Vacuum Laser Research Articles

Microstructure analysis and interfacial wave formation mechanism research of Mg/Al dissimilar metal laser impact welding in a vacuum environment

Laser impact welding (LIW) joints for the center exists springback region, resulting in a small effective welding area seriously affects the LIW joints performance problems. This paper for the first time put forward the vacuum environment LIW process, to carry out the vacuum environment of the two dissimilar lightweight metal magnesium/aluminum (Mg/Al) LIW. Results of the research showed that no springback occurred in the welded area. In order to reveal the vacuum environment LIW mechanism, the surface and cross-section morphological characteristics, weld interface microstructure, interface waveform element content and mechanical properties of laser impact welded Mg/Al dissimilar metals were investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), energy spectrometry (EDS), and the universal testing machine. Studies have shown that the experimental success rate in the vacuum environment is much higher than that in the atmospheric environment, and the vacuum environment eliminates the springback cracking defect phenomenon generated in the center of the welded joints, which greatly increases the effective welding area of the weld. The number of Mg grain refinement in the interface region of the vacuum environment welding is more, and the bonding force of the two-plate welding is increased. Significant orientation differences, severe plastic deformation and high strain at the weld interface are one of the reasons for the successful LIW. Mg/Al welding samples produced elemental diffusion phenomenon, no obvious melting phenomenon, which is conducive to improving the welding quality. Tensile strength of the welded samples in the vacuum environment was higher than that in the atmospheric environment. Using the SPH-Lagrange coupling method, numerical simulations were carried out to study the trends shear stress, pressure, velocity, temperature and equivalent plastic strain distribution at the weld interface under vacuum environment, which revealed the interface wave formation mechanism in the center of laser impact welded joints with no springback cracking phenomenon. Vacuum laser impact welding opens up a new technology pathway for LIW of Mg/Al welded joints without springback in the center, which plays an important role in improving Mg/Al welding performance.

Enhanced electron acceleration through Hermite higher-ordered cosine-hyperbolic-gaussian laser in vacuum

Enhanced electron acceleration through Hermite higher-ordered cosine-hyperbolic-gaussian laser in vacuum

Artificial synapses based on HfOx/TiOy memristor devices for neuromorphic applications

As a result of enormous progress in nanoscale electronics, interest in artificial intelligence (AI) supported systems has also increased greatly. These systems are typically designed to process computationally intensive data. Parallel processing neural network architectures are particularly noteworthy for their ability to process dense data at high speeds, making them suitable candidates for AI algorithms. Due to their ability to combine processing and memory functions in a single device, memristors offer a significant advantage over other electronic platforms in terms of area scaling efficiency and energy savings. In this study, single-layer and bilayer metal-oxide HfOxand TiOymemristor devices inspired by biological synapses were fabricated by pulsed laser and magnetron sputtering deposition techniques in high vacuum with different oxide thicknesses. The structural and electrical properties of the fabricated devices were analysed using x-ray reflectivity, x-ray photoelectron spectroscopy, and standard two-probe electrical characterization measurements. The stoichiometry and degree of oxidation of the elements in the oxide material for each thin film were determined. Moreover, the switching characteristics of the metal oxide upper layer in bilayer devices indicated its potential as a selective layer for synapse. The devices successfully maintained the previous conductivity values, and the conductivity increased after each pulse and reached its maximum value. Furthermore, the study successfully observed synaptic behaviours with long-term potentiation, long-term depression (LTD), paired-pulse facilitation, and spike-timing-dependent plasticity, showcasing potential of the devices for neuromorphic computing applications.

