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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Laser Weldability of AlSi{sub 10}Mg Alloy Produced by Selective Laser Melting: Microstructure and Mechanical Behavior

Selective laser melting (SLM) allows 3D complex parts to be produced with integrated functionalities but does not permit to realize large dimension parts, as the building chamber volume of commercial SLM systems is limited. Therefore, the possibility of joining SLM-built parts by welding appears as extremely valuable. In this work, laser weldability of SLMed AlSi{sub 10}Mg parts has been investigated. The cooling rates induced by the welding process are lower than the ones of SLM; therefore, typical eutectic silicon network of SLM-built parts appears broken in both the melted zone and part of the heat-affected zone, as confirmed by calorimetric measurement. This microstructural evolution caused a local decrease of hardness from 132 HV to 73 HV and a reduction of ductility caused by porosity formation in the weld bead. Moreover, the thermal treatment, performed at 320°C, can limit the gap of tensile response among welded bead and base SLM material.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The Characterization of Laser Ablation Patterns and a New Definition of Resolution in Matrix Assisted Laser Desorption Ionization Imaging Mass Spectrometry (MALDI-IMS)

Matrix assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) is a technique that has seen a sharp rise in both use and development. Despite this rapid adoption, there have been few thorough investigations into the actual physical mechanisms that underlie the acquisition of IMS images. We therefore set out to characterize the effect of IMS laser ablation patterns on the surface of a sample. We also concluded that the governing factors that control spatial resolution have not been correctly defined and therefore propose a new definition of resolution. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Microstructure and microhardness of wire-based laser metal deposited AA5087 using an Ytterbium fibre laser

Highlights: • Heat conduction strongly affects the microstructural development. • Heat conduction conditions changes with increasing part height. • Anisotropic microstructural development affects the microhardness of the part. • Anisotropic mechanical properties along the structure are assumed. - Abstract: Wire-based additive manufacturing has been increasingly investigated in recent years. Although it is possible nowadays to manufacture structures that are free from inner defects such as porosity and cracks using wire and arc additive manufacturing, there is still a lack of knowledge regarding wire-based laser metal deposition of aluminium and its alloys. In order to be able to produce locally tailored part properties, it is necessary to understand the process parameter to material property relationships. Using laser energy sources, it becomes possible to analyse in detail the heat input and to observe occurring microstructural evolutions. This work includes a microstructural and mechanical characterization of an AA5087 wall structure. Detailed analyses of the chemical composition, texture, and microhardness of the structure have been performed. The microstructure contains different grain orientations as well as grain shapes and sizes along the structure, resulting in locally different material properties. The results have been analysed and discussed in reference to fundamental theories such as the Hall–Petch and Orowan mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interaction between laser radiation and metallic powder of 316L austenitic steel during selective laser melting

Highlights: • Single and multiple tracks on a loose bulk powder substrate were generated. • Understanding of the microstructure development during SLM was achieved. • Single tracks reveal a nearly symmetrical crystallography with elongated grains. • Multiple tracks show elongated grains perpendicular to the build direction. - Abstract: During selective laser melting (SLM), a complex heat state develops that leads to a characteristic crystallography and microstructure of the processed materials. Depending on the geometry of the processed part, most scan tracks of a new layer, so-called hatches, are located above a dense substrate or already solidified structures whereas others are located above loose powder. This is, inter alia, the case for overhanging structures. Attributable to the lower thermal conductivity of loose powder, temperature gradients and cooling rates of the melt pool differentiate in these areas, resulting in a different microstructural build-up. In this work, the microstructure and the crystallographic orientation of grade 316L austenitic stainless steel processed by SLM was investigated to understand the interaction between the laser radiation and the metallic powder during SLM-processing and to investigate the remelting of a track on a previous SLM-densified track. Single and multiple tracks on a loose bulk powder substrate, as well as single tracks on a dense substrate plate, were generated. A parameter study revealed that high energy densities are necessary to build continuous tracks on a loose bulk powder substrate. In addition, the amount of adhered particles, which are sintered on the fully melted and solidified tracks, is determined in comparison to the melted powder because the sintered particles strongly influence the surface roughness. To understand the microstructure development and, particularly, the influence of adjacent hatches during SLM-processing, investigations on the resulting microstructure and crystallographic orientation of a single track and two connected multiple tracks were carried out. During SLM processing of the tracks, the substrate plate and the solidified structures influence the temperature gradient and cooling rate of the melt pool, thus directionally solidified and elongated grains occur. Furthermore, the solidification is characterized by an epitaxial growth due to a distinct thermal gradient between the melt pool and the surrounding elements.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Active control of laser beam pointing for the Zettawatt-Equivalent Ultrashort pulse laser System: a proof-of-principle study with 16-inch optics

