Single Track Research Articles

Locating Red Supergiants in the Galaxy NGC 6822

Abstract Using archival near-IR photometry, we identify 51 of the K-band brightest red supergiants (RSGs) in NGC 6822 and compare their physical properties with stellar evolutionary model predictions. We first use Gaia parallax and proper motion values to filter out foreground Galactic red dwarfs before constructing a J–K versus K color–magnitude diagram to eliminate lower-mass asymptotic giant branch star contaminants in NGC 6822. We then cross match our results to previously spectroscopically confirmed RSGs and other NGC 6822 content studies and discuss our overall completeness, concluding that radial velocity alone is an insufficient method of determining membership in NGC 6822. After transforming the J and K magnitudes to effective temperatures and luminosities, we compare these physical properties with predictions from both the Geneva single-star and Binary Population and Spectral Synthesis (BPASS) single and binary-star evolution tracks. We find that our derived temperatures and luminosities match the evolutionary model predictions well, however, the BPASS model, which includes the effects of binary evolution, provides the best overall fit. This revealed the presence of a group of cool RSGs in NGC 6822, suggesting a history of binary interaction. We hope this work will lead to further comparative RSG studies in other Local Group galaxies, opportunities for direct spectroscopic follow-up, and a better understanding of evolutionary model predictions.

Comprehensive Study of the 3D Printing of Single Tracks and Cubic Samples by Selective Laser Melting of AlSi10MgCu Alloy

Comprehensive Study of the 3D Printing of Single Tracks and Cubic Samples by Selective Laser Melting of AlSi10MgCu Alloy

Rethinking Consciousness: Extraordinary Challenges for Contemporary Science edited by John H. Buchanan and Christopher M. Aanstoos

This slender volume is the twentieth member of a series entitled “Toward Ecological Civilization,” organized under the leadership of distinguished process philosopher and process theologian John B. Cobb, Jr. It grew directly from the 10th Whitehead International Conference, held in Claremont, California, in June 2015, and more particularly from a single conference track (out of the more than 80 making up the program) devoted specifically to various kinds of “extraordinary experiences” (especially, parapsychological and transpersonal experiences) that directly challenge the materialist/physicalist worldview which arose in the 17th century and still dominates the contemporary scientific, educational, and cultural mainstream. The central premises of the series as a whole, the 2015 conference, and the present volume are that postmodern civilization faces life-threatening crises rooted in that impoverished physicalist worldview, that we desperately need a more commodious, life-affirming, and ecologically sound alternative to it, and that Whitehead’s metaphysical vision can help take us in the needed direction. Like Stanley Krippner in the book’s brief Foreword, I am strongly sympathetic to these views.

Understanding the Rayleigh instability in humping phenomenon during laser powder bed fusion process

The periodic undulation of a molten track’s height profile in laser-based powder bed fusion of metals (PBF-LB/M) is a commonly observed phenomena that can cause defects and building failure during the manufacturing process. However a quantitative analysis of such instabilities has not been fully established and so here we used Rayleigh–Plateau theory to determine the stability of a single molten track in PBF-LB/M and tested it with various processing conditions by changing laser power and beam shape. The analysis discovered that normalized enthalpy, which relates to energy input density, determines whether a molten track is initially unstable and if so, the growth rate for the instability. Additionally, whether the growth rate ultimately yields significant undulation depends on the melt duration, estimated by dwell time in our experiment.

Nature of radio-wave radiation from particle cascades

The nature of the radio-wave radiation generated by particle cascades in both the Earth's atmosphere and dense media such as ice has, historically, been much debated. This situation changed in the early 2010's, with the community converging on the common terminology of "geomagnetic" and "Askaryan" radiation to describe the two emission mechanisms. However, this convergence arose from discussions at various conferences and workshops, and was ultimately reached through agreement between simulation codes and experimental measurements. In this article therefore, I use relatively simple geometrical arguments, and a minimum of calculations based on single particle tracks, to explain the nature of radiation from extensive air showers (EAS) and cascades in dense media such as ice. I identify well-determined frequency regimes where the radiation from the Askaryan effect will be bremsstrahlung-like and Cherenkov-like, being respectively below/above 1 GHz in EAS and 100 MHz in dense media; and where geomagnetic emission will be transverse-current-like and where it will resemble synchrotron radiation, respectively below/above a few GHz in EAS, depending on the height of cascade development. I suggest how these transitions in the nature of the emission may be experimentally observed.

