Power Density Of Laser Beam Research Articles

The effect mechanism of laser beam defocusing on the surface quality of IN718 alloy prepared by laser powder bed fusion

The surface quality issue of the laser powder bed fused (LPBF-ed) parts deteriorates the mechanical properties. Laser beam defocusing (LBD) can effectively improve the surface quality. To reveal the effect mechanism of LBD on the surface quality of the LPBF-ed parts, a laser powder bed fusion (LPBF) numerical model is established. Based on the calculated results, the formation process of the surface defects such as bulges, depressions, partially melted powders and spatters and the corresponding melt pool dynamic behaviors are investigated. The effects of LBD on the melt pool dynamic behaviors during the surface defects formation and the track width are discussed. The results show that LBD can improve the surface quality by reducing Marangoni force and recoil pressure to reduce bulge height and depression depth, increasing track width to decrease partially melted powders, and increasing surface tension and reducing kinetic energy to decrease spatters.

Ionization of Helium Atoms by Triply Charged Metal Atoms during Laser Ablation of Metals in Superfluid Helium

The applicability of laser ablation of metal targets for obtaining triply charged ions of metal atoms, including low-melting metals, has been experimentally demonstrated. By analyzing the luminescence spectra of a plasma plume during laser ablation of a metal target immersed in superfluid helium, the main channel for the formation of helium ions in plasma at a laser beam power density below the breakdown threshold of the helium medium has been determined. It has been shown that the ionization of helium atoms occurs in two steps, the formation of the HeM3+ ionic complex and the dissociation of the complex via its interaction with a metal atom.

Improvement of Thermochemical Processes of Laser-Matter Interaction and Optical Systems for Wavefront Shaping

Laser thermochemical processes of metal surface oxidation are promising for creating new advanced technologies to meet the growing needs of opto- and micro-electronics, photonics, catalysis, sensorics and other high-tech industries. The features of thermochemical processes of laser-matter interaction occurring in matter under exposure to intense light flows and optical systems for controlling the irradiance and wavefront spatial distribution were reviewed. The laser beam offers the possibility of good focusing, which allows us to conduct chemical reactions, including the heterogeneous oxidation of metals, locally, with high spatial resolution. In this case, the absorption mechanisms of the laser beam vary for metals and for oxides, resulting from a thermochemical reaction and represent semiconductors. For semiconductors, the intrinsic, intraband, impurity, or lattice absorption takes place. The morphology of a metal surface also influences its optical absorption capacity. The improvement of beam shaping systems with elements of computer optics, namely diffractive freeform optics, provides an opportunity for an efficient control of chemical processes by achieving the desired redistribution of the laser beam power density. Laser thermochemical processes of the formation of quasi-one-dimensional nanostructured metal oxides are of great interest for advanced research and for a wide range of applications. A special feature of these processes is that, in the case of a frequency-modulated laser beam the synergy between the heat associated effects of the laser pulses and the laser-induced vibrations allows for a significant increase in the diffusion coefficient, which is stimulated by the non-stationary stress-strain state of the material. Ensuring the means of control over the thermochemical reaction in local sections of the laser exposure zone is an issue that can be solved by adapting the shape of the laser beam by the diffractive freeform optics. The gained knowledge contributes as a foundation for new photonic technologies oriented on the formation of nanostructured metal oxides, involving control over the morphology of the synthesized structures.

Experimental investigation on the ductile machinability of fused silica during in-situ laser assisted diamond cutting

Fused silica finds widespread applications in optical equipment; nevertheless, the machining of fused silica to obtain high-quality surfaces was a common problem in the industry. In-situ laser assisted diamond cutting (LADC) is a promising process for machining hard and brittle materials. In this study, systematic numerical analysis and experiments were conducted to investigate the ductile machinability of fused silica in in-situ LADC. The laser beam path and power density passing through the diamond tool were determined through optical simulation. The corresponding laser heating experiment of fused silica was carried out using the finite element (FE) simulation, aiming to derive the temperature distribution under different laser power levels. The comparison between the temperature values obtained experimentally and those predicted by the FE simulation confirmed the high accuracy of the developed FE model. The influence of laser power on the ductile machinability of fused silica was investigated quantitatively through grooving and end face turning experiments. The experimental results have shown that the ductility and machinability of fused silica under in-situ LADC were improved. With the laser assistance, the critical depth of cut (DOC) was increased up to 294.9 %, from 82.06 nm to 324.03 nm. Compared to conventional single point diamond turning, a significant improvement in the surface quality was obtained, resulting in the formation of a smooth and homogenous surface with a Sa of 19.4 nm for a laser power of 11 W.

