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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Vertical Translation System for the Common Habitat Architecture

The Common Habitat is a large, long-duration habitat that uses an SLS core stage Liquid Oxygen (LOX) tank as its primary structure. Measuring 8.4 meters in diameter and 15 meters in length, it is manufactured as a habitat and launched as such into space. It is intended for use on the Moon as part of a permanently occupied outpost, on Mars as part of an outpost that will be occupied for hundreds of days at a time, and in deep space as part of the Deep Space Exploration Vehicle where it will support crewed missions up to 1200 days in duration. A study of internal orientation and crew size resulted in a Common Habitat configuration sized for a crew of eight with a three-deck horizontal orientation. The Common Habitat Vertical Translation System provides a means for transporting crew and cargo between decks in a Common Habitat spacecraft in gravity levels varying from 0g to 1g. A crowdsourcing campaign was conducted through the GrabCAD platform to initially solicit ideas for restraints and mobility aids, including vertical translation. Four of the five top responses repeated ideas that would be incorporated into features of the Vertical Translation System. The first was a safety barrier (to prevent falls into the opening between decks) that could collapse to form a floor surface covering the opening when not in use. The second idea was a folding ladder that could be stowed in the ceiling when not in use. The third idea was an elevator platform that could traverse the ladder. Several key driving requirements were established for the Vertical Translation System: it may not penetrate into or through the lower deck; it must work on the Earth, Moon, Mars, and in microgravity; it must be easy to operate; it must enable translation of any item that can fit through the Common Habitat’s 40” x 60” hatches, inclusive of suited and unsuited crew with any degree of incapacitation and any equipment or cargo item; and it must include three component systems – deploying floor / safety barriers, a deployable ladder, and an elevator platform. Additional requirements were established for each of the component systems. The safety barriers must form a roughly 40-inch tall, complete wall enclosure on all four sides when deployed; it must include an easy to open gate that allows access to/from the ladder when deployed; and when retracted, the safety barrier must form a smooth, load-bearing floor that can be walked on, and wheeled objects can be rolled across in gravity, without being a trip hazard. The deployable ladder must be composed of multiple ladders that work together; it must stow in the ceiling when not in use; and it must not penetrate into the 40” x 60” vertical passage corridor. The elevator platform must work with the deployable ladder system; it must be able to bridge any gap in ladders between decks; it must stop at each deck flush with the deck surface; it must be capable of transporting an incapacitated crew member as a single rescuer operation; it must be capable of transporting a full-size subsystems pallet; it must function as an elevator for a crew member carrying large objects; it must have safety functions to prevent falls from the platform, or crew/cargo collisions with edges of hatch openings, or entanglement with ladder rungs/structure; it must stow when not in use; and it must autonomously both connect itself to the ladder and deploy itself to any deck where needed when called (e.g., a crew member on any deck can call for the platform and it must connect itself to the ladders without assistance and translate to the requestor’s deck). These requirements were developed into a system concept with the assistance of a NASA Pathways Intern who also added the requirement to size the design based on the use of commercial components, using existing motors and other mechanisms to ensure that the resulting system could be inexpensively produced. The Floor and Safety Barrier consists of four panels, two roughly 40 inches long and two roughly 60 inches long that can fold into the floor on top of each other when not in use. The uppermost panel is load bearing and acts as the floor surface. When deployed, they connect with each other to form a rigid barrier surrounding the vertical passageway. One of the panels contains a hinged gate that can be opened when deployed to allow for access to/from the passageway. The Deploying Ladder consists of two ladder segments, one mounted on the ceiling of the lower deck and the other mounted on the ceiling of the mid deck. A rotating mechanism is mounted on the ladder to allow it to rotate into a horizontal position against the ceiling for stowage, or down to a vertical position for use. A second rotating mechanism is built into the ladder, allowing the rungs to rotate. A toothed surface intended to work with the elevator platform covers the front of the ladder rails and the top and bottom of the rails are designed to be flush when aligned with another ladder segment. The elevator platform is essentially a motorized, self-propelled deck. It has a mechanism that holds it in contact with the ladder rails and drives itself against the toothed surface. This mechanism allows the elevator platform to ascend or descend the ladder. In order to stow the platform when not in use, a set of short ladder rails (without rungs) are mounted to the ceiling of the mid deck. When the mid deck ladder is stowed, it is flush with these rails and the platform can drive itself onto those short rails for stowage. An additional mechanism on the platform can pitch its deck surface 90 degrees, such that when the ladder is to be stowed, the platform can fold up against the ceiling. As a consequence of the ladder and elevator platform design, the opening between decks in the Common Habitat was enlarged to ensure that the elevator platform can accept a payload up to 40”x60” in dimension.