We present a proof-of-principle study of active beam-pointing control for the Zettawatt-Equivalent Ultrashort pulse laser System (ZEUS) using a piezo-actuated 16-inch mirror. To the best of our knowledge, this is the largest actively controlled mirror reported in a high-power laser system. A simple proportional feedback control was implemented based on a field-programmable gate array, which reduced the standard deviation of beam-pointing fluctuations by 91% to 0.075 μrad in the horizontal direction and by 78% to 0.25 μrad in the vertical direction. We also demonstrated the elimination of long-term pointing jitter caused by temperature drift using the same apparatus.

laser pointing control↗
DOE OSTI2023

Colloidal Semiconductor Nanocrystal Lasers and Laser Diodes

Lasers and optical amplifiers based on solution-processable materials have been long-desired devices for their compatibility with virtually any substrate, scalability, and ease of integration with on-chip photonics and electronics. These devices have been pursued across a wide range of materials including polymers, small molecules, perovskites, and chemically prepared colloidal semiconductor nanocrystals, also commonly referred to as colloidal quantum dots. The latter materials are especially attractive for implementing optical-gain media as in addition to being compatible with inexpensive and easily scalable chemical techniques, they offer multiple advantages derived from a zero-dimensional character of their electronic states. These include a size-tunable emission wavelength, low optical gain thresholds, and weak sensitivity of lasing characteristics to variations in temperature. Here we review the status of colloidal nanocrystal lasing devices, most recent advances in this field, outstanding challenges, and the ongoing progress toward technological viable devices including colloidal quantum dot laser diodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Solid matrix transformation and tracer addition using molten ammonium bifluoride salt as a sample preparation method for laser ablation inductively coupled plasma mass spectrometry

Solid sampling and analysis methods, such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), are challenged by matrix effects and calibration difficulties. Matrix-matched standards for external calibration are seldom available and it is difficult to distribute spikes evenly into a solid matrix as internal standards. While isotopic ratios of the same element can be measured to high precision, matrix-dependent effects in the sampling and analysis process frustrate accurate quantification and elemental ratio determinations. Here we introduce a potentially general solid matrix transformation approach entailing chemical reactions in molten ammonium bifluoride (ABF) salt that enables the introduction of spikes as tracers or internal standards. Proof of principle experiments show that the decomposition of uranium ore in sealed PFA fluoropolymer vials at 230 °C yields, after cooling, new solids suitable for direct solid sampling by LA. When spikes are included in the molten salt reaction, subsequent LA-ICP-MS sampling at several spots indicate that the spikes are evenly distributed, and that U-235 tracer dramatically improves reproducibility in U-238 analysis. Precisions improved from 17% relative standard deviation for U-238 signals to 0.1% for the ratio of sample U-238 to spiked U-235, a factor of over two orders of magnitude. These results introduce the concept of solid matrix transformation (SMT) using ABF, and provide proof of principle for a new method of incorporating internal standards into a solid for LA-ICP-MS. This new approach, SMT-LA-ICP-MS, provides opportunities to improve calibration and quantification in solids based analysis. Finally, looking forward, tracer addition to transformed solids opens up LA-based methods to analytical methodologies such as standard addition, isotope dilution, preparation of matrix-matched solid standards, external calibration, and monitoring instrument drift against external calibration standard

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Time-resolved imaging of atoms and molecules in laser-produced uranium plasmas

