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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Temperature dependence of penetration depth in thin film niobium

A novel technique is presented which should allow precise determination of the temperature dependence of the inductance, and hence of the penetration depth, of superconducting niobium thin-film structures. Four niobium thin-film stripline inductors are arranged in a bridge configuration, and inductance differences are measured using a potentiometric technique with a SQUID (superconducting quantum interference device) as the null detector. Numerical simulations of the stripline inductances are presented which allow the performance of the measurement technique to be evaluated. The prediction of the two-fluid model for the penetration-depth temperature dependence is given for reduced temperatures of 0.3 to 0.9. The experimental apparatus and its resolution and accuracy are discussed.

More, N.↗
NASA NTRS1992

Creep behavior of tungsten fiber reinforced niobium metal matrix composites

Tungsten fiber reinforced niobium metal matrix composites were evaluated for use in space nuclear power conversion systems. The composite panels were fabricated using the arc-spray monotape technique at the NASA Lewis Research Center. The creep behavior of W/Nb composite material was determined at 1400 and 1500 K in vacuum over a wide range of applied loads. The time to reach 1 percent strain, the time to rupture, and the minimum creep rate were measured. The W/Nb composites exceeded the properties of monolithic niobium alloys significantly even when compared creep strength also was evaluated. Kirkendall void formation was observed at the fiber/matrix interface; the void distribution differed depending the fiber orientation relative to the stress axis. A relationship was found between the fiber orientation and the creep strength.

Grobstein, Toni L.↗
NASA NTRS1994

Reactive Melt Infiltration of Silicon-Niobium Alloys in Microporous Carbons

Studies of the reactive melt infiltration of silicon-niobium alloys in microporous carbon preforms prepared by the pyrolysis of a polymer precursor have been carried out using modeling, Differential Thermal Analysis (DTA), and melt infiltration. Mercury porosimetry results indicate a very narrow pore size distribution with virtually all the porosity within the carbon preforms open to infiltrants. The morphology and amount of the residual phases (niobium disilicide and silicon) in the infiltrated material can be tailored according to requirements by careful control of the properties (pore size and pore volume) of the porous carbon preforms and alloy composition. The average room temperature four-point flexural strength of a reaction-formed silicon carbide material (made by the infiltration of medium pore size carbon preform with Si - 5 at. % Nb alloy) is 290 +/- 40 MPa (42 +/- 6 ksi) and the fracture toughness is 3.7 +/- 0.3 MPa square root of m. The flexural strength decreases at high temperatures due to relaxation of residual thermal stresses and the presence of free silicon in the material.

Singh, M.↗
NASA NTRS1993

The Gravity Probe B `Niobium bird' experiment: Verifying the data reduction scheme for estimating the relativistic precession of Earth-orbiting gyroscopes

Gravity Probe B (GP-B) is a relatively gyroscope experiment begun at Stanford University in 1960 and supported by NASA since 1963. This experiment will check, for the first time, the relativistic precession of an Earth-orbiting gyroscope that was predicted by Einstein's General Theory of Relativity, to an accuracy of 1 milliarcsecond per year or better. A drag-free satellite will carry four gyroscopes in a polar orbit to observe their relativistic precession. The primary sensor for measuring the direction of gyroscope spin axis is the SQUID (superconducting quantum interference device) magnetometer. The data reduction scheme designed for the GP-B program processes the signal from the SQUID magnetometer and estimates the relativistic precession rates. We formulated the data reduction scheme and designed the Niobium bird experiment to verify the performance of the data reduction scheme experimentally with an actual SQUID magnetometer within the test loop. This paper reports the results from the first phase of the Niobium bird experiment, which used a commercially available SQUID magnetometer as its primary sensor, and adresses the issues they raised. The first phase resulted in a large, temperature-dependent bias drift in the insensitive design and a temperature regulation scheme.

Uemaatsu, Hirohiko↗
NASA NTRS1995

Niobium-Matrix-Composite High-Temperature Turbine Blades

High-temperture composite-material turbine blades comprising mainly niobium matrices reinforced with refractory-material fibers being developed. Of refractory fibrous materials investigated, FP-AL(2)0(3), tungsten, and polymer-based SiC fibers most promising. Blade of this type hollow and formed in nearly net shape by wrapping mesh of reinforcing refractory fibers around molybdenum mandrel, then using thermal-gradient chemical-vapor infiltration (CVI) to fill interstices with niobium. CVI process controllable and repeatable, and kinetics of both deposition and infiltration well understood.

Kaplan, Richard B.↗
NASA NTRS2003

Creep Resistance of Disk Alloy CH98 with Tungsten and Niobium Additions

Gas turbine engines for future subsonic transports will likely have higher pressure ratios which will require nickel-base superalloy disks with temperature capability up to 1400 F, an increase of about 200 F over current engines. Several advanced disk alloys are being developed to fill this need. One of these, CH98, is a promising candidate for gas turbine engines and is being studied in NASA's AST Program. Additions of the refractory elements tungsten and niobium have been shown to improve tensile and creep properties while maintaining good high temperature fatigue crack growth resistance. Further improvements in creep and crack growth resistance can be achieved with a coarse grain microstructure. The purpose of the present study is aimed at providing a detailed assessment of 0.2 percent creep rates for coarse grain CH98 with tungsten and niobium additions over a range of temperatures and stresses of interest to disk applications.