Human Centered Design↗
NASA NTRSDate not supplied

DeepONet-Assisted Optimization of Surface Topography for Transition Delay in a Mach 4.5 Boundary Layer

We use deep learning, an ensemble variational technique (EnVar), and direct numerical simulations(DNS) to design an optimal topography for a two-dimensional roughness element that delays the on-set of laminar-turbulent transition in a Mach 4.5 flat-plate boundary layer. Deep operator networks (DeepONets), which have the known ability to learn complex nonlinear operators within dynamical systems, are used for machine learning. For the baseline configuration of a smooth flat plate, the second-mode waves at the DNS inflow cause a quick nonlinear breakdown of the high-speed boundary layer within the computational domain. Results reported in the present study validate the ability of DeepONets to model the transition delay via a given topography of the roughness element. The computing cost to optimize the rough-ness element for minimal skin-friction drag is substantially lowered by the DeepONets-based reduced-order model. In comparison to the baseline method of EnVar optimization based on DNS alone, the DeepONets-based EnVar optimizer is able to delay transition past the outflow boundary of the computational domain while utilizing almost 5–6 times fewer DNS.

Machine Learning↗
NASA NTRSDate not supplied

NASA/ONERA Collaboration on Small Hovering Rotor Broadband Noise Prediction using Lattice-Boltzmann and Structured Navier-Stokes Solvers

This work compares two lattice-Boltzmann method solvers, PowerFLOW and ProLB, and two structured Navier-Stokes solvers, OVERFLOW2 and FAST, used by NASA and ONERA, respectively, for the broadband noise prediction of an ideally twisted rotor as part of Implementing Arrangement number FR-0685-0, ‘Comparing Computational Fluid Dynamics Solvers for Broadband Noise Prediction.’ Predicted results are evaluated against measured data from both smooth and rough blade sets acquired in the Small Hover Anechoic Chamber at the NASA Langley Research Center. Aerodynamic thrust predictions are seen to agree more favorably with the rough-blade measurements, whereas torque predictions agree better with the smooth-blade measurements. A tonal noise comparison shows better agreement to the measured data with the two structured Navier-Stokes solvers than with the two lattice-Boltzmann solvers, which is thought to be caused by the different geometric discretization associated with each solver paradigm. Broadband noise comparisons show that both lattice-Boltzmann method solvers trend well with the smooth-blade measurements, with the exception of an overprediction by ProLB between 4 kHz and 15 kHz. OVERFLOW2 is seen to capture the measured nondeterministic tonal content between 3 kHz and 8 kHz on a narrowband spectral basis and FAST agrees well with the rough blades on a one-third octave band basis.

Christopher S. Thurman↗
NASA NTRSDate not supplied

Assessments of Physiology and Cognition in Hybrid-Reality Environments (APACHE)