Gas-phase oxidation of uranium (U), plume chemistry, and its impact on optical emission features of the uranium plasma are investigated. Plasmas were produced via nanosecond laser ablation of a natural uranium target in a chamber where uranium oxidation was controlled by varying the oxygen partial pressure within argon cover gas. Monochromatic imaging of uranium atoms and monoxide molecules was performed using narrowband optical filters, which clearly reveals the spatio-temporal evolution of these species in the plasma. Uranium oxides are found to be formed at the plasma edges, where lower temperatures favor molecular recombination. Segregation between the distribution of uranium atoms and monoxide species is observed at later times of plasma evolution, and is more apparent at lower oxygen partial pressures. At higher oxygen partial pressures, significant variation in plume morphology is noticed for UO species, which is attributed to higher rate of oxide (UxOy) formation at the plume edges. The monochromatic images of U atoms and molecules and corresponding spectral features at various oxygen partial pressures presented here provide a unique insight into gas-phase, high-temperature uranium oxidation, and its chemistry and have implications for a wide range of nuclear applications, from stand-off detection of radioisotopes to forensics and safeguards.

(140.3440) Laser-induced breakdown, (280.4788) Opt↗
DOE OSTI2014

Investigation of effect of solenoid magnet on emittances of ion beam from laser ablation plasma

A magnetic field can increase an ion current of a laser ablation plasma and is expected to control the change of the plasma ion current. However, the magnetic field can also make some fluctuations of the plasma and the effect on the beam emittance and the emission surface is not clear. To investigate the effect of a magnetic field, we extracted the ion beams under three conditions where without magnetic field, with magnetic field, and without magnetic field with higher laser energy to measure the beam distribution in phase space. Then we compared the relations between the plasma ion current density into the extraction gap and the Twiss parameters with each condition. We observed the effect of the magnetic field on the emission surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Development of the C{sup 6+} laser ablation ion source for the KEK digital accelerator

A laser ion source that provides a fully ionized carbon ion beam is under joint development at the High Energy Accelerator Research Organization and Brookhaven National Laboratory. Long-pulse (6 ns) and short-pulse (500 ps) laser systems were tested by using them to irradiate a graphite target. Notable differences between the systems were observed in these experiments. Preliminary experimental results, such as the charge-state spectrum, beam intensity, and stability, are discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

K{sub α} x-ray imaging of laser-irradiated, limited-mass zirconium foils

X-ray fluorescence measurements to determine the effect of target heating on imaging efficiency, at a photon energy of 15.7 keV corresponding to the K{sub α} line of zirconium, have been carried out using limited-mass foils irradiated by the Texas Petawatt Laser. Zirconium foils that ranged in volume from 3000 × 3000 × 21 μm{sup 3} to 150 × 150 × 6 μm{sup 3} were irradiated with 100 J, 8 ps-long pulses and a mean intensity of 4 × 10{sup 19} W/cm{sup 2}. The K{sub α} emission was measured simultaneously using a highly ordered pyrolytic graphite crystal spectrometer and a curved quartz imaging crystal. The measured ratio of the integrated image signal to the integrated spectral signal was, within the experimental error, constant, indicating that the imaging efficiency's dependence on temperature is weak throughout the probed range. Based on our experience of target heating under similar conditions, we estimate a temperature of ∼200 eV for the smallest targets. The successful imaging of K{sub α} emission for temperatures this high represents an important proof of concept for Zr K{sub α} imaging. At these temperatures, the imaging of K{sub α} emission from lower-Z materials (such as Cu) is limited by temperature-dependent shifts in the K{sub α} emission energy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A new spectrometer design for the x-ray spectroscopy of laser-produced plasmas with high (sub-ns) time resolution

This paper describes a new type of x-ray crystal spectrometer, which can be used in combination with gated x-ray detectors to obtain spectra from laser-produced plasmas with a high (sub-ns) time resolution. The spectrometer consists of a convex, spherically bent crystal, which images individual spectral lines as perfectly straight lines across multiple, sequentially gated, strip detectors. Since the Bragg-reflected rays are divergent, the distance between detector and crystal is arbitrary, so that this distance can be appropriately chosen to optimize the experimental arrangement with respect to the detector parameters. The spectrometer concept was verified in proof-of-principle experiments by imaging the Lβ{sub 1}- and Lβ{sub 2}-lines of tungsten, at 9.6735 and 9.96150 keV, from a micro-focus x-ray tube with a tungsten target onto a two-dimensional pixilated Pilatus detector, using a convex, spherically bent Si-422 crystal with a radius of curvature of 500 mm.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