Varying Laser Power Research Articles

Evolution of the \u03b5 and \u03b3 phases in biodegradable Fe\u2013Mn alloys produced using laser powder-bed fusion

The key feature of Fe–Mn alloys is gradual degradability and non-magneticity, with laser power bed fusion (LPBF) parameters influencing the microstructure and chemical composition. Our study focuses on biodegradable Fe–Mn alloys produced by mechanically mixing pure metal feedstock powders as part of the LPBF process. The Mn content and, consequently, the γ-ε phase formation in LPBF samples are directly correlated with an adapted energy–density (E) equation by combining the five primary LPBF parameters. We varied laser power (P) in a range of 200–350 W and scanning speed at 400 and 800 mm/s, and a comprehensive study was performed on samples with similar E. The study also showed an almost linear correlation between the LPBF's laser power and the material's hardness and porosity. The corrosion resistance was significantly reduced (from 13 to 400 μm/year) for the LPBF samples compared to a conventionally produced sample due to the dual-phase microstructure, increased porosity and other defects. The static immersion test showed that the process parameters greatly influence the quantity of oxides and the distribution of their diameters in the LPBF samples and, therefore, their corrosion stability. The most challenging part of the study was reducing the amount of ε phase relative to γ phase to increase the non-magnetic properties of the LPBF samples.

Passivated, Highly Reflecting, Laser Contacted Ge Rear Side for III-V Multi-Junction Solar Cells

This article describes the successful integration of a passivated, highly reflecting Ge rear side into a III-V multijunction solar cell. The use of lowly doped Ge and the new rear side leads to the aimed increase in Ge cell current up to 1.6 mA.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , demonstrated by external quantum efficiency and I-V measurements. For the contact formation, two different types of laser processes were conducted and evaluated-the laser fired contact route and the PassDop route. In both cases, the formation of a local back surface field preserves the passivation of the contact points. A laser pitch and laser power variation leads to a good performing back contact. The passivation effect is proven experimentally and is qualitatively accessed with cell simulations.

A simple analytical model of laser direct-drive thin shell target implosion

A high-neutron yield platform imploded by a thin shell target is generally built to probe nuclear science problems, and it has the advantages of high neutron yield, ultrashort fusion time, micro fusion zone, isotropic and monoenergetic neutron. Some analytical models have been proposed to interpret exploding-pusher target implosion driven by a long wavelength laser, whereas they are imperfect for a 0.35 μm laser implosion experiment. When using the 0.35 μm laser, the shell is ablated and accelerated to high implosion velocity governed by Newton’s law, ablation acceleration and quasi-adiabatic compression models are suitable to explain the implosion of a laser direct-drive thin shell target. The new analytical model scales bang time, ion temperature and neutron yield for large variations in laser power, target radius, shell thickness, and fuel pressure. The predicted results of the analytical model are in agreement with experimental data on the Shenguang-III prototype laser facility, 100 kJ laser facility, Omega, and NIF, it demonstrates that the analytical model benefits the understanding of experiment performance and optimizing the target design of high neutron yield implosion.

Comparison of the microstructure, mechanical properties and distortion of stainless steel 316 L fabricated by micro and conventional laser powder bed fusion

Micro laser powder bed fusion (μLPBF) technology offers great benefits to industries as it enables fabrication of complicated metallic components with greater accuracy and minimum feature size as small as 50 µm. Employing finer laser beam and smaller metal powder in μLPBF leads to many variations from the conventional LPBF (cLPBF) in terms of microstructure, mechanical properties and distortion, which have not yet been well understood. This work provides a comparative study of the μLPBF and cLPBF of the well-known material, stainless steel 316 L based on the surface quality, crystal structure, solidification microstructure, tensile properties and distortion of as-printed parts, and their sensitivities to μLPBF process parameters are also studied. Results show that lower surface roughness (Ra= 3.4 µm for top surfaces) is obtained after μLPBF. Stronger < 110 > texture along building direction is developed in the μLPBFed samples, accompanied with smaller grain size, higher density of low-angle grain boundary (LAGB) and geometrically necessary dislocation (GND). μLPBF creates a cellular microstructure with smaller cell size and cell wall thickness compared with cLPBF. The yield strength of μLPBFed samples is marginally lower than cLPBFed ones, which is dominated by the difference of compositional microsegregation in the cellular structures. Both cLPBFed and μLPBFed samples show a strong anisotropy in terms of yield strength, ductility and deformation behavior. The distortion measurement of the printed cantilever design suggests a lower level of macroscopic residual stresses in the μLPBFed samples due to the smaller molten pool and more thermal cycles. Moreover, the microstructure, mechanical properties and distortion of μLPBFed samples remain at the same level with variation of laser power and scanning speed. Overall, better surface finish, finer microstructure, more desirable mechanical properties and smaller part distortion can be obtained by μLPBF.