NASA is planning to return to the Moon in the mid-2020s as a stepping stone to Mars missions in the 2030s. Spacewalks, or extravehicular activities (EVAs), performed on the Moon and Mars will differ in a variety of ways from those that have been performed in decades past. NASA has identified multiple risks to human health and performance associated with a crewed mission to Mars, especially those associated with exploration EVAs which are expected to be a primary mission activity. Crew may be expected to conduct up to 24 hours of EVA per person per week, where the likelihood of injury and/or mental mistakes are increased compared to ground-based training or current microgravity EVAs and the consequences of which can be catastrophic. Current test environments for exploration EVA research and technology development are large, costly facilities that are limited in their availability or capabilities. Spacesuit testing in a reduced gravity environment such as NASA’s Neutral Buoyancy Laboratory, while a good representation of the crew’s physical workload during exploration EVAs, typically has small datasets and is difficult to integrate physiological sensors or other types of crew performance measures. Meanwhile, scientific field-based testing such as NASA’s Desert Research and Technology Studies offers an operationally relevant environment for exploration EVAs, particularly for cognitive workload, but is also limited by small datasets, lack of a pressurized spacesuit, and obtrusive measures. The limitations of current analogs for exploration EVAs identify a need for a new test environment that can approximate both the physical and cognitive demands associated with exploration EVAs to enable rapid, controlled, and repeatable evaluations of human health and performance risks of exploration missions. In response, the Human Physiology, Performance, Protection, and Operations Laboratory (H-3PO) at NASA Johnson Space Center has developed a hybrid reality exploration EVA analog named the Assessments of Physiology And Cognition in Hybrid-reality Environments (APACHE) to address these limitations using a combination of virtual, physical, and hybrid reality techniques. The APACHE facility resides at NASA Johnson Space Center and serves as a large “sandbox” for EVA research and simulation. At its center is a roughly 15x20ft space surrounded by a 14” tall sandbox partially filled with lunar regolith simulant to emulate the physical feeling of walking on a planetary surface and to allow for simulated geology operations. Nearby, a curved passive treadmill (Skillmill Connect, Technogym, Fairfield, NJ) and an omnidirectional treadmill (Infinadeck, Infinadeck, Rocklin, CA) are included to enable exploration of these large virtual environments while also imposing the physical demands, representative timelines, and cognitive burdens required to navigate and traverse these distances during exploration EVA. A 6DOF motion platform is used to simulate rover operations and supports various human performance evaluations and associated risks. Lastly, APACHE can support two extravehicular (EV) crewmembers working in tandem. A computer workstation is located nearby and also supports an intravehicular (IV) crewmember as part of a full mission simulation. The IV crewmember has direct video and audio communication with the EV crew in VR to provide operational and procedural support. The software used in APACHE was created by the JSC Engineering Directorate, in partnership with Buendea, powered by a custom Unreal Engine 5 (UE5.3, Epic Games) project. APACHE currently utilizes the HTC Vive Pro Eye in a wireless configuration for VR simulations. There are two virtual environments that subjects can explore within APACHE, a Lunar and Martian surface. The virtual Lunar surface was created from LIDAR data of the Lunar South Pole to create roughly 16 sq km of explorable terrain. The virtual Martian surface contains roughly 400 sq km of explorable terrain derived from Mars Reconnaissance Orbiter LIDAR data of the Jezero Crater. The immersion and related cognitive burdens of conducting a planetary EVA is simulated through a series of EVA-relevant tasks performed in the VR environment, using these high-fidelity visual representations. Additionally, APACHE includes biosensor driven informatics, such as real-time heart rate monitoring and/or derived values from model simulations, for active monitoring by the EV crew and added cognitive demand. A “Wizard of Oz” control panel enables test operators to activate contingency events such as simulated spacesuit malfunctions, loss of communications, and/or limited visibility. Embedded performance measures such as accuracy, completeness, and execution time have been developed for various exploration tasks to objectively quantify crew performance during an EVA and compare impacts to performance when different environmental stressors, both physical and cognitive, are added to or removed from the simulation. Additionally, validated cognitive and operational performance measures such as the Digit Symbol Substitution Task have been recreated and embedded in VR for direct and relatively unobtrusive measurement of motor perception. The APACHE environment currently supports multiple research studies at NASA. Examples include the CHAPEA project, a series of simulated year-long missions on Mars by a 4-person crew; and the CO2 Contingency Walk Back Study, an investigation of elevated CO2 exposure on crew performance during a contingency EVA scenario. APACHE also provides a test environment to support the development of the Crew State and Risk Model, which is a collection of individualized, mathematical models of crew physical and cognitive state; and the Personalized EVA Informatics and Decision Support system, an operational tool for flight controllers, and eventually a self-reliant Martian crew, to make biomedically-informed decisions in real-time to optimize the EVA planning and execution with respect to crew health and performance. Some technical challenges associated with developing the APACHE environment, as well as current limitations, include VR limitless natural walking with a hybrid spacesuit simulator, optimizing performance for wireless PC VR streaming while maintaining a high degree of visual fidelity, and the integration of various physiological (metabolic masks) and psychometric (eye tracking) sensors with the VR headset.