Centrifugal atomization of stainless-steel rotating rods melted by a high-power LASER beam

316L grade stainless steel powders were produced by centrifugal atomization during the melting of a rotating rod heated by a high-power LASER beam. The feasibility has been demonstrated by atomizing a range of stainless steel rods. The atomization process has been observed via high-speed imaging and fragmentation regimes have been identified according to a literature review on the rotating electrode process (REP). Results were compared with literature data and an existing prediction model for such a process. High-speed observation can monitor the present process and it is shown that a solidified layer of metal is formed at the edge of the rod during the process inducing metal flake ejection due to the centrifugal stresses. Effects of incident LASER beam power density, ejection speed and oxygen content of the surrounding atmosphere on the particle size distribution and the sample surface have been studied and compared with literature data on classical REP atomizers. The study focuses on the production of irregular particles during the atomization process and highlights the influence of the oxygen content in the surrounding atmosphere on the fragmentation regime and the resulting particle size distribution.

Beam Shaping in Laser Powder Bed Fusion: Péclet Number and Dynamic Simulation

A uniform distribution of power density (energy flux) in a stationary laser beam leads to a decrease in the overheating of the material in the center of the laser beam spot during laser powder bed fusion and a decrease in material losses due to its thermal ablation and chemical decomposition. The profile of the uniform cylindrical (flat-top) distribution of the laser beam power density was compared to the classical Gaussian mode (TEM00) and inverse Gaussian (donut) distribution (airy distribution of the first harmonic, TEM01* = TEM01 + TEM10). Calculation of the Péclet number, which is a similarity criterion characterizing the relationship between convective and molecular processes of heat transfer (convection to diffusion) in a material flow in the liquid phase, shows that the cylindrical (flat-top) distribution (TEM01* + TEM00 mode) is effective in a narrow temperature range. TEM00 shows the most effective result for a wide range of temperatures, and TEM01* is an intermediate in which evaporation losses decrease by more than 2.5 times, and it increases the absolute laser bandwidth when the relative bandwidth decreases by 24%.

Influence of Microstructure and Chemical Composition on Microhardness and Wear Properties of Laser Borided Monel 400.

In this study, wear properties of Monel 400 after laser alloying with boron are described. Surfaces were prepared by covering them with boron paste layers of two different thicknesses (100 µm and 200 μm) and re-melting using diode laser. Laser beam power density was equal to 178.3 kW/cm2. Two laser beam scanning velocities were chosen for the process: 5 m/min and 50 m/min. Surfaces alloyed with boron were investigated in terms of wear resistance, and the surface of untreated Monel 400 was examined for comparison. Wear tests were performed using counterspecimen made from steel 100Cr6 and water as a lubricant. Both quantitative and qualitative analysis of surfaces after wear test are described in this paper. Additionally, microstructures and properties of obtained laser alloyed surfaces are presented. It was found that the wear resistance increased from four to tens of times, depending on parameters of the laser boriding process. The wear mechanism was mainly adhesive for surfaces alloyed with initial boron layer 100 µm thick and evolves to abrasive with increasing boron content and laser beam scanning velocity. Iron particles detached from counterspecimens were detected on each borided surface after the wear test, and it was found that the harder the surface the less built-ups are present. Moreover, adhered iron particles oxidized during the wear test.

Microstructural banding of directed energy deposition-additively manufactured 316L stainless steel

The microstructures of 316 L stainless steel created by rapid solidification are investigated by comparing the similar microstructures of individual hatches of directed energy deposition additive manufacturing (DED-AM) and those of single, laser surface-melted tracks formed on a solid plate. High recoil pressure, which is exponentially dependent on the laser beam power density, induces convection of the melt pool, which causes formation of microstructural bands in the as-solidified microstructure. The microstructural bands are associated with changes in the chromium concentration and are a significant component of the inhomogeneous microstructure of DED-AM.