Additive manufacturing of aluminium alloy 2024 by laser powder bed fusion: microstructural evolution, defects and mechanical properties

PurposeThe purpose of this study is to investigate the microstructural evolution of high-strength 2024 Al alloy prepared by the laser powder bed fusion (L-PBF) additive manufacturing (AM) route. The high-strength wrought Al alloy has typically been unsuitable for AM due to its particular solidification characteristics such as hot cracking, porosity and columnar grain growth.Design/methodology/approachIn this research work, samples were fabricated using L-PBF under various laser energy densities by varying laser power and scan speed. The microstructural features that developed during the solidification are correlated with operating laser parameters. In addition, finite element modelling (FEM) was performed to understand the experimentally observed results.FindingsMicrostructure evolution and defect formation have been assessed, quantified and correlated with operating laser parameters. Thermal behaviour of samples was predicted using FEM to support experimental observations. An optimised combination of intermediate laser power and scan speed produced the least defects. Higher energy density increased hot tearing along the columnar grain boundaries, while lower energy density promoted void formation. From the quantitative results, it is evident that with increasing energy density, both the top surface and side wall roughness initially reduced till a minimum and then increased. Hardness and compressive strength were found to decrease with increasing power density due to stress relaxation from hot tearing.Originality/valueThis research work examined how L-PBF processing conditions influence the microstructure, defects, surface roughness and mechanical properties. The results indicates that complete elimination of solidification cracks can be only achieved by combining process optimisation and possible grain refining strategies.

Architectural tunability of mechanical metamaterials in the nanometer range

Mechanical metamaterials can exhibit extraordinary mechanical properties due to a specific architecture rather than the base material. When the structural dimensions reach the sub-micrometer range, such micro- and nanolattices may also benefit from size-affected mechanical properties. However, well-defined geometric adjustments on this length scale are limited by the resolution limits of the underlying manufacturing technology. Here, we used a 3D direct laser writing (3D-DLW) process with integrated laser power variation to fabricate polymeric microlattices, which were then pyrolized to obtain glassy carbon structures. The laser power was varied by a quadratic function along the beams from one node to another over the length of a unit cell, thus enabling geometric adjustments in the range of a few nanometers. Rounded and notch-like joints were realized by increased and reduced laser power at the nodes, respectively. Furthermore, the beam cross section was varied along the beam length, thereby creating convex or concave beam shapes. A laser power variation opens up new design possibilities for micro- and nanolattices in the sub-micrometer range by overcoming process related limitations.

Exploring the Use of Ramsey-CPT Spectroscopy for a Microcell-Based Atomic Clock.

We investigate the application of Ramsey spectroscopy for the development of a microcell atomic clock based on coherent population trapping (CPT). The dependence of the central Ramsey-CPT fringe properties on key experimental parameters is first studied for optimization of the clock's short-term frequency stability. The sensitivity of the clock frequency to light-shift effects is then studied. In comparison with the continuous-wave (CW) regime case, the sensitivity of the clock frequency to laser power variations is reduced by a factor up to 14 and 40.3 for dark times of 150 and [Formula: see text], respectively, at the expense of intensity 3.75 times higher for short-term stability optimization. The dependence of the clock frequency on the microwave power is also reduced in the Ramsey case. We demonstrate that the Ramsey-CPT interrogation improves the clock Allan deviation for averaging times higher than 100 s. With a dark time of [Formula: see text], a clock fractional frequency stability of 3.8 ×10-12 at 104 s is obtained, in comparison with the level of 8×10-11 obtained in the standard CW case, in similar environmental conditions. These results demonstrate that Ramsey-based interrogation protocols might be an attractive approach for the development of chip-scale atomic clocks (CSACs) with enhanced mid- and long-term stability.