Human Performance↗
NASA NTRSDate not supplied

Electrical Discharge Machining of Additively Manufactured Superalloys Containing Oxide Dispersions

Superalloys can be strengthened by oxide dispersions to potentially improve their mechanical properties at high temperatures. Additive manufacturing has opened new paths for introducing oxide particles into superalloys with increased processing flexibility, to potentially provide oxide dispersion strengthening. Numerically controlled electrical discharge machining (EDM) has often been used as a machining process for initial sectioning, detailed roughing, and even finishing operations of conventional superalloys. The objective of this study was to examine how additively manufactured superalloys containing oxide dispersions respond when sectioned using EDM. Consistent sections of several superalloys, two containing an oxide dispersion, were sliced using a typical EDM machine with standard brass wire and a typical roughing condition set. Roughness, microstructure, and residual stress at the EDM surfaces were compared for the varied superalloys.

superalloys↗
DOE OSTI2020

ScAIN etch mask for highly selective etching

A fabrication process employing the use of ScAlN as an etch mask is disclosed. The ScAlN etch mask is chemically nonvolatile in fluorine-based etch chemistries and has a low sputter yield, resulting in greater etch mask selectivity and reduced surface roughness for silicon and other semiconductor materials. The ScAlN etch mask has an etch mask selectivity of greater than 200,000:1 relative to silicon compared to an etch mask selectivity of less than 40,000:1 for a prior art AlN etch mask relative to silicon. Further, due to reduced sputtering of the ScAlN etch mask, and thus reduced micromasking, the ScAlN etch mask yielded a surface roughness of 0.6 μm compared to a surface roughness of 2.8 μm for an AlN etch mask.

36 MATERIALS SCIENCE↗
DOE OSTI2022

HEAT TRANSFER ASPECTS OF TWO PISTON SPLAT QUENCHING

This thesis investigates the heat transfer aspects of the two-piston splat quench system by modifying surface roughness and by using copper and stainless steel platens. In additive manufacturing, specifically selective laser melting (SLM), metal is subjected to a very rapid heating and cooling that produces cooling rates in the range from 105-106 °C/s. This rapid solidification produces microstructures that deviate far from equilibrium. Splat quenching is an experimental method that produces rapidly solidified structures under cooling rates that are comparable to those found in additive manufacturing. The splat quenching approach allows for more efficient testing of the rapid solidification behavior of a wide variety of alloys. In this thesis, two platen characteristics, surface roughness and material thermal conductivity, were examined to determine their role in controlling the heat transfer and the subsequent cooling rate during splat quenching of austenitic stainless steel 316L. To that objective, 5 surface finishes were produced using metallographic techniques, from 7046-203 Å Rms. Copper and 316L stainless steel platen material were used to reach different levels of thermal conductance. The combination of these 2 variables created 10 scenarios, which were examined using, backscatter imaging, secondary imaging, and electron back scatter diffraction. Cooling rates were estimated using cell sizing obtained through electrolytic etching and secondary imaging. This thesis determined that both surface modification and changes in material type had a statistically significant impact on the cell sizes observed. Where material type far outweighed surface roughness in its effect on cell size.