On weldability of aerospace grade Al-Cu-Li alloy AA2065 by wire-feed laser metal deposition

Al-Cu-Li alloys exhibit a superior strength to weight ratio, making the alloys attractive for applications within aviation and aerospace. However, their widespread application has been somewhat limited by the challenges associated with porosity and crack formation during welding. The purpose of this study was to evaluate the weldability of aerospace grade Al-Cu-Li alloy AA2065 by wire-based Laser Metal Deposition (LMD) by using a self-produced wire. The influence of selected process parameters on deposition geometry (width, height and deposition depth), porosity, microstructure and hardness were evaluated by producing single tracks on a base plate. Defect-free tracks with minimal porosity could be produced with a laser power of 2700 W, 800 μm spot size and 1 m/min scanning speed, providing an energy density of 5.4 J/mm2. Depending on the desired deposition rate, the wire-feed rate could be varied between 1 and 1.9 m/min. The microstructure of the deposited material consisted of columnar and globular equiaxed grains with a Cu-rich second phase network throughout the deposited material. The results presented in this study show the potential in utilizing wires produced of AA2065 for laser welding and potentially additive manufacturing by wire-based LMD, increasing the possible areas of application for such high-strength, low weight alloys.

Influence of selective laser melting process parameters on the characteristics of SiC/Ti6Al4V(ELI) single tracks

Process parameters of selective laser melting, such as track height, track width and depth of penetration, affect the characteristics of laser fused single tracks. The properties of additively manufactured 3D parts depend strongly on the quality of laser melted single tracks and resultant single layers. Layers formed with a good depth of laser penetration provide strong bonding between consecutive layers and the substrate. Poor depth of laser penetration leads to delamination of layers. In this study the effect of the critical process parameters of laser power, laser scanning speed, and laser linear energy density on the characteristics of SiC/Ti6Al4V(ELI) single tracks at different SiC volume fractions (5 %, 10 %, 15 %, 20 %, 25 % and 30%) was investigated. Phenomena, such as the keyhole effect, pre-balling, and balling of single tracks, were also investigated. The obtained results showed that increase of power at a constant speed increase both the track width and depth of penetration but the track height above the substrate is decreased.

Single Track Transportation in a Two-Machine Production System

The paper is concerned with scheduling traffic on a single track between two stations which generate requests for transportation with different release times. These requests are served by a fleet of identical vehicles, each of which can serve (carry) several requests for transportation simultaneously. The single track, used by the vehicles, does not permit traffic in both directions simultaneously. The presented polynomial-time algorithms are based on dynamic programming.

Effect of Process Parameters on Surface Integrity of LPBF Ti6Al4V

Laser powder bed fusion(LPBF) is an emerging manufacturing process by which components ranging from bulk to micro size are fabricated by layer upon layer. Though the micro features are fabricated by LPBF, it is very difficult to super finish them by the secondary processes. There is a demand to fabricate a micro features with high surface finish and high dimensional accuracy. To meet such a demand the one of the options is the optimization of the process parameters for getting high surface finish. Hence, this study investigates the effect of the laser power and scanning speed on the surface integrity of the Ti6Al4V single tracks. The waviness, adhered powder particles, and track profile were analysed. The findings show the significance of the process parameters on the surface quality of a single track.

Understanding the Parameter Effects on Densification and Single Track Formation of Laser Powder Bed Fusion Inconel 939

Inconel 939 is a nickel-based superalloy highly preferred in aerospace applications where excellent material properties are required under extreme service conditions. However, Inconel 939 is a relatively challenging material due to densification behavior during laser processing, leading to micro-cracking and low density. Therefore, the correlation between the parameters and material properties requires a comprehensive evaluation to achieve desired results. In this study, the formation of single tracks and densification properties of Inconel 939 processed by laser powder bed fusion are investigated based on the different parameter combinations. The melt pool characteristics with respect to high laser power and scanning speed are analyzed.

Evaluating the thermal characteristics of laser powder bed fusion

• Dynamic temperature behaviour around the melt pool during the PBF-LB/M was evaluated. • Temperature distribution was influenced by morphological changes of metal powder. • Laser beam incident was characterized by direct heating and heat conduction. • Dynamic temperature behaviour provided a direct explanation for the cooling rate. This study investigates the dynamic temperature behaviour around a melt pool in metal-based powder bed fusion using a laser beam (PBF-LB/M) to clarify the influence of the associated morphological changes of the metal powder experimentally. Gas-atomized 18Ni (300-grade) maraging steel powders were processed by PBF-LB/M while high-speed photography with a two-colour radiometric thermal imaging system that was employed to correlate the temperature with melt pool behaviour. In addition, the cooling rate of the melt pool was measured directly using the dynamic temperature distribution. The temperature distribution of the melt pool was influenced by the morphological changes of the metal powder induced by physical and thermal interactions, and the melt pool exhibited an asymmetric temperature distribution in the direction parallel to the laser scan. The significant factors were droplet cohesion at low melt pool temperatures, remaining heat energy from previous laser beam irradiation, and the heat conduction inside the melt pool. The laser beam incident on the metal powder was primarily characterized by two modes: direct heating induced by laser beam irradiation and heat conduction through the single track, droplets, and substrate. In addition, the dynamic temperature behaviour provided a direct explanation for the cooling rate, the values of which ranged from 0.1 to 0.9 × 10 6 K/s owing to the self-cooling induced by PBF-LB/M.