Influence of welding parameters on electromagnetic supported degassing of die-casted and wrought aluminum

Laser beam welding of aluminum die casting is challenging. A large quantity of gases (in particular, hydrogen) is absorbed by aluminum during the die-cast manufacturing process and is contained in the base material in solved or bound form. After remelting by the laser, the gases are released and are present in the melt as pores. Many of these metallurgic pores remain in the weld seam as a result of the high solidification velocities. The natural (Archimedean) buoyancy is not sufficient to remove the pores from the weld pool, leading to process instabilities and poor mechanical properties of the weld. Therefore, an electromagnetic (EM) system is used to apply an additional buoyancy component to the pores. The physical mechanism is based on the generation of Lorentz forces, whereby an electromagnetic pressure is introduced into the weld pool. The EM system exploits the difference in electrical conductivity between poorly conducting pores (inclusions) and the comparatively better conducting aluminum melt to increase the resulting buoyancy velocity of the pores. Within the present study, the electromagnetic supported degassing is investigated in dependence on the laser beam power, welding velocity, and electromagnetic flux density. By means of a design of experiments, a systematic variation of these parameters is carried out for partial penetration laser beam welding of 6 mm thick sheets of wrought aluminum alloy AlMg3 and die-cast aluminum alloy AlSi12(Fe), where the wrought alloy serves as a reference. The proportion of pores in the weld seams is determined using x-ray images, computed tomography images, and cross-sectional images. The results prove a significant reduction of the porosity up to 70% for both materials as a function of the magnetic flux density.

Laser Alloying Monel 400 with Amorphous Boron to Obtain Hard Coatings.

In this study, Monel 400 is laser heat treated and laser alloyed with boron using diode laser to obtain adequate remelting and to improve the microhardness Single laser tracks were produced on the surface with three different laser beam scanning velocities: 5, 25, and 75 m/min. In order to enrich Monel 400 with boron surfaces were covered with initial layers of two different thicknesses before the process: 100 μm and 200 μm. In all experiments, laser beam power density was equal to 178 kW/cm2. Produced laser tracks were investigated in areas of microstructure, depth of remelting and microhardness. It was found that remelted zones are mainly composed of dendrites and the more boron is present in the laser track, the dendritic structure more fragmented is. Depth of remelting and microhardness depend not only on the laser beam scanning velocity but also on thickness of the initial boron layer. While microhardness of Monel 400 is equal to approximately 160 HV0.1, microhardness up to 980 HV0.1 was obtained in areas laser alloyed with boron.

Improvement of adhesion force of hard coatings to cemented carbides by laser heating

ABSTRACTLaser heating with different power densities was applied to hard coatings to improve their adhesion to cemented carbides substrate (cutting edges). The adhesion force was determined by critical load Lc in the scratch test using an automatic scratch tester constructed at Poznan University of Technology. The determination of adhesion force (the value of critical load, measured during the scratch test) was carried out based on the analysis of the vibration spectrum. Scanning electron microscopy, 3D surface profiling and X-ray mapping were used to verify the coating state after laser heating. The results indicate that significant increase of Lc can be achieved for the laser beam power density of up to 4100 W/cm2, for monolayer (single – Ti(C,N) and double – Ti(C,N)+TiN) coatings only. Higher beam power leads to coating cracking and decohesion of the substrate. Rapid laser heating is not recommended for the alumina layer in tri-layer coating (TiC+Al2O3+ Ti(C,N)) because alumina layer has low heat impact resistance. Also new in this article is the fact that as a result of laser heating, the chemical composition of the coating changes, which affects its adhesion to the substrate. Considerable increase in adhesion after laser heating of single and double coatings to substrate made of cemented carbides should contribute to better wear resistance of coated edges during machining.