Gayda, John↗
NASA NTRS2003

The Effect of Tungsten and Niobium on the Stress Relaxation Rates of Disk Alloy CH98

Gas turbine engines for future subsonic transports will probably have higher pressure ratios which will require nickel-base superalloy disks with 1300 to 1400 F temperature capability. Several advanced disk alloys are being developed to fill this need. One of these, CH98, is a promising candidate for gas turbine engines and is being studied in NASA s Advanced Subsonic Technology (AST) program. For large disks, residual stresses generated during quenching from solution heat treatment are often reduced by a stabilization heat treatment, in which the disk is heated to 1500 to 1600 F for several hours followed by a static air cool. The reduction in residual stress levels lessens distortion during machining of disks. However, previous work on CH98 has indicated that stabilization treatments decrease creep capability. Additions of the refractory elements tungsten and niobium improve tensile and creep properties after stabilization, while maintaining good crack growth resistance at elevated temperatures. As the additions of refractory elements increase creep capability, they might also effect stress relaxation rates and therefore the reduction in residual stress levels obtained for a given stabilization treatment. To answer this question, the stress relaxation rates of CH98 with and without tungsten and niobium additions are compared in this paper for temperatures and times generally employed in stabilization treatments on modern disk alloys.

Gayda, John↗
NASA NTRS2003

The Effect of Tungsten and Niobium Additions on Disk Alloy CH98

Gas turbine engines for future subsonic transports will probably have higher pressure ratios which will require nickelbase superalloy disks with 1300 F to 1400 F temperature capability. Several advanced disk alloys are being developed to fill this need. One of these, CH98, is a promising candidate for gas turbine engines and is being studied in NASA's AST Program. For AST applications, compressor/turbine disks must withstand temperatures of 1300 F for several hundred hours over the life of the engine. Additions of the refractory elements tungsten and niobium to CH98 could improve tensile and creep properties, however, the impact on high temperature fatigue crack growth is uncertain. In this paper, these three key properties, tensile, 0.2 percent creep, and fatigue crack growth of CH98 with and without tungsten and niobium additions will be assessed at l300 F.

Gayda, John↗
NASA NTRS2006

JSC Materials Laboratory Reproduction and Failure Analysis of Cracked Orbiter Reaction Control System Niobium Thruster Injectors

In April 2004 a Space Shuttle Orbiter Reaction Control System (RCS) thruster was found to be cracked while undergoing a nozzle (niobium/C103 alloy) retrofit. As a failure resulting from an in-flight RCS thruster burn-through (initiated from a crack) could be catastrophic, an official Space Shuttle Program flight constraint was issued until flight safety could be adequately demonstrated. This paper describes the laboratory test program which was undertaken to reproduce the cracking in order to fully understand and bound the driving environments. The associated rationale developed to justify continued safe flight of the Orbiter RCS system is also described. The laboratory testing successfully reproduced the niobium cracking, and established specific bounding conditions necessary to cause cracking in the C103 thruster injectors. Each of the following conditions is necessary in combination together: 1) a mechanically disturbed / cold-worked free surface, 2) an externally applied sustained tensile stress near yield strength, 3) presence of fluorine-containing fluids on exposed tensile / cold-worked free surfaces, and 4) sustained exposure to temperatures greater than 400 F. As a result of this work, it was concluded that fluorine-containing materials (e.g. HF acid, Krytox , Brayco etc.) should be carefully controlled or altogether eliminated during processing of niobium and its alloys.

Castner, Willard L.↗
NASA NTRS1991

Niobium-aluminum base alloys having improved, high temperature oxidation resistance

A niobium-aluminum base alloy having improved oxidation resistance at high temperatures and consisting essentially of 48%-52% niobium, 36%-42% aluminum, 4%-10% chromium, 0%-2%, more preferably 1%-2%, silicon and/or tungsten with tungsten being preferred, and 0.1%-2.0% of a rare earth selected from the group consisting of yttrium, ytterbium and erbium. Parabolic oxidation rates, k.sub.p, at 1200.degree. C. range from about 0.006 to 0.032 (mg/cm.sup.2).sup.2 /hr. The new alloys also exhibit excellent cyclic oxidation resistance.

Hebsur, Mohan G.↗
DOE OSTI2021

Methods for synthesizing high purity niobium or rhenium powders

Methods are provided for synthesizing high purity niobium or rhenium powders by a combustion reaction. The methods can include: forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and at least one base-soluble, ammonium salt of niobium or rhenium in amounts that yield a stoichiometric burn when combusted; and heating the combustion synthesis solution to a temperature sufficient to substantially remove the water and to initiate a self-sustaining combustion reaction.