CA single track simulation of laser conduction welding with stainless steel 316L (1.4404)

The study presents a coupled cellular automata (CA) approach for a single track microstructure simulation for laser conduction welding. A high-power CO2 laser beam (1000 W) traverses the substrate, with the beam shaped by conventional optics, which produces a Gaussian profile. The process parameters produce a shallow melt phase maintaining a conduction limited weld seam. The stainless steel material 1.4404 was used as substrate material with a grain size of approximately 20 µm without any filler material. The cooling rates and initial grain size influence the grain morphology and were determined. The size of a single crystal was simulated for different cooling rates. The simulation outputs of the melt pool boundary are qualitatively and quantitatively compared to experimental results. The micrograph results have shown that fine sub cells are developed. This fine cellular microstructure was only satisfactorily resolved experimentally along the melt pool boundary. The simulation results are in acceptable agreement with the experiments at the melt pool boundary. They match in terms of cooling rate, grain angle, and primary dendrite spacing. However, the simulated grains are longer which indicates the necessity of homogenous nucleation in the liquid melt pool.

Numerical simulation of fluid dynamic behavior of melting, mixing, vaporization and solidification for process optimization in in-situ alloying additive manufacturing

Metal additive manufacturing (AM) is a promising digital manufacturing technology that can produce parts of complicated shapes. Fluid flow dynamics in melting and solidification determines the final shape accuracy and mechanical properties. Here, detailed numerical simulation is used for in-situ alloying to elucidate the processes of heating, melting, mixing, vaporization and solidification. The solidification process by the phase field method is coupled with the fluid flow dynamics. The laser heat input melts the powders of each element and a melt pool is formed. Here, entrainment and stirring of each element can enhance mixing in the melt pool, but complete mixing is not achieved in a single track. Grain growth is mostly governed by the thermal gradient and columnar grain growth is dominantly observed. The inhomogeneity of the chemical species induces a difference in the timing of grain growth, which may lead to collision of nearby growing grains. The second track melting induces remelting and further mixing occurs due to the stirring effect of the keyhole. It is suggested that controlling the keyhole dynamics by the heat input can control the species mixing and the grain growth. Optimization of such processes is our next future issue to be pursued.

Single and multiple track formation mechanism of laser powder bed fusion 316L/CuSn10 multi-material

This paper focuses on the influence mechanism of process parameters on the geometry morphology and microstructure characteristic of single-track and multi-track 316L/CuSn10 multiple materials manufactured by laser powder bed fusion (LPBF). The width of single-track increases with the increase of laser power and layer thickness, and decreases with the increase of scanning speed. Both variations in the copper content and wetting angle of the molten pool were investigated. In addition, the comparison of defect characteristics shows that the scanning speed and layer thickness have a greater influence on the formation of single cracks. The traces of Marangoni convection are observed directly in the centre of the molten pool due to the difference in microstructure between 316L and CuSn10 alloys. It is found that the copper penetration cracks appear on the steel side at the molten pool bottom. Moreover, fine grains appear in the copper-rich region, and the large-angle grain boundary distribution seems to be the reason for the concentration of dislocations. Four types of crack formation mechanisms are found in the cross section of the multi-track: crack formation inside the molten pool, passing through the track boundary, extending to the steel substrate, and copper penetration cracks.

Femtosecond Laser Machining of Flexible Printed Circuit Boards

As the demand grows for high-density electronic components and highly integrated printed circuit boards, femtosecond laser micromachining provides unique opportunities for creating fine conductive tracks and patterns on flexible printed circuit boards (FPCBs) without the use of a mask. Here, the effects of femtosecond laser power and pulse frequency on micromachining depth, surface roughness and copper content of the machined zone were investigated, and optimum laser parameters, i.e., laser power 280 mW and pulse repetition frequency 39.5 kHz, were achieved with the help of a 3D optical profilometer and energy dispersive spectroscopy (EDS). On this basis, a single conductive track with varying widths and two parallel conductive tracks with different widths/spacings were micromachined on FPCBs without noticeable substrate damage. The results indicate that a single conductive line with a feature width as small as 25 µm can be achieved, and two parallel copper tracks can be created with no evidence of the presence of copper residues between the tracks when the pre-defined spacing is no less than 45 µm . In order to achieve high micromachining accuracy, look-up tables that correlate measured widths/spacing of conductive tracks with the pre-defined ones were built.besides, machining conductive tracks with 135 degree corner is possible and by selecting optimized processing parameters. Finally, a driving circuit for a display panel was micromachined on FPCBs using femtosecond laser, and an average micromachining accuracy of 0.67 μm was achieved. This work will be quite useful for creating high density and precision patterns on FPCBs using femtosecond laser.