Roze, Jonathan↗
DOE OSTI2022

ADDITIVELY MANUFACTURED SURFACE HEAT TRANSFER ENHANCEMENTS FOR THE TRANSFORMATIONAL CHALLENGE REACTOR

The Transformational Challenge Reactor (TCR) is a high-temperature gas-cooled reactor design that uses additively manufactured fuel elements. TCR fuel elements have walls made of silicon carbide and are filled with tristructural-isotropic fuel particles. These fuel elements can have radically different shapes and integrated features than existing designs due to the reduced cost for complex structures in binder jet additive manufacturing. As such, binder jet additive manufacturing enables wall surface features to be embedded that can deliver superior heat transfer performance than smooth wall designs. In this work, the authors conducted a computational fluid dynamics study to evaluate selected wall features integrated into TCR fuel elements. Results show that surface features can outperform smooth wall designs; however, there are unique challenges for gas-cooled reactor core designs that have not been fully explored by previous research. For example, the rough surface finish and process variability of ceramics additive manufacturing make it challenging to predict surface roughness effects before fabrication. Additionally, the small hydraulic diameters of coolant channels in reactor cores make it difficult to engineer surface features that do not significantly increase the pressure drop. Engineers must carefully size surface features for heat transfer enhancement in additive fuel elements to operate above the base material's surface roughness effects and below the coolant channel size.

Weinmeister, Justin↗
DOE OSTI2022

Remote Epitaxy of III-V Solar Cells via Hydride Vapor Phase Epitaxy

The promise of remote epitaxy, in which epitaxial registry of a film can still be maintained through two-dimensional layers, has emerged from an advanced understanding of the interactions between two dimensional materials and bulk semiconductors. A promising application of this technology is to facilitate substrate reuse in epitaxial III-V systems, which could significantly reduce material cost and improve commercial viability of this high-efficiency photovoltaic technology. In this process the weak van der Waal bonds between the 2D layer and the III-V substrate make separation of epitaxially-grown layers simple and leaves a smooth substrate that can be reused for cost reduction. Here we present a study of growth parameters of GaAs on AlGaAs through a low dimensional carbon interlayer via hydride vapor phase epitaxy (HVPE). We Investigate the effect of various GaAs nucleation conditions such as V/III ratio, temperature and growth rate on film roughness, crystallinity, and degree of epitaxial alignment. We demonstrate growth of single crystal GaAs layer on top of the low dimensional carbon that follow the crystal orientation of the substrate. Surface roughness measured via AFM found that lower V/III ratios result in smoother III-V films grown on the low dimensional carbon, with a lowest RMS of ~60 nm obtained at a V/III ratio of 5. Growth temperatures are optimized at 650 C, as temperatures below 550 C show non-crystalline growth and higher temperature samples display very rough surfaces. Additionally, we investigate HVPE growth on various forms of low-dimensional carbon including transferred graphene, CVD-grown graphene, and MOCVD-growth amorphous carbon and find the latter to be most well suited for III-V growth as this method results in cleaner interface and potential for direct, large-area coverage. We also identify techniques to mitigate surface degradation in carbon layers as a function of both exposure time and growth environment by analyzing surface changes via x-ray reflectivity. We show growth of heteroepitaxial III-V solar cells on carbon interlayers and preliminary cell results, which are currently limited to 4% efficiency under one sun.

AlGaAs↗
DOE OSTI2022

Methods of forming electrode structures

An electrode structure and its method of manufacture are disclosed. The disclosed electrode structures may be manufactured by depositing a first release layer on a first carrier substrate. A first protective layer may be deposited on a surface of the first release layer and a first electroactive material layer may then be deposited on the first protective layer. Subsequently, the first carrier substrate may be delaminated from the first release layer. The first release layer may then be removed from the first protective layer by dissolution in an electrolyte. The first protective layer may have a low mean peak to valley surface roughness and/or may be thin. In some embodiments, an interface between the first protective layer and the first electroactive material layer has a low mean peak to valley surface roughness. In some embodiments, a thickness of the first protective layer is greater than a mean peak to valley roughness of the first release layer. In some embodiments, an adhesive strength between the first release layer and the first protective layer is greater than an adhesive strength between the first release layer and the first carrier substrate.

