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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The Sliding Wear and Friction Behavior of M50-Graphene Self-Lubricating Composites Prepared by Laser Additive Manufacturing at Elevated Temperature

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si{sub 3}N{sub 4} ball from 25 to 550 °C at 18 N–0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10{sup −7} mm{sup 3} N{sup −1} m{sup −1}. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10{sup −7}mm{sup 3} N{sup −1} m{sup −1}). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Tribological Performance of M50-Ag-TiC Self-Lubricating Composites at Elevated Temperature

M50 steel is widely used in aero-engine bearings and other high-temperature bearings. However, the poor wear of M50 steel resistance restrains its further applications. In this paper, the sliding tribological behaviors of M50 steel, M50-Ag composites (MAC) and M50-Ag-TiC composites (MATC) against Si{sub 3}N{sub 4} ball were investigated from 150 to 600 °C at 15 N-0.2 m/s. MATC showed better tribological properties in comparison with M50 and MAC. Especially at 450 °C, MATC obtained the lowest friction coefficient of 0.15 and smallest wear rate of 1.3 × 10{sup −5} mm{sup 3} N{sup −1} m{sup −1}. The excellent tribological performance of MATC during the friction test was attributed to the continuous lubricating film containing lubricant Ag and reinforcement TiC, as well as the subsurface compacted layer that could well support the lubricating film to prevent it from being destroyed. At 600 °C, because of the tribo-chemical reaction between Ag and Mo oxide during sliding process, the newly formed Ag{sub 2}MoO{sub 4} lubricating film was well spread out on the friction surface, which could continuously improve the tribological behavior of MATC. This investigation was meaningful to improve the anti-friction and wear resistance of M50 matrix bearing over a wide temperature range.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Sliding Wear and Frictional Behavior of M50-10 wt.%(Sn-Ag-Cu) Self-Lubricating Materials at Elevated Temperatures

As the main steel used in the aero-engine main shaft bearings, the tribological properties of M50 can directly affect the performance of aero-engine. The purpose of this study is to design the reasonable composition of Sn-Ag-Cu alloy and investigate the wear mechanisms of M50-10 wt.%(Sn-Ag-Cu) composites (MSACC) prepared by SPS sliding against Si{sub 3}N{sub 4} ball from 25 to 550 °C at 12 N-0.25 m/s. XRD, EPMA, FESEM and EDS mappings are conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MSACC. The results indicate that MSACC with different specifications of Sn-Ag-Cu alloy shows excellent friction and wear properties from 25 to 550 °C compared to M50. M50-10 wt.%(50Sn40Ag10Cu) (MSACC-2) shows the distinguished tribological performance for the lower friction coefficients of 0.22-0.61 and less wear rates of 1.7-4.1 × 10{sup −6} mm{sup 3} N{sup −1} m{sup −1}, which is attributed to the formed excellent lubricating structure consisting of the lubricating film with massive Sn-Ag-Cu alloy and intermetallic compounds formed during the friction process, as well as the underneath mixed layer who can well support the lubricating film due to the good intersolubility between the designed Sn-Ag-Cu alloy and M50 (Fe).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Constitutive Behavior and Forming Limit of Mg-Al-Ca-Gd Alloy Sheets at Room and Elevated Temperatures

The constitutive behavior and forming limit of a newly developed magnesium alloy sheet containing rare earth elements (Mg-Al-Ca-Gd) were investigated. Anisotropic constitutive constants were obtained through tensile tests at various temperatures and strain rates. A modified Grosman equation was adopted to describe the constitutive behavior of the magnesium alloy, taking into account the effects of temperature and strain rate. Results revealed that the proper forming temperature and the strain rate for the newly developed magnesium alloy were 210 °C and 0.001 s{sup −1}, respectively. Forming limit curves at room temperature and 210 °C were, respectively, established by the combination of hemispherical punch tests and theoretical predictions using a modified Marciniak–Kuczynski model. The accuracy of the theoretical prediction of FLD was discussed. The forming limit of Mg-Al-Ca-Gd alloy sheet increased when heated from room temperature to 210 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Characteristics and Tribological Behaviors of TiAlN/Cr-Ni Composite Coatings at Elevated Temperatures

