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NASA NTRS2004

Laser ablation process for single-walled carbon nanotube production

Different types of lasers are now routinely used to prepare single-walled carbon nanotubes. The original method developed by researchers at Rice University used a "double-pulse laser oven" process. Several researchers have used variations of the lasers to include one-laser pulse (green or infrared), different pulse widths (ns to micros as well as continuous wave), and different laser wavelengths (e.g., CO2, or free electron lasers in the near to far infrared). Some of these variations are tried with different combinations and concentrations of metal catalysts, buffer gases (e.g., helium), oven temperatures, flow conditions, and even different porosities of the graphite targets. This article is an attempt to cover all these variations and their relative merits. Possible growth mechanisms under these different conditions will also be discussed.

Review↗

NASA NTRS2024

Correlations of Additive Manufacturing Model-Based Process Metrics With Spatter-Induced Porosity in the Powder Bed Fusion-Laser Beam/Metallic Process

Components fabricated using the powder bed fusion laser beam metallic (PBF-LB/M) additive manufacturing (AM) process comprise a multitude of sequential weld passes. Qualifying materials for components in critical applications requires a thorough understanding of pertinent processing-microstructure-property relationships. Porosity defects have a strong adverse effect on the mechanical properties of a material. The morphology of porosity defects created by lack of fusion in PBF-LB/M often exhibit high aspect ratios that can act as stress concentrators and become crack initiation sites. The occurrence of spatter induced porosity is studied using synchronized AM model-based process metrics and porosity measured by high-resolution X-ray computed tomography. A novel AM process metric is introduced to quantify the relative exposure to spatter ejecta impacts and incorporation throughout the sequence of the PBF-LB/M process. Further characterization using optical metallography and scanning electron microscopy indicated that both keyhole and lack of fusion porosity correlated statistically with the spatter ejecta impact field of the PBF-LB/M process. Both keyhole and lack of fusion porosity can be predicted by the spatter exposure process metric, which can be exploited to control the fusion sequence.

Additive Manufacturing↗

NASA NTRS1985

Computer aided processing using laser measurements

The challenge exists of processing the STS and its cargo through KSC facilities in the most timely and cost effective manner possible. To do this a 3-D computer graphics data base was established into which was entered the STS, payloads, and KSC facilities. The facility drawing data are enhanced by laser theodolite measurements into an as-built configuration. Elements of the data base were combined to study orbiter/facility interfaces payload/facility access problems and design/arrangement of various GSE to support processing requirements. With timely analysis/design utilizing the 3-D computer graphics system, costly delays can be avoided. Better methodology can be analyzed to determine procedures for cost avoidance.

Davis, R. M.↗

DOE OSTI2024

Creating microfluidic channels functionalized with micro- and nano-scale features via femtosecond laser surface processing

We demonstrate the ability to create functionalized microfluidic channels using femtosecond laser surface processing (FLSP). FLSP is an emerging advanced manufacturing technology used to modify the surface properties of materials directly and permanently by producing self-organized quasi-periodic micro- and nano-scale surface features along with surface and subsurface chemical and grain structure changes. We demonstrate on Hastelloy X that by controlling the laser fluence and pulse count, the depth of the microchannels and height of the FLSP microstructures within the microchannels can be controlled independently.

Ultrashort pulse laser applications, micro- and na↗

DOE OSTI2022

Effects of Particle Size Distribution with Efficient Packing on Powder Flowability and Selective Laser Melting Process

The powder bed-based additive manufacturing (AM) process contains uncertainties in the powder spreading process and powder bed quality, leading to problems in repeatability and quality of the additively manufactured parts. This work focuses on identifying the uncertainty induced by particle size distribution (PSD) on powder flowability and the laser melting process, using Ti6Al4V as a model material. The flowability test results show that the effect of PSDs on flowability is not linear, rather the PSDs near dense packing ratios cause significant reductions in flowability (indicated by the increase in the avalanche angle and break energy of the powders measured by a revolution powder analyzer). The effects of PSDs on the selective laser melting (SLM) process are identified by using in-situ high-speed X-ray imaging to observe the melt pool dynamics during the melting process. The results show that the powder beds made of powders with dense packing ratios exhibit larger build height during laser melting. The effects of PSD with efficient packing on powder flowability and selective laser melting process revealed in this work are important for understanding process uncertainties induced by feedstock powders and for designing mitigation approaches.