Mikhaylik, Yuriy V.↗
DOE OSTI2022

A Study on Surface Texture and Wettability of Femtosecond Laser Treated Aluminum Alloys

This research aims to study the effects of femtosecond laser treatment on surface texture and wettability properties. The first portion of this research studies 2024-T3 aluminum alloy concerning surface texture (e.g., roughness), wettability, and surface free energy. SEM images help aid the researchers in detecting minuscule changes in surface texture. Profilometry extracts topographical data from the surface. A contact angle goniometer measures contact angle, which follows the sessile drop method. Owens, Wendt, Rabel, and Kaelble's method calculates the surface free energy in conjunction with the contact angle. Femtosecond laser modification produces relatively uniform surface morphology at the macroscale. When looking at the microscale, surface morphology differs depending on the interplay between material melting and self-assembly, where the surface becomes rougher after laser treatment. Contact angle results show that all but the control sample and sample 7 exhibit hydrophobic behavior, i.e., contact angle >90°, with Sample 1 having the most significant angle of 115°. The effects of laser parameters on surface energy is apparent. More work is needed to establish correlations among these three quantities: contact angle, surface energy, and laser parameters. The second portion of this research studies aluminum alloy 6061 as the subject material with the primary goal of creating a superhydrophobic surface. A central composite design creates the laser surface texturing design of experiments. SEM images help aid the researchers in detecting minuscule changes in surface texture. A 3D optical profiler extracts topographical data from the surface. The sessile drop method incorporates a contact angle goniometer to measure the contact angle. The response surface method builds a second-order polynomial model for the contact angle and obtains optimized parameters to maximize the contact angle. This research shows that laser surface texturing can generate a wide range of surface profiles and roughness values with geometric features ranging from hundreds of μm to submicron. All three laser parameters (pulse energy, pulse duration, repetition rate) affect surface roughness and contact angle to some degree. To quantify the relationship between the contact angle, pulse energy, and pulse repetition rate, a response surface model for Al 6061 is identified and used to find the optimal conditions of E=214 μJ, tp=10 ps, and fp=2427 Hz with a predicted maximum contact angle of 161°. A confirmation experiment produces a contact angle of 168°, in good agreement with the predicted value.

Angell, Dakota↗
DOE OSTI2023

Laser Characterization of Optically Smooth BREAD parts

The Broadband Reflector Experiment for Axion Detection is a dish antenna experiment probing the axion and dark photon parameter space in the [1 μeV, 1 eV] mass range, or [.02, 200] THz frequency range. In the pilot design for the InfraBREAD model, the dish antenna includes an optically smooth coaxial parabolic reflector to focus incoming photons in the near Infrared spectrum, created by the spontaneous photoconversion of axions and dark photons, onto a Superconducting Nanowire Single Photon Detector at the focus point of the reflector. As the pilot begins as a dark photon detector, sensitivity estimates hypothesize that it could cover unprobed parameter space in the search for the dark photon. Because of this, it is of critical importance that the reflector and SNSPD be placed at the correct points in the dish antenna, as previous work has shown that in addition to the focal spot of the photons being smeared to an area larger than the SNSPD, detection efficiency is s ensitive to shifts on the millimeter scale. In order to constrain this barrier to efficiency, the reflector had its focal spot, roughness, and length of surface waves measured by lasers in an optical bench setup. Results show the focal point diverging slightly from its theorized position in the antenna, while uncertainty in the height at which the detector should be placed was constrained to 10s of microns, the uncertainty in radial position could not be constrained to smaller than the detector given the methods used. Results for the roughness and surface wavelength show that the reflector was uniformly machined in a diamond-turning process used to fabricate optically smooth parts, as well as support a roughly 90% detection efficiency, reinforcing the sensitivity estimates presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Optimization of Processing, Microstructure, and Hardness of an Al–Ce–Ni–Mn–Zr Alloy With Laser Additive Manufacturing

