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At least 253 records · Page 14

Magneto-acoustic Interfacial Reaction-Based Nanoparticle Synthesis: A Direct Path to Manufacturing Metal Matrix Nanocomposites

This work investigates a novel nanoparticle fabrication methodology: combined reaction and acoustic cavitation abrasion of a solid in contact with a liquid. Magneto-Acoustic Mixing Technology is used to produce nanometer- to micron-sized particles by chemical and acoustic mechanisms between diamond particles and a stainless steel surface in the presence of a metallic liquid (Mg), where it is found that particle–surface interactions and cavitation generate particles more efficiently together than independently, producing unique chemistries. The individual and combined influence of sonic power and chemical reaction on particle size, volume fraction, chemistry, magnetic properties, and applicability to metal matrix nanocomposite fabrication are studied.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Investigation on Tribological Properties of the Pre-oxidized Ti{sub 2}AlN/TiAl Composite

Different oxidation layers on the Ti{sub 2}AlN/TiAl substrate which was fabricated by in situ synthesis were prepared through thermal oxidation process. The microstructure, phase identification and elements distribution of the oxidation layers were analyzed. The tribological performance of pre-oxidized composites against Si{sub 3}N{sub 4} ball at 25 and 600 °C, as well as the effect of pre-oxidation layers on tribological performance was systematically investigated. The results show that, compared to Ti{sub 2}AlN/TiAl, the pre-oxidized composites present more excellent tribological properties, especially the wear resistance at 600 °C. It is a significant finding that, different from severe abrasive wear and plastic deformation of Ti{sub 2}AlN/TiAl, the tribo-films formed by the pre-oxidation layers on the worn surface of pre-oxidized composites weaken abrasive wear and suppress the development of plastic deformation to protect the underlying composite substrate from wear. Moreover, the stable cooperation on the interface between tribo-films and Si{sub 3}N{sub 4} ball results in the relatively steady friction coefficient.

36 MATERIALS SCIENCE↗

Tribological Behavior and Wear Mechanism of TZ20 Titanium Alloy After Various Treatments

Abrasion is one of the most common failure forms of metals and alloys. The study of the friction and wear behavior of metals and alloys is greatly beneficial to improve their long life and safe service. The friction coefficient, weight loss, specific wear rate, and wear mechanism of Ti-20Zr-6.5Al-4V (TZ20) alloy after various treatments were investigated using a pin–disk-type wear apparatus at various normal loads. The wear results revealed that at a normal load, the friction coefficient steadily decreased, whereas the weight loss increased. By contrast, different specimens displayed distinct variation trends of specific wear rate with respect to the normal load. Further investigations indicated that the effects of hardness and toughness on the wear properties were markedly influenced by the normal load. The main characteristic of the abrasion surface gradually changed from grooves to plastic deformation as the normal load increased. The findings promote the practical application of TiZrAlV series alloys and expand wear theory.

36 MATERIALS SCIENCE↗

Subsurface mechanical damage correlations after grinding of various optical materials

Loose abrasive grinding was performed on a wide range of optical workpiece materials [single crystals of Al 2 O 3 (sapphire), SiC, Y 3 Al 5 O 12 (YAG), CaF 2 , and LiB 3 O 5 (LBO); a SiO 2 -Al 2 O 3 -P 2 O 5 -Li 2 O glass-ceramic (Zerodur); and glasses of SiO 2 : TiO 2 (ULE), SiO 2 (fused silica), and P 2 O 5 -Al 2 O 3 -K 2 O-BaO (phosphate)]. Using the magneto rheological finishing (MRF) taper wedge technique (where a wedge was polished on each of the ground workpieces and the resulting samples were appropriately chemically etched), the subsurface mechanical damage (SSD) characteristics were measured. The SSD depth for most of the workpiece materials was found to scale as E1 1/2 / H 1 , where E 1 is the elastic modulus and H 1 is the hardness of the workpiece. This material scaling is the same as that for the growth of lateral cracks, suggesting that lateral cracks are a dominant source for SSD rather than radial/median cracks, as previously proposed. Utilizing the SSD depth data from both this study and others, semiempirical relationships have been formulated, which allows for estimating the SSD depth as a function of workpiece material and important grinding parameters (such as abrasive size and applied pressure).