36 MATERIALS SCIENCE↗

NASA NTRS2001

Technology Assessment of Laser-Assisted Materials Processing in Space

Lasers are useful for performing operations such as joining, machining, built-up freeform fabrication, shock processing, and surface treatments. These attributes are attractive for the supportability of longer-term missions in space due to the multi-functionality of a single tool and the variety of materials that can be processed. However, current laser technology also has drawbacks for space-based applications, specifically size, power efficiency, lack of robustness, and problems processing highly reflective materials. A review of recent laser developments will be used to show how these issues may be reduced and indicate where further improvement is necessary to realize a laser-based materials processing capability in space. The broad utility of laser beams in synthesizing various classes of engineering materials will be illustrated using state-of-the art processing maps for select lightweight alloys typically found on spacecraft. With the advent of recent breakthroughs in diode-pumped solid-state lasers and fiber optic technologies, the potential to perform multiple processing techniques is increasing significantly. Lasers with suitable wavelengths and beam properties have tremendous potential for supporting future space missions to the moon, Mars and beyond.

Nagarathnam, Karthik↗

NASA NTRS2001

Technology Assessment of Laser-Assisted Materials Processing in Space

Nagarathnam, Karthik↗

DOE OSTI2022

Improving Structural Integrity of Direct Laser-Deposited Ni – Co – Cr – Al – Y Superalloys by Alloy Modification

Abstract Ni- and Co-based M–Cr–Al–Y (M = Ni and/or Co), dual phase β and γ/γ′, β—Ni–Al, γ—Ni(Co, Cr), and γ′—Ni3–Al superalloys exhibit several beneficial high-temperature (>1000 °C) (2012 °F) strength and corrosion resistance properties. Our study investigates the feasibility of fabricating a commercially available Ni–Co–Cr–AlY alloy (tradename “Amdry 386”) using laser directed energy deposition (laser-DED). A significant challenge for laser fabrication of bulk Amdry 386 (A386) structures stems from the presence of relatively higher amounts of the β phase than γ/γ′ phases. While prior studies report laser fabrication of these materials in coating and cladding configurations, bulk structures have not been realized. To investigate these challenges, this study was developed to systematically evaluate the effects of modifying the A386 alloy by adding 10, 20, and 30% by weight of a Ni–20%Cr (Ni–Cr) alloy (mainly γ/γ′). Laser-DED-fabricated A386 coupons exhibited a metastable, rapidly solidified β-rich microstructure typical to laser processes. The A386 + Ni–Cr mixtures were processed using laser-DED, and small coupons from each composition were evaluated using SEM, XRD, and microhardness to characterize the as-processed microstructure. Thermodynamic modeling was performed to determine the phase evolution as a function of the alloy composition. The dominating phase switches from β to γ/γ’ between the A386 and A386 + 10% Ni–Cr mixtures, but the increase in structural integrity is not observed until the Ni–Cr additions reach a minimum of 20%. Our results show that the alloy chemistry can be successfully modified to improve the structural integrity of laser-processed structures.

Engineering↗

DOE OSTI2023

In situ synchrotron X-ray diffraction analysis of ultrasonically assisted microstructure refinement during laser melting process

This work investigates the effect of ultrasonic treatment (UST) on the microstructure of AA4043 alloy during laser melting process. Here, the study utilizes in situ synchrotron X-ray diffraction (SXRD) and postmortem electron backscatter diffraction (EBSD) techniques to examine the ultrasonic grain refinement mechanism. The SXRD diffraction patterns exhibit higher continuity of major diffraction rings in the UST-test pattern, indicating a more refined grain structure. The presence of new diffraction spots in the post-test diffraction pattern with UST suggests the breakdown of epitaxial growth of columnar dendrites during solidification. Thermal profiles determined by analyzing the lattice parameter evolution show a faster cooling rate with UST. The inverse pole figures and aspect ratio distribution from EBSD reveal that the UST samples exhibit a refined, more equiaxed grain structure along the weld centerline. UST sample also develops more fine-sized low angle grain boundaries (LAGBs). These features offer better hot-cracking resistance in aluminum alloys.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Dynamic beam shaping—Improving laser materials processing via feature synchronous energy coupling

Today, tailored laser beams are rarely used and thus an opportunity to optimize existing or introduce new processes is missed. New methods of dynamic beam shaping have the potential to change that in future. This keynote paper deals with methods allowing a transient energy input into the workpiece at such time scales that the underlying interaction processes are guided towards the desired result. It shows principles, categorizes necessary system technology, and gives application examples to familiarize the reader with the topic. It postulates that time-scale-dependent coupling between transient energy input and addressed process features is key for achieving the optimum.