Biostimulation Effects and Temperature Variation in Stimulated Dielectric Substance (Diabetic Blood Comparable to Non-Diabetic Blood) Based on the Specific Absorption Rate (SAR) in Laser Therapy

Human blood exposed to irradiation absorbs electromagnetic energy which consequently effect temperature variation. The evaluation of Specific Absorption Rate (SAR) of human blood helps to ascertain the values for optimum laser power, time, and temperature variation for fair therapy to avoid blood-irradiation pollution but to enhance its rheological properties when using lasers. Prior knowledge of blood SAR evaluating its dielectric properties is significant, but this is under investigation. We investigate the appropriate SAR threshold value as affected by temperature variation using fundamental blood dielectric parameters to optimize the effect of low-level laser therapy based on physiological and morphological changes of the stimulated diabetic blood. Studies were carried out with Agilent 4294A impedance analyser at frequencies (40Hz – 30 MHz) and designed cells (cuvettes) comprises of electrodes were used in the pre- and post-irradiations measurements. At different laser power outputs, blood samples were subjected to various irradiation durations using portable laser diode-pumped solid state of wavelength 532 nm. Results showed laser at low energy is capable of moderating morphologically the proportion of abnormal diabetic red blood cells. Hence, there is a significant effect using a laser at low energy, as non-medicinal therapy in controlling diabetic health conditions. The positive biostimulation effects on the irradiated diabetic blood occurred within absorbance threshold SAR values range of 0.140?0.695 W/kg and average temperatures range of 24.2?28.0 0C before blood saturation absorbance peak. There is morphological stimulation at a laser power of 50 mW for an exposure time of 10–15 minutes and 60 mW for 5–10 minutes of laser therapy that demonstrates better blood rejuvenated conditions. This occurred within the threshold SAR of 0.140?0.695 W/kg and average temperatures range of 24.2?28.0 0C. Therefore, the diabetic blood irradiated using laser output powers of 70 and 80 mW during exposure durations of 5,10, 15 and 20 minutes rather bio-inhibits positive blood stimulation which has resulted to crenation due to excessive irradiation.

Innovative Infrared-pulsed laser assisted RF sputtered β-Ga2O3 thin film at low temperature process

Innovative new method for the pulsed laser assisted radio-frequency sputtering at low temperature process was successfully applied for the β phase Ga2O3 thin film as wide band gap materials. Thin film of wide bandgap material, β-Ga2O3, was successfully deposited on SiO2/Si and quartz substrates by employing radio-frequency sputtering system with assisting process of ytterbium-laser irradiation. Both sputtering system and infrared pulsed laser irradiation process were employed at the same time to increase the acquired energy densities for the adatoms on the thin film growth process. X-ray diffraction patterns (XRD) showed the prominent peaks of unique crystalline properties of Ga2O3 thin films in β phase. The optical energy bandgap of Ga2O3 thin films derived from spectral transmittance was measured in the range of 4.90–5.06 eV for a variation of laser power. High resolution X-ray photon spectroscopy (XPS) analysis showed that O 1s and Ga 3d position in core level. We confirm that infrared optical energy was effectively added to fabricate β-Ga2O3 thin film by employing the Yb-laser-assisted RF sputtering process.

In situ X-ray tomography investigations on laser welding of copper with 515 and 1030 nm laser beam sources