36 MATERIALS SCIENCE↗

Influence of Processing Techniques on the Surface Microstructure of V{sub 85}Ni{sub 15} Membrane Alloy

Vanadium-based alloys with a BCC structure are considered to be an alternative to palladium alloys for hydrogen purification. Since the performance of membranes is influenced by not only their bulk characteristics but also their surface condition, we have investigated the effect of different surface preparation techniques (abrasive grinding and polishing, electrolytic polishing, and ion etching) on the surface microstructure of V{sub 85}Ni{sub 15} membrane alloy using X-ray photoelectron spectroscopy. After electrolytic polishing and ion etching, we observed an increase in the percentages of vanadium and nickel metals in the surface layer of the alloy in comparison with its state after abrasive polishing. Such changes are expected to be favorable for an increase in the rate of hydrogen dissociation and recombination on the surface of the membrane material, eventually improving hydrogen transport efficiency.

36 MATERIALS SCIENCE↗

Resultant Cutting Trajectories on Machine Tools with Raster Tool Motion

The formation of the resultant raster trajectories in machine tools are established on the basis of Lissajous figures, taking account of additional workpiece motion for finishing purposes. Kinematic and geometric formulas are obtained for the relative tool and workpiece trajectory with strict kinematic coupling. These formulas are required in practice for abrasive lapping. They permit control of the resultant abrasive-cutting trajectory in finishing the precision planes of the workpiece.

42 ENGINEERING↗

Testbed for Lunar Extreme Environment Wear Tolerant Applications

The abrasive dust from lunar regolith poses significant long-term durability and performance challenges to materials, vehicles, mechanisms and structures that will be used for the next generation of lunar exploration. The development of advanced materials, coatings and device technologies that can withstand these abrasive particles and extreme environmental conditions is critical. However, the lack of standardized and accessible methods for evaluating such materials and devices in a facsimile of the harsh lunar environment hinders progress in dust-tolerant technologies. To address this challenge, NASA Langley Research Center is creating an extreme environment testbed. This reconfigurable testbed will allow rapid, repeatable wear testing of material and candidate mechanisms under vacuum conditions, facilitating the development of critical materials technologies for lunar exploration. Preliminary results from exposing an actuating mechanism similar to a pin joint to lunar regolith simulant under high vacuum are reported.

lunar dust↗

Testbed for Lunar Extreme Environment Wear Tolerant Applications

The abrasive dust from lunar regolith poses significant long-term durability and performance challenges to materials, vehicles, mechanisms and structures that will be used for the next generation of lunar exploration. The development of advanced materials, coatings and device technologies that can withstand these abrasive particles and extreme environmental conditions is critical. However, the lack of standardized and accessible methods for evaluating such materials and devices in a facsimile of the harsh lunar environment hinders progress in dust-tolerant technologies. To address this challenge, NASA Langley Research Center is creating an extreme environment testbed. This reconfigurable testbed will allow rapid, repeatable wear testing of material and candidate mechanisms under vacuum conditions, facilitating the development of critical materials technologies for lunar exploration. Preliminary results from exposing an actuating mechanism similar to a pin joint to lunar regolith simulant under high vacuum are reported.

lunar dust↗

Testbed for Lunar Extreme Environment Wear Tolerant Applications

The abrasive dust from lunar regolith poses significant long-term durability and performance challenges to materials, vehicles, mechanisms and structures that will be used for the next generation of lunar exploration. The development of advanced materials, coatings and device technologies that can withstand these abrasive particles and extreme environmental conditions is critical. However, the lack of standardized and accessible methods for evaluating such materials and devices in a facsimile of the harsh lunar environment hinders progress in dust-tolerant technologies. To address this challenge, NASA Langley Research Center is creating an extreme environment testbed. This reconfigurable testbed will allow rapid, repeatable wear testing of material and candidate mechanisms under vacuum conditions, facilitating the development of critical materials technologies for lunar exploration. Preliminary results from exposing an actuating mechanism similar to a pin joint to lunar regolith simulant under high vacuum are reported.