A TiAlN/Cr-Ni composite coating was fabricated on H13 hot work mold steel using a cathode ion arc plating and laser cladding. The surface and cross-sectional morphologies, chemical compositions, phases and surface roughness of obtained coating were analyzed using a scanning electron microscope, energy disperse spectroscopy, x-ray diffraction and atomic force microscope, respectively, and the bonding strength was measured using a scratch test. The friction-wear properties of TiAlN/Cr-Ni coating at 400, 500 and 600 °C were investigated using a ball-on-disc wear test. The results show that the TiAlN coating is primarily composed of c-TiN and c-AlN hard phases, and the bonding strength of TiAlN coating with the Cr-Ni coating is 22.15 N. The average coefficients of friction of TiAlN/Cr-Ni coating at 400, 500 and 600 °C are 0.458, 0.318 and 0.449, respectively, and the corresponding wear rates are 0.329 × 10{sup −3}, 0.384 × 10{sup −3} and 0.205 × 10{sup −3} mm{sup 3} N{sup −1} s{sup −1}, respectively, and the wear mechanism includes adhesive wear and oxidation wear.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microstructure Evolution and Mechanical Response of Nanolaminate Composites Irradiated with Helium at Elevated Temperatures

In this paper, we summarize recent work on helium (He) interaction with various heterophase boundaries under high temperature irradiation. We categorize the ion-affected material beneath the He-implanted surface into three regions of depth, based on the He/vacancy ratio. The differing defect structures in these three regions lead to the distinct temperature sensitivity of He-induced microstructure evolution. The effect of He bubbles or voids on material mechanical performance is explored. Finally, overall design guidelines for developing materials where He-induced damage can be mitigated in materials are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Elevated-Temperature Strength Enhancement of a Low-Cost β Titanium Alloy Through Thermomechanically-Induced Phase Transformation

The effects of temperature and thermomechanical loading on the tensile strength and hardness were studied for a rolled, low-cost metastable β titanium alloy, Ti-13Cr-1Fe-3Al (wt.%). Tensile tests were performed at temperatures between room temperature (RT) and 410°C. The results indicated that the ultimate tensile strength (UTS) decreased with increasing temperatures up to 300°C. However, the UTS was 1400 MPa at 410°C, which was approximately 150% higher than the RT UTS. It is believed that the formation of nanoscale ω and α precipitates, identified using transmission electron microscopy, hindered the dislocation motion, which resulted in the exceptionally high UTS at 410°C. However, ductility was maintained, as the elongation-to-failure (ϵ f ) was 10% at 410°C. Dynamic mechanical analysis suggested that phase transformations occurred between 370°C-475°C. To evaluate the effect of the phase transformations on the hardness, the as-received material was heat treated at 400°C, 450°C, and 500°C for 2 h, which resulted in hardness values of approximately 340 Hv, 380 Hv, and 470 Hv, respectively. However, the greatest hardness value (500 Hv) was exhibited by the as-received material after it was tensile tested at 410°C. This suggested that both temperature and loading history affected the phase transformations. Finally, as all the samples exhibited a ductile fracture mode, this work indicates that it is possible to maintain both high strength and adequate ϵ f for Ti-13Cr-1Fe-3Al (wt.%).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Shortened Duration of Global Warming Slowdowns with Elevated Greenhouse Gas Emissions

Continuous emissions of anthropogenic greenhouse gases (GHGs) and aerosols in the last 160 years have resulted in an increasing trend of global mean surface temperatures (GMSTs). Due to interactions with natural variability, rates of the combined anthropogenically and naturally induced warming trends are characterized by significant slowdowns and speedups on decadal timescales. In this work, by analyzing observed and model-simulated data, we investigate how the duration of these episodes will change with different strengths of GHG and aerosol forcing. We found that the duration of warming slowdowns can be more than 30 yr with a slower rate of anthropogenic emissions but would shorten to about 5 yr with a higher one. This duration reduction depends on both the magnitude of the climate response to anthropogenic forcing and the strength of the internal variability. Moreover, the warming slowdowns can still occur even towards the end of this century under high emissions scenarios but with significantly shortened duration.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