Here, this study examines the processing behavior, microstructure, surface roughness, and hardness properties of an aluminum alloy containing 8.2 Ce, 4.5 Ni, 0.5 Mn, and 0.7 Zr (wt%) fabricated using laser powder bed fusion. Sixty samples were produced across a range of laser powers, scan speeds, and hatch spacings to evaluate their effect on porosity, hardness, and microstructural features. Porosity was measured using X-ray computed tomography, while microstructure and surface roughness were characterized by scanning electron (SEM) and laser confocal microscopy. High dense and cracking-free Al–Ni–Ce alloy was successfully manufactured. Porosity showed a U-shaped dependence on energy input, increasing under both insufficient and excessive melting conditions. Hardness increased with cooling rate due to finer cellular structures and solute redistribution. A general statistical model was developed to capture the relationships between processing parameters and material response. Results identify a narrow processing window defined by laser powers between 350 and 370 W, scan speeds from 1400 to 1800 mm/s, and hatch distances between 0.14 and 0.18 mm. Within this window, porosity is minimized (below 0.01%) and hardness is maximized (up to 160 HV), demonstrating that careful control of these parameters enables dense, high strength aluminum components suitable for demanding structural applications.

Aluminum alloys↗
DOE OSTI2021

Time-Resolved Grazing Incidence X-Ray Absorption Spectroscopy for the In Situ Investigation of the Initial Stages of Sputter-Deposited Copper Thin Films

The sputter deposition and the growth of thin copper films on float glass substrates are in situ studied using grazing incidence, reflection mode X-ray absorption fine structure spectroscopy with subsecond time resolution. The experimental data are compared with model calculations, assuming the presence of crystalline, face-centered cubic metallic Cu nanostructures. From a detailed analysis of the measured spectra, the film thickness as well as the surface roughness is determined, leading to a detailed understanding of the films growth as a function of the sputter deposition time. In particular, different stages of film growth can clearly be distinguished from the fits of the experimental data. The results suggest the formation of isolated, approximately nm-sized copper clusters in the initial phase of the film deposition for the first few seconds, a coalescence phase with a nominal thickness of ≈1.5–2.8 nm, constant roughness of about 1.4 nm for the subsequent ≈5 s, and finally 3D growth of the Cu crystallites in the film for later stages of film growth. Further prospects of the methodology are given.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Experimental approach for development of a powder spreading metric in additive manufacturing

The powder spreading is a vital step of powder-based additive manufacturing (AM) processes. The quality of spread powder can considerably influence the properties of fabricated parts. Poorly packed powder beds with high surface roughness result in printed part layers with large porosity and low dimensional accuracy, leading to poor mechanical properties. Therefore, the powder spreadability and its dependence on process parameters and powder characteristics should be quantified to improve the efficiency of powder-based AM methods. This study proposes a novel dimensionless powder spreadability metric that can be commonly used in different powder-based AM processes. The quality of spread powder in terms of powder bed density and surface roughness was evaluated by adjusting the process parameters including recoating velocity and layer thickness, and powder characteristics including particle size distribution. In addition, the dynamic repose angle was proposed and examined as another powder spreadability metric. Furthermore, the results showed that these two proposed metrics were strongly correlated and lower recoating velocity and larger layer thickness led to higher spreadability and lower dynamic repose angle.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Efficient SnO{sub 2}/CuO/porous silicon nanocomposites structure for NH{sub 3} gas sensing by incorporating CuO nanoparticles