lunar dust↗

Strategies Toward Lunar Dust Adhesion Mitigation

Recently, the NASA Space Technology Mission Directorate solicited feedback to prioritize shortfalls, which were defined as technology areas needed to enable future exploration missions. Lunar dust mitigation emerged as a critical area and is cross-cutting with many of the highest ranked shortfalls with passive dust mitigation technologies being directly ranked in the top 50. Hazards associated with lunar dust are ubiquitous across all aspects of long duration lunar surface missions, whether crewed or robotic, due to the abrasive, electrostatically charged, and chemically reactive properties of lunar dust. Compounding the issue, lunar dust moves across the lunar surface due to levitation, twilight craters, and plume-surface interactions, which can result in particle velocities exceeding 1 km/h. To address lunar dust challenges, NASA is developing active and passive adhesion mitigation technologies to address specific mission needs, including electrodynamic dust screens, piezoelectric materials, biomimetic engineered surfaces, among many others. Additionally, abrasion-resistant materials are being evaluated for applications for use near landing sites and in surface manipulation and excavation equipment. These approaches, as well as test methodologies both in the laboratory and on the lunar surface to evaluate technology efficacy, will be described.

Dust Mitigation↗

Engineering the Interface: Advanced Surface Technologies for Lunar Dust Management and Equipment Longevity

Through the Artemis program, NASA intends to develop a sustainable human foothold on the Moon, ultimately paving the way for crewed exploration of Mars. The Moon's hostile environment poses numerous obstacles, including exposure to radiation, temperature extremes, micrometeoroid threats, and particularly the persistent problem of lunar dust. Lunar dust impacts nearly every aspect of surface operations through adhesion and abrasion mechanisms, with contamination from anthropogenic activities (landing, rovers) far outweighing natural phenomena. Multiple adhesion pathways contribute to surface contamination in the lunar environment, including van der Waals forces, electrostatic forces, chemical reaction, and magnetic forces from elemental iron deposits. Sharp asperities from micrometeoroid bombardment and atmospheric absence increase interaction potential and enable mechanical interlocking. Low cohesion between dust particles exacerbates these challenges, as minimal interaction potential between dust and nearby surfaces overcomes particle cohesion, causing contamination. Lunar dust adhesion mitigation technologies can be categorized as either active, requiring external energy, or passive, relying on intrinsic material properties. Ultrasonic and electrodynamic technologies have been developed to the highest technology readiness level for active approaches. Passive strategies primarily focus on surface chemistry and topography modifications. At NASA Langley Research Center, approaches include surface migration agents to reduce surface energy, topographical modification using laser ablation patterning, and tailored surface conductivity to reduce intrinsic adhesion force. Performance has been evaluated using custom-built ultrasonic and centrifuge instruments. Plume-surface interactions from lunar landers can propel micrometer-sized particles at velocities up to 1000 m s-1.8 These particles pose risks to landers, habitats and infrastructure, leading to erosion, degradation, and reduced component lifespan. A panel recovered from Surveyor III was determined to have been severely abraded because of lunar dust displaced from the Apollo 12 lunar module that landed 160 m away. The performance of metallic surfaces has been evaluated via high velocity single particle impact using the laser-induced project impact test (LIPIT) facility at the University of Utah. Peridynamics modeling, a form of continuum mechanics that uses a nonlocal approach enabling greater simulation capabilities of crack initiation and fracture, has also been utilized to gain greater insight into material response during impact events. Lunar dust contamination challenges extend to power generation systems and moving equipment. Cables, rotation stages, and other mechanisms may experience limited range of motion and reduced lifetime due to dust infiltration. NASA Langley Research Center has evaluated traditional aerospace alloys, softgoods, wear resistant ceramics, and several polymer and polymer composite materials. Test methods have included traditional techniques like Taber abrasion testing, as well as designed test configurations developed in the DUSTE (dust, ultraviolet radiation, and space thermal environmental) chamber that reproduce mechanism functions in operational environment. Beyond laboratory experiments, several flight experiments have been conducted. Materials were exposed to the low Earth orbit environment on the Materials International Space Station Experiment (MISSE) and to the lunar surface environment through the Aegis Aerospace Regolith Adherence Characterization (RAC) payload and the Honeybee Robotics PlanetVac payload. Determining lunar dust's impact on surface exploration and habitation requires comprehensive experimental and computational capabilities combined with lessons learned from initial lunar activities. Identifying the greatest environmental challenges and developing mitigation technologies provides the clearest path toward successfully, expeditiously, and efficaciously completing NASA's mission. This presentation will discuss ongoing efforts at NASA Langley Research Center and collaborator contributions to these critical objectives.