Vacuum laser zone refining of titanium towards lunar metallurgy: Experimental and numerical study

The development of in-situ utilisation technologies for lunar resources is crucial for future human deep-space exploration. This paper presents a novel vacuum laser zone refining technique aimed at in-situ separation of titanium and iron. The experimental and numerical simulation results indicate that increasing laser power while reducing the melting speed significantly increases the temperature gradient of the melt pool, thereby enhancing molten flow velocity. These factors effectively redistribute the elements at the solid-liquid interface, improving Fe and Ti separation efficiency. Additionally, increasing the number of refining passes can also significantly improve the separation efficiency of Fe and Ti. Under the conditions of 1000 W laser power, 0.05 mm/s melting speed, and 5 refining passes, the separation efficiency of Fe reached 76.5 %. Notably, the maximum molten flow velocity reached 0.157 m/s, which ensured a uniform distribution of Fe in the melting zone. Hence, the proposed vacuum laser zone refining technique is a promising approach for efficient separation of titanium and iron from titanium–iron alloys, providing potential support for deep-space exploration efforts.

Relativistic Electrons from Vacuum Laser Acceleration Using Tightly Focused Radially Polarized Beams.

We generate a tabletop pulsed relativistic electron beam at 100Hz repetition rate from vacuum laser acceleration by tightly focusing a radially polarized beam into a low-density gas. We demonstrate that strong longitudinal electric fields at the focus can accelerate electrons up to 1.43MeV by using only 98GW of peak laser power. The electron energy is measured as a function of laser intensity and gas species, revealing a strong dependence on the atomic ionization dynamics. These experimental results are supported by numerical simulations of particle dynamics in a tightly focused configuration that take ionization into consideration. For the range of intensities considered, it is demonstrated that atoms with higher atomic numbers like krypton can favorably inject electrons at the peak of the laser field, resulting in higher energies and an efficient acceleration mechanism that reaches a significant fraction (≈14%) of the theoretical energy gain limit.

Unforeseen advantage of looser focusing in vacuum laser acceleration

Acceleration of electrons in vacuum directly by intense laser fields holds great promise for the generation of high-charge, ultrashort, relativistic electron bunches. While the energy gain is expected to be higher with tighter focusing, this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation that exposed nanotips to relativistic few-cycle laser pulses. We demonstrate the vacuum laser acceleration of electron beams with 100s pC charge and 15 MeV energy. Two different focusing geometries, with normalized vector potential a0 of 9.8 and 3.8, produced comparable overall charge and electron spectra, despite a factor of almost ten difference in peak intensity. Our results are in good agreement with 3D particle-in-cell simulations, which indicate the importance of dephasing.

Effect of Al(OH)3 on the Properties of Silica-based Ceramic Cores Prepared by Laser Powder Bed Fusion Combined with Vacuum Infiltration

Silica-based ceramic cores, with low coefficients of thermal expansion, low sintering temperatures, and excellent acid and alkali leaching capabilities, are essential materials for the production of hollow blades. However, their mechanical properties are suboptimal, and they present various processing challenges. In this study, silica-based ceramic cores were prepared using a combination of vacuum infiltration (VI) and laser powder bed fusion (LPBF) techniques. Al(OH)3 was employed as a mineralizer to enhance the post-sintering mechanical properties and improve the efficiency of the vacuum infiltration process, thereby enhancing the overall performance of the silica-based ceramic cores. The VI process facilitated the penetration of nano-SiO2 into the samples, increasing their density and promoting the formation of cristobalite during sintering at 1225°C. Additionally, the Al(OH)3 powder, through pyrolysis into Al2O3 during sintering, reduced microcracks, inhibited excessive cristobalite transformation, and improved the VI process, resulting in enhanced room-temperature flexural strength. By optimizing the Al(OH)3 content and the VI process, significant improvements in the microstructure and properties of the silica-based ceramic cores were achieved. After three rounds of vacuum infiltration and the addition of 4wt.% Al(OH)3, the samples exhibited a high-temperature creep of 0.17mm, with flexural strengths of 15.23MPa at room temperature and 23.55MPa at high temperature.