36 MATERIALS SCIENCE↗

DOE OSTI2026

A transport-based framework for solidification cracking in Ni-based superalloys processed by laser powder bed fusion

Solidification cracking remains a persistent barrier to laser powder bed fusion (LPBF) processing of solid-solution-strengthened (SSS) Ni-based superalloys and is commonly attributed to carbide formation, liquation-type failure, or elemental segregation. In this work, the cracking behavior of three SSS Ni-based superalloys—Inconel 625 (625), Inconel 617 (617), and Haynes 230 (230)—is examined under comparable LPBF conditions to evaluate the origins of their cracking susceptibility. Carbides were present in both 625 and 230, yet cracking behavior differed significantly. MC-type carbides in 625 remain discrete and preserve liquid connectivity, whereas Cr-rich M23C6 carbides in 230 form at cellular triple junctions that bottleneck the interdendritic liquid network, influencing cracking through liquid connectivity rather than as an independent cause. Alloy 617 exhibited anomalous segregation without resolvable secondary phases yet cracked mildly, indicating that extensive carbide formation is not a prerequisite for cracking. To rationalize these observations, a transport-limited framework is proposed in which cracking occurs when terminal-liquid feeding cannot accommodate solidification-induced strain; among the mechanisms evaluated, this framework is most consistent with the physical constraints imposed by LPBF solidification. Transport-based crack-susceptibility indexes incorporating permeability, viscosity, and solidification kinetics distinguish the alloy hierarchy; permeability ratios Krat increased from approximately 7 (625) to 11.5 (617) and 14.5 (230), with corresponding increases in the μ-weighted mushy zone risk index (CSIMZRM). These results are consistent with transport-limited liquid feeding as a rate-limiting contributor to solidification cracking in LPBF-processed SSS Ni-based superalloys, providing a physically grounded basis for alloy and process design.

Hyer, Holden [ORNL] (ORCID:0000000343915561)↗

DOE OSTI2025

Time-resolved probing of laser-induced nanostructuring processes in liquids

Laser synthesis and processing of colloids (LSPC) in liquids has gained widespread applications in producing nanomaterials of different classes of solids. While the technical processes in different cases of ablation, fragmentation or colloidal fusion may look macroscopically different in each application, the underlying fundamental mechanisms are always the same cascade of laser interaction with matter, non-thermal or thermal energy deposition, phase transitions, and the subsequent structure formation processes. Disentangling these mechanisms represents a veritable challenge, as ultrafast and structurally sensitive experimental methods are required. This review presents a discussion of how state-of-the-art experimental protocols using ultrafast lasers and sensitive structural probes, such as electrons or X-rays are able to address this challenge. In particular, it is possible to investigate LSPC on single objects using single probe pulses and avoid accumulation effects in a heterogeneous sample. The presented results capture structure formation with femtosecond and atomic scale resolution. Ultrafast time-resolved probing approaches are key to revealing the transient states and pathways that govern material transformation in LSPC.

X-ray scattering↗

DOE OSTI2020

Laser Crystallization and Dopant Activation of a-Si:H Carrier-Selective Layer in TOPCon Si Solar Cells

Herein, we present a pulsed-laser processing method for crystallization and dopant activation of a highly n-doped amorphous silicon (a-Si:H) carrier-selective layer in a tunnel oxide passivated contact (TOPCon) Si solar cell structure. Here, the laser method provides enhanced conductivity and implied open circuit voltage while reducing emitter saturation current density and surface heating, as opposed to conventional high-temperature furnace annealing of the bulk Si wafer with a TOPCon structure. We identify an appropriate laser wavelength, fluence, and layer thickness using modeling and simulations. Raman and Hall effect measurements demonstrate increased crystallinity and dopant activation, whereas photoconductive decay shows enhanced surface and interface passivation quality. Additionally, we examine the role of subsequent SiNx deposition on further improving the passivation of laser-processed TOPCon layers to achieve a 5.9 kΩ/sq film sheet resistance, 2 ms effective carrier lifetime, 718 mV implied open-circuit voltage (iVOC), and 8.6 fA/cm 2 one-side recombination current density (J0) with the potential for further passivation improvement via laser process and a-Si layer thickness optimization.