High-contrast low-dose proton radiography of thin samples at the Tandetron accelerator

We investigate the ability of using high-resolution position-sensitive pixel detector and standard non-scanning beams of low-energy protons in air as a flexible tool and simplified technique for density-sensitivity imaging of thin samples. Proton radiography can provide high contrast and low radiation dose delivered to the inspected sample. Density-sensitive contrast response can be provided by a single proton per imaging pixel. For this purpose, we use the silicon semiconductor high-resolution pixel detector Timepix3 to evaluate particle radiography of thin samples with monoenergetic low-energy proton beams from the Tandetron light-ion accelerator. Measurements were performed with various well-defined thin samples. A proton micro beam was used to test and evaluate the technique. Spatial information of the samples is provided by the imaging detector. Density-sensitive contrast is obtained from the measurement of small differences in the deposited energy of transmitted protons across the sample. The transmitted protons are detected with high spatial resolution in the pixel detector. The single particle tracks registered in the detector are analysed by detailed pattern recognition algorithms. Various of these track parameters of spectral response are used for imaging contrast. Resulting proton radiographies for various well-defined thin samples are presented.

The interaction of volatile metal coatings during the laser powder bed fusion of copper

The high optical reflectance of Cu at near-infrared wavelengths narrows the process window to fabricate Cu parts by laser powder bed fusion (LPBF). Coating powders with optically absorptive materials has been investigated to improve processability and enhance part properties. However, given the intense heat localization and thin coating layers relative to the powder, the mechanisms of thin film coating interaction in LPBF remain unclear, despite recent work showing the importance of the near-track environment in deposition behavior. In this study, optically absorptive Zn-coated Cu powders were prepared by physical vapor deposition and characterized. Single LPBF tracks were fabricated to elucidate material incorporation phenomena influenced by the volatile Zn coating. It is shown that Zn-coated powder enhances accretion at fastest effective scan speed tested (100 mm/s), where mean track volumes are increased from 0.72 ± 0.05 mm3 (as-received) to 0.91 ± 0.01 mm3 (Zn-coated). This has been correlated to the stronger vapor jet from the volatile Zn-coating, which denudes the surrounding powder bed. This exhausts the powder bed at slower effective scan speeds, causing instability and balling when compared to the as-received powder. It is shown that Zn is localized at the track surface and is undetectable in the track bulk, indicating Zn vaporization on interaction with the incident beam. Zn present mainly occurs through secondary deposition mechanisms like spatter and condensation, rather than in-process alloying. Coating powder feedstocks for use in LPBF therefore affects composition, laser beam absorptivity, and the near-track vapor environment that is known to influence material incorporation behavior.

Analysis of single tracks of IN718 produced by laser powder directed energy deposition process

Despite the powerful capabilities of the Laser Powder Directed Energy Deposition (LP-DED) process, the applications are limited almost to feasibility analyses of simple case studies. This arises from the knowledge gap in the process parameters identification and optimization of the deposition quality. A practical approach is to delineate the process parameters window by producing single tracks with different sets of parameter levels. This paper aims to study, through statistical analysis, the effect of process parameters on the characteristic dimensions of IN718 single tracks. Results will allow empirical relations to be identified between track geometry and the analysed parameters. These relations will support process optimization.

A Comparison of Generative Adversarial Networks to Convolutional Neural Networks for Single Track Melt Pool Segmentation Evaluated by Hausdorff Distance

A Comparison of Generative Adversarial Networks to Convolutional Neural Networks for Single Track Melt Pool Segmentation Evaluated by Hausdorff Distance

Nanosized SiC particle reinforced Ti6Al4V matrix composites manufactured by laser melting deposition

In this work, in-situ (TiC+Ti5Si3)/Ti6Al4V matrix composites (TMCs) with enhanced hardness and wear performance were manufactured by laser melting deposition (LMD) via the addition of nanosized SiC powder. The microstructures of single tracks were investigated to determine the optimal parameters for LMD. Besides, the influence of the SiC content on the microstructural evolutions and mechanical properties was explored. Results demonstrate that the in-situ reaction occurs between SiC and titanium during the LMD process. In-situ TiC and Ti5Si3 were distributed uniformly at grain boundaries and titanium matrix with a full-columnar grains for 0.5 wt.% and 1.0 wt.% SiC addition. The morphology of the composites consists of equiaxed grains with a three-dimensional quasi-continuous network structure when the content of SiC increases to 1.5 wt.% and 3.0 wt.%. The hardness of the composites is 321.1, 342.3, 347.8, and 442.1 Hv with the increasing formation of reinforcements. Meanwhile, the average coefficient of friction decreases from 0.39 to 0.32 with the wear mechanism changing from abrasion to adhesive wear.