Abstract A paramount challenge in laser micro welding is to design welding processes both highly energy efficient and precise regarding weld depth and surface roughness. With society’s increasing interest in alternative energy storage systems, the demand for copper connections increases and processes for contacting electronic components for batteries and fuel cells are gaining in importance. Fiber lasers with a wavelength in the near infrared range have established themselves for this purpose [1,2]. However, the high thermal conductivity and low energy absorption of infrared radiation of copper cause significant difficulties such as pore and spatter formation. An increase in absorption of the electromagnetic radiation from 55 % (515 nm) of copper at room temperature, leads to a higher energy input into the material during the process which promotes lasers in the visible wavelength range as a more efficient alternative to near infrared lasers [3]. In this work, we investigate in situ X-ray tomography experiments during laser beam welding of copper with 515 nm and 1030 nm laser beam sources. Both lasers are equipped with similar optical setups to achieve identical focal diameters on the material surface. We investigate the difference in the geometric shape of the keyholes during the process. A wide range of laser parameters is investigated to create a basis for comparison with our numerical keyhole model [4]. It is found, that a significant difference in the depth of the keyhole depending on the wavelength occurs. A higher sensitivity to the variation of feed rate and laser power is observed for the 1030 nm laser source than for the 515 nm laser source.

Effect of laser power density on the electrochromic properties of WO3 films obtained by pulsed laser deposition

Pulsed laser deposition (PLD) was used to prepare tungsten trioxide (WO3) films on ITO substrates with a varying laser power density of 4.0–5.5 W/cm2. XPS indicated that when the laser power density decreased, the peak positions of the W 4f and O 1s orbits shifted slightly to low energy due to the difference in oxygen vacancies. As the laser power density decreased, W6+ gradually replaced the lattice position of O2−, increasing oxygen vacancies in the lattice. The transmittance modulated values (ΔT) were over 44% at 830 nm, indicating strong absorption by the WO3 thin films in the near-infrared ray. The switching time of the WO3 thin films between bleached states and coloured states decreased as the laser power density increased due to the amorphous structure, morphology, and lower oxygen deficiency at a high power density. The high ΔT and very fast switching time of tb (1.09 s) and tc (6.01 s) demonstrated the excellent electrochromic (EC) properties of the WO3 films prepared by PLD.

A Motion State-based Printing Time Modeling and Printing Cost Analysis for Laser Direct Deposition Process

Laser direct deposition (LDD) process is widely used in the manufacture of complex parts with the advantages of high-precision and high-performance, while it is facing the problems of low efficiency, high-energy consumption, and high cost. During LDD, printing time not only affects efficiency, energy, and cost but also is constrained by factors of parts—volume, process parameters, and deposition modes. Printing time modeling is quite difficult when taking cladding head motion and deposition path into consideration. In this research, the discontinuous and non-uniform motion state of cladding head was obtained by analyzing the variation of laser power, and the discontinuous deposition path was further acquired by discussing the occurrence of light powder coupling. Therefore, a motion state-based printing time model was proposed to quantify sub-time during deposition process. Subsequently, a printing time-driven printing cost model was established to reveal the correlation of efficiency, energy, and cost under different deposition modes. Orthogonal experiment and comparative experiment were carried out. Results showed that the printing time model accuracy exceeds 90%. The comparative results of different deposition modes suggested that printing time is positively related to the continuity length of deposition path, thus leading to significant differences in energy consumption and printing cost. According to the structure and sensitivity analysis of printing cost, machine and powder cost account for 40 and 36%, respectively, and machine purchase price and powder price are the most sensitive factors. This research provides a novel methodology for measuring printing time and offers a comparative assessment of deposition modes for sustainable manufacturing.

Effect of powder size and processing parameters on surface, density and mechanical properties of 316L elaborated by Laser Powder Bed Fusion

Despite the attractive capabilities of additive manufacturing (AM) technology, the industrialization of these processes remains very low. This is attributed to the complexes physical phenomena involved in the AM process and the layered structure of the produced parts. Intense research work is still needed for the prediction and optimization of AM parts mechanical properties. In this study, the influence of particle size distribution (PSD) of stainless steel 316L (SS 316L) powders on AM parts properties was investigated. Four PSD were used to produce test parts and compare the resulting porosity, surface roughness and macro-hardness. The SS 316L specimens were fabricated by Laser Powder Bed Fusion process (LPBF) on a SLM 125HL machine using variations in laser power and scan velocity. Computed scan tomography (CT) was used to characterize the defects. Lack of fusion and keyhole defects were detected. Defects were detected even in nearly dense parts. The powder size distribution was found to affect the porosity. Results from CT tests were used to identify the minimum achievable porosities for each powder, through the appropriate selection of process parameters. The macro-hardness and surface roughness were found to vary with the powder properties.