Ripple formation on TA2 pure titanium surface induced by annular laser beam at low pressure environment

Formation of the micron-scale circular ripples on metal surfaces produced by continuous wave laser irradiation in low-pressure environment was investigated experimentally and numerically in this manuscript. It is found that splashing of the molten material and oxidation of the metal surface, which usually happened in the atmospheric environment, were avoided in low-pressure environment. Therefore, circular ripples were formed during the solidification process of the molten pool. Numerical simulations based on the finite element method (FEM) and the moving mesh method were applied to investigate the evolution of the flow field behavior of the molten pool. It is found that the Marangoni effect and capillary force during solidification process dominate the formation of the micron-scale circular ripples. In addition, the ripple spacing can be controlled by the temperature gradient. At the same power density, a higher temperature gradient on the molten surface can be produced by an annular laser beam, compared to a Gaussian beam, thus a denser circular ripple structure were produced, which were confirmed by the experimental results. The results of this paper may enrich the investigations on the metal surface texturing methods, laser vacuum processing and laser material engineering.

Investigations on MoS2 plasma by infra-red pulsed laser irradiation in high vacuum

MoS2 targets were irradiated by infra-red (IR) pulsed laser in a high vacuum to determine hot plasma parameters, atomic, molecular and ion emission, and angular and charge state distributions. In this way, pulsed laser deposition (PLD) of thin films on graphene oxide substrates was also realized. An Nd:YAG laser, operating at the 1064 nm wavelength with a 5 ns pulse duration and up to a 1 J pulse energy, in a single pulse or at a 10 Hz repetition rate, was employed. Ablation yield was measured as a function of the laser fluence. Plasma was characterized using different analysis techniques, such as time-of-flight measurements, quadrupole mass spectrometry and fast CCD visible imaging. The so-produced films were characterized by composition, thickness, roughness, wetting ability, and morphology. When compared to the MoS2 targets, they show a slight decrease of S with respect to Mo, due to higher ablation yield, low fusion temperature and high sublimation in vacuum. The pulsed IR laser deposited MoS x (with 1 < x < 2) films are uniform, with a thickness of about 130 nm, a roughness of about 50 nm and a higher wettability than the MoS2 targets. Some potential applications of the pulsed IR laser-deposited MoS x films are also presented and discussed.

Analysis of Maintenance Methods and Process Improvement of Vacuum Laser Collimation System for Dams

The method and process of vacuum laser collimation system maintenance is one of the key technologies directly related to the accuracy of dam vacuum laser collimation system measurement value. Taking the maintenance methods and processes of vacuum laser collimation system in Lianlu and Xiacheng as the background, a new set of dam vacuum laser collimation system maintenance methods and processes are proposed, aiming to make up for the gaps in the maintenance of vacuum laser collimation system. It was found that the vacuum pipeline operates at vacuum values between 400 Pa and 900 Pa. The influence of light on the vacuum laser is avoided by correcting the system and shading the transmitting end as well as the connecting part of the receiving end and the vacuum pipeline with a rubber sheet. This new maintenance method and process also provides a useful reference for the safety monitoring of similar projects.

Complete-joint-penetration vacuum laser beam welding of nickel-based superalloy 718Plus

Deep-penetration welding of nickel-based superalloys is an indispensable manufacturing technique for aircraft engines, aerospace engines, and nuclear containers. In this study, a newly developed vacuum laser beam welding method was used to weld a 9 mm thick superalloy 718Plus. A defect-free complete joint penetration weld with a high depth-to-width ratio was fabricated. The macro/microstructures, microhardness, tensile properties, and fatigue properties of weld joints under both as-welded and heat-treated conditions were systematically examined. The weld joint showed a microstructure of planar, cellular, columnar, and equiaxed crystals from the fusion line to the center line. The post-weld heat treatment had an insignificant effect on the grain structure but changed the precipitated phase in the weld. The newly formed γ′ and η phases were observed in the heat-treated sample. The mechanical properties showed microhardness, tensile strength, elongation, and fatigue strength of 488.6 HV, 1347.0 MPa, 13.7%, and 399 MPa, respectively, which were 104.6%, 93.2%, 77.8%, and 74.2% of those of the base metal, respectively. Both as-welded and heat-treated samples exhibited ductile ruptures. The excellent mechanical properties of the heat-treated joints were attributed to the formation of precipitated phases.