14 SOLAR ENERGY↗

NASA NTRS2022

Development and Testing of Femtosecond Laser Surface Processing (FLSP) Treated Guide Vanes for Application to Advanced Cryogenic Liquid Acquisition Devices

Liquid Acquisition Devices (LADs) are used inside propellant tanks in microgravity to collect liquid propellant to move towards the sump or outlet of a tank during expulsion or transfer. In microgravity, vehicle thrusters can produce necessary phase separation, but in the absence of thrust, surface tension is the driver of fluid behavior. Liquid in microgravity will tend to form a sphere to minimize surface area. If a LAD can be made more “attractive” to a propellant (omniphilic), then it should perform its function more effectively. This paper presents preliminary results on using femtosecond laser surface processing (FLSP) to change the wetting properties of a vane LAD. FLSP can make metals superhydrophilic or omniphilic; by controlling the applied laser parameters, the resulting micro and nanoscale surface features can be tailored to control and optimize hydrophilic/omniphilic properties. Two LAD galleries with guide vanes were recently fabricated, a control sample and an FLSP-treated sample. The LADs were ground tested and also implemented in a parabolic flight experiment. Based on contact angle and roll-off angle measurements of the surface-treated vane, FLSP appears to be a promising technique to improve efficiency of LADs

Liquid Acquisition Devices↗

NASA NTRS2002

Parametric Study of Carbon Nanotube Production by Laser Ablation Process

Carbon nanotubes form a new class of nanomaterials that are presumed to have extraordinary mechanical, electrical and thermal properties. The single wall nanotubes (SWNTs) are estimated to be 100 times stronger than steel with 1/6th the weight; electrical carrying capacity better than copper and thermal conductivity better than diamond. Applications of these SWNTs include possible weight reduction of aerospace structures, multifunctional materials, nanosensors and nanoelectronics. Double pulsed laser vaporization process produces SWNTs with the highest percentage of nanotubes in the output material. The normal operating conditions include a green laser pulse closely followed by an infrared laser pulse. Lasers ab late a metal-containing graphite target located in a flow tube maintained in an oven at 1473K with argon flow of 100 sccm at a 500 Torr pressure. In the present work a number of production runs were carried out, changing one operating condition at a time. We have studied the effects of nine parameters, including the sequencing of the laser pulses, pulse separation times, laser energy densities, the type of buffer gas used, oven temperature, operating pressure, flow rate and inner flow tube diameters. All runs were done using the same graphite target. The collected nanotube material was characterized by a variety of analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman and thermo gravimetric analysis (TGA). Results indicate trends that could be used to optimize the process and increase the efficiency of the production process.

Arepalli, Sivaram↗

DOE OSTI2025

Fatigue behavior of low-cost, non-spherical Ti-6Al-4V powder processed via laser powder bed fusion

Hydride-dehydride Ti-6Al-4V powder with particle size distribution of 75–175 μm were used to manufacture fatigue samples. Optimized processing parameters were used to maintain a relative density of >99.5% in the samples. Fatigue tests were carried out in R = σ min /σ max = -1 condition under stresses ranging from 150 to 500 MPa and the results were compared to samples that were additively manufactured using spherical powders. The fatigue lives were similar between the two types of powder; i.e., powder morphology has no effect on fatigue performance. However, the high surface roughness and martensitic microstructure resulting from the laser powder bed fusion process result in poor performance compared to samples machined from conventionally produced materials. In conclusion, crack initiation occurred consistently from surface defects because of high surface roughness of the additively manufactured parts.

36 MATERIALS SCIENCE↗

NASA NTRS1990

Processing Laser-Velocimetric Data By Vector Scanning

Velocity plots obtained in minutes instead of hours. Velocity scanning technique for processing flow-field data from pulsed-laser-velocimetry images into two-dimensional velocity-vector maps. Requires no special equipment other than charge-coupled-device (CCD) camera, circuitry to digitize output of camera, and computer. Once image data digitized, all processing done in computer.

Wernet, Mark P.↗

NASA NTRS1980

A comparison between pulsed and CW laser annealing for solar cell applications

The application of laser processing in solar cell fabrication is considered. Specific emphasis is placed on a process developed for the fabrication of a 16.6% silicon solar cell using pulsed laser processing. Results are presented which compare pulsed laser annealing with CW laser annealing in solar cell fabrication.

Jellison, G. E., Jr.↗