Surface Engineering↗

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO{sub 2}, anatase-TiO{sub 2} and Al{sub 2}TiO{sub 5}. PEO/α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) composite coating only had small micropores and appeared some α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) phase. Besides, the addition of α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.

36 MATERIALS SCIENCE↗

A Hybrid Plasma Treatment of H13 Tool Steel by Combining Plasma Nitriding and Post-Oxidation

Pulsed plasma nitriding and post-oxidizing process have been applied to hot work H13 tool steel to enhance the tribological properties (friction coefficient and wear rate). Nitriding was accomplished under specific conditions to generate a free white layer surface in order to avoid an abrasive wear mechanism. Post-oxidizing treatment was carried out in the same reactor after finishing the nitriding treatment; processing time was varied for 30 and 60 min. The morphology, phase’s composition and wear performance of duplex-treated samples were evaluated by scanning electron microscopy, x-ray diffraction analysis and pin-on-ball wear technique. The results show that the duplex treatment produces a bilayer arrangement constituted by an 80 μm diffusion zone with expanded martensite as the main phase underneath a 2–4 μm hematite–magnetite-oxidized layer. The duplex treatment modified the main wear mechanism of the nitrided sample from abrasive to plastic yielding. The changes in wear mechanisms resulted in a noticeable decrease, about 40%, in friction coefficient for oxidized samples in comparison with the nitrided-only sample. It was also established that the lowest friction coefficient values can be obtained when hematite is the main phase in the oxidized layer.

36 MATERIALS SCIENCE↗

Surface Treatment of Powder-Bed Fusion Additive Manufactured Metals for Improved Fatigue Life

High-cycle fatigue (HCF) tests were conducted on samples fabricated by two powder-bed additive manufacturing techniques. Samples were tested with as-produced surfaces and after various non-contact surface improvement treatments. Ti-6Al-4V samples were made using both electron beam melting (EBM) and selective laser melting (SLM), while Inconel 625 was fabricated using SLM. Ti-6Al-4V was treated with a commercial chemically accelerated vibratory polishing process, with target material removal of approximately 200 µm from each surface for EBM samples and 100 µm for SLM samples. This technique led to increases in both the number of cycles before failure at a given loading condition and endurance limit (at 10{sup 7} cycles) compared to samples with as-produced surfaces. The results are interpreted as the reduction in elastic stress concentration factor associated with surface defects where fatigue cracks initiate. SLM 625 was treated with both an abrasive polishing method and laser surface remelting. Both methods led to improvements in surface roughness, but these did not lead to improvements in fatigue properties of SLM 625. For abrasive polished samples, the combination of improved measured surface roughness without fatigue property enhancement suggests that surface material is removed, but the roots of surface defects, where fatigue cracks initiate, were left intact. For laser treatment, the remelted surface layer retained a rapidly solidified microstructure that did not increase the number of cycles before crack initiation even though the surface was smoother compared to the surface prior to polishing.

