerical simulation results.
关键词： pre-bunched,tapered undulator,free-electron laser,energy-extraction efficiency
更新于2025-09-23 15:19:57
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Design and achievement of hardware-in-the-loop simulation system for strapdown semi-active laser seeker
摘要： According to the work characteristics of semi-active laser-guided weapon system, at first, the optical characteristics of the laser received by seeker were analyzed; and mathematical model of the optical signal power received by seeker was established. Secondly, a hardware-in-the-loop simulation(HILS) system was designed for strapdown seeker. In order to simulate energy and laser spot’s continuous variations, a high-precision continuous dynamic laser energy attenuation system and a digital micromirror device(DMD) spot projection system were designed respectively. In the end, the HILS system was used to evaluate the performances of strapdown seeker and the seeker was tested for response coherence among the four quadrants, field of view(FOV), linear field of view, minimum received optical power, and angle measurement accuracy.
关键词： strapdown seeker,hardware-in-the-loop simulation,DMD spot projection,laser energy attenuation,semi-active laser-guided weapon
更新于2025-09-19 17:13:59
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[Laser Institute of America ILSC? 2019: Proceedings of the International Laser Safety Conference - South Kissimmee, Florida, USA (March 18–21, 2019)] International Laser Safety Conference - Probabilistic laser hazard modelling for a fifth-generation low-observable laser designator system
摘要： The advent of so-called “fifth-generation” low-observable strike aircraft with a laser designation capability raises a potentially unique laser hazard. In order to be “stealthy”, the laser designator is likely to be embedded within the aircraft rather than carried externally as a podded system. The difference between an integrated and a pod-based configuration is that the laser exit window in a stealth design is likely to be fixed to the aircraft fuselage, as opposed to being able to move with the laser beam, and it is also likely to be faceted. Unless carefully engineered, a faceted exit window may generate unintended laser beam reflections resulting in stray laser energy (SLE) emissions, as the laser head rotates within the window assembly. High intensity SLE can engender impractically large laser hazard zones using traditional deterministic analysis techniques. The purpose of this paper is to outline the probabilistic modelling of uncontrolled SLE from a hypothetical integrated laser designator system. The discussion will also show the importance of including the aircraft behaviour in the analysis, due to the effect of the aircraft position relative to the target on the SLE scatter patterns.
关键词： probabilistic modelling,fifth-generation aircraft,laser hazard,stray laser energy,laser designator
更新于2025-09-16 10:30:52
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Application of laser energy deposition to improve performance for high speed intakes
摘要： Research interest has been growing in recent years in supersonic transport, particularly supersonic propulsion systems. A key component of a commonly studied propulsion system, ramjets, is the air intake. For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery. This refers to the ratio of the average total pressure after the intake to that of the freestream. One phenomenon that can have a large effect on this performance index is flow separation at the inlet. The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet. This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel. Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ. Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance. Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone. Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake. At the optimal laser frequency, found for this Mach number to be 10 kHz, the pressure recovery is found to increase by up to 4.7%. When the laser power added to the system is considered, this results in an overall increase in propulsive power of 2.47%.
关键词： Intakes,Supersonic,Flow dynamics,Flow separation,Laser energy deposition
更新于2025-09-16 10:30:52