Laser Welding of Grey Cast Iron with Spheroidal Graphite-Influence of Process Parameters on Crack Formation and Hardness

In the investigation at hand, sheets of ferritic and pearlitic grey cast iron with spheroidal graphite are welded using a fiber-laser. The influence of varying laser power and welding speed on the macroscopic characteristics of the weld seam and crack formation are analyzed and discussed. Substantial crack formation with crack densities of up to 2.93 cm−1 are found. Furthermore, hardness measurements are conducted to evaluate the formation of brittle phases within the weld metal and heat-affected zone. Peak hardness values of up to 860 HV0.3 and 975 HV0.3 are identified in EN-GJS-400-15 and EN-GJS-700-2, respectively. Subsequently, a proposition on the dependence of crack formation on weld seam width is given. Furthermore, the influence of nickel-containing filler material on the microstructure, crack formation and hardness is studied. It can be derived from the results that laser-beam welding of grey cast iron with spheroidal graphite requires further research in order to achieve crack-free weld seams and hinder the formation of undesirable, brittle phases.

Processability and Optimization of Laser Parameters for Densification of Hypereutectic Al–Fe Binary Alloy Manufactured by Laser Powder Bed Fusion

Centimeter-sized samples of hypereutectic Al–15 mass% Fe alloy were manufactured by a laser powder bed fusion (L-PBF) process while systematically varying laser power (P) and scan speed (v). The effects on relative density and melt pool depth of L-PBF-manufactured samples were investigated. In comparison with other Al alloys, a small laser process window of P = 77–128 W and v = 0.4–0.8 ms−1 was found for manufacturing macroscopically crack-free samples. A higher v and P led to the creation of macroscopic cracks propagating parallel to the powder-bed plane. These cracks preferentially propagated along the melt pool boundaries decorated with brittle θ-Al13Fe4 phase, resulting in low L-PBF processability of Al–15%Fe alloy. The deposited energy density model (using P·v−1/2) would be useful for identifying the optimum L-PBF process conditions towards densification of Al–15%Fe alloy samples, in comparison with the volumetric energy density (using P·v−1), however, the validity of the model was reduced for this alloy in comparison with other alloys with high thermal conductivities. This is likely due to inhomogeneous microstructures having numerous coarsened θ–Al13Fe4 phases localized at melt pool boundaries. These results provide insights into achieving sufficient L-PBF processability for manufacturing dense Al–Fe binary alloy samples.

Comparative study between furnace brazing and laser brazing

Nowadays, brazing has been widely used in many industries, especially in the automotive application. The brazing process is introduced as it can be used to join the different metals together without melting the parent material. In this present study, furnace brazing and laser brazing of Ti-6Al- 4V titanium alloy and 316 L stainless steel (SS) with silver-based, BAg 8-1.5Ti filler metal were studied. There are significantly different between furnace brazing, also known as conventional brazing method and laser brazing in terms of joining strength and microstructure reaction. Furnace brazing was performed at 870°C and 880°C with 30 minutes of heating duration. Meanwhile, laser brazing was performed using a 200Watt continuous wave laser with varying laser power. Both of brazing method was conducted with a vacuum pressure of 3×10−3 Pa. Besides, to maintain the accuracy of the temperature measurement of laser brazing, an infrared thermometer is used. The tensile test was conducted to analyse the mechanical properties. The cross-sections of the brazed joints have been examined using an optical microscope. The brazed joints of the furnace brazing show an average tensile strength of 55.89 kPa for 880°C and 43.16 kPa for 870°C. Nonetheless, the maximum tensile strength of laser brazed joints was 27.95 kPa, which is lower than furnace brazed joints.