Microstructure, Hardness, Wear Resistance, and Corrosion Resistance of As-Cast and Laser-Deposited FeCoNiCrAl0.8Cu0.5Si0.5 High Entropy Alloy

FeCoNiCrAl0.8Cu0.5Si0.5 high-entropy alloys were fabricated using vacuum induction melting and laser deposition processes, followed by a comparison of the structural and mechanical properties of two distinct sample types. The as-cast FeCoNiCrAl0.8Cu0.5Si0.5 alloy is comprised of BCC1, BCC2, and Cr3Si phases, while the laser-deposited alloy primarily features BCC1 and BCC2 phases. Microstructural analysis revealed that the as-cast alloy exhibits a dendritic morphology with secondary dendritic arms and densely packed grains, and the laser-deposited alloy displays a dendritic structure without the formation of granular interdendritic regions. For mechanical properties, the as-cast FeCoNiCrAl0.8Cu0.5Si0.5 alloy demonstrated higher hardness than the as-deposited alloy, with values of 586 HV0.2 and 557 HV0.2, respectively. The wear rate for the as-cast alloy was observed at 3.5 × 10−7 mm3/Nm, with abrasive wear being the primary wear mechanism. Conversely, the as-deposited alloy had a wear rate of 9.0 × 10−7 mm3/Nm, characterized by adhesive wear. The cast alloy exhibited an icorr of 4.062 μA·cm−2, with pitting as the form of corrosion. The laser-deposited alloy showed an icorr of 3.621 μA·cm−2, with both pitting and intergranular corrosion observed. The laser-deposited alloy demonstrated improved corrosion resistance. The investigation of their microstructure and mechanical properties demonstrates the application potential of FeCoNiCrAl0.8Cu0.5Si0.5 alloys in scenarios requiring high hardness and enhanced wear resistance.

Enhanced electron acceleration efficiency through laser and electron parameter optimization in vacuum

Enhanced electron acceleration efficiency through laser and electron parameter optimization in vacuum

Effect of heat treatment on microstructures and properties of vacuum laser welding Ti–6Al–4V titanium alloy

Vacuum laser welding of titanium alloys is currently being explored for use in UAVs and military-related fields, but the impact of post-weld heat treatment has been seldom studied. In this paper, the Ti–6Al–4V titanium alloy was welded by vacuum laser welding(VLW)with IPG 50 kW fiber laser, and analyze the microstructure and properties of the welds in as-welded state and post-welding heat treatment (850 °C/2h/FC(FC:furnace cooling)and 980 °C/10min/FC+720 °C/2h/FC).The results show that the microstructure of the as-welded weld is composed of primary columnar crystal (primary β phase) and grain boundary martensite (α′), and the microstructure of primary columnar crystal is composed of α'+ (α'+β). The proportion of high-angle grain boundary(HAGB) is 92.3%. The tensile strength is 1009 MPa, and the elongation is 9.3%. The average impact toughness at room temperature is 13J. The weld microstructure at 850 °C/2h/FC is composed of the acicular α phase and the α+β between the acicular α phases, the primary columnar crystals basically disappear, and the acicular α phases criss-cross weave into the net basket structure.The proportion of HAGB is 97.4%.The tensile strength is 988.3 MPa,and the elongation is 14.8%. The average impact toughness is 17J. The microstructure of the weld at 980 °C/10min/FC+720 °C/2h/FC is composed of the coarser acicular α phase and the (α+β) between the coarser acicular α phases. The proportion of HAGB is about 83.2%. The tensile strength is 586 MPa, and the elongation is 1.6%. The average impact toughness is 1.4J.