Frye, Jr., John G.↗
DOE OSTI2022

Niobium to Titanium Electron Beam Welding for SRF Cavities

Titanium and niobium are the main materials used for the fabrication of Superconducting Radio Frequency (SRF) cavities. These two metals are usually joined , using various welding techniques, using a third material in between. This contribution focuses on the development of an innovative electron beam welding technique capable of producing a strong bond between these two different materials. Several samples are produced and tested to assess the mechanical strength at room and cryogenic temperature as well as the composition of the resulting welded joint. Also, the first units of the Single Spoke Resonator type 2 (SSR2) cavities for the Proton Improvement Plan-II (PIP-II [1]) have been fabricated joining directly various grades of titanium to niobium and results gathered through the fabrication will be reported.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Effect of successive heat treatment on the performance of superconducting radio frequency niobium cavities

One of the primary sources of radio frequency residual losses leading to lower quality factor is trapped residual magnetic field during the cooldown of superconducting radio frequency cavities. It has been reported that non-uniform recrystallization of niobium cavities after the post fabrication heat treatment leads to higher flux trapping during the cooldown, and hence the lower quality factor. Here, we fabricated two 1.3 GHz single cell cavities from high purity fine grain niobium and processed with successive heat treatments in the range 800-1000 ?C to measure the flux expulsion and flux trapping sensitivity. The results show the improved flux expulsion with increase in heat treatment temperature and flux trapping sensitivity depends on the final surface preparation prior to the rf test.

Khanal, Bashu↗
DOE OSTI2022

Temperature Mapping analysis of Nitrogen-doped Niobium Radio Frequency Cavity

Nitrogen-doping of niobium superconducting radio-frequency (SRF) cavity has been shown to significantly improve the quality factors as compared to the standard treated niobium cavities. However, the nitrogen-doped cavities generally quench at lower accelerating gradients. To understand the possible sources of rf losses in nitrogen-doped cavities that could reduce the quench field, we used 576 thermometer sensors to map the temperature distribution of the outer cavity surface while increasing the accelerating field. Our measurements have revealed a strong effect of the cavity cooldown rate on the intensity of hot spots and their spatial distribution, indicating a significant contribution from trapped vortices on the RF losses.

Makita, Junki↗
DOE OSTI2023

Demonstration of Niobium Tin in 218 MHz Low-beta Quarter Wave Accelerator Cavity

A 218 MHz quarter wave niobium cavity has been fabricated for the purpose of demonstrating Nb3Sn technology on a low-beta accelerator cavity. Niobiumtin has been established as a promising next generation SRF material, but development has focused primarily in high-beta elliptical cell cavities. This material has a significantly higher TC than niobium, allowing for design of higher frequency quarter wave cavities (that are subsequently smaller) as well as for significantly lowered cooling requirements (possibly leading to cryocooler based designs). The fabrication, initial cold testing, and Nb3Sn coating are discussed as well as test plans and details of future applications.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Growth of Native Oxides of Niobium Thin Films for Superconducting Qubits with Etching Chemistry

Niobium thin films have been broadly applied in building superconducting qubits for quantum computing hardware. While improvements have been made by device engineering efforts, scaling the energy-sensitive quantum system requires materials study for further improvements. In this study, we performed XPS and ToF-SIMS analysis for Nb thin films across samples with different manufacturing techniques. By varying the air exposure time of the samples, this research comparatively investigates the chemical and depth profile of native oxides before and after the etching process. We observe a rapid logarithmic growth of oxide thickness across all samples and the dominant presence and growth of Niobium pentoxide in atomic percentage concentration on the surface. This comparative study provides insight into oxides mitigation strategies and correlation with qubits performance.

Lei, Zhicheng↗
DOE OSTI2024

Study of Mechanical Grinding Effects on Niobium Surface

Mechanical grinding is commonly employed to eliminate surface defects such as scratches and pits from niobium cavity surfaces or sheets before cavity fabrication. Subsequently, chemically buffered polishing or electropolishing is often utilized to completely remove residues of the polishing media and any defects induced by mechanical grinding, ensuring a pristine surface. In this study, we conducted a systematic investigation to assess the influence of mechanical grinding using silicon carbide and aluminum oxide polishing media on niobium surfaces. Additionally, the study examines the effects of post-mechanical grinding chemical treatments on surface quality.

Chouhan, V.↗
DOE OSTI2026

Improving the performance of mid-T baked niobium cavities through post-bake surface treatment

The Medium temperature (mid-T) baking of niobium superconducting radio-frequency cavities at 300 350 C in a vacuum furnace is known to enhance the quality factor (Q₀). However, despite this improvement, cavities treated with this process often exhibit premature quench at relatively low accelerating fields. This limitation is suspected to arise from the formation of surface contaminants, such as niobium carbides, during the furnace bake at 350 C for 3 h. To investigate the influence of potential surface contamination, this study applied an ultralight chemical removal to 1.3 GHz and 650 MHz single-cell cavities that had undergone medium-temperature baking. The removal of the top RF surface layer led to a notable improvement in the quench field and Q₀, indicating a beneficial effect of eliminating possible surface residues introduced during the bake.

Chouhan, V. [Fermilab] (ORCID:0000000282004931)↗