36 MATERIALS SCIENCE↗

Tribocorrosion Behavior of SAF 2205 Duplex Stainless Steel in Artificial Seawater

Tribocorrosion behaviors of SAF 2205 duplex stainless steel sliding against an Al{sub 2}O{sub 3} counterpart were investigated in artificial seawater. The tribocorrosion mechanisms and synergistic actions between corrosion and wear were analyzed in this work. The results indicated that a higher load was beneficial for the formation of the σ intermetallic phase and strain hardening; thus, the hardness increased first, and then the pure mechanical wear resistance of SAF 2205 was improved by the hardening effect. The wear mechanisms of SAF 2205 were dominated by abrasive wear under lower loads and by abrasive wear and plastic deformation under higher loads. Furthermore, galvanic corrosion was established between the σ intermetallic phase/ferritic/austenitic and passive film (cathode)/fresh surface, which caused corrosion-accelerated wear. Thus, the total damage to SAF 2205 during tribocorrosion in artificial seawater was determined by the mechanical wear and synergetic effects between corrosion and wear. Therefore, improving hardness was an effective way to increase the tribocorrosion properties of metal materials, such as SAF 2205 and 316L.

36 MATERIALS SCIENCE↗

Dry Sliding Behavior of a TiZr-Based Alloy under Air and Vacuum Conditions

In this study, dry sliding tribological properties of a TiZr-based alloy with the chemical composition Ti-20Zr-6.5Al-4V (wt.%) were tested in air and vacuum under different normal loads (10, 20, and 30 N) at various sliding velocities. Results showed that the coefficient of friction in air was lower than that in vacuum, whereas the wear volume at sliding velocity presented an opposite trend. The surfaces and cross-sectional morphology of wear scar on the TiZrAlV alloy was analyzed through scanning electron microscopy to determine the wear mechanisms. The observations showed that abrasive wear and delamination wear were dominant in air. In vacuum, the main wear mechanism changed from slightly abrasive and adhesive wear to severe adhesive wear and delamination wear as the normal load increased. Wear mechanism maps were also constructed and compared. The comparison showed that severe wear (including delamination wear) was prevalent in air.

36 MATERIALS SCIENCE↗

Effect of Tungsten Inert Gas Arc Remelting on Microstructure and Wear Properties of Plasma-Sprayed NiCr-Cr{sub 3}C{sub 2} Coating

In this work, a NiCr-Cr{sub 3}C{sub 2} coating was prepared on an AISI 1045 steel substrate by plasma spraying and then remelted with the tungsten inert gas (TIG) arc method. The purpose was to study the effects of TIG remelting treatment on the microstructure, mechanical properties and wear properties of a plasma-sprayed NiCr-Cr{sub 3}C{sub 2} coating. The results show that after TIG remelting, the density of the coating increased, the internal porosity decreased from 8.1 to 0.2%, and the number of cracks and inclusions greatly reduced. The hardness of the coating also became uniform and increased from 1007 to 1141 HV{sub 0.1}, with an obvious increase of 13.3%, and the fracture toughness increased by 321.3%. The wear volume after TIG remelting at room temperature was reduced by 59.5%, and the wear pattern changed from brittle fracture and abrasive wear to abrasive wear and adhesive wear. The wear loss at 700 °C was also reduced by 43.6%, and the wear pattern was transformed from brittle fracture and fatigue wear caused by oxidation to oxidative wear and adhesive wear. Therefore, TIG remelting treatment can effectively improve the microstructure, mechanical properties and wear resistance of a plasma-sprayed NiCr-Cr{sub 3}C{sub 2} coating.

36 MATERIALS SCIENCE↗

Industrial scale mesofluidic particle separation

Here we explore the potential of a mesofluidic separator that fits within industrial piping and is designed to remove large aspherical particles out of an abrasive slurry at fast flow rates. Mesofluidic separators have recently demonstrated separation of spherical particles at flow rates of ~1 gallon/min (gpm) (6.3.10 -5 m 3 /s). Yet, the performance of these separators at flow rates achievable within industrial piping have not been explored. Here we evaluate the permeate flowrate fraction, large particle mass fraction, and pressure drop from approximately 35-100 gpm (2.2.10-3-6.3.10-3 m 3 /s) in a three inch tube using an abrasive and modestly non-spherical slurry. Faster flow rates may be achieved with larger pumps and larger diameters. We find the permeate fraction and pressure drop both increase with flow rate, though the pressure drop remains modest. Only two feet of inserts removed 97.6±2.1% of large particles for conditions tested. Separation was demonstrated in both vertical and horizontal orientations with the horizontal orientation benefiting marginally from gravitational settling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