Pathogenetic strategies for addressing periodontal morphological and functional disorders in plaque-induced gingivitis

Relevance. Plaque-induced gingivitis represents the initial phase of periodontal diseases and a significant medical and social challenge within global healthcare frameworks, particularly prevalent among younger people.Demographics. This prevalence arises from its multifactorial etiology, complex developmental mechanisms, and notable pathogenetic features, most evidently microcirculatory disruptions leading to tissue hypoxia. Addressing these pathological conditions requires the development of novel diagnostic methodologies and therapeutic interventions to prevent further complications.Materials and methods. The study encompassed 54 subjects with an average age of 22.5 ± 1.7 years. The control group included 34 participants (GroupI), and the comparison group 20 participants (Group II). Group II received vacuum laser therapy in conjunction with Mexidol-based dressings, noted for their antihypoxant and antioxidant properties.Results. Evaluations conducted post-treatment indicated enhancements in both arterial and venous capillary functions. Amid the antioxidant and antihypoxant treatment regimen, capillary diameters were reduced to match those observed in the control group.Conclusion. Regimen implemented in this study was clinically and functionally effective in a combined treatment protocol involving vacuum laser therapy on periodontal tissues of plaque-induced gingivitis patients. This regimen is recommendable as a corrective measure for microcirculatory disturbances within the scope of managing inflammatory periodontal diseases.

Vacuum laser therapy as part of combined treatment for plaque-induced gingivitis

Relevance. The increasing prevalence of plaque-induced gingivitis among the working-age population worldwide is leading to more cases of tooth loss and diminished quality of life, highlighting the need for early intervention in periodontal inflammation. Given the rising resistance of periodontal flora to pharmacological treatments and the potential for macroorganism sensitization, exploring the efficacy of non-pharmacological interventions that stimulate adaptive mechanisms in periodontal tissues becomes crucial for managing plaque-induced gingivitis effectively.Materials and Methods. This investigation details the findings from young adults who consented to participate after being informed about the study's protocol. The focus was on evaluating the clinical and functional health of intact periodontal tissues showing early signs of inflammation at the beginning of the treatment, upon completion, and one month after treatment. In addition to standard periodontal treatment, subjects in the experimental cohort underwent daily vacuum laser therapy sessions using a 650 nm wavelength red laser at a pulse rate of up to 10 Hz. Functional monitoring was performed utilizing vital computer capillaroscopy and dynamic vacuum sampling to evaluate capillary resistance in the microcirculation of periodontal tissues.Results. Vacuum laser therapy demonstrated significant therapeutic benefits in treating plaque-induced gingivitis, notably reducing the diameter of capillaries by approximately 14.5%. This reduction was attributed to enhanced capillary resistance and normalized microvascular wall permeability. Notably, the time to petechial formation doubled following dosed vacuum application to periodontal tissues, indicating enhanced reticuloendothelial system activity and capillary network regeneration. Patient assessments using the oral health index showed notable improvements in oral hygiene and the absence of inflammation signs.Conclusion. The study's results affirm the effectiveness of combining vacuum laser therapy with conventional treatment modalities for plaque-induced gingivitis, highlighting its benefits in improving periodontal health without relying on pharmacological interventions.

Effect of beam oscillation on weld formation, microstructure and mechanical properties in vacuum laser beam welding of thick section 5083 aluminum alloy

Beam oscillation in the laser welding process has demonstrated numerous advantages in suppressing spatters, eliminating pores, and reducing gap sensitivity, particularly for joining thin plates. This study presents the welding of thick section aluminum alloy using laser beam oscillation in a vacuum environment. During vacuum laser welding, the effect of beam oscillation variables, which include oscillating path, amplitude, and frequency, on weld seam morphology, microstructures, and mechanical properties was symmetrically evaluated. The findings indicate that in a vacuum environment, beam oscillation with a small amplitude can optimize the contour of the weld sidewall and increase the penetration depth, which is different from that observed in an atmospheric environment, where the melting penetration depth decreases with increasing oscillating amplitude. The deep penetration weld seam in a vacuum environment can achieve an extremely small size of 19 ∼ 30 µm. The addition of small oscillations causes a slight increase of the average grain size. The stirring effect of beam oscillation was weakened because of the minimized weld pool size under vacuum. This increased grain size is mainly attributed to the changes in the size of the molten pool caused by the oscillation cause changes in solidification parameters which accelerate grain growth. However, increasing the oscillation frequency can greatly increase the strength of the stirring effect and the refinement ability of small-sized grains. On further increasing the oscillation frequency to 200 Hz, the grown grains are refined. The results showed the tensile strength of the vacuum laser weld joints with and without beam oscillation can achieved a value of about 90 % of the base metal, which is superior to the strength of the joints welded by atmospheric pressure laser welding and can meet the vast majority of welding needs.