The amorphization of 3C-SiC irradiated at moderately elevated temperatures as revealed by X-ray diffraction

Mechanisms of radiation damage buildup in 3C-SiC remain poorly understood. Here, we use X-ray diffraction in combination with numerical simulations to study depth profiles of radiation-produced strain and lattice damage in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal increased defect recombination with increasing temperature, with a critical amorphization fluence increasing from 0.17 to 0.44 displacements per atom. The amorphization process is found to be correlated with the evolution of lattice strain. We find that, at fluences corresponding to the onset of amorphization, lattice strain is ~2% and is independent of temperature. With continuing bombardment above the onset of amorphization, the strain in the crystal bulk increases and reaches a saturation value that decreases from 7% to 5% with increasing temperature. Based on strain profiles, we compute depth profiles of the effective concentration of point defect clusters in the crystalline phase. Bombardment at higher temperatures results in lower maximum defect concentrations pointing to enhanced defect mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Bubble formation in helium-implanted nanostructured ferritic alloys at elevated temperatures

Helium bubble formation was examined by scanning/transmission electron microscopy (S/TEM) in Fe-9/10Cr binary alloys and two dispersion strengthened nanostructured alloys (CNA3 and 14YWT containing 5–10 nm diameter carbide and oxide particles, respectively) after ex-situ and in-situ He implantation to ~10,000 appm at 500 to 900 °C. The combination of high-resolution STEM images and electron energy loss spectroscopy (EELS) revealed that the Y-Ti-O nanoparticles in 14YWT were uniformly distributed and exhibited a one-to-one relationship for bubble attachment to the nanoclusters. In the in-situ experiment at 900 °C, grain boundary cracking was severe in the Fe-10Cr model alloy, but not in the nanostructured alloys. From 500 to 900 °C, the bubble size generally increased with increasing irradiation temperature, while the bubble density decreased with increasing temperature. At the same temperatures, the bubble size in the implanted materials was in the order of Fe-9/10Cr > CNA3 > 14YWT, while the bubble density showed the opposite order. The observed bubble number densities for the nanostructured alloys are comparable to the nanoparticle density, suggesting that the nanoparticles in both alloys were effective in trapping He. Overall, our results indicate that very high He concentrations can be managed in nanostructured alloys by sequestering the helium into smaller bubbles (which leads to a lower volume swelling value) and to shield He from the grain boundaries. This can be attributed to the much higher sink strength associated with the nanoclusters or the He trapping ability between different types of nanoclusters.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental evaluation of a prototype hybrid CPV/T system utilizing a nanoparticle fluid absorber at elevated temperatures

Novel approaches for solar energy conversion continue to garner interest as a potential thermal and electrical energy source. Additionally, the need for systems capable of producing thermal energy at temperatures up to 300 °C is growing as a means to provide process heat to industry and distributed generation for small communities. An approach that has seen recent increased interest is the hybrid concentrating photovoltaic/thermal collector that can co-produce electricity and heat energy above 100 °C. A technique for this is to use nanoparticles in the heat transfer fluid to spectrally filter off wavelengths poorly utilized by the photovoltaic component. Here, we have demonstrated the first on-sun operation of a nanoparticle based hybrid CPV/T solar collector at temperatures exceeding 100 °C using a combination of gold and indium tin oxide nanoparticles in Duratherm S flowing in the receiver, with an aperture area a full order of magnitude larger than other tests. At 14× concentration the system achieved a photovoltaic efficiency of 4% while achieving a peak thermal efficiency of 61% with an outlet temperature of the fluid of 110 °C.

14 SOLAR ENERGY↗