Laser-stimulated piezo-optical and third harmonic generation studies for Na2O–Sb2O3 glass ceramics-influence of gold ions

Sodium antimonate glass ceramics with different concentrations of Au2O3 were synthesized. The prepared samples were characterized by XRD, XPS, SEM and TEM techniques. These studies have revealed that the samples consist of multiple crystalline phases composed of Sb3+, Sb5+, Au3+ ions, and Au0 particles; moreover these studies have indicated growing proportion of Au0 particles and Sb5+crystal phases (Na2Sb2O6) with increase of Au2O3 concentration. IR and Raman spectral studies have pointed out an increasing degree of polymerization of the glass network with increase of Au2O3 content while optical absorption studies indicated surface plasmon resonance effects. Nd: YAG laser (λ = 1320 nm and pulse width 8 ns) was used for inducing third harmonic generation (THG) signal. Later, THG signal intensity of Nd: YAG laser (λ = 1064 nm and pulse width of 20 ns) vs fundamental beam power density was recorded. The results indicated the maximum intensity for the samples containing a low concentration of Au2O3. For inducing piezo-optical effects, Nd: YAG laser (λ = 1064 nm) and its doubled frequency beam λ = 532 nm (with simultaneous mechanical pressure) were used. The cw He-Ne laser of 20 mW (with beam diameter about 0.5 mm) was used as probing beam for measuring the piezo-optical effects in the photo-polarized samples. The variation of the intensity of the THG beam and piezo-optical coefficients were found to be the maximal for the samples mixed with small quantities of Au2O3. The detailed analysis of XRD, SEM, EPR, IR, optical absorption spectral results suggested that concentrations of Na3SbO3 and also Au2O3 crystal phases are maximal in these samples and are responsible for the maximal photoinduced effects, while the increasing presence of Na2Sb2O6 crystal phases and Au0 metallic particles are found to be hindrance for generation of third harmonic beams and also piezo-optical effects. Overall, the obtained results of nonlinear optical (NLO) and piezo-optical studies indicated that Na2O-Sb2O3 glass ceramics containing small traces of Au2O3 are useful for considering them for nonlinear optical triggering devices and piezo-electric devices.

Investigation on rock breaking for sandstone with high power density laser beam

High power density laser was applied during rock breaking for sandstone with different laser parameters. The fracture morphologies and quantitative characterization as well as the parameters on specific energy and rate of perforation were analyzed. It was found that a complex crack net structure was formed and the cracks area and length on the surface of sandstone specimen almost increased linearly with the number of laser perforation. Furthermore, the diameter and depth of laser perforation, the maximum width of cracks, the maximum depth and total circumferential length of side cracks increased with laser power and laser irradiation time. The experimental results demonstrated that the SE values gradually decreased with laser power while the ROP values increased. However, the SE values of sandstone by laser perforation presented a trend of first increase and then decrease, while the ROP values decreased gradually with laser irradiation time. A smooth glaze layer was formed on the inner wall of the laser perforation, where there also was plenty of shrinkage hole. Obvious cracks were generated and propagated along the inner wall. Typical brittle fracture occurred with the mix fracture mechanisms of intergranular fracture and transgranular fracture.

Optimizing of porous silicon alloying process with bimetallic nanoparticles

Bimetallic Ag–Au alloy nanoparticles with a tunable size and composition were synthesized by laser beam power density. A set of Psi substrates with different morphologies fabricated by laser-assisted etching process with laser power density from 10 to 40 mW/cm2 was explored as a substrate for materialization bimetallic Ag–Au alloy nanoparticles by a simple immersion plating process of Psi in a mixture of AgNO3 and HAuCl4 solutions. The materialization of alloy nanoparticles was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray analysis (EDS). The results showed that the sizes and distribution of Ag–Au alloy nanoparticle sizes were easily well-ordered by changing the surface morphologies of Psi layer. Pore-like structures with different pores shapes: ultra-fine pores, irregular (grotto form), circular, and star full pore shape (gambling pores) with different sizes were prepared by changing the irradiation laser power density. Bimetallic Ag–Au alloy nanoparticles, phases, crystalline size, specific surface area, and growth sites of Ag–Au alloy nanoparticles were significantly influenced by pore shape. The lower nanoparticle size with higher S.S.A was obtained when the laser power intensity was about 30 mW/cm2.