Comparison of low-cycle fatigue properties of two kinds of high energy beam welded joints of TC4 alloy

The low-cycle fatigue properties of 30 mm Ti6Al4V titanium alloy joints welded by vacuum electron beam welding and laser wobble welding with filler wire were compared. The test results show that the low-cycle fatigue performance of the electron beam welding joint is close to that of the base meal, while the low-cycle fatigue performance of the laser wobble welding with a filler wire joint is clearly inferior to that of the electron beam welding joint and base meal. An examination of the microhardness of the base metal, heat-affected zones and weld area of the two joints found that the microhardness of the weld area of the electron beam welding joint is close to that of the base meal, but is lower than that of the heat-affected zones on both sides. The weld area of the laser wobble welding with the filler wire joint is significantly weakened.

Vacuum laser beam welding of AZ31 magnesium alloy: Weld formability, microstructure and mechanical properties

Laser welding of magnesium alloy is still challenging because of the frequently occurred defects. In this work, a promising vacuum laser welding technique was used to join AZ31 magnesium alloy. The effect of ambient pressure on weld surface appearances and weld fusion cross sections was symmetrically investigated. It was found that the penetration depth increased and the weld width became narrower with the descending of ambient pressure from 101 kPa to 10 kPa. However, the penetration depth did not increase and even decreased when the ambient pressure further decreased to 1 kPa and 0.1 kPa. In addition, hump defects occurred at lower ambient pressure of 1 kPa and 0.1 kPa. The weld pool and keyhole behaviors were in-site observed using a high-speed camera at various ambient pressures. The results showed that unstable keyhole and turbulent flow were found in the molten pool at 101 kPa. The keyhole became more stable as the ambient pressure decreased from 101 kPa to 10 kPa. When the ambient pressure further decreased to 1 kPa and 0.1 kPa, the liquid metal thickness between keyhole wall and weld pool periphery became very narrow, which sometimes resulted in unstable absorption of the laser energy. Finally, a 10 mm-thick bottom-locking weld was made under vacuum. The average grain diameter of the weld in vacuum is 28.4 μm, which is much lower than 46 μm in atmosphere. The tensile results showed that the average ultimate tensile strength and the elongation of the joints welded in vacuum at 10 kPa was 8.8 % and 44.0 % higher than that of the joints welded in atmosphere respectively. The enhanced mechanical properties were attributed to the reduced porosity and refined microstrustures of the weld joint made under vacuum.

Realizing deep penetration and superior mechanical properties in a titanium alloy thick plate joint via vacuum laser beam welding

It is usually very difficult for achieving deep penetration in titanium alloy thick plates by conventional laser beam welding (LBW) under the atmospheric environment, since the laser beam energy is easily dissipated in air. In this study, LBW in a low vacuum environment (100 Pa) was proposed to realize the deep weld penetration of 16 mm of Ti–6Al–4V alloy thick plate, which was over 1 time deeper than that in the atmospheric joint (7 mm). In addition, the contents of the impurity gas elements (N, H and O) hardly changed after vacuum LBW (VLBW), ensuring the welding quality. The fusion zone mainly consisted of acicular α′ martensite, which enhanced the α′/α′ interface strengthening, resulting in the higher microhardness than that of the base material. The average tensile strength of the joint achieved 1010 MPa, with the strength efficiency 100%. Microstructure evolution mechanisms during VLBW were discussed. This study provides a reference for the engineering application of VLBW of titanium alloy thick plates.