In this paper, a porous silicon (Psi) surface modification process, including the incorporating of pure and CuO mixed SnO{sub 2} within a Psi layer, was investigated. A Psi layer with a pore-like structure prepared via laser-assisted etching process with a laser illumination intensity of (40) mW/cm{sup 2} was employed as a substrate for materialization SnO{sub 2}/CuO/Psi nanocomposites for gas sensing application. Pure SnO{sub 2} and SnO{sub 2}:CuO nanoparticles were synthesized via a chemical spray pyrolysis process on the Psi surface at 350 °C. The materialization of SnO{sub 2}:CuO/Psi nanocomposites were recognized through Field-Emission Scanning Electron Microscopy, X-ray Diffraction, Atomic Force Microscopy, and Energy-dispersive X-ray Analysis. The results displayed that the morphological properties of SnO{sub 2}:CuO nanoparticles were definitely controlled by varying the CuO contents. Different shapes (nearly cubic shape and spherical shape) with various sizes of SnO{sub 2} and SnO{sub 2}:CuO within the Psi surface were achieved by increasing the CuO content. SnO{sub 2}:CuO/Psi nanocomposites, plans, grain size, average surface roughness, homogeneity and specific surface area of SnO{sub 2}:CuO nanoparticles were considerably influenced by CuO content. The lower grain size and higher average surface roughness and specific surface area were attained when the percentage of CuO was about 30% within the structure of 70% SnO{sub 2}:30% CuO, and the performance of the NH{sub 3} gas sensor revealed a short response time with a high sensitivity of (88%).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Mechanical Surface Treatments of AISI 304 Stainless Steel: Effects on Surface Microrelief, Residual Stress, and Microstructure

The surface roughness, residual stress, and microstructure of AISI 304 stainless steel specimens after laser shock peening (LSP), water jet cavitation peening (WjCP), water jet shot peening (WjSP), and multi-pin ultrasonic impact treatment (UIT) were studied in this work. Compared to the initial state, the surface roughness (Ra) was, respectively, decreased by approx. 5.5, 7.8, 38.2, and 91.1% after the LSP, WjCP, WjSP, and UIT processes. The volume fraction of ε-martensite of ~ 3-5% was observed in all treated specimens except for the LSP-treated ones. The volume fraction of α′-martensite was increased in the following sequence: WjCP (~ 5%), LSP (~ 5%), WjSP (~ 25%), UIT (~ 50%). The studied mechanical surface treatments promote a significant reduction in grains size of both austenite (~ 15-20 nm) and martensite (~ 20-37 nm) leading to essential hardening. All studied processes result in the formation of compressive residual stresses (− 377…693 MPa) and the improvement in the bearing curve parameters. The microhardness estimated accounting for the contributions of different hardening mechanisms to the yield strength magnitude correlates well with the experimental data. The grain boundary hardening and dislocation hardening are concluded to be the most influential mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electrodeposition and Characterization of Cr-MoS{sub 2} Composite Coatings

In this study, Cr-MoS{sub 2} composite coatings were electrodeposited from conventional Cr{sup +6} baths containing different amounts of MoS{sub 2} particles and various types of surfactant (cationic and anionic). The effect of bath chemical composition on the coatings properties like their microstructure, morphology, chemical composition, corrosion behavior, surface roughness and microhardness was investigated using x-ray diffraction, scanning electron microscopy (SEM), energy-dispersive x-ray analysis, potentiodynamic polarization, electrochemical impedance spectroscopy, surface profilometry and Vickers microhardness measurement techniques, respectively. The results showed that incorporation of MoS{sub 2} particles into the composite coatings is very limited and Cr matrix with very low crystallinity will be electrodeposited at various experimental conditions. The presence of MoS{sub 2} particles in the bath (up to an optimum value) leads to the formation of the composite coatings with lower surface roughness values than that of conventional chromium coating. Although more MoS{sub 2} particles will be incorporated into the electrodeposits when the solid content of the bath increases, chromium cannot be electrodeposited from baths containing high amounts of MoS{sub 2} particles. Application of cationic surfactant promotes incorporation of particles into the Cr metallic matrix. Moreover, the presence of surfactant in the bath results in the formation of coatings with less microcracks. All the composite coatings have more hardness values than that of conventional chromium coating; maximum hardness is attributed to the coatings that were electrodeposited from baths containing no surfactant. The corrosion test results revealed that the smooth coatings containing more MoS{sub 2} particles and less microcracks exhibit more corrosion resistance than the other ones.

36 MATERIALS SCIENCE↗