An Investigation on Laser Welding Parameters on the Strength of TRIP Steel

The energy required for joining steel segments by using laser welding is relatively very low compared with arc welding, gas welding, or any other conventional welding techniques. Moreover, the rapid cooling may create a significant effect on different regions, such as the fusion zone (FZ), heat affected zone (HAZ), and base metal (BM), and in turn affect different parameters. In this study, the characteristics of the laser-welded joint were investigated by varying laser power, welding velocity and incident angle, and tensile strength. In our, experiments. the microhardness was increased by varying the power of laser welding. The strength of the joint was increased to 549 MPa with 2200 W high power, 30 mm/s velocity, and 80º laser incident angle. By increasing the power and velocity of the laser, the welding gun strength was improved; conversely, the angle of laser incident on the welding location decreased while its strength was increased.

Effect of laser powder bed fusion parameters on the microstructural evolution and hardness of 316L stainless steel

In this study, parts were fabricated using variations of laser power, scanning speed, and hatch spacing (volumetric energy density (VED)) to understand the effect of processing parameters on the structure and properties of 316L stainless steel. It was observed that parts with good microstructural integrity and properties (hardness, porosity, and density) were obtained when using VEDs between 40 and 100 J/mm3. Also, VED was valuable when comparing the extent of consolidation and unfused/unmelted powders (porosity). The individual printing parameters offered a better understanding of the microstructure evolution, part density, and hardness of the material when compared with the VED. Also, it was shown that the relative beam spot size to the hatch spacing creates unique conditions that result in either a melt track offset or overlap which dictates the energy requirement for the creation of a part with good qualities. Melt track overlaps require low power while melt track offsets require high power to create parts with good qualities (density, porosity, and hardness). In addition, it was observed that the hatch spacing dominates the scanning speed in determining part porosity while the scanning speed dominates the hatch spacing in determining part density. The individual printing parameters had a significant effect on the morphology, size, and spatial distribution of columnar and cellular subgrain structures. Higher laser power and high scanning speed resulted in coarser, well-defined cellular and columnar subgrains with relatively low hardness. Also, increasingly hatch spacing resulted in finer subgrain structures with dense columnar structures and sparsely distributed cellular structures.

Microstructures and mechanical property of 5052 aluminum alloy/Q235 steel butt joint achieved by laser beam joining with Sn-Zn filler wire

Butt joining of 5052 aluminum alloy and Q235 low carbon steel was achieved using laser beam welding with Sn-30Zn filler wire. The weld formation, microstructures, and mechanical property were investigated with varied laser power. The results show that joining of 5052 Al/Q235 steel dissimilar metals in a butt configuration by laser beam welding with Sn-30Zn filler wire is feasible. The solid solution interface formed at the aluminum side and the reaction layer formed at the steel side. With increasing laser power, the joining mode transformed from brazing to welding-brazing due to the melt of aluminum alloy. The thickness of the interfacial intermetallic compounds (IMCs) layer was also increased with laser power. However, when the laser power was 1200 W, the thickness of the interfacial IMCs layer sharply decreased due to the detachment of the IMCs layer. The fracture of the joint occurred at the steel interface and partially through the weld seam on the top surface. The fracture surface was characterized by both brittle and ductile fracture. When the joints were obtained at the laser power of 800 W and 1200 W, the tensile strength reached 79 MPa and 78 MPa, respectively. Furthermore, the formation mechanism of microstructures and its influence on mechanical property was discussed.

A Robust Optical Sensor for Remote Multi-Species Detection Combining Frequency-Division Multiplexing and Normalized Wavelength Modulation Spectroscopy.

By combining frequency-division multiplexing and normalized wavelength modulation spectroscopy, a robust remote multi-species sensor was developed and demonstrated for practical hydrocarbon monitoring. Independently modulated laser beams are combined to simultaneously interrogate different gas samples using an open-ended centimeter-size multipass cell. Gas species of interest are demodulated with the second harmonics to enhance sensitivity, and high immunity to laser power variation is achieved by normalizing to the corresponding first harmonics. Performance of the optical sensor was experimentally evaluated using methane (CH4) and acetylene (C2H2) samples, which were separated by a 3-km fiber cable from the laser source. Sub-ppm sensitivity with 1-s time resolution was achieved for both gas species. Moreover, even with large laser intensity fluctuations ranging from 0 to 6 dB, the noise can be kept within 1.38 times as much as that of a stable intensity case. The reported spectroscopic technique would provide a promising optical sensor for remote monitoring of multi hazardous gases with high robustness.