Microstructure and selected properties of Monel 400 alloy after laser heat treatment and laser boriding using diode laser

This study concentrates on describing effects of laser heat treatment of Monel 400 and laser alloying its surface with boron. Surfaces without and with initial boron layers of two different thicknesses (100 and 200 μm) were processed using diode laser. Laser beam power density was constant and equal to 178.3 kW/cm2. To determine the influence of laser beam scanning velocity on final properties of treated surfaces, laser beam scanning velocity was set on four different values: 5, 25, 50, and 75 m/min. Microstructures of pure Monel 400 and Monel 400 alloyed with 100 μm boron content are composed of dendrites. Areas laser alloyed with 200 μm boron layer contain mainly nickel borides. Boron addition in Monel 400 surface results in microhardness increase in which the level depends on boron content and the laser beam scanning velocity. Increasing the thickness of initial boron layer and speeding up the laser beam lead to obtain higher microhardness. On the other hand, areas laser alloyed with 200 μm boron layer using laser beam scanning velocity equal to 75 m/min contain deep cracks which propagate from the surface through the produced layer. Furthermore, it was found that the depths of laser heat-treated areas depend significantly on the boron content. As the result of differences in thermal properties between Monel 400 and boron, depth of re-melted zones in some conditions does not lower with increasing laser beam scanning velocity.

Optically poled SHG and THG effects in cesium doped zinc oxide nanorods

The hexagonal wurtzite structure of the synthesized undoped and cesium (Cs) doped zinc oxide (ZnO) nanorods were confirmed with X-ray diffraction patterns. Further analysis with field emission scanning electron microscope images and energy dispersive X-ray spectra revealed the c-axis oriented hexagonal morphology of the samples with chemical composition. Optical poling through 337 nm nitrogen laser has been adopted to enhance the nonlinear optical properties. When the power density of the fundamental laser beam from Nd:YAG laser of 1064 nm matched with the band edge of the samples, resonant absorption takes place leading to the enhanced NLO properties. The interstitial occupancy of the dopants in 3 and 5 mol% CsZnO increases the band tailing in the forbidden energy gap. The minimum of Urbach energy calculated from UV–Vis absorption spectra corresponding to 1 mol% CsZnO revealed more ordering in the sample. More enhanced second and third order NLO effects were observed in this sample having larger crystallite size, lesser diameter, lesser band gap, minimum urbach energy and higher electron–phonon interaction.

THE POSSIBILITIES OF STRENGTHENING OF THE SURFACE LAYER OF NODULAR IRON BY LASER ALLOYING WITH SILICON NITRIDE ON THE EXAMPLE OF A ROCKER ARM

In the order to increase the resistance to the friction wear of machine parts appropriate surface treatment application is needed. The aim of presented research was to evaluate the laser alloying with silicon nitride effects obtained in the surface layer of nodular iron and to select the laser treatment parameters that should be appropriate for the treatment of the one of the engine parts, which is a rocker arm. After implementation of silicon nitride into the nodular iron surface layer using laser heating, a uniform, fine, dendritic microstructure similar to the hardened white cast of the allayed zone was created in all performed variants. This microstructure resulted in at least 4-times higher hardness in comparison to the core material. The hardness and the alloyed zone dimensions were dependent on the laser heat treatment variant. The laser beam power density of 41 W/mm2 and its velocity of 2.8 mm/s were selected for the treatment of the rocker arm. It was caused by the effects obtained in the surface layer. With these parameters, it was possible to achieve the hardness of 1300 HV0.1 and the width of the alloying zone of over 4 mm, which is enough to strengthen the surface area of the rocker arm most exposed to the tribological wear.

Development of highly sensitive optical sensor from carbon nanotube-alumina nanocomposite free-standing films: CNTs loading dependence sensor performance Analysis

We report a highly sensitive optical sensor based on free-standing thin films derived from multi-walled carbon nanotubes (MWCNTs)-Alumina nanocomposite by Gel-cast technique. The sensing principle involves the change in the resistance/conductance of the fabricated nanocomposite film on interaction with the optical stimulus. The performance of the sensor strongly depends − on loading and dispersion of MWCNTs in Alumina host matrix; wavelength; and power density of the laser beam. The optimized loading of CNTs to achieve maximum sensitivity was 1.5wt%. The sensitivity of the sensor shows linear relationship with power density of the laser beam and found to be highly sensitive in Vis-NIR region. The maximum sensitivity of the sensor is found to be 13.2% at 635nm wavelength, 3.5mW/mm2 power density of laser beam and at 1.5wt% MWCNTs loading in Alumina host matrix. At this loading, the response time and recovery time of the sensor are found to be 1.7s and 2.1s respectively. The additional advantage of the present sensor is that it is facile and cost-effective method to fabricate high performance optical sensors.

Influence of laser heat treatment on microstructure and properties of surface layer of Waspaloy aimed for laser-assisted machining

In this study, a nickel-based superalloy, Waspaloy, was laser heat treated with diode laser. Single laser tracks were manufactured with different laser beam power densities between 63 and 331 kW/cm2, and scanning laser beam speed ranged from 5 to 100 m/min. It was found that laser heat treatment of Waspaloy causes decrease in material hardness—the microhardness in laser tracks is about 300 HV0,1 while the microhardness of substrate is ranged from 300 to 600 HV0,1—which is a positive phenomenon for laser-assisted machining of investigated material. Impacts of laser heat treatment parameters on laser tracks properties were identified for obtaining multiple laser tracks with the most homogenous thickness. Moreover, roughness of heated layers was measured to specify surface quality after laser heat treatment. Multiple laser tracks were produced using different scanning laser beam speed and distances between laser tracks ranged from 0.125 to 1 mm. It was found that if scanning laser beam speed is 75 m/min and distance between laser tracks is equal to or lower than 0.25 mm, in microstructures of multiple laser tracks, cracks are occurring. The most suitable laser heat parameters for obtaining heated layers, and which can be used for laser-assisted machining, were identified as laser beam power density 178.3 kW/cm2, scanning laser beam speed 5 m/min, and distance between laser tracks 0.125 mm.

Photobiomodulation therapy action in wound repair skin induced in aged rats old: time course of biomarkers inflammatory and repair.

Previous studies have discussed an inverse correlation between age and wound healing, because it relates to the association of aging with a gradual decrease in healing capacity. Treatment with photobiomodulation therapy (PBMT) improves wound healing by inducing increases in mitotic activity, numbers of fibroblasts, collagen synthesis, and neovascularization. Therefore, this study aimed to evaluate the effects of PBMT in cutaneous wound healing in aged rats. A punch biopsy of 8mm in diameter was performed to produce a skin wound. The study included 45 male rats, of which 15 were young (30days) and 30 were elderly (500days). The 45 animals were distributed into 3 experimental groups, which were subjected to skin wounds and 1 aged group received PBMT, with a 30-mW laser beam (power density of 1.07W/cm2), beam area of 0.028cm2, and λ660nm produced through active phosphide Gallium-Aluminum-Indio (InGaAIP). The PBMT application took the form of a single-point transcutaneous method, with a total energy of 2 joules per wound site, energy density of 72J/cm2, and time of 1min and 7s. Analysis was performed to verify the effect of PBMT on the quantity of collagen I and III, metalloproteinase 3 and 9 (MMP-3 and MMP-9), tissue inhibitor of metalloproteinase-2 (TIMP-2) and of vascular endothelial growth factor (VEGF) at the wound site by immunohistochemistry, cytokine-induced neutrophil chemoattractant (CINC)-1, by enzyme-linked immunosorbent assay (ELISA) and interleukin (IL)-6 real-time polymerase chain reaction (RT-PCR). That we conclude LLLT is effective in the modulation of inflammatory mediators IL-6, CINC-1, VEGF, MMP-3, MMP-9 and TIMP-2 as well as increased collagen production in aged animals during different phases of the tissue regeneration process. However, the effects of PBMT obtained in the aged animals (aged LLLT group) suggest that new dosimetries should be tested